Need of Electric Drives:

Motion control is required in large number of industrial and domestic applications. Systems employed
for getting the required motion and their smooth control are called Drives. Drives require prime movers
like Diesel or petrol engines, gas or steam turbines, hydraulic motors or electric motors. These prime
movers deliver the required mechanical energy for getting the motion and its control. Drives employing
Electric motors as prime movers for motion control are called Electric Drives.

Advantages of Electrical Drives:

 The steady state and dynamic performance can be easily shaped to get the desired load
characteristics over a wide range of speeds and torques.
 Efficient Starting /Braking is possible with simple control gear.
 With the rapid development in the field of Power Electronics and availability of high speed/high
power devices like SCRs, Power MOSFETs, IGBTs etc., design of Efficient Power Converters to
feed power to the electric drives has become simple and easy.
 With the rapid development in the computer’s HW & SW, PLCs and Microcontrollers which can
easily perform the control unit functions have become easily available.
 Electric motors have high efficiency, low losses, and considerable overloading capability. They
have longer life, lower noise and lower maintenance requirements.
 They can operate in all the four quadrants of operation in the Torque/Speed plane. The resulting
Electric braking capability gives smooth deceleration and hence gives longer life for the
equipment. Similarly Regenerative braking results in considerable energy saving.
 They are powered from electrical energy which can be easily transferred, stored and handled.

Block diagram of an Electrical drive:

The main parts of the electrical drives are power modulator, motor, controlling unit and sensing units.
Their parts are explained below in details. The block diagram is shown in the figure below.

Functional Block diagrams of an electric drives.

Source: 1-φ and 3-φ, 50-Hz AC supplies are readily available in most locations. Very low power drives
are generally fed from 1-φ source; however, the high power drives are powered from 3-φsource; some
of the drives are powered from a battery.
Power Modulator: The power modulator regulates the output power of the source. It controls the
power from the source to the motor in such a manner that motor transmits the speed-torque
characteristic required by the load. During the transient operations like starting, braking and speed
reversing the excessive current drawn from the source. This excessive current drawn from the source
may overload it or may cause a voltage drop. Hence the power modulator restricts the source and
motor current.
The power modulator converts the energy according to the requirement of the motor e.g. if the source
is DC and an induction motor is used then power modulator convert DC into AC. It also selects the mode
of operation of the motor, i.e., motoring or braking.
Control Unit: The control unit controls the power modulator which operates at small voltage and
power levels. The control unit also operates the power modulator as desired. It also generates the
commands for the protection of power modulator and motor. An input command signal which adjusts
the operating point of the drive, from an input to the control unit.
Sensing Unit: Sensing unit consists of speed sensor or current sensor. The sensing of speed is required
for the implementation of closed loop speed control schemes. Speed is usually sensed using
tachometers coupled to the motor shaft. Current sensing is required for the implementation of current
limit control.
Electrical motors: Motors commonly used in electric drives are DC motors, induction motors,
synchronous motors, blushless DC motors, stepper motors, and switched reluctance motors, etc. In
olden days, induction and synchronous motors were employed mainly for constant speed drives but not
for variable speed drives, because of poor efficiency and are too expensive. But in nowadays, AC motors
employed in variable speed drives due to the development of semiconductors employing SCRs, power
transistors, IGBTs, and GTOs.
Load: It is usually machinery, such as fans, pumps, robots, and washing machines, designed to perform
a given task, usually load requpirements, can be specified in terms of speed and torque demands.
This difference introduces the concept of motor duty class, which divides motor duty
cycles into eight categories:

Continuous duty

Short time duty

Intermittent periodic duty

Intermittent periodic duty with starting

Intermittent periodic duty with starting and braking

Continuous duty with intermittent periodic loading

Continuous duty with starting and braking

Continuous duty with periodic speed changes

Continuous Duty

This duty denotes that, the motor is running long enough AND the electric motor
temperature reaches the steady state value. These motors are used in paper mill drives,
compressors, conveyors etc.

Short Time Duty

These motors operate for short periods, and their heating time is much less than their
cooling time. Thus, the motor cools down to ambient temperature before operating again.
These motors are used in crane drives, household appliances, and valve drives
Intermittent Periodic Duty

In this duty, the motor runs for a while and then rests. Neither period is long enough to
reach steady state temperature or cool down completely. This type is used in press and
drilling machine drives.

Intermittent Period Duty with Starting

In this type of drives, heat loss during starting and braking cannot be ignored. So, the
corresponding periods are starting period, operating period, braking period and resting
period, but all the periods are too short to attain the respective steady state temperatures,
these techniques are used in billet mill drive, manipulator drive, mine hoist etc.

Continuous Duty with Intermittent Periodic Loading

This motor duty is similar to periodic duty, but it includes a no-load running period instead
of a rest period. Examples include pressing and cutting machines.

Continuous Duty with Starting and Braking

It is also a period of starting, running and braking and there is no resting period. The main
drive of a blooming mill is an example.

Continuous Duty with Periodic Speed Changes

In this type of motor duty, there are different running periods at different loads and speeds.
But there is no rest period and all the periods are too short to attain the steady state
temperatures.

Static Kramer Drive

Definition: The static Kramer-drive is the method of controlling the speed of an induction
motor by injecting the opposite-phase voltage in the rotor circuit. The injected voltage
increases the resistance of the rotor, thus controlled the speed of the motor. By changing
the injected voltage, the resistance and speed of an induction motor are controlled.

The static Kramer-drive converts the slip power of an induction motor into AC power and
supply back to the line. The slip power is the air gap power between the stator and the rotor
of an induction motor which is not converted into mechanical power. Thus, the power is
getting wasted. The static Kramer drives fed back the wasted power into the main supply.
This method is only applicable when the speed of the drive is less than the synchronous
speed.

Static Kramer Drive Working

The rotor slip power is converted into DC by a diode bridge. This DC power is now fed into
DC motor which is mechanically coupled to an induction motor. The torque supplied to the
load is the total sum of the torque produced by the induction and DC motor drive.

The figure shown below represents the variation of Vd1 and Vd2 with a speed of two values
of DC motor field current. When the value of Vd1 is equal to the value of Vd2 then the
steady state operation of the drive is obtained, i.e., at A and B for field current of If1 and If2.

The speed control is possible only when speed is less or half of the synchronous speed.
When the large range speed is required, the diode bridge is replaced by the thyristor bridge.
The relationship between the Vd1 and the speed can be altered by controlling the firing
angle of thyristor amplifier. Speed can now be controlled up to stand still.
Indian electricity Rules 2023 (In easy)

Regulation 13

Regulation 13 requires electricity suppliers to create and maintain

Detailed maps of their service areas. These maps should show the

Location of all electrical lines, distribution boxes, and other

Equipment, both above and below ground. The maps should be

Updated annually to reflect any changes.

Key points:

• Map creation: Suppliers must create maps of their service areas,

Including the location of all electrical equipment.

• Map updates: Maps must be updated annually to reflect changes

In the electrical infrastructure.

• Map accessibility: Maps must be available for inspection by the

Public and copies can be purchased.

• Compatibility: Maps should be compatible with modern mapping

Technologies like GPS.

• Free copies: Suppliers must provide free copies of maps to

Government inspectors.

• Fees: Copies of maps may be sold to the public for a fee.

Regulation 14: Safety Standards for Electrical Supply Lines

This regulation outlines safety requirements for electrical supply

Lines and equipment. It states that:

• Safety is the priority: All electrical equipment must be strong

Enough, well-insulated, and able to handle the expected load. It

Should be installed and maintained in a way that protects people,

Animals, and property.

• Follow standards: The National Electrical Code and National

Building Code, or international standards if Indian ones aren’t

Available, should be followed for guidance. However, if there’s a

Conflict, the specific regulations in this document take precedence.

• Use approved materials: The materials used in electrical

Equipment must meet the required standards.

• Protect from flooding: All electrical equipment should be installed

Above the highest flood level. If this isn’t possible, measures must

Be taken to prevent water from entering or accumulating near the

Equipment.

Regulation 15: Safety of Electrical Equipment on Consumer Premises

This regulation outlines the responsibilities of the electricity

Supplier and the consumer regarding the safety of electrical

Equipment on the consumer’s property. It states that:

• Supplier’s responsibility: The supplier is responsible for ensuring

That all electrical equipment they own or control, up to the point

Where the electricity supply starts, is safe and suitable for

Delivering electricity. They must take precautions to prevent

Dangers caused by this equipment.

• Underground service lines: The supplier must properly insulate

And protect underground or accessible service lines to prevent

Damage from electrical, mechanical, chemical, or other factors.

• Consumer’s responsibility: Consumers should take reasonable

Precautions to protect the supplier’s equipment on their property.

• Consumer’s installation: Consumers must also maintain their own

Electrical installations in a safe condition.

Regulation 16: Switchgear on consumer’s premises. –

In simpler terms:

This regulation is about the safety switches installed in homes or

Businesses.

• Every electrical line going into a building should have a switch to

Control the power.

• These switches should be easy to reach and protected from fire.

• If multiple buildings are connected to the same power line, each

Building should have its own switch.

Basically, this regulation ensures that people can easily control and

Protect their electrical supply.

Regulation 17: Identification of earthed and earthed neutral

Conductors and position of switches

And switchgear therein. –

This regulation is about the safety of electrical systems, especially

Those with a grounded wire.

• Clear identification: The grounded wire should be easily

Recognizable compared to the live wires. This is usually done with

Markings or colors.

• No individual switches: You can’t have a separate switch to

Control just the grounded wire. It should always be connected or

Disconnected together with the live wires.

Basically, this regulation helps prevent electrical accidents by

Ensuring that grounded wires are always connected and easily

Identified.

Regulation 18: Earthed terminal on consumer’s premises. –

This regulation is about the safety connection between your home’s

Electrical system and the ground.

• Grounded terminal: The power company will install a special

Connection point (grounded terminal) in your house near where the

Electricity enters.

• Safety: This connection helps protect you from electric shocks if

There’s a problem with the wiring.

• Higher voltage: If your electricity supply is over 250 volts, you

Need to have an additional safety system installed by a professional.

This system will connect to both the grounded terminal provided by

The power company and your own grounding system.

• Protect the terminal: You should be careful not to accidentally

• Damage the grounding terminal or its connecting wire.

Basically, this regulation ensures that your home has a safe and

Reliable connection to the ground for electrical protection.

Regulation 30: Display of instructions for resuscitation of persons

Suffering from electric shock. –

In simpler terms:

This regulation is about safety procedures in places that use

Electricity.

• Instructions: There should be clear instructions posted in places

Like power plants, factories, and substations on how to help

Someone who has been shocked by electricity. These instructions

Should be in English, Hindi, and the local language.

• Training: People who work with electrical equipment should know

How to follow these instructions and help someone who has been

Shocked.

Basically, this regulation helps ensure that people are prepared to

Respond to electrical emergencies.

Regulation 31: Precautions to be adopted by consumers, owners,

Occupiers, electrical

Contractors, electrical workmen and suppliers. –

This regulation is about who can do electrical work in your home or

Business.

• Licensed professionals: Only licensed electrical contractors can

Do major electrical work like rewiring or installing new outlets.

• Minor repairs: You can usually replace things like light bulbs,

Fans, and fuses yourself, but only if it doesn’t change the electrical

System.

• Government projects: Government buildings and some other

Places might have different rules about who can do electrical work.

Basically, this regulation ensures that electrical work is done safely

By people who know what they’re doing.

Regulation 38: Provisions for supply and use of electricity in

Multistoried building more than

Fifteen meter in height. –

In simpler terms:

This regulation is about safety rules for tall buildings and other

Important places.
 • Inspections: Tall buildings need to be inspected by professionals

Before they can get electricity.

• Safety measures: These buildings must have safety features like:

• A main switch to turn off the power completely.
• Safe wiring and maintenance.
• Special fire-resistant cables.
• Lightning protection.
• Regular inspections of electrical systems.

Basically, this regulation helps ensure that tall buildings and other

Important places have safe electrical systems.

Regulation 42: Test of insulation resistance. –

Where any electric supply line for use at voltages not exceeding 650

V has been disconnected from a system

This regulation is about safety checks for electrical lines.

• Safety test: If you’re working on an electrical line (like for

Repairs), you must do a safety test before turning it back on. This

Test checks if the wire is properly insulated and safe to use.

Basically, this regulation helps prevent electrical accidents by

Ensuring that lines are safe before being used again.

Regulation 43: Connection with Earth

This regulation applies to earthing systems for electrical systems

With voltages between 50 V and 650 V. The key points are:

1. Earthing the neutral conductor: In a three-phase, four-wire

System, and a two-phase, three-wire system, the neutral conductor

Must be earthed according to standards.

2. Additional earthing: The neutral conductor must be earthed at Various points in the
distribution system, not just at the consumer’s

Premises.
 3. Concentric cables: Systems with concentric cables must have the

External conductor or armor earthed at two distinct points.

4. Direct current systems: Earthing and safety measures must

Follow the relevant standards.

5. Building earthing: Every building must have protective bonding

Between exposed and extraneous metal parts to ensure safety.

6. Interconnection: AC systems connected to earth must be

Electrically interconnected, with each connection bonded to the

Metal sheathing and armor of supply lines.

7. Equipment earthing: Generators, motors, transformers, and other

Devices above 250 V but below 650 V must be earthed with two

Separate connections.

8. Metal casings: All metal casings and coverings protecting

Electrical lines must be connected to earth and provide a solid

Electrical connection across the system.

9. Exemptions: If the supply voltage is below 250 V, some devices

Like wall tubes, switches, or ceiling fans don’t need to be earthed,

Unless they have earth terminals. However, new or renovated

Installations must use three-pin sockets with the third pin earthed.

9. Earthing system requirements:

The system must handle fault current without exceeding

Temperature limits.

It must have low impedance to ensure the protective devices work

Properly.

The system must be mechanically strong, corrosion-resistant, and

Maintain continuity over time.

 10. Annual testing: The supplier must test earthing systems for

Resistance once a year during dry conditions.

11. Earth fault testing: The earth fault loop impedance must be

Tested regularly to ensure protective devices work, and records

Must be kept for two years.

12. Circuit limitations: The impedance of each circuit must be low

Enough to ensure that, during a fault, the power is disconnected

Before dangerous voltages are reached.

13. Generator and transformer earthing: The neutral point of every

Generator and transformer must be earthed with two separate

Connections.

Regulation 44: Residual Current Device (RCD)

Electrical installations must have an RCD to automatically

Disconnect the supply if the residual current exceeds standards.

For domestic installations, the RCD must have a residual operating

Current no higher than 30 milliamps.

RCDs are not required for systems with protective devices that are

Bonded to the neutral of supply transformers and meet regulation

76 standards.

Regulation 60: Clearance in Air for the Lowest Conductor of

Overhead Lines

1. Minimum Clearance: The lowest conductor of an alternating

Current overhead line (including service lines) must maintain a

Minimum clearance above the ground, roads (such as National

Highways, Expressways, or State Highways), railways, rivers, or

Other surfaces. The specific clearance values are listed in Schedule

VIII A.

2. High Voltage Direct Current: For high voltage direct current lines,

The minimum clearances are given in Schedule VIII B.

3. Protected Areas: For electric lines of 33 kV or below passing

Through protected areas like National Parks, Wildlife Sanctuaries,

Eco-sensitive zones, and Wildlife Corridors, only underground cables

Are allowed

4. Distance from Pipelines: No structure or tower for overhead lines

Of 33 kV or above, or high voltage direct current, can be placed

Within 25 meters from the edge of a Petroleum or Natural Gas

Pipeline’s right of way.

5. Crossing Pipelines: When overhead lines of 33 kV or above, or

High voltage direct current, need to cross a Petroleum or Natural

Gas pipeline, the crossing angle should ideally be 90 degrees, but

Must be no less than 75 degrees.

Regulation 60: Maximum Interval Between Supports

Conductors must be attached to supports at intervals that do not

Exceed the safe limits based on their tensile strength and safety

Factors, as per Regulation 59.

For overhead lines carrying conductors with a voltage of 650V or

Less, running over, along, or across streets, the interval between

Supports must not exceed 65 meters without written approval from

The Electrical Inspector.