DESIGN OF FLY-WHEEL FOR ENERGY STORAGE

SYSTEM, USING HIGH-SPEED

MOTOR/GENERATOR ASSEMBLY

Dissertation submitted
in
partial fulfillment of requirement for the award of
degree of

Master of Technology
In
Integrated Power System

by
Mr. ABHISHEK A. DHONDSE

Supervisor

Prof. H. S. DALVI

Department of Electrical Engineering

G.H. Raisoni College of Engineering, Nagpur
An Autonomous Institute under UGC act 1956 & affiliated to Rashtrasant Tukadoji
Maharaj Nagpur University, Nagpur

June 2013
DESIGN OF FLY-WHEEL FOR ENERGY STORAGE
SYSTEM, USING HIGH-SPEED
MOTOR/GENERATOR ASSEMBLY

Dissertation submitted
in
partial fulfillment of requirement for the award of
degree of

Master of Technology
In
Integrated Power System

by
Mr. ABHISHEK A. DHONDSE

Supervisor
Prof. H. S. DALVI

Department of Electrical Engineering

G.H. Raisoni College of Engineering, Nagpur
(An Autonomous Institute under UGC act 1956 & affiliated to Rashtrasant Tukadoji
Maharaj Nagpur University, Nagpur)

June 2013

© G.H.Raisoni College of Engineering, Nagpur 2013

 Declaration
I, hereby declare that the dissertation titled “Design of Fly-wheel for Energy
storage system, using high-speed motor/generator assembly” submitted herein has
been carried out by me in the Department of Electrical Engineering of G.H. Raisoni
College of Engineering, Nagpur. The work is original and has not been submitted earlier
as a whole or in part for the award of any degree / diploma at this or any other Institution
/ University.

Abhishek A Dhondse

Date:

Certificate
The thesis titled “Design of Fly-wheel for Energy storage system, using high-
speed motor/generator assembly” submitted by Abhishek A Dhondse for the award of
degree of Master of Technology in Integrated Power System, has been carried out under
my supervision at the Department of Electrical Engineering of G.H. Raisoni College of
Engineering, Nagpur .The work is comprehensive, complete and fit for evaluation.

Dr. S.B. Bodkhe Supervisor

Professor & Head of Department of
Prof. H.S. Dalvi
Electrical Engineering Associate Professor, Department of
G.H.R.C.E, Nagpur Electrical Engineering, G.H.R.C.E,
Nagpur

Forwarded by –
Dr.U.S.Wankhede Dr.P.R.Bajaj
Dean (PG Programmes) Director

External Examiner
 ACKNOWLEDGEMENT

I would like to thank my advisor Prof. H.S Dalvi sir for giving me the
opportunity to work on this thesis. I am greatly indebted for his encouragement, support
and guidance given during this project. It is an honor and pleasure to have him as my
advisor.
I am greatly thankful to Dr. S.G Tarnekar sir for his valuable suggestions
throughout this project.
I also extend my sincere thanks to our Head of the Electrical Engineering
Department, Dr.S.B.Bodkhe sir for his co-operation which motivated me at all levels of
project.
I am also thankful to our Director madam Dr.P.R.Bajaj, who with her efficient
management and good administration made the environment conductive for developing
this project.
I also take this opportunity to thank my parents, for their constant guidance and
support, and also my friends who have directly or indirectly helped me in completing my
dissertation work successfully.

Abhishek A. Dhondse
 ABSTRACT

The world’s energy sources are derived from conventional sources i.e. fossil fuels. These
are non renewable energy sources and are limited on the earth whatever energy generated
from these primary energy sources should be utilized optimally. A fly wheel is an inertial
energy storage device which absorbs mechanical energy and serves as reservoir, storing
energy during the period when the supply of energy is more than requirement or in other
words, flywheel can store electricity from the electrical supply system in the form of
kinetic energy, and can dispense that energy back to the electrical supply system in quick
bursts. It is significant and attractive for energy futures sustainable. The key factors of
flywheel energy technology, such as flywheel material, Flywheel shape and its
supporting assembly are described, which directly influence the amount of energy
storage and flywheel specific energy. It is very suitable to such applications including,
Cloud Mitigation for Solar PV, Ramp Mitigation for Wind, Wind/Diesel/Flywheel
Hybrid, Stabilization of Distributed Generation (DG) Systems, Peak Power Support,
Frequency Response Reserve (FRR), Uninterruptible Power Supply (UPS), Reactive
Power Support (VAR support) and many other applications, with the view of new
technologies the cost of Flywheel technology can be lowered and this technology will
play a vital role in securing global energy sustainability.

The basic idea of our project is to develop a prototype flywheel energy storage
system. We are using a alternator which is driving with an existing electrical machine in
which we are using an industrial motor as a prime mover and both machines are loaded
with steel flywheel on its shaft and coupled to each other and array of LED’s serves as
electrical load to alternator. The Alternator gives constant output irrespective of the
fluctuations in supply voltages or due to surrounding air pressure. Due to inertia of the
flywheel when industrial motor is running by energy conservation technique using
Electrical/electronic control it can be made ON and OFF. During the OFF period of
motor the alternator gives output due to kinetic energy stored in the two flywheels. The
two flywheels placed on alternator and motor side is advantageous in getting more inertia
as the requirement of kinetic energy can be satisfied easily.

i
 LIST OF FIGURES

Fig 1.1 Pumped Hydro Storage Plant - I-2

Fig 1.2 Compressed Air Systems - I-3
Fig 1.3 Air Conditioning Thermal Energy Storage setup - I-5
Fig 1.4 Ultra – Capacitor - I-6
Fig 1.5 Super Conducting Magnetic Energy Storage System - I-6
Fig 1.6 Flywheel Energy storage Module Assembly - I-9
Fig 1.7 Different Flywheel shapes - I-12
Fig 1.8 Cut section view of Homo polar Inductor motor - I-15
Fig 1.9 Permanent Magnet Synchronous motor - I-16
Fig 1.10 Active Magnetic Bearing - I-18
Fig 1.11 SKF Magnetic Bearings - I-18
Fig 1.12 Passive Magnetic Bearing - I-19
Fig 1.13 Connection of FESS - I-20
Fig 1.14 FESS at NASA research - I-20
Fig 1.15 FESS at Urenco Technologies - I-20
Fig 1.16 FESS at Beacon Power - I-21
Fig 1.17 Pentadyne DC Flywheels - I-21
Fig 2.1 Appearance of Fly Wheel Energy Storage - II-2
Fig 2.2 Prototype Slot-less Rotor - II-2
Fig 2.3 Flywheel Energy Storage system using SMB and PMB - II-3
Fig 2.4 Configuration of an ordinary Flywheel system - II-4
Fig 2.5 Configuration of the proposed system - II-4
Fig 2.6 FESS with active magnetic bearing - II-5
Fig 2.7 FESS with bearing-less drive technique - II-5
Fig 2.8 Structure of the FES system - II-6
Fig 2.9 Flywheel UPS by Nippon Flywheel Corporation - II-7
Fig 3.1 Energy Flow Chart for FESS - III-2

ii
 LIST OF FIGURES

Fig 3.2 Block Diagram for Prototype FESS III-3

Fig 3.3 Industrial Exhaust fan motor and Circuit diagram III-4
Fig 3.4 Automotive Car Alternator III-5
Fig 3.5 Claw shape Alternator rotor III-5
Fig 3.6 Six diode bridge Rectifier III-6
Fig 3.7 LED array III-7
Fig 3.8 Steel Flywheel III-7
Fig 3.9 Conceptual overview of Beacon Power Flywheel System III-14
Fig 3.10 Ten 100 kW/25kWh Flywheel unit III-15
Fig 3.11 Beacon power 20 MW Smart energy matrix test Facility III-15
Fig 4.1 Hardware model of Flywheel Energy storage system with Single
IV-1
Flywheel
Fig 4.2 Hardware model of Flywheel Energy storage system with Double
IV-3
Flywheel

iii
 LIST OF TABLES

Table 1.1 Maximum Flywheel energy storage for various materials I-11
Table 1.2 Results for different shape and factor K I-13
Table 1.3 Characteristics of different Machines Suitable for FESS I-16
Table 4.1 Theoretical Calculation Results with Single Flywheel IV-2
Table 4.2 Experimental Results with Single Flywheel IV-2
Table 4.3 Theoretical Calculation Results with Double Flywheel IV-3

iv
 LIST OF SYMBOLS

Ek Kinetic Energy Joule

J Moment of inertia Kg-m2
P power Watts
T torque N-m
ω Angular velocity Rad-sec-1
σ Tensile strength of material N-m-2
ρ Mass density of material Kg-m-3
M Mass of material kg

v
 LIST OF PUBLICATIONS

[1] A. A Dhondse, H.S Dalvi Department of Electrical Engineering, G.H Raisoni College
of Engineering Nagpur, India, “Fly wheel Energy Storage System: A Survey”, All
India Seminar with International participation Clean Energy & Energy Conservation
2012.
Date of Conference: Oct.13 2012-Oct.14 2012, Page(s): 249 – 251

[2] A. A Dhondse, H.S Dalvi Department of Electrical Engineering, G.H Raisoni College
of Engineering Nagpur, India, “Fly wheel Energy Storage System”, National
Conference On Green Power & Energy: A Step towards Better Future, NCGPAE-2012.
Date of Conference: Nov.30 2012-Dec.01 2012, Page(s):

[3] A. A Dhondse, H.S Dalvi Department of Electrical Engineering, G.H Raisoni College
of Engineering Nagpur, India, “Design of Flywheel for Energy storage system using
high speed motor/alternator assembly”, National Conference on Innovative Paradigms
in Engineering and Technology , NCIPET-2013, Organized by SBJITMR.
Date of Conference: Feb.17 2013, Page(s): 187 - 190

vi
 CONTENTS

ABSTRACT - i

LIST OF FIGURES - ii

LIST OF TABLES - iv

LIST OF SYMBOLS - v

LIST OF PUBLICATIONS - vi

I. REVIEW OF DIFFERENT ENERGY STORAGE

TECHNOLOGIES AND FLWHEEL ENERGY STORAGE
SYSTEM

1.1 Introduction - I-1

1.2 Different types of Energy Storage System - I-2

1.3 Flywheel Energy Storage Concept I-7

1.4 Classification of Flywheel Energy Storage System - I-10

1.5 Material used for making Flywheel - I-10

1.6 Different Shapes of Flywheel - I-12

1.7 Electrical Machines used in Flywheel Energy Storage System - I-13

1.8 Magnetic Bearings - I-17

1.9 Power Interface - I-19

1.10 Commercially Installed Flywheel Energy Storage System - I-20

1.11 Conclusion - I-22

References - I-23
II. LITERATURE SURVEY ON FLYWHEEL ENERGY
STORAGE SYSTEM

2.1 Literature Review - II-1

2.2 Finding and limitation from the papers - II-8

References - II-9

III. DEVELOPMENT OF PROTOTYPE FLYWHEEL ENERGY

STORAGE SYSTEM

3.1 Introduction - III-1

3.2 Generation using Prototype FESS - III-1

3.3 Energy flow diagram for FESS - III-2

3.4 Design aspects of FESS - III-3

3.5 Construction of Prototype FESS - III-4

3.6 Applications of Flywheel energy storage system - III-8

3.7 Commercial Potential of FESS - III-13

3.8 Conclusion - III-17

References - III-19

IV. RESULTS AND DISCUSSION

4.1 Hardware model - IV-1

4.2 Theoretical Result - IV-2

4.3 Experimental Result - IV-2

 V. CONCLUSIONS - V-1

VI. RECOMMENDATIONS FOR FUTURE RESEARCH - VI-1

ANNEXURE

APPENDIX
CHAPTER - I
REVIEW OF DIFFERENT ENERGY
STORAGE TECHNOLOGIES AND
FLYWHEEL ENERGY STORAGE SYSTEM
1.1 Introduction

Energy is one of the major inputs for the economic development of any country. In case
of the developing countries, the power sector assumes a critical importance in view of
the ever increasing energy needs requiring huge investments to meet them.
The consumption of electrical energy is increasing at a fast speed while available
resources remain limited. Energy consumption has a significant impact on our natural
environment. The current consumption of fossil fuels is not sustainable in the long term.
Owing to this scenario energy storage is becoming increasingly important for such
developing countries. Electrical energy storage uses forms of energy such as chemical,
kinetic or potential energy to store energy that will later be converted to electricity. Such
storages can provide the following basic services like, supplying peak electricity demand
by electricity stored during periods of lower demand, balancing electricity supply and
demand fluctuations over a period of seconds and minutes and deferring expansion of
electric grid capacity.
Electrical Energy Storage technologies vary by method of storage, the amount of
energy they can store, and how quickly and for how long they can release stored energy.
Some Electrical Energy Storage technologies are more appropriate for providing short
bursts of electricity for power quality applications, such as smoothing the output of
variable renewable technologies from hour to hour (and to a lesser extent within a time
scale of seconds and minutes). Other Electrical Energy Storage technologies are useful
for storing and releasing large amounts of electricity over longer time periods (this is
referred to peak-shaving, load-levelling, or energy arbitrage). These Electrical Energy
Storage technologies could be used to store variable renewable electricity output during
periods of low demand. For example, wind farms often generate more power at night
when winds speeds are high but demand for electricity is low; Electrical Energy Storage
could be used to shift this output to periods of high demand. Another example is of
Flywheel Energy Storage System whish stores energy during OFF peak periods and
releases the stored energy during peak periods when the load on the system is more as
compared to that of generation capacity of the system. There are many types of Electrical
Energy Storage having their features are explained briefly in this chapter.

I-1
1.2 Different types of Energy Storage Systems

1) Pumped Hydro Storage

2) Compressed Air Storage
3) Thermal Energy Storage
4) Ultra Capacitors Storage
5) Super conducting Magnetic Energy Storage
6) Flywheel Energy Storage System

1.2.1 Pumped Hydro Storage

Pumped hydro storage uses low-cost electricity generated during periods of low demand
to pump water from a lower-level reservoir (e.g. a lake) to a higher-elevation reservoir.
During periods of high electricity demand (and higher prices), the water is released to
flow back down to the lower reservoir while turning turbines to generate electricity,
similar to conventional hydropower plants. Pumped hydro storage is appropriate for load
levelling because it can be constructed at large capacities of 100-1000 of megawatts
(MW) and discharged over long periods of time (6 to 10 hours). The potential use of this
technology is limited by the availability of suitable geographic locations for pumped
hydro facilities.

Fig 1.1 Pumped Hydro Storage Plant

I-2
1.2.2 Compressed Air Storage

Compressed Air Energy Storage (CAES) stores energy in the form of compressed air in a
deep underground geological vessel or reservoir. During off-peak hours, electricity from
the grid powers compressors that drive air into the underground storage vessel. When
demand increases, the air is released to the surface and heated with clean burning natural
gas to expand its volume and velocity. The air-gas mixture is used to drive a specialised
combustion turbine that can generate up to 300MW of power. Because off-peak
electricity rather than gas is used to compress the air, a CAES plant uses less than half
the amount of natural gas required by a conventional combustion turbine. Although
CAES facilities have been operating in Germany since 1978 and in the US since 1991,
the technology has not been in widespread use. Now a number of converging factors in
electricity markets are creating new value drivers for CAES, making it a commercially
viable storage technology. These include high penetration of intermittent renewable such
as wind, the requirement for greater flexibility in power systems and the need to reduce
dependence on generation from fossil fuels.

Fig 1.2 Compressed Air Systems

I-3
1.2.3 Thermal Energy Storage

Thermal energy storage comprises a number of technologies that store thermal energy in
energy storage reservoirs for later use. They can be employed to balance energy demand
between day time and night time. The thermal reservoir may be maintained at a
temperature above (hotter) or below (colder) that of the ambient environment. The
applications today include the production of ice, chilled water, or eutectic solution at
night, or hot water which is then used to cool / heat environments during the day.
Thermal energy is often accumulated from active solar collector or more often CHP
Plants, and transferred to insulate repositories for use later in various applications, such
as space heating, domestic or process water heating.

There are two very different types of thermal energy storage (TES): TES
applicable to solar thermal power plants and end-use TES. TES for solar thermal power
plants consists of a synthetic oil or molten salt that stores solar energy in the form of heat
collected by solar thermal power plants to enable smooth power output during daytime
cloudy periods and to extend power production for 1-10 hours past sunset. End-use TES
stores electricity from off-peak periods through the use of hot or cold storage in
underground aquifers, water or ice tanks, or other storage materials and uses this stored
energy to reduce the electricity consumption of building heating or air conditioning
systems during times of peak demand.

A number of thermal applications are used instead of electricity to provide

heating and cooling including Aquifer Thermal Storage (ATS), and Duct Thermal
Storage (DTS). However, these are heat‐generation techniques rather than energy storage
techniques and therefore will not be discussed in detail here. In terms of storing energy,
there are two primary thermal energy storage options. The first option is a technology
which is used to supplement air conditioning in buildings and is displayed in Fig 1.3

I-4
 Fig 1.3 Air Conditioning Thermal Energy Storage setup

1.2.4 Ultra Capacitor Storage

Ultra capacitors are electrical devices that consist of two oppositely charged metal plates
separated by insulators. The ultra capacitors stores energy by increasing the electric
charge accumulation on the metal plates and discharges energy when the electric charges
are released by the metal plates. Ultra capacitors could be used to improve power quality
because they can rapidly provide short bursts of energy in under a second and store
energy for a few minutes. A bank of ultra capacitors releases a burst of energy to help a
crane heave its load aloft; they then capture energy released during the descent to
recharge. Because no chemical reaction is involved, ultra capacitors also known as super
capacitors and double-layer capacitors are much more effective at rapid, regenerative
energy storage than chemical batteries. Rechargeable batteries usually degrade within a
few thousand charge-discharge cycles. In a given year, a light-rail vehicle might go
through as many as 300 000 charging cycles, which is far more than a battery can handle.
The synergy between batteries and capacitors has been growing, to the point where ultra
capacitors may soon be almost as indispensable to portable electricity as batteries are
now. Ultra capacitors are already all over the place. Millions of them provide backup
power for the memory used in microcomputers and cell phones. Perhaps most exciting is
could do for electric cars. They are being explored as replacements for the batteries in
hybrid cars. In ordinary cars, they could help level the load on the battery by powering
acceleration and recovering energy during braking. Most deadly to the life of a battery

I-5
are the moments when it is subjected to high-current pulses and charged or discharged
too quickly.

Fig 1.4 Ultra - Capacitor

1.2.5 Super conducting Magnetic Energy Storage

A SMES device is made up of a superconducting coil, a power conditioning system, a

refrigerator and a vacuum to keep the coil at low temperature, see Fig 1.5

Fig 1.5 Super Conducting Magnetic Energy Storage System

I-6
Energy is stored in the magnetic field created by the flow of direct current in the coil
wire. In general, when current is passed through a wire, energy is dissipated as heat due
to the resistance of the wire. However, if the wire used is made from a superconducting
material such as lead, mercury or vanadium, zero resistance occurs, so energy can be
stored with practically no losses. In order to obtain this superconducting state within a
material, it must be kept at a very low temperature. There are two types of
superconductors; low‐temperature superconductors that must be cooled from 0 K to 7.2
K and high‐temperature superconductors that have a temperature range of 10 K to 150 K,
but are usually in the 100±10K region. The overall efficiency of SMES is in the region of
90% to 99%. SMES has very fast discharge times, but only for very short periods of
time, usually taking less than one minute for a full discharge. Discharging is possible in
milliseconds if it is economical to have a PCS that is capable of supporting this. Storage
capacities for SMES can be anything up to 2 MW, although its cycling capability is its
main attraction. SMES devices can run for thousands of charge/discharge cycles without
any degradation to the magnet, giving it a life of more than 20-years. Due to the high
power capacity and instantaneous discharge rates of SMES, it is ideal for the industrial
power quality market. It protects equipment from rapid momentary voltage sags, and it
stabilizes fluctuations within the entire network caused by sudden changes in consumer
demand levels, lightening strikes or operation switches. As a result, SMES is a very
useful network upgrade solution with some sources claiming that it can improve the
capacity of a local network by up to 15%.

1.3 Flywheel Energy Storage Concept

Several hundred years ago pure mechanical flywheels where used solely to keep
machines running smoothly from cycle to cycle, thereby possible the industrial
revolution. During that time several shapes and designs where implemented, but it took
until the early 20th century before flywheel rotor shapes and rotational stress were
thoroughly analyzed. Later in the 1970s flywheel energy storage was proposed as a
primary objective for electric vehicles and stationary power backup. At the same time
fiber composite rotors where built, and in the 1980s magnetic bearings started to appear.
Thus the potential for using flywheels as electric energy storage has long been
established by extensive research. More recent improvements in material, magnetic

I-7
bearings and power electronics make flywheels a competitive choice for a number of
energy storage applications. The progress in power electronics, IGBTs and FETs, makes
it possible to operate flywheel at high power, with a power electronics unit comparable
in size to the flywheel itself or smaller. The use of composite materials enables high
rotational velocity with power density greater than that of chemical batteries. Magnetic
bearings offer very low friction enabling low internal losses during long-term storage.
High speed is desirable since the energy stored is proportional to the square of the speed
but only linearly proportional to the mass. One of the major advantages of flywheels is
the ability to handle high power levels. This is a desirable quality in e.g. a vehicle, where
a large peak power is necessary during acceleration and, if electrical breaks are used, a
large amount of power is generated for a short while when breaking, which implies a
more efficient use of energy, resulting in lower fuel consumption. Individual flywheels
are capable of storing up to 500MJ and peak power ranges from kilowatts to giga-watts,
with the higher powers aimed at pulsed power applications. The fast response time in
flywheels makes them suitable to balance the grid frequency. As the energy contribution
from more irregular renewable energy sources increases, this can be an important quality
which will grow in importance. The tools used for motor/generator design are also
continuously improving to yield a more correct picture of the induction process.
Powerful computer programs, where full electromagnetic field calculations are
considered, have reduced a number of limitations and approximations at the design stage.
Along with technical progress, especially regarding high voltage generators, each
machine can be designed to match the physical conditions of the energy source and of
the load. In this way the electric efficiency of new machines can be increased
significantly. High current yields substantial resistive power loss in the stator cables. To
maximize the conductor area and thereby reduce the cable resistance, conventional
generators use rectangular conductors. In theory it would be advantageous to build a
generator that produces high voltage and low current, as the resistive power loss in the
stator cables is proportional to the square of the current. Such a generator needs insulated
circular conductors, for example conventional high voltage extruded solid dielectric
cables. This new class of generators is called Power former [4].
Flywheel energy storage works by accelerating a cylindrical assembly called a
rotor (flywheel) to a very high speed and maintaining the energy in the system as
rotational energy. The energy is converted back by slowing down the flywheel. The

I-8
flywheel system itself is a kinetic or mechanical battery, spinning at very high speeds to
store energy that is instantly available when needed.

Fig 1.6 Flywheel Energy storage Module Assembly

A flywheel stores energy in a rotating mass. Depending on the inertia and speed
of the rotating mass, a given amount of kinetic energy is stored as rotational energy. The
flywheel is placed inside a vacuum containment to eliminate friction-loss from the air
and suspended by bearings for a stabile operation.

Kinetic energy is transferred in and out of the flywheel with an electrical machine
that can function either as a motor or generator depending on the load angle (phase
angle). When acting as motor, electric energy supplied to the stator winding is converted
to torque and applied to the rotor, causing it to spin faster and gain kinetic energy. In
generator mode kinetic energy stored in the rotor applies a torque, which is converted to
electric energy. Apart from the flywheel additional power electronics is required to
control the power in- and output, speed, frequency etc [4].

I-9
The kinetic energy stored in a flywheel is proportional to the mass and to the square of
its rotational speed according to,

1
Ek = J 𝜔2
2

J = M r2

Where,
„Ek‟ is kinetic energy stored in the flywheel,
„J‟ is moment of inertia,
„ω‟ is the angular velocity of the flywheel,
„M‟ is the mass of the flywheel,
„r‟ is the radius of the flywheel.

1.4 Classification of Flywheel Energy Storage System

The flywheel spinning speed ω allows classifying FBESSs in two types: low speed
FBESSs (less than 6000 rpm) and high speed FBESSs (104-105 rpm). In order to
maximize the energy efficiency low speed FBESSs make use of conventional
technologies, whereas high speed FBESSs make use of advanced technologies. For this
reason, the price of low speed FBESSs can be up to five times lower than the cost of high
speeds FBESSs although their performance are always inferior [2].

1.5 Material used for making Flywheel

The maximum spinning speed ω is determined by the capacity of the material to

withstand the centrifugal forces affecting the Flywheel, which is the material tensile
strength σ the relation is given by,

σ = r2 ω2

I - 10
Mass of the Flywheel is also depends on mass density ρ and the relation is given by,

M=ρv

Where,

‘v’ is the volume of disc

The maximum energy stored in the Flywheel energy storage is depends on the tensile
strength and mass density of the Flywheel and the relation is given by,

𝐸𝑘𝑚𝑎𝑥 𝜎
=
𝑀 𝜌

1 𝑀𝜎
Ekmax =
2 𝜌

The practical values taken from the paper for different materials used for the Flywheel
as,

M σ ρ Ekmax Ekmax
Material Ekmax/M
(kg) (Pascal) (kg/m3) ( joules) (kWh)

Carbon
450 4 x 109 1799 5 x 108 139 1.1 x 106
Fiber

Steel 450 6.9 x 108 8050 1.9 x 107 5 4.3 x 104

Aluminium 450 5 x 108 2700 4.2 x 107 12 9.2 x 104

Table 1.1 Maximum Flywheel energy storage for various materials

I - 11
In order to obtain high energy, flywheel materials must be with low mass density ρ, and
high tensile strength σ allowing high spinning speeds, such as modern composite
material like Carbon fiber [7].

1.6 Different Shapes Flywheel

The maximum energy density with respect to volume and mass respectively is,

ev = K σ

𝜎
em = K
𝜌

Where,

„ev‟ is the kinetic energy per unit volume

„em‟ is the kinetic energy per unit mass

„K‟ is the shape factor

The kinetic energy per unit volume and mass changes as the Flywheel shape changes, the
practical values taken from the paper for different shapes of the Flywheel as [2],

Fig 1.7 Different Flywheel shapes

I - 12
 K
M σ ρ 𝝈
Material 3
(shape ev = K σ em = K
𝝆
(kg) (Pascal) (kg/m )
factor)

1 4 x 109 2.22 x 106

Carbon 0.606 2.424 x 109 1.345 x 106

450 4 x 109 1799
Fiber 0.305 1.22 x 109 677.1 x 103

0.50 2 x 109 1.11 x 106

1 6.9 x 108 85.71 x 103

0.606 418.14 x 106 51.94 x 103

Steel 450 6.9 x 108 8050
0.305 210.45 x 106 26.14 x 103

0.50 345 x 106 42.85 x 103

1 5 x 108 185.18 x 103

Aluminiu 0.606 303 x 106 112.21 x 103

8
450 5 x 10 2700
m 0.305 152.5 x 106 56.47 x 103

0.50 250 x 106 92.59 x 103

Table 1.2 Results for different shape and factor K

1.7 Electrical Machines used in Flywheel Energy Storage System

The electrical machine, acting as generator, slows down the flywheel transforming its
mechanical energy into electrical energy. The electrical machine, acting as motor, speeds
up the flywheel increasing its mechanical energy and consuming electrical energy. Table
summarizes main characteristics of the electrical machines suitable to be used for FESS.

I - 13
1.7.1 Homo-polar Inductor Motor

These motors are not widely used in practice, homo-polar inductor motors have been
researched for a variety of applications. They are sometimes referred as synchronous
homo-polar motor. The defining feature of these motors is the homo-polar -axis magnetic
field created by a field winding, PMs, or a combination of PMs and windings. The
principle is the same as in a traditional synchronous generator, with which the homo-
polar inductor motor has similar terminal characteristics. However, in the case of the
homo-polar inductor motor, the field winding is fixed to the stator and encircles the rotor
rather than being placed on the rotor, as shown in Fig I.8 the field winding and the
magnetizing flux path in the present motor design are shown schematically in Fig I.8
Note that the rotor pole faces on the upper part of the rotor are offset from the
pole faces on the lower part. There are several advantages to having the field winding in
the stator. Among these is elimination of slip rings and greatly simplified rotor
construction, making it practical to construct the rotor from a single piece of high
strength steel. This feature makes homo-polar motors very attractive for high-speed
operation; a single piece steel rotor is used in the design presented here and in. Other
homo-polar rotor designs include laminations, PMs, or other nonmagnetic structural
elements to increase strength and reduce wind age losses.

Additional advantages of having the field winding in the stator include ease in
cooling the field winding and increased volume available for this winding. The large
volume available for the field winding allows high flux levels to be achieved efficiently,
making a slot less stator design feasible. As described previously, the slot less stator is an
advantage for solid rotor machines because it eliminates slotting induced rotor losses. A
slot less stator also allows for higher gap flux densities because saturation of the stator
teeth is no longer a concern. The design principle is similar to a slot less PM machine,
with the advantage that the magnetizing field can be controlled to keep efficiency high at
low and zero torque. A possible disadvantage of the slot less stator is the difficulty in
constructing the armature winding, which must be bonded to the smooth inner bore of
the stator iron. A relatively simple and effective process was developed in this work to
construct the winding [3].

I - 14
 Fig 1.8 Cut section view of Homo polar Inductor motor

1.7.2 Asynchronous machine

Asynchronous machines are used for high power applications because of its rough
construction, high torque and low cost. Copper rotor losses exclude asynchronous
machine for vessels with absolute vacuum as cooling results difficult. This is because of
absolute vacuum allows only heat transfer by radiation. Doubly fed asynchronous
machines have also been used as they allow reducing power electronics sizing [2].

1.7.3 Permanent magnet Synchronous Machine

Permanent magnet synchronous machine has become the most usual choice for FESS
due to its high efficiency. Permanent magnet synchronous machine has no rotor losses
resulting suitable for confinement in vacuum. The so-called Hall-bach array for the
permanent magnets allows eliminating all the iron losses at expense of lower magnetic
flux and thus lower power. Permanent magnets have concern of accidental
demagnetization, which increases with temperature. In addition, permanent magnets
have high price and low tensile strength. In order to solve these disadvantages, variable
reluctance machines for FESS have been proposed. Variable reluctance motors have no
demagnetization concern as torque is exclusively due to reluctance variation. Materials
for constructing reluctance machines have high tensile strength and low cost. Variable
reluctance motor rotor losses due to slots are low enough to allow confinement with
absolute vacuum. In high speed FESS, the electrical machine and the flywheel are fully
integrated forming a single compact element. In low speed FESS they are separated apart
or just partially integrated in a common enclosure [2].

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 Fig 1.9 Permanent Magnet Synchronous motor

The characteristics of different Electrical Machines suitable for the Flywheel Energy
storage system is as,

Permanent Magnet
Asynchronous Variable
Machine Synchronous
motor reluctance motor
motor

Power High Medium and low Medium and low

Rotor Losses Copper and Iron Iron due to slots None

Removable by Removable by Non-removable,

Spinning losses
annulling flux annulling flux Static flux

Efficiency High (93.4%) High (93%) Very High (95.2%)

Synchronous: Sinusoidal: Vector

Control Vector Control Vector control. control.
Switched: DSP Trapezoidal: DSP

Tensile strength Medium Medium Low

Cost Low Low High

Table 1.3 Characteristics of different Machines Suitable for FESS

I - 16
1.8 Magnetic Bearings

Kinetic energy storage requires a high efficiency motor, taking into account the method
of storage is still expensive and the energy has to move through the device twice that is
charging and discharging.

Being able to store energy for reasonable time further imposes that the frictional losses
should be low. This consists mainly of bearing and air friction losses. The air friction is
adequately catered for by removal i.e. operating in vacuum. Limiting bearing losses are
achieved by using magnetic bearings [5].

A magnetic bearing is a bearing that supports a load using magnetic levitation. Magnetic
bearings support moving parts without physical contact. For instance, they are able to
levitate a rotating shaft and permit relative motion with very low friction and no
mechanical wear. Magnetic bearings support the highest speeds of all kinds of bearing
and have no known maximum relative speed.

Magnetic Bearings are of two types:

Active Magnetic Bearings (AMB)

Passive Magnetic Bearings (PMB)

1.8.1 Active Magnetic Bearings

An active magnetic bearing (AMB) works on the principle of electromagnetic suspension

and consists of an electromagnet assembly, a set of power amplifiers which supply
current to the electromagnets, a controller, and gap sensors with associated electronics to
provide the feedback required to control the position of the rotor within the gap. The
power amplifier supplies equal bias current to two pairs of electromagnets on opposite
sides of a rotor. This constant tug-of-war is mediated by the controller which offsets the
bias current by equal and opposite perturbations of current as the rotor deviates from its
centre position. The gap sensors are usually inductive in nature and sense in a differential
mode. The power amplifiers in a modern commercial application are solid state devices

I - 17
which operate in a pulse width modulation (PWM) configuration. The controller is
usually a microprocessor or DSP [8].

Active bearings have several advantages, they do not suffer from wear, have low friction,
and can often accommodate irregularities in the mass distribution automatically,
allowing rotors to spin around their centre of mass with very low vibration.

Fig 1.10 Active Magnetic Bearing

SKF magnetic bearings match a wide diversity of industrial and commercial

applications. They cover a large range of load capacities from a few Newton‟s for the
light and high speed vacuum turbo molecular pumps, up to axial bearings providing with
more than 30 tons to levitate 8 meter long water turbines shafts. The corresponding
power electronics with digital control are available from a few amps at 48VDC up to 30
amps at 300VDC as used on 30 MW pipeline compressors.

Fig 1.11 SKF Magnetic Bearings

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1.8.2 Passive Magnetic Bearings

A type of magnetic bearing that does not require an external controlling system. Passive
magnetic bearings are not capable of operating under as high of temperatures or sustain
as high of a load as active magnetic bearings. Passive magnetic bearings (PMB) achieve
contact-free levitation of an object by permanent magnetic attractive or repulsive forces.
Depending on the configuration, stabilization in radial, axial and tilt direction are
possible. It is, however, not possible, to stabilized all degrees of freedom of a body by
passive magnetic levitation, alone. This has been shown by Braunbeck who interpreted
the prior findings of Earnshaw on the stability conditions in force fields for magnetic
levitation. A very simple PMB design consists of permanent magnetic rings on the
rotating shaft and the stator which stabilize the radial degree of freedom by repulsive
forces [8].

Fig 1.12 Passive Magnetic Bearing

1.9 Power Interface

The power interface includes the motor/generator, a variable speed power electronics
converter, and a power controller. The motor/generator is usually a high speed
permanent magnet machine, integrated with the rotor. The power electronics interface is
usually a pulse width modulated bi-directional converter using insulated gate bi-polar
transistor technology. The power electronics interface can achieve full load efficiency at
near full load and falls off at low loads [2].

Finally a power controller is required to monitor the Flywheel and control the power
flow. The controller operation will depend on the application, for example where the

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system is interfaced to an AC network, reactive power as well as active power will be
controlled.

Fig 1.13 Connection of FESS

1.10 Commercially Installed Flywheel Energy Storage System

This technology of energy storage is new and therefore is not being installed in
developing countries like India. However some manufacturers from developed countries
like USA, China, Japan and Russia have started the production on commercial level and
particularly in USA a 1MW plant has been installed to serve during peak loads. Fig 1 to
2 shows the FESS in use at NASA, Beacon Power, Urenco Technologies, Active Power
Corporation and Pentadyne.

Fig 1.14 FESS at NASA research Fig 1.15 FESS at Urenco Technologies

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 Fig 1.16 FESS at Beacon Power

Fig 1.17 Pentadyne DC Flywheels

In the flywheel energy storage system the same motor is used as a motor/generator and a
same machine takes and gives the energy from the system there is an unnecessary
consumption of energy. And the energy consumption is more than the energy back.

A low speed Flywheel is installed on the existing electrical machine which is driving the
other application like industrial exhaust fan. And the another flywheel mounted car
alternator is coupled to the same industrial exhaust fan so that the two flywheels are
maintain the constant speed due to inertia of the Flywheel and the car alternator which is
coupled to the industrial exhaust fan, is giving continuous DC output. If we made a
electronic timer contactor switching and connected to the industrial exhaust fan then by
giving specified timing to the timer the fan gets ON and OFF and the car alternator is
continue to give DC output to the load, due to inertia of the installed flywheels. So there
is no extra consumption of energy.

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1.11 Conclusion

The voltage quality and the reliability of power supply can be guaranteed if the FESS can
be installed in the distribution network. Compared with other energy storage techniques,
FESS has such merits as high efficiency, long life span and free of environmental
pollution. The magnetic suspension of bearing and the vacuumed space around the
Flywheel enable the FESS to work with 80 % efficiency. The FESS unit can be installed
underground the customer site. It takes no space and needs no more new facilities.
Further study will make it possible to design FESS unit with high efficiency and large
capacity. If the numbers of FESS units are installed separately in the power system, the
problem of electric utility load leveling could be solved.

I - 22
 REFERENCES

[1] TomaszSiostrzonek, StanislawPirog, “The Flywheel Energy Storage with

Brushless DC Motor-the Practical Results”, 12th International Conference on Motion
Control -2006 on Power Electrionics Page(s): 1541 - 1545

[2] R. Peña-Alzola, R. Sebastián, J.Quesada, and A.Colmenar, “Review of Flywheel

based Energy Storage Systems”, International Conference “Power Engineering, Energy
and Electrical Drives 2011”, Page(s): 1 – 6

[3] Perry Tsao, Matthew Senesky, and Seth R. Sanders, “An Integrated Flywheel
Energy Storage System with Homo-polar Inductor Motor/Generator and High-
Frequency Drive”, IEEE Transactions on Industry applications Volume: 39 Page(s):
1710 – 1725.

[4] M. Subkhan and M. Komori, “New Concept for Flywheel Energy Storage System
Using SMB and PMB”, IEEE Transactions on Applied Superconductivity, Volume no:
21, June 2011, Page(s): 1485 – 1488

[5] Yu Li Qiang, Cao Yongjuan, Liu Hexiang, Hu Qiansheng, “Design of a High

Efficiency Generator/Motor for Flywheel Energy Storage System” IEEE Conference
Publications Year: April 2009, Page(s): 1-3

[6] Adrien Schouleur, Julien Spain, Virgine Kluyskens, Francis Labrique, Bruno Dehez ,
“Study and control of a magnetic bearing for Flywheel energy storage system”,
POWERENG 2007, International conference April 12-14, 2007, Setubal, Portugal
Page(s): 24-28

I - 23
CHAPTER - II
LITERATURE SURVEY ON FLYWHEEL
ENERGY STORAGE SYSTEM
2.1 Literature Review

The paper titled on includes some prior studies carried out on Flywheel energy storage
technology.
The paper “Design of a High Efficiency Generator/Motor for Flywheel Energy Storage
System” by Yu Li Qiang et al. [1] discusses the theory and design of a high speed
brushless direct current motor for use in a flywheel energy storage system. In high speed
motor, the iron loss increases along with the alternant frequency of the magnetic field in
the iron. A relatively virtual analytical model for predicting the iron loss in high speed
BLDC machines has been described. It accounts for the influence of rotor rotation. The
analytical method should, therefore, be useful for comparative design studies, and aid
design optimization.

Recent advances in permanent magnet materials and power electronics have simulated
research into the development of permanent magnet synchronous machine for this
application. A design of the motor-alternator that performs electrochemical energy
conversion in the EMB system (electro-mechanical batteries) proposed by Marc J.Carlin
[2].

The paper “Review of Flywheel based Energy Storage Systems” shows classification of
Fly Wheel Energy Storage System i.e. low speed FESS and high speed FESS,
characteristics of different Fly Wheel material, characteristics of different electrical
machines suitable to be used for FESS and comparison of different Energy storage
systems is discussed [3].

In the paper “An Integrated Flywheel Energy Storage System with Homo-polar Inductor
Motor/Generator and High- Frequency Drive”, the practical result of research of
the rotating energy accumulator is described. In the study the brushless DC motor with
permanent magnet was used as the motor-generator. The rotating mass made up the steel
pipe. This accumulator stored about 4MJ kinetic energy. The rotation speed was 6000

II-1
rpm. The inverter was constructed from Intelligent Power Modules. The appearance of
Fly Wheel Energy Storage is as shown by Tomasz Siostrzonek et.al [4].

Fig 2.1 Appearance of Fly Wheel Energy Storage

The design, construction, and test of an integrated flywheel energy storage system with a
homo-polar inductor motor / generator and high-frequency drive is shown in this paper.
The motor design features low rotor losses, a slot-less stator, construction from robust
and low cost materials, and a rotor that also serves as the energy storage rotor for the
flywheel system, was implemented by Perry Tsao et.al [5]

Fig 2.2 Prototype Slot-less Rotor

In the paper, “New Concept for Flywheel Energy Storage System Using SMB and PMB”
experimental machine using a superconducting magnetic bearing (SMB) together with a
permanent magnet bearing (PMB) and plans to reduce the overall cost and cooling cost

II-2
which results in long life, high energy density, and high efficiency. M. Subkhan et.al [6]
shows the new model of flywheel by using the concept of yajirobei (balancing toy) that
the center of gravity of mass is lower than supporting point and by using this concept, the
flywheel has higher storage energy compared with conventional ones. The new Flywheel
Energy Storage system using SMB and PMB is as shown in Fig II.3,

Fig 2.3 Flywheel Energy Storage system using SMB and PMB

Miao-miao et.al [7] investigated, a simple setup of a flywheel induction motor device is
proposed which is composed of a flywheel and an induction motor directly connected in
parallel to the inverter-controlled load. Also, a novel control method to improve the
overload capability of the stand-alone power systems is presented by applying frequency
control to the load side inverter. The requirement for the frequency variation can be
satisfied by a proper capacity design of the flywheel induction motor.

A design method to meet the utility’s demand is introduced in this paper. Some
experiments are conducted to verify the proposed system and the frequency control

II-3
method. The experimental results show that the proposed system is easy and practical as
an overload improvement method.

Fig 2.4 Configuration of an ordinary Fig 2.5 Configuration of the proposed

Flywheel system system

A simple configuration of flywheel induction motor system has been developed to

improve the overload capability of the stand-alone power supply. The frequency control
strategy for the inverter has been investigated with theoretical analysis and experimental
verification. Both the simulation and the experimental results have proved the proposed
system’s good effect on the overload capability improvement of the stand-alone power
system.

M. Ooshima et.al [8] presents the magnetic suspension test results of a bearing-less
motor/generator for flywheel energy storage systems. A prototype bearing-less
motor/generator is built on the basis of the computed results by Finite Element Method
(FEM). It is an outer rotor-type permanent magnet (PM) synchronous motor/generator
and the rotor is wrapped by the flywheel (CFRP).

Thus, the motor/generator, the magnetic bearings and the flywheel are successfully
integrated so that the flywheel system configuration is quite compact. In addition, the
coreless stator is employed to decrease the iron loss. The magnetic unbalance pull force
is much smaller than that of the cored-stator; as a result, the necessary power for rotor
suspension is quite small.

II-4
 Fig 2.7 FESS with bearing-less drive
Fig 2.6 FESS with active magnetic
technique
bearing

The rotor levitation test results using a prototype bearing-less motor/generator for
flywheel energy storage systems have been presented. The prototype machine is an outer
rotor-type and the flywheel (CFRP) is wound on the outer rotor surface. Thus, the system
is totally quite compact. The coreless-type stator is employed so that the magnetic
unbalance pull force is smaller than that of the cored stator. The necessary power for
rotor suspension is much less. It is confirmed using the prototype machine that the rotor
is stably supported without mechanical contact and the basic performance of magnetic
suspension is observed by the experiments. As a result, the bearing-less drive technique
is enough to apply in the flywheel energy storage systems.

The paper, “Research on Flywheel energy storage system for power quality” presents a
design of flywheel energy storage (FES) system in power network; the control methods
and strategy of the FES system for power quality are introduced in detail. A new rapid
method to calculate the amplitude of sinusoidal voltage and current is presented which
could improve the performance of the FES system. To realize the high efficiency of the
energy conversion and to minimize the torque ripple of the motor/generator, the
waveform of the AC power converter output currents is controlled to be sinusoidal by
using sinusoidal pulse width modulation (SPWM) control method. During the storage
period, the AC power converter accelerates the flywheel storing energy. At the
generating times, the AC power converter drives the flywheel to decelerate and then the
kinetic energy is transformed into electric energy and returned to power system.

II-5
 Fig 2.8 Structure of the FES system

The power quality and supplying reliability will be improved if FES systems are installed
in power network. Compared with the UPS system, the FES system has such merits as
high energy density, high efficiency, long service life, and free of environmental
pollution. The FES system can be installed at substations, and needs no more new
facilities. The designed FES system is composed of a flywheel made of steel, a bearing
assembled by a permanent magnet and an oil-lift bearing, a asynchronous
motor/generator and a smart AC power converter. The new method to calculate the
amplitude of sinusoidal waveforms could improve the real time computation of the FES
system. The SPWM control method could minimize the torque ripple of the
motor/generator and realize high efficiency of the energy conversion [9].

The high precision synchronous detection and the control methods enable the FES
system to operate synchronized with power systems. The control validity is verified
through the experimental results. Further study will make it possible to design FES unit
with high efficiency and large capacity. Flywheel energy storage system is focused as an
uninterruptible power supplies (UPS) from the view point of a clean ecological energy
storage system, however in high speed rotating machines, e.g. motor, generator and
flywheel, the wind-age loss amounts to a large ratio of the total losses. The reason is that
wind-age loss is proportional to the cube of its angular velocity; a wind-age loss may
lead to the reduction of total system efficiency.

II-6
To cope with this problem, Ajisman et al. [10] proposed the use of helium–air mixture
gas into the housing and indicated that the helium (50 vol%)–air (50 vol %) mixture gas
can reduce the wind-age loss to 42% of that in the air (100 vol %) case. Helium is the
second lightest and smallest monatomic molecule gas. Its molecular weight and gas
density are about 1/7 those of air, thermal conductivity is 10 times as large as that of air.
Then, enclosing helium–air mixture gas into the housing of rotating machine, a large
amount of wind-age loss can be reduced.

In his first work, applying this mixture gas to the conventional flywheel UPS,
they indicate that idling energy loss of the flywheel UPS which is caused by the rotation
can be easily reduced, and thus the energy storage efficiency can be improved. Second,
they propose one of the novel utilization of a low speed steel flywheel energy storage
system for a momentary power failure called a momentary voltage drop.

Fig 2.9 Flywheel UPS by Nippon Flywheel Corporation

II-7
2.2 Finding and limitation from the papers

In the Flywheel energy storage system the same motor is used as a motor/generator and a
same machine takes and gives the energy from the system there is an unnecessary
consumption of energy. And the energy consumption is more than the energy back.

A low speed flywheel is installed on the existing electrical machine which is

driving the other application like industrial exhaust fan. And the another flywheel
mounted car alternator is coupled to the same industrial exhaust fan so that the two
flywheels are maintain the constant speed due to inertia of the flywheel and the car
alternator which is coupled to the industrial exhaust fan, is giving continuous DC output.
If we made a electronic timer contactor switching and connected to the industrial exhaust
fan then by giving specified timing to the timer the fan gets ON and OFF and the car
alternator is continue to give DC output to the load, due to inertia of the installed
flywheels. So there is no extra consumption of energy.

II-8
 REFERENCES
[1] Yu Li Qiang, Cao Yongjuan, Liu Hexiang, Hu Qiansheng, “Design of a High
Efficiency Generator/Motor for Flywheel Energy Storage System” IEEE Conference
Publications Year: April 2009, Page(s): 1-3

[2] R. Peña-Alzola, R. Sebastián, J.Quesada, and A.Colmenar “Review of Flywheel

based Energy Storage Systems” paper from “Power Engineering, Energy and
Electrical Drives 2011”, International Conference Page(s): 1 – 6

[3] Tomasz Siostrzonek, Stanislaw Pirog, “The Flywheel Energy Storage with
Brushless DC Motor-the Practical Results” 12th International Conference on Power
Electronics and Motion Control -2006”, Page(s): 1541 – 1545

[4] Perry Tsao, Matthew Senesky, and Seth R. Sanders, “An Integrated Flywheel
Energy Storage System with Homo-polar Inductor Motor/Generator and High-
Frequency Drive” IEEE Transactions on Industry Applications Volume: 39 Page(s):
1710 – 1725

[5] M. Subkhan and M. Komori, “New Concept for Flywheel Energy Storage System
Using SMB and PMB”, IEEE Transactions on Applied Superconductivity Volume:
21, Publication Year: June 2011, Page(s): 1485 – 1488

[6] Miao-miao Cheng, Shuhei Kato, Hideo Sumitani and Ryuichi Shimada, “A novel
method for improving the overload capability of stand-alone power generating
systems based on a flywheel induction motor” IEEE International Conference: June
2008, Page(s): 3677 – 3683

II-9
[7] M. Ooshima, S. Kobayashi, and H. Tanaka, “Magnetic suspension performance of
a bearing-less motor/generator for flywheel energy storage systems” IEEE
International Conference July 2010, Page(s): 1 – 4

[8] Zhang Jiancheng, Huang Lipei, Chen Zhiye, and Wu Su, “Research on Flywheel
energy storage system for power quality”, IEEE International Conference on Power
Quality, Volume I, Oct 2002, Page(s): 496 – 499

II-10
CHAPTER - III
DEVELOPMENT OF PROTOTYPE
FLYWHEEL ENERGY STORAGE SYSTEM
3.1 Introduction

Modern Flywheels function by using electricity to accelerate a carbon fiber rotor inside
vacuum. When the power grid needs a burst at peak demand times, that kinetic energy is
released and the Flywheel slows down. When more energy is being generated it can be
sent to Flywheel, which will speed up. Electrical utilities use Flywheels for electrical
load leveling purpose to maintain steady flow of electricity between power generation
peaks for storing surplus energy during load demand periods to prevent the brownouts
later on. Flywheel can maintain the balance between the supply and surging demand.
Currently, utilities use natural gas power plants to maintain that balance.

3.2 Generation using Prototype FESS

The basic idea of our project is to develop a prototype flywheel energy storage system,
for this purpose we are using a alternator which is driving with an existing electrical
machine in which we are using an industrial motor as a prime mover and both machines
are loaded with steel flywheel on its shaft and coupled to each other and array of LED’s
serves as electrical load to alternator. The Alternator gives constant output irrespective of
the fluctuations in supply voltage or due to surrounding air pressure due to inertia of the
flywheel when Industrial motor is running due to energy conservation technique.
Electrical/electronic control can be made ON and OFF. During the OFF period of motor
the alternator gives output due to kinetic energy stored in the two flywheels. The two
flywheels placed alternator and motor side. It is advantageous in getting more inertia as
the requirement of kinetic energy can be satisfied.

III - 1
3.3 Energy flow diagram for FESS

The flow chart shown below deflects the various stages of energy transfer using
Flywheel energy storage system.

Source

Industrial
Exhaust fan
motor

Automobile Car
Alternator Excitation

Rectifier
Assembly

Electrical Load

Fig 3.1 Energy Flow Chart for FESS

III - 2
3.4 Design aspects of FESS

Design for the Flywheel energy storage system is as shown below. Here the existing
industrial exhaust fan is coupled to the automotive car alternator and two steel Flywheels
are installed on both the machines. The output of the automotive car alternator is three
phase AC. The rotor of the alternator is wound with the winding and the external DC
supply is given to the winding to develop a DC field. The three phase AC output of the
alternator is given to the six diode bridge rectifier which converts AC to power DC.
The industrial exhaust fan is fed with 230 volt single phase 50 Hz AC supply.

50 AMP

Fig 3.2 Connection Diagram for Prototype FESS

III - 3
3.5 Construction of Prototype FESS
We are going to discuss various parts required in the assembling of Flywheel Energy
storage system. Following are the various parts,

1. Industrial Exhaust fan Motor

2. Automobile Car Alternator
3. Six diode rectifier
4. LED array load
5. Steel Flywheel
6. Nylon coupling

3.5.1 Industrial Exhaust fan Motor

Industrial exhaust fan motor is a heavy duty motor; basically it is a single phase
permanent split capacitor induction motor. In this motor the capacitor and the auxiliary
winding are not disconnected from the motor after starting. Here the auxiliary winding
and capacitor would be so designed that the motor works as a perfect two phase motor at
anyone desired load.

Fig 3.3 Industrial Exhaust fan motor and Circuit diagram

III - 4
3.5.2 Automobile Car Alternator

Fig 3.4 Automotive Car Alternator

Car alternator consists of three windings placed 120o apart on stator having robust
construction. The windings are connected in star connection and the three terminals are
removed from the alternator for the connection to the six bridge rectifier.

Rotor consists of winding fed through slip ring. The rotor design is such that it produces
12 poles and it is called as claw pole rotor. The rotor winding is fed through external DC
supply.

Fig 3.5 Claw shape Alternator rotor

III - 5
 3.5.3 Rectifier assembly

An avalanche diode is a diode made from silicon or other semiconductor that is designed
to go through avalanche breakdown at a specified reverse bias voltage. The junction of
an avalanche diode is designed to prevent current concentration at hot spots, so that the
diode is undamaged by the breakdown.

+
+
Rotor Winding

DC Output

Stator -
Winding
Fig 3.6 Six diode bridge Rectifier

Three phase full wave uncontrolled bridge rectifiers are commonly used in high power
applications so here the same is used. A bridge connection of six diodes is used between
three phase AC output of stator and load. Only two diodes conduct at a time and each
diode conducts for 120o.

III - 6
3.5.4 LED Array Load

LED array load is used at the output of the alternator. For the experimental study after
each five LED in series the switch is connected to connect another five series LED. The
LED array is as shown,

Fig 3.7 LED array

3.5.5 Steel Flywheel

The steel plates are used as a Flywheel disc. It is generally used in low speed Flywheel
energy storage systems.

Fig 3.8 Steel Flywheels

III - 7
3.5.6 Nylon Coupling

Here nylon coupling is used for the coupling of motor and alternator. Advantage of using
nylon coupling is, if there is any out in the alignment of both machines the nylon
coupling flexibility will absorb them. The nylon coupling is nothing but the water tap
nozzle.

3.6 Application of Flywheel Energy storage system

There are number of companies around the world that manufacture flywheel energy
storage system. This section provides an overview over some of the systems that are
commercially available today. Flywheel energy storage system is usually categorized as
either low speed or high speed. The border between these two types is found around
10000 rpm. Low speed Flywheel have long been commercially available, these systems
typically utilize metal rotor and are characterized by low energy density. The most
common application for low speed Flywheels is to act as a power quality device to
provide ride through of interruptions up to 15s long or to bridge the shift from one power
source to another. Examples of leading commercial manufactures of low speed
Flywheels are Piller and Active power.

The current R&D on flywheel energy storage systems has focused towards high speed
composite machines, running at rotational speed over 10000 rpm. As shown above the
high directional strength properties of composites materials, combined with their
comparatively low density, allows optimal design of the overall system with respect to
specific energy. Examples of leading commercial manufacturers of high speed Flywheel
systems are Beacon power and Vycon energy.

III - 8
Beacon potential applications for flywheel technology are briefly described below [2].

1) Cloud Mitigation for Solar PV

2) Ramp Mitigation for Wind
3) Wind/Diesel/Flywheel Hybrid
4) Stabilization of Distributed Generation (DG) Systems
5) Peak Power Support
6) Frequency Response Reserve (FRR)
7) Uninterruptible Power Supply (UPS)
8) Reactive Power Support (VAR support)

3.6.1 Cloud Mitigation for Solar PV

Power outputs from solar photovoltaic (PV) assets are subject to rapid fluctuations due to
clouds. A passing cloud, for example, can easily decrease PV power output by 80 percent
or more within seconds. Conversely, as the cloud passes, power output can increase just
as rapidly. Most PV resources are interconnected at distribution voltages, and such
power fluctuations can cause unacceptable voltage disturbance. Depending on local
conditions, utilities may refuse to allow a PV resource to interconnect unless something
is done to mitigate these fast ramps in power output. Flywheel technology has the ability
to buffer these fluctuations and, where they are unacceptable to the local distribution
utility, energy storage can neatly solve the problem.

3.6.2 Ramp Mitigation for Wind

A safe, reliable and energy-efficient modern grid should be capable of integrating

pollution-free renewable energy resources on a large scale without causing deterioration
of generation, transmission or distribution operations. Renewable Portfolio Standards
have been put in place at the state level to encourage greater market penetration of wind
and solar power. However, the variable nature of these resources poses a challenge. For

III - 9
example, in one western state, wind developers filed plans to add new wind capacity that
exceeds the current peak load of the region. Without a new and more effective approach
for integrating variable wind resources, the deployment of wind power could be severely
curtailed. Fast ramp-rate flywheel energy storage systems can be coordinated as part of
an integrated energy balancing system that includes variable wind generation, slower-
ramping conventional fossil generation, and demand response resources. Such a system
could be effective in levelling out the big peaks and valleys that adding more wind
generation is expected to create.

Flywheel-based energy storage could act as both a buffer and balancing resource
between variable wind generation, slower-ramping conventional fossil generation, and
various fast- and slow-acting demand response resources. Flywheel energy storage offers
an excellent set of features to accomplish this new energy balancing application. These
include a ramp rate up to 100 times faster than conventional fossil-fired generation
plants; high-cyclic capability without any degradation of energy storage capacity over
time; low maintenance; zero fuel consumption and no direct CO2 emissions; no use of
toxic materials; and a 20-year life.

3.6.3 Wind/Diesel/Flywheel Hybrid

The number of wind/diesel power systems operating around the world continues to
increase at a rapid pace. A wind turbine placed in parallel with a diesel generator works
to reduce the fuel used by that generator by allowing it to be shut down when wind
power exceeds load. However, when load approximately matches available wind power,
the generator must be kept at idle for the occasional event when wind power drops for a
few seconds or minutes below connected load. This mode of operation is not very
efficient, since much of the diesel generator's time is spent either at idle or inefficient
low power settings.

The introduction of energy storage can act to further reduce diesel fuel
consumption by using the stored energy to provide both load following and supplying the
occasional shortfall, while leaving the generator turned off. Flywheel energy storage
should be ideal for this application thanks to its low maintenance, long design life, high

III - 10
cycling capability without any degradation in storage value, its ability to respond almost
instantaneously (thus improving load following), and its ability to provide real and/or
reactive power.

3.6.4 Stabilization of Distributed Generation (DG) Systems

Functionally, Flywheel technology can supplant the grid with respect to the grid's normal
provision of a synchronization signal. Flywheel technology can also provide load
following capability above the capacity rating of the DG asset, as well as voltage and
reactive power support and control. For Combined Heat and Power (CHP) systems,
Flywheel technology has the potential to facilitate the use of natural gas reciprocating
engines and/or gas turbines as part of a CHP system, by improving these systems' ability
to follow fast-changing loads. The benefits to grid operators would be to improve the
ability of the DG asset to operate on an islanded basis during a blackout, as well as to
reduce emissions.

3.6.5 Peak Power Support

A large number of applications exist that collectively can be categorized under "peak
power support." For example, oil drilling rigs typically maintain a number of diesel
power systems to meet the peak power needs of an oil drilling platform. Collectively,
much of this diesel power capacity stands idle or operates at a low capacity factor (often
with high emissions) based on the irregular power demands of drilling. A flywheel
system could augment the capacity of the diesel generators, thereby making it possible
for fewer diesels to meet peak power demand requirements. The economics of this
application are based on the ability to reduce the needed investment in power generation
assets. Added value may derive from reduced wear and tear on generating equipment and
reduced air emissions, especially in ecologically sensitive areas and/or air basins
currently operating outside of EPA-mandated air pollution limits.

III - 11
3.6.6 Frequency Response Reserve (FRR)

When there is a sudden loss of a power plant, transmission line or distribution line, a
rapid drop in grid frequency can occur. While most generators must be able to
compensate for a rapid drop in frequency on a fractional basis according to their capacity
rating, some parts of the grid lack sufficient frequency response resources, either because
there is not enough fast-response generating capacity, and/or because of transmission
constraints.

Beacon's 20 MW frequency regulation plants have the inherent ability to provide

frequency response support without compromising the efficacy of the primary frequency
regulation application. As with the other potential secondary overlay applications for our
flywheel regulation plants, the economics of this application will compete with other
technology solutions on the basis of incremental versus stand-alone cost. Since nearly all
the equipment needed to provide FRR is already built into a 20 MW frequency
regulation plant, the economics of this application are potentially quite attractive.

The Western Electricity Coordinating Council, which is responsible for

coordinating and promoting electric system reliability across 14 western states between
Canada and Mexico, is currently evaluating the possible inclusion of a 30-second tariff
for FRR.

3.6.7 Uninterruptible Power Supply (UPS)

A global industry exists for Uninterruptible Power Supply (UPS) systems. Beacon's
flywheels have the capability to supply highly reliable backup power. As a replacement
for battery-based UPS systems, flywheel technology has the advantage of being virtually
maintenance-free compared to maintenance-intensive and less-reliable battery-based
UPS. The challenge for market acceptance of flywheel-based UPS is cost. As Beacon
scales up production of its flywheels for frequency regulation, we expect to lower costs
based on the learning curve and volume production effect. Over time, we expect to be
able to participate in the global UPS market in a variety of sub-applications, especially

III - 12
those requiring very high reliability and minimal need for maintenance. Our core
technology can also be used as part of a flywheel design with a higher power-to-energy
ratio, cost-effectively aligning with some UPS application requirements.

3.6.8 Reactive Power Support (VAR support)

Reactive power support can be provided on either a unitary or small-system basis, or as a

secondary overlay application for a full-scale 20 MW frequency regulation power plant.
For industrial and commercial end users, potential benefits include lower fees from
utilities resulting from improvement of power factor levels that would otherwise fall
below specified minimums, as well as higher power quality for sensitive industrial and
commercial applications. For grid operators or utilities, potential benefits include the
ability to defer investments in transmission and/or distribution infrastructure.

3.7 Commercial Manufacturer of FESS in world

3.7.1 Beacon Power

Beacon power corporation [2], based in Massachusetts, USA, aims to develop advanced
Fly based energy storage systems. Their first system was backup power solutions for
telecommunication application but the focus have now change toward development of
grid scale flywheel energy storage system for application such as grid scale frequency
regulation service. Beacon power’s main product is the “Smart Energy Matrix”, based on
a concept of a multi flywheel energy storage system. This system consists of multiple
100kW/25kWh flywheel units. The main components each flywheel unit are the
following:

Rotor assembly - Composite flywheel, metal hub and shaft, interface for active lift and
magnetic bearing, motor rotor

Motor/generator - Permanent magnet machine

Magnetic bearings and active lift system

III - 13
Vacuum system

Vacuum housing – Structural support for the rotor assembly and low pressure vessel

Fig 3.9 Conceptual overview of Beacon Power Flywheel System

Each flywheel unit is coupled to a bi-directional power converter, which acts as an

inverter and variable speed motor drive. The power converter provides a DC interface
which makes it possible to connect multiple units in parallel to a common DC bus-bar in
order to meet higher power demands.

Beacon power has a 20 MW test “Smart energy matrix” plant in operation,

located in Stpentown, USA. The purpose of this plant is to provide frequency regulations
services. This plant is comprised of 200 parallel connected 100 kW/25kWh flywheel
units. The speed range of rotor is 8000 – 16000 rpm. The plant can provide a maximum
output power of 20 MW for 15 min. The response time is less than 4 seconds,
input/output voltage is 480 V three phase AC, 50/60Hz.

III - 14
 Fig 3.10 Ten 100 kW/25kWh Flywheel unit

Fig 3.11 Beacon power 20 MW Smart energy matrix test Facility

III - 15
3.7.2 Vycon Energy

Vycon market a system with product name VDC-XE which consists of a high speed steel
flywheel with a speed range of 14500 – 36750 rpm. The flywheel is coupled to a high
speed motor/generator that interfaces via power electronics to a 400 – 600 V DC-link.
The maximum output power for one unit is 300 kW. Discharge time at rated output is
around 14s. It is possible to parallel several units to increase power output and/or
discharge time. Vycon targets the UPS market segment and the flywheel system can be
an alternative to lead acid batteries. Another application is in the railway industry
(traction application). The flywheel system absorbs breaking energy from the train,
which can be used when the train accelerates. This can give subway operator a way to
lower their energy consumption. Vycon also market their flywheel system for usage in
large cranes. The use is similar to traction system; breaking energy is stored in the
flywheel and released when the crane needs power to lift [3].

3.7.3 Piller

Piller is another company that provides flywheel based UPS solution and load leveling in
local grids, such as traction applications. Piller flywheel technology is based on a low
speed steel flywheel with a speed range of 3600 to 15000 rpm. The electrical machine is
high power synchronous machine with a maximum power rating of 1.65 MW. The
maximum discharge time is around 10 seconds [4].

3.7.4 Active power

Active provides Flywheel based UPS solutions. The core technology is a vacuum
operated low speed flywheel with a power rating of 250 kW. The flywheel is made from
forged steel and has an operational rotational speed range of 2500 – 7700 rpm. The
system utilizes a combination of ceramic ball bearings and magnetic lifts to increase
bearing lifetime. The power is available either at a DC link or AC terminal. One single
flywheel unit can provide the nominal output power if 250 kW for 14 seconds. The
standby efficiency is 99.8 %. Modular system design, were multiple flywheel units is
parallel connected can provide power up to 2 MW [5].

III - 16
3.8 Conclusion

 Features that flywheel energy storage system include:

 High power density
 Relative high specific energy density
 Low or no capacity degradation during discharge/charge
 Flywheel have very high cycling capacity, up to 90000 charge/discharge cycles
have been reported
 Easy to measure the state of charge
 Very low maintenance
 Quick response time
 Scalable and no geological barrier
 Low environmental impact
 Long lifetime

Flywheel systems using steel or composite rotors have been successfully developed and
are being produced by several manufacturers. The technology is already highly
developed, and standard products are on the market.

Most standard flywheel systems have storage times in the region of 5 to 30 sec,
where the power electronics interface is the most significant capital cost. Despite this,
current development is aimed at rotor cost deduction by achieving higher specific energy
and reduced rotor mass. Advanced bearings are being actively developed including the
use of HTS magnetic bearings, to provide reduced losses, higher efficiency, reduced
running cost and longer bearing life. Both these developments are particularly significant
to systems with longer storage times of greater than one hour, where the rotor and
bearing cost become the most significant system cost. Successful reduction of rotor
losses and cost would make flywheel systems attractive to a wider range of applications.

The main market for flywheel systems is UPS systems, power quality improvement and
traction applications. Analysis by Sandia has indicated that flywheels can be cost
competitive with batteries in some UPS applications. There are already some

III - 17
applications of high power (low energy) flywheel systems for smoothing wind power
fluctuations in weak networks, and new requirements are emerging for stability
improvement and protection of wind farms against network voltage dips. These
applications are ideally suited to high power cycling capabilities of flywheels. The
development of lower loss and reduced cost systems with longer storage times could
make flywheel systems competitive with batteries in stand-alone renewable energy
systems.

III - 18
 REFERENCES

[1] Matthew L. Lazarewicz, Todd Ryan, “Grid-Scale Frequency Regulation Using

Flywheels”, year-2010

[2] Site: www.beaconpower.com

[3] Site: www.vyconenergy.com

[4] Site: www.piller.com

[5] Site: www.activepower.com

III - 19
CHAPTER - IV
RESULT AND DISCUSSION
4.1 Hardware Model

The Model shown in Fig 4.1 was designed and successfully tested with single phase
Induction motor coupled to alternator.

Fig 4.1 Hardware model of Flywheel Energy storage system with Single Flywheel

When the motor alternator set is coupled with high inertia low weight flywheel,
the energy stored in the flywheel can be converted into electrical energy. If number of
flywheel is synchronized further the complete assembly can be extended for power
generation in isolated grid also. The existing setup coupled with the flywheel shows a
energy conversion system, how a mechanical energy can be converted into electrical
energy. The advantage of using two flywheels is to improve the inertia and store
maximum energy which can be further discharged to get electrical energy.

IV-1
4.2 Theoretical Results

Free
Moment of
Mass in Disk dia K.E in Joules by Spin K.E in
RPM Inertia Kg
Grams in mm Calculations Time in watts
mm2
sec

2000 127 1400 43.34 0.00403 3 14.44

2000 127 1000 22.115 0.00403 3 7.37

Table 4.1 Theoretical Calculation Results with Single Flywheel

4.3 Experimental Results

Free
Mass in Disk dia Spin K.E in
RPM
Grams in mm Time in watts
sec

2000 127 1400 3 10

2000 127 1000 3 8

Table 4.2 Experimental Results with Single Flywheel

IV-2
 Fig 4.2 Hardware model of Flywheel Energy storage system with Double Flywheel

From the experimental study it is observed that for higher RPM of the exhaust fan the
kinetic energy is more.
As the flywheel weight increase the kinetic energy increase and the alternator gives more
output.

Free
Moment of
Mass in Disk dia K.E in Joules by Spin K.E in
RPM Inertia Kg
Grams in mm Calculations Time in watts
mm2
sec

4000 127 1400 86.69 0.00806 5 17.33

Table 4.3 Theoretical Calculation Results with Double Flywheel

IV-3
CHAPTER - V
CONCLUSION
Conclusion

A technical description of a flywheel energy storage system has been outlined. The main
system components, i.e. flywheel, electrical machine, power electronics interface,
bearing system has been discussed in details. It has been shown that composite materials
are more advantageous when building flywheel rotors due to its higher tensile strength to
density ratio. They allow high-speed rotation and therefore high specific energy, which
enables compact design. There are multiple options when choosing the electrical
machines. It can be concluded that a permanent magnet synchronous machine have
robust design, mainly due to its efficiency and high power density.
Standard flywheel systems have storage time variation from of 5 to 30 seconds,
where the power electronics interface is the most significant factor which can increase
the capital cost. Despite this, current development is aimed at rotor cost reduction by
achieving higher specific energy and reduced rotor mass. Advanced bearing are being
actively developed including the use of HTS magnetic bearings, to provide reduced
losses, higher efficiency, reduced running cost and longer bearing life. Both these
developments are particularly significant to systems with longer storage times more than
one hour, where the rotor and bearing costs become the most significant. Successful
reduction of rotor losses and costs will make flywheel systems attractive to a wide range
of applications. The main markets for flywheel systems are UPS systems, power quality
improvement, and traction applications. Flywheels can be cost competitive with batteries
in some UPS applications. There are already some applications of high power (low
energy) flywheel systems for smoothing wind power fluctuations in weak networks, and
new requirements are emerging for stability improvement and protection of wind farms
against network voltage dips. These applications are ideally suited to high power cycling
capabilities of flywheels. The development of less reduced cost systems with longer
storage times can make flywheels comparatively more competitive with batteries in
stand-alone renewable energy systems. As the grid is likely to swing into dynamic
system with future development of smart grid technology, the conclusion can be drawn
that the functional requirements on the power interface of the FESS is expected to
increase. It should be able to handle the load and improve the power quality.

V-1
 FESS can be the solution for a multiple applications in the electrical utility
system, such as load leveling, frequency regulation and renewable energy capacity
farming. FESS is best suited for such applications, which are characterized by dynamics.
The limitations are the relative short discharge time. FESS has advantages such as higher
power density, no cycling degradation, environmentally friendly and fast response time.
However FESS system can become cheaper so that it can be a replacement for battery
system (UPS). With further development of flywheel rotors, power electronics and
magnetic bearings flywheel energy storage system can be a strong component for grid
applications up to multiple powers. Today fully commercial FESS exists in the UPS
market with both high-speed and low-speed technology. The systems are commercialized
an alternative to other UPS solutions, such as lead acid batteries.
Beacon Power leading manufacturer of flywheels, focused on large scale FESS.
Beacon power markets their FESS as a competitive solution for frequency regulation.
However, they are still in a developing stage of the technology and have only limited
testing facility. The main model components include PMSM coupled to a variable speed
drive and grid connected converter. It can be concluded that the model has lot of research
potential to make modification, FESS can be a good solution to electrical energy storage,
however there is still a need of extensive development (R&D) and further cost reduction
in order to make it competitive alternative.
The battery industry has now gained more attention in R&D and financial
support. The interesting fact that batteries will literally erode with time, as constant
cycling degrades their capacity. This issue is not present in the FESS. It is clear that
energy storage is needed in the smart grid environment. In future, the most probable
scenario is a market with various technologies of FESS. Flywheel systems using steel or
composite rotors have been successfully developed and are being produced by several
manufacturers. The technology is already developed, and standard products are on the
market.
A non conventional energy storage system was constructed and the same system
was used for the experimental study on flywheel. Flywheel-based energy storage
systems, unlike fossil-fuel power plants are used on the grid for frequency regulation,
also sustainable "green" technology solutions that consume no fossil fuel, nor produce
CO2 or other emissions during operation. It is one of the viable solutions for energy
conservation techniques.

V-2
 By constructing model with two flywheels the energy store on the
motor/generator side will store more kinetic energy and the discharging time during full
load will be more.

V-3
CHAPTER - VI
RECOMMENDATIONS FOR FUTURE
RESEARCH
Future Scope

A low cost hybrid BLDC motor can be constructed by using car alternator and the
Flywheel energy storage system. The modification can be made on the alternator side,
and the permanent magnets can be fitted on the alternator rotor so that the frictional
losses of slip ring are removed. The ESC (Electronic speed controller, which is used in
toy helicopters to run brushless out runner motor) which has two wire DC input and three
wire DC output and is a MOSFET based controller. The same controller is used to run
alternator as a Hybrid BLDC motor. The flywheel can be installed on alternator rotor
shaft and the same alternator can be used as motor/alternator.

New and advance materialistic engineering should pick the technology and with
the advancement in materialistic science the weight of the flywheel can be reduced. With
more inertia the material can withstand the amount of angular momentum that the
Flywheel itself posses and the complex design of flywheel can be made simple, with
lowering the initial cost and increasing the efficiency of the FESS.

In future there is a potential to use magnetic levitation as a way to prolong ate the
life of FESS since there is no friction on the system because of the magnetic levitation
there will be no wear and tear of the system and hence system could last for more years
when compared with conventional storage system like batteries, solar cell etc.

VI-1
ANNEXURES
Annexure - A
Annexure - A
Annexure - A
Annexure - A
Annexure - B
Annexure - B
Annexure - B
Annexure - B
Annexure - B
APPENDIX
 APPENDIX

A) Specifications of Components used for making Prototype Flywheel Energy

storage system

1. Industrial Exhaust fan Motor

Specifications:
220-240 V, 1.6 amps, 410 watts
1400 rpm
Capacitor – 8 μfd

2. Automobile Car Alternator

Specifications:
Output – 12-20 volt, 50 amps
DC excitation - 12 volt 5 amps
Max RPM – 7000-8000 rpm

3. Rectifier assemblies
Specifications:
Diode – 6-50 amps, 35-43 volts
IN5408 MIC

4. LED Array Load

Specifications:
1.5 volt, 0.25 Watt Led
75 ohms 0.25 watt ceramic resistance
5. Steel Flywheel
Specifications:
Weight – 2000 grams
Width – 15 mm
Diameter – 127 mm

B) Image for Kinetic energy storage calculation window for different values

1. Calculation of kinetic energy for-

M = 2000 grams
D = 127 mm
RPM = 1400
2. Calculation of kinetic energy for-
M = 2000 grams
D = 127 mm
RPM = 1000

3. Calculation of kinetic energy for-

M = 4000 grams
D = 127 mm
RPM = 1400