XIX International Conference on Electrical Machines - ICEM 2010, Rome

Design and Analysis of a Brushless Doubly Fed

Induction Machine with Rotary Transformer
M. Ruviaro, F. Rüncos, N. Sadowski, I. M. Borges

Φ
Abstract -- This paper analyses design and performance The Doubly Fed Three-Phase Induction Machine with
aspects of a brushless doubly fed three-phase induction machine Rotary Transformer is one alternative to overpass these
with wound rotor circuit accessed by rotary transformer. It difficulties. Working with induction machine rotor
focuses firstly on the advantages of substituting brushes and frequency, rotary transformers permit act on rotor circuit
slip-rings by rotary transformers. Secondly it shows the device without any mechanical contact. By using an appropriated
operation conditions and rotary transformer calculation by
drive, it is possible to control the induction machine to
using Finite Element Software in 2D domain. In sequence are
presented analytical dynamic and steady state models for operate as generator as well as motor at almost any speed,
prediction of machine behavior. The analytical dynamic model except on synchronicity. This is especially convenient for
is obtained by transforming the equations written in machine systems that must generate constant frequency voltage by the
variables into equations written in arbitrary reference frame. use of variable speed devices, like wind turbines [1].
The steady state model considers electrical circuit techniques to The use of rotary transformers working direct with rotor
obtain information about current, power factor and efficiency frequency has been practically not studied. Until nowadays,
on load. Design data of a 90kW prototype were considered for studies are more concentrated in applications involving
numerical results presented on this study. frequencies higher than hundreds of Hz [7], [8].
To evaluate the proposed device capabilities, it is
Index Terms -- brushless rotating machines, doubly fed
important to use pertinent analytical models to aide in the
induction machines, rotary transformers
machine design and to have a better insight on its peculiar
characteristics mainly in what concerns the rotary
I. INTRODUCTION
transformer module [4].

T HREE-PHASE induction machine is a very popular kind

of motor for industrial application and a largely used
generator in wind energy farms. In this context doubly
This paper shows machine operation and main design
aspects; in sequence it discusses about steady state and
dynamic analytical models that enable performance
fed induction machines calls special attention for its torque prediction of the Doubly Fed Three-Phase Induction
and speed control characteristics [1], [2]. Machine with Rotary Transformer. Results presented are
When it is possible to access rotor winding, speed and based on the design data of a prototype.
torque can be controlled by rheostats or variable frequency
drivers (VFD). The accessibility to rotor circuit permits the
use of VFD whose power is proportional to the range around II. OPERATION
synchronous speed. This reduces VFD costs once it works The Doubly Fed Three-Phase Induction Machine with
only with a fraction of induction machine power.
Rotary Transformers is the set of a three-phase induction
Comparatively, the connection of VFD to the stator winding
machine with 2pm poles stator winding directly connected to
would require a more expensive device able to work with no
the electrical grid and a three-phase rotary transformer
less than 100% power of the controlled induction machine
[3]. system whose stator winding can be short-circuited or
The benefits of doubly fed induction machines use are connected to rheostat banks or to electrical grid through a
undeniable; nevertheless to take advantages of them it is vector-controlled VFD [1].
necessary to provide electrical connection between rotor Electrical connections for the use of VFD, i.e. converter,
winding and statics rheostat or VFD. are shown in Fig. 1. This configuration allows controlling
Nowadays the most common form to access rotor winding torque, speed, power factor and current of induction machine
is by brushes and slip-rings. However the establishment of by the converter connected to the stator winding of rotary
mechanical contact between moving slip-rings and static transformer. VFD controls the machine acting on amplitude,
brushes wears these components and involves maintenance frequency and phase of voltage applied in stator winding of
of them. Powder generated by brushes wearing can be also rotary transformer [2].
prejudicial for motor insulation. Additionally any fault on
electrical contact can generate sparks, limiting machine
installation only at non-explosive environments.
Development of brushless technologies is extremely
interesting for reducing maintenance costs and expanding the
possibility of using doubly fed induction machines also in
explosive atmospheres [4], [5], [6].

Fig. 1 – Grid connection of the doubly fed three-phase induction machine

This work was supported in part by WEG Equipamentos Elétricos S.A. with rotary transformer
Maurício Ruviaro, Fredemar Rüncos and Iduan Machado Borges are
with WEG Equipamentos Elétricos S.A., Jaraguá do Sul, SC, 89256-900,
Brazil (e-mail: mauricior@weg.net, fredemar@weg.net, iduanb@weg.net). If stator winding of the rotary transformer is connected
Nelson Sadowski is with the Department of Electrical Engineering, only to a resistive bank, it is possible to control torque, speed
Universidade Federal de Santa Catarina, Florianópolis, SC CP 476, 88.040- and current. However, power factor is not controllable.
970, Brazil (e-mail: nelson@grucad.ufsc.br).

978-1-4244-4175-4/10/$25.00 ©2010 IEEE

 The industrial design of a Doubly Fed Three-Phase When used VFD connected to stator winding of the
Induction Machine with Rotary Transformer is presented in transformer, as shown in Fig. 1, not only frequency can be
Fig. 2. imposed, but also the amplitude and phase of the voltage on
transformer stator, allowing in this way a complete control of
the Doubly Fed Induction Machine. This control is not
possible only on synchronous speed, when electric frequency
on rotary transformer is null and it is impossible to transmit
energy between its rotor and stator. This energy transference
depends necessarily of alternating current (AC) presence.
Fig. 4 shows the frequency on induction machine stator
and induced frequencies under induction machine rotor and
rotary transformer windings. Induced electric frequencies are
Fig. 2 – Doubly fed three-phase induction machine with rotary transformer function of mechanical frequency or speed of machine shaft.
The synchronous rotating frequency is represented by fsyn.
To be a brushless system is the great advantage of the
solution shown in Fig. 2. Additionally it permits to adjust Electric frequency
stator transformer voltage (Vt1) with great flexibility without fm1
any change on induction machine windings as can be noticed
through Fig. 3. In the equivalent circuit, Vm1 is induction
machine stator voltage; Nm1 and Nm2 are respectively the
number of equivalent turns at stator and rotor windings of the fsyn 2.fsyn fmec
induction machine.

-fm1
Frequency of induction machine stator
Frequencies of induction machine rotor, rotary
transformer rotor and rotary transformer stator

Fig. 3 – Simplified equivalent circuits for induction machine and rotary Fig. 4 – Current frequency in induction machine and rotary transformer
transformer

From Fig. 3, rotor voltage of the rotary transformer (Vt2)

must agree with the voltage of induction machine rotor (Vm2) III. DESIGN CRITERIA
for locked shaft, i. e. slip (s) = 1. On the other hand, stator Physically the studied device consists of a three-phase
voltage (Vt1) can be adjusted to desired levels by changing induction machine in cascade with a three-phase rotary
the relation of turns between the primary or stator (Nt1) and transformer system [5].
secondary or rotor (Nt2) of the rotary transformer: The induction machine is designed as an ordinary three
Vt1 = ( N t1 N t 2 ) .Vt 2 (1) phase wound rotor asynchronous machine.
The rotary transformer design [7], [8], [9], different from
The fundamental frequency of the air-gap induction wave conventional transformers, has the particularity of an air-gap
generated by the induction machine stator winding induces a to permit movement between primary (stator) and secondary
rotor winding current with electric frequency fm2 given by: (rotor) as can be observed in Fig. 5.
f m 2 = f m1 − p m f mec (2)

where fm1 is electric frequency of induction machine stator

and fmec is mechanical frequency of the shaft, both in Hz.
Rotor winding of the induction machine is electrically
Stator
connected to rotor winding of the transformer; consequently
their currents have the same electric frequency fm2. Rotor
Despite mechanical movement between rotor and stator
transformer, there is no slip between their magnetic flux. So,
currents on rotor and stator windings of the rotary
transformer also keep the same frequency fm2.
The synchronous mechanical frequency fsyn of the
induction machine is calculated by: Fig. 5 – Design of three-phase rotary transformer system
f syn = f m1 pm (3)
The three transformers are shell-form with primary and
Mechanical frequency of the shaft of the machine is: secondary windings totally involved by the core.
For rotary transformers design, the software Finite
f mec = ( f m1 − f m 2 ) pm (4) Element Method Magnetics (FEMM) and his resources were
used [10]. Fig. 6 presents simulation for secondary (rotor)
Equation (4) shows that is possible to control the speed of
winding supplied by three-phase voltage at 60Hz while
induction machine by changing the frequency fm2 of the
primary (stator) is open circuit., i.e., no-load connected.
voltage on stator winding of rotary transformer [2], [5], [6].
 where:
Vm1: stator voltage of the induction machine
Im1: stator current of the induction machine
fm1: electric frequency at induction machine stator
pm: number of induction machine poles pairs
Pshaft: mechanical power on shaft
Vm2: induction machine rotor voltage (s=1)
St: apparent power of rotary transformer (at 60Hz)

In the rotary transformer, the permanent alignment of

rotor and stator windings results in no slip between their
Fig. 6 – Rotary transformer simulation by finite element method resources magnetic fields. In this way, despite of one moving part the
transformer does not develop any torque on shaft.
Design option by 3 single-phase units has the objective to
reduce flux unbalance on rotary transformer system. The IV. ANALYTICAL APPROACH
presence of air-gap introduces reluctances that strongly
change transformer magnetic circuit when compared to A. Dynamic Model
conventional transformers. The analytical dynamic model is obtained by transforming
Core magnetic permeability is naturally much higher than the equations written in machine variables into equations
air-gap permeability. Consequently for a non-saturated written in an arbitrary reference frame.
magnetic core, air-gap reluctance is comparatively high and
The stator circuit of the induction machine is considered
affects strongly transformer magnetizing reactance. Like
fixed to the stationary reference frame and all machine
other devices for contactless energy transmission [4], rotary
transformer is characterized by high leakage/magnetizing variables (rotor and rotary winding parameters) are referred
reactance ratio. to the induction machine stator winding. The rotor circuit
In the developed prototype, induction machine and rotary rotates with an angular speed of ωm2 electric rad/s; q and d
transformer cores are both made with silicon steel axes rotate with an angular speed of ωqd0 electric rad/s and
lamination. As can be observed in Fig. 5, lamination the angular displacement between the rotor circuit and the
direction is longitudinal to the shaft. arbitrary q axis is βm2. Rotary transformer parameters are
Induction machine parameters were obtained through considered rotating with the same angular speed of induction
software for asynchronous machines designing used by the machine rotor, due to there is no slip between them.
manufacturer WEG Equipamentos Elétricos S.A. Rotary By transforming the equation system to the arbitrary
transformer parameters are obtained by FEMM [10]. reference frame, we obtain the following set of equations:
Fig. 7 and table I present main dimensions of the designed
single-phase rotary transformers. [
 vmqdo1 ] [R ] m1 [0] [0]  [imqdo1 ]
  
l ta
 [0 ]  =  [0 ] [Rm′ 2 + Rt′2 ] [0]   [imdo 
′ 2 ] +
h t 1b
 [
 v'tqdo1 ]
  [0 ]
  [0] [Rt′1 ]  [itqdo
′ 1 ] 
Nt1 h t 1a
g [
 ω qdo ] [0] [0]  [λmdq1 ]

N t2 h t 2a
 [0 ] [ωqdo − ωm2 ] [0]  [λmdq 
′ 2 ] +
(5)
rt
l tb h t 2b
 [0 ]
 [0] [ωqdo − ωm2 ]  [λtdq′ 1 ] 
[
 λmqdo1 ]
d 
dt 
′ 2[
λmqdo ]
 λtqdo
 ′ 1 [ ] 
Fig. 7 – Single-phase rotary transformer

TABLE I
ROTARY TRANSFORMER DIMENSIONS
Tel =
3
2
'
pm .Lmm imq1.imd ( '
2 − i md 1 .imq 2 ) (6)

d ω 
ht1a ht1b ht2a ht2b Nt1 TL = Te − J .  m 2  (7)
32mm 21mm 65mm 33mm 19 dt  pm 
lta ltb rt g Nt2
52mm 110mm 192mm 1,5mm 19 In equations (5), (6) and (7), the sub-indices m and t are
related to the induction machine and the rotary transformer,
Nominal data of the prototype discussed in this paper are respectively. In the same way, indices 1 and 2 are related to
shown in table II. the stator and rotor. Rm1, R’t1 are stator resistances of
induction machine and rotary transformer reflected to
TABLE II
NOMINAL DATA OF THE PROTOTYPE
induction machine stator; R’m2, R’t2, the rotor resistances of
induction machine and rotary transformer also reflected to
Vm1 Im1 fm1 2.pm Pshaft Vm2 St induction machine stator; λ_qd0, the flux linkage; v_qd0, the
690V 99A 60Hz 6 90kW 525V 90kVA voltages; i_qd0, the currents; Lmm, magnetizing inductance of
induction machine; Tel and TL, electromagnetic and load
 Torque ( Tbase = 741N.m, nbase = 1200 rpm )
torques; J is the inertia of the system. 5
Equations (5), (6) and (7) are solved by the fourth order 4
Tel
TL
Runge-Kutta method and, as a result, the dynamic behavior 3

of the machine is obtained. 2

Fig. 8 presents abc currents on stator winding of induction 1

Torque (p.u.)
machine. 0

Current "abc" on induction machine stator (I base = 140Apeak , nbase = 1200 rpm ) -1
6
-2

-3
4
-4

2 -5
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Current (p.u.)

Im a1 Speed (p.u.)
Im b1
0
Im c1
Fig. 11 – Electromagnetic torque for doubly fed three-phase induction
machine with rotary transformer
-2

All dynamic curves are obtained by the imposition of a

-4
constant and negative load torque (TL) as can be observed at
-6
Fig. 11.
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Speed (p.u)

Fig. 8 – Dynamic current on induction machine stator B. Steady-State Model

The steady-state behavior is obtained using the machine
Fig. 9 shows that current on the rotor of induction machine
equivalent circuit [11]. In Fig. 12 is presented the cascaded
and on the rotor of transformer has very low frequency close
connection between windings of induction machine and
to synchronous speed. This is in accordance with that was
rotary transformer. From this model it is possible to analyze
predicted on Fig. 4.
the machine operating at steady-state as motor and as
Current "abc" on induction machine rotor (Ibase = 140Apeak , nbase = 1200 rpm )
6
generator for any load condition with inductive or capacitive
power factors. All parameters are reflected to the stator of
4 the induction machine.
2
Current (p.u.)

I`m a2

0 I`m b2
I`m c2

-2

-4
Fig. 12 - Equivalent circuit of doubly fed induction machine with rotary
-6 transformer
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Speed (p.u.)

Fig. 9 – Dynamic current on induction machine and rotary transformer The meaning of the parameters is as following:
rotors Rm1: stator resistance of induction machine
Xm1: stator leakage reactance of induction machine
Fig. 10 shows dynamic current on stator transformer. The R’m2: rotor resistance of induction machine
frequency profile of this graph is very similar to that X’m2: rotor leakage reactance of induction machine
presented in Fig. 9; the difference between currents of Fig. 9 Rmfe1: stator iron resistance of induction machine
and 10 is only a small reduction on amplitude, due to R’mfe2: rotor iron resistance of induction machine
magnetizing current absorbed by the transformer.
Xmm: magnetizing reactance of induction machine
Current "abc" on rotary transformer stator (Ibase = 140Apeak , nbase = 1200 rpm )
6
R’t2: rotor resistance of rotary transformer
X’t2: rotor leakage reactance of rotary transformer
4 R’t1: stator resistance of rotary transformer
X’t1: stator leakage reactance of rotary transformer
2
R’tfe2: rotor iron resistance of rotary transformer
Current (p.u.)

I`t a1

0 I`t b1 R’tfe1: stator iron resistance of rotary transformer

I`t c1
X’tm: magnetizing reactance of rotary transformer
-2
R’ext: external resistance
-4
Im1: stator current of induction machine
I’m2: rotor current of induction machine
-6
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Imm: magnetizing current of induction machine
Speed (p.u.)
I’t2: rotor current of rotary transformer
Fig. 10 – Dynamic current on rotary transformer stator I’tm: magnetizing current of rotary transformer
I’t1: stator current of rotary transformer
Fig. 11 shows electromagnetic dynamic torque developed s: slip of induction machine
by induction machine when it is accelerated from 0 to 2 p.u.
Until 1 p.u. machine works like motor; above this speed it Table III presents numerical values for all equivalent
works like generator. circuit parameters reflected to induction machine stator
 Torque vs. speed (Tbase = 740N.m, nbase = 1200 rpm)
expressed in ohms ( Ω ). 3
R`ext = 0.R`m2
R`ext = 5.R`m2
TABLE III 2
R`ext = 10.R`m2
EQUIVALENT CIRCUIT PARAMETERS IN OHMS ( Ω ) R`ext = 15.R`m2
1 R`ext = 20.R`m2

Rm1 Xm1 R’m2 X’m2 Rmfe1 Xmm R’mfe2

Torque (p.u.)
0.045 0.228 0.047 0.346 505 10.0 500 0

R’t1 X’t1 R’t2 X’t2 R’tfe1 X’tm R’tfe2

-1
0.017 0.161 0.015 0.142 226 2.98 72
-2

Fig. 13 displays power curves of the Doubly Fed Three-

Phase Induction Machine with Rotary Transformer. From 0 -3
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Speed (p.u.)
to 1 p.u. speed, the machine works as motor, transforming
electrical power in mechanical power on shaft. From 1 to 2 Fig. 15 – Electromagnetic torques for transformer stator winding connected
to external resistances
p.u. speed, machine works as generator, converting
mechanical power in electrical power injected on grid. These Torque vs. speed (Tbase = 99N.m, nbase = 1200 rpm)
5
results consider the stator winding of rotary transformer
4.5
short-circuited.
Power vs. speed (Pbase = 90kW, nbase = 1200 rpm) 4
4
3.5
Pm 1
3 Pshaft 3

Current (p.u.)
2 2.5

2
1 R`ext = 0.R`m2
Power (p.u.)

1.5
R`ext = 5.R`m2
0
1 R`ext = 10.R`m2

-1 R`ext = 15.R`m2
0.5
R`ext = 20.R`m2
-2 0
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Speed (p.u.)
-3
Fig. 16 – Induction machine stator winding current for transformer stator
-4
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
winding connected to external resistances
Speed (p.u.)

Fig. 13 – Power for transformer stator winding short-circuited Fig. 17 presents a comparison between the induction
machine with and without rotary transformer connected to its
Fig. 14 shows the behavior of the diverse currents rotor winding. As can be observed, presence of rotary
presented on the equivalent circuit from Fig. 12. transformer does not change synchronous speed. In all
situations shown synchronous speed is always 1p.u.
Current vs. speed (Ibase = 99A, nbase = 1200 rpm)
5
Torque vs. rotação (Tbase = 740N.m, nbase = 1200 rpm)
4.5
5
Without RT
4
4 With RT (R`ext = 0.R`m2)
3.5 With RT (R`ext = 10.R`m2)
Im1 3

3
Current (p.u.)

Imm 2
I`m2 = I`t2
2.5 1
Torque (p.u.)

I`tm
2
I`t1 0

1.5
-1

1
-2

0.5
-3

0 -4
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Speed (p.u.)
-5
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Fig. 14 – Currents for transformer stator winding short-circuited Rotação (p.u.)

Fig. 17 – Electromagnetic torques for doubly fed three-phase induction

Like a conventional induction machine, the minimum machine with and without rotary transformer coupling
current is verified at synchronous speed, when no active
power is delivered on shaft. At synchronous speed, the Leakage reactances of rotary transformer are main
current absorbed by induction machine stator is equal to its responsible by torque curve depreciation. To minimize this
magnetizing current. undesirable phenomenon, solution is designing a transformer
The influence of rheostats insertion on stator winding of with air-gap and number of turns smaller as possible.
rotary transformer is shown in Fig. 15 and 16. Increasing Moreover, closer primary and secondary winding are,
external resistance values is possible to have higher starting smaller are leakage reactances.
torque and lower locked rotor current. The use of rheostat Fig. 18 shows that current is strongly reduced by adding
also permits load speed control, by changing the point where rotary transformer to the rotor circuit of induction machine.
motor and load torques are in equilibrium.
 Current vs. speed (Ibase = 99A, nbase = 1200 rpm)
8
Reduction of power factor of the set induction machine +
rotary transformer when compared with the induction
7

Without RT
machine running alone with short-circuited rotor is
6 With RT (R`ext = 0.R`m2)
comprehensible due to inductive nature of the rotary
With RT (R`ext = 10.R`m2)
5 transformer. Nevertheless using VFD coupled to rotor, it is
Current (p.u.)

4 possible to control power factor and get around this inherent

3
difficult.
2
VII. ACKNOWLEDGMENT
1
Authors wish to thank WEG Equipamentos Elétricos S.A.
0
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 for the prototype building and the use of its facilities.
Speed (p.u.)

Fig. 18 – Currents for doubly fed three-phase induction machine with and
without rotary transformer coupling VIII. REFERENCES
[1] F. Rüncos, N. Sadowski, R. Carlson, A. M. Oliveira, P. Kuo-Peng,
Table IV presents a comparison for the three-phase “Performance Analysis of a Brushless Double Fed Cage Induction
induction machine operating in two conditions: rotor short- Generator”, presented at Nordic Wind Power Conference, Chalmers
University of Technology, Göteborg, Sweden, 2004.
circuited and rotor connected to rotary transformer module. [2] G. M. Joksimovic, “Double-fed Induction Machine-Dynamic
For both conditions results are referent to motor operation. Modeling using Winding Function Approach”, in Proc. 2007 IEEE
International Electric Machines and Drives Conference, pp. 694-697.
TABLE IV [3] B. V. Gorti, G. C. Alexander, R. Spée, A. K. Wallace, “Characteristics
INDUCTION MACHINE WITH ROTOR SHORT-CIRCUITED AND WITH ROTOR of a Brushless Doubly-Fed Machine in Current-Fed Mode of
CONNECTED TO ROTARY TRANSFORMER (MOTOR OPERATION) Operation”, in Proc. 1995 IEEE/IAS International Conference on
Industrial Automation and Control, pp. 143-148.
Induction Induction Machine + [4] R. Mecke, “Contactless Inductive Energy Transmission Systems with
Machine Rotary Transformer Large Air Gap”, in Proc. 2001 European Conference on Power
Electronics and Applications [CD-ROM].
Voltage supply 690V 690V [5] F. Rüncos, “Double-Fed in Cascade Brushless Three-Phase
Power from grid 94.2kW 95.1kW Asynchronous Machine” (in Portuguese), Master’s dissertation,
Universidade Federal de Santa Catarina, Brazil, 2001.
Power on shaft 90.0kW 90.0kW [6] F. Rüncos, “Modeling, Project and Analysis of Brushless Double-Fed
Current 91.8A 98.6A Three-Phase Asynchronous Machine” (in Portuguese), Doctoral
thesis, Universidade Federal de Santa Catarina, Brazil, 2006.
Speed (rpm) 1188 1180 [7] J. Legranger, G. Friedrich, S. Vivier, J. C. Mipo, “Design of a
Power factor 0.859 0.807 Brushless Rotor Supply for a Wound Rotor Synchronous Machine for
Integrated Starter Generator”, in Proc. 2007 IEEE Vehicle Power and
Efficiency 95.5% 94.7% Propulsion Conference, pp. 236-241.
[8] S. H. Marx, R. W. Rounds, “A Kilowatt Rotary Power Transformer”,
In efficiency calculation stray losses of 0.5% of power IEEE Transactions on Aerospace and Electronic Systems, vol. AES-
from grid and mechanical losses of 800W at 1200 rpm are 7, issue 6, pp. 1157-1163, Nov. 1971.
[9] C. Wm. T. McLyman, “Transformer and Inductor Design Handbook”,
considered. 3rd ed., Ed. New York: Marcel Dekker Inc., 2004, chapter 19.
The rotary transformer module is an inductive load; [10] D. Meeker, “Finite Element Method Magnetics (FEMM) – User’s
natural consequences are some reduction on power factor Manual”, Version 4.2, 2009.
and current increasing, like presented on the table IV. [11] S. J. Chapman, “Electric Machinery Fundamentals”, 3rd ed., Ed. New
York: McGraw-Hill, 1999, pp. 371-378.

V. PROTOTYPE BUILDING
IX. BIOGRAPHIES
Results presented in this paper are based on design
parameters of a prototype shown in Fig. 2. Maurício Ruviaro is Electrical Engineer at WEG Equipamentos
Elétricos S.A. and Master’s student at Universidade Federal de Santa
Industrial conception of rotary transformer was an Catarina. He received his Engineering Diploma from the same university at
interesting challenge as well as its construction. 2006. His work and research topics are electrical calculation of large
Prototype building is an important stage to verify practical induction machines and wind energy generation.
results for the developed study. Fredemar Rüncos is Engineering Manager at WEG Equipamentos
Elétricos S.A. and Professor at Centro Universitário de Jaraguá do Sul. He
received his Doctoral Diploma from Universidade Federal de Santa
VI. CONCLUSION Catarina at 2006. His work and research topics are induction and
Substituting brushes and slip-rings is a great advantage of synchronous machines. He is author or co-author of nearly 20 technical
papers in journals and conferences.
using rotary transformers in doubly fed induction machines.
Avoiding mechanical contact between brushes and slip-rings, Nelson Sadowski is full Professor at the Universidade Federal de Santa
Catarina. He received his Doctoral Diploma from de Institut National
motors and generators maintenance can be drastically Polytechnique de Toulouse at 1993 and his Habilitation à la Direction des
reduced. Additionally the studied device became possible to Recherches from the same institute at 2002. His research topics are the
install wound rotor machines on explosive environments. calculation of electromagnetic fields by numerical methods. He is author or
Moreover, this solution keeps available all the benefits co-author of nearly 300 technical papers in journals as well as in
conferences. With Professor Joao Pedro Assumpção Bastos, he is author of
inherent to the use of induction machine rotor circuit for the book Electromagnetic Modeling by Finite Elements Methods.
machine controlling.
Iduan Machado Borges is Mechanical Engineer at WEG
Results verified in the design stage of a real machine give Equipamentos Elétricos S.A. He received his Engineering Diploma from
good expectations about using this technology on industrial Universidade Federal de Santa Catarina at 2008. His work topics are the
motors and wind power generators. structural calculation of large induction machines.