Motor Command and Supervision Using the Magnetic Components of the Insulation Fault Protection System for Power Line Communication

International Journal of Power Electronics and Drive System (IJPEDS)
Vol. 8, No. 1, March 2017, pp. 204~212
ISSN: 2088-8694, DOI: 10.11591/ijpeds.v8i1.pp204-212  204
Journal homepage: http://iaesjournal.com/online/index.php/IJPEDS
Motor Command and Supervision Using the Magnetic
Components of the Insulation Fault Protection System
for Power Line Communication
Matias F. Bulacio1
, Hernan E. Tacca2
1,2
Department of Electronics, Facultad de Ingenieria, Universidad de Buenos Aires, Argentina
Article Info ABSTRACT
Article history:
Received Oct 07, 2016
Revised Dec 13, 2016
Accepted Dec 23, 2016
This work proposes an additional function for a VSD (Variable Speed Drive)
which sends and receives information over the power lines
and simultaneously, implements the protection against insulation faults to
earth. Using the magnetic components of the insulation fault protection
system of the motor, the prototype injects and detects the communication
signals over the power line. The system works on both communication
schemes, with and without the PWM (Pulse Width Modulation) perturbation
in the power lines, which are the two possible real applications. In order to
set a proper communication between the motor and the drive, the
communication channel was modeled and the noise was characterized. An
FSK modulation and demodulation scheme was developed and tested. A 10
kbps communication over a 125m length of cable and over a 1km pi-section
model of the same cable was successfully achieved with the laboratory
prototype.
Keyword:
Induction motor
Motor command
Motor protection
Motor supervision
Power line communication
Copyright © 2017 Institute of Advanced Engineering and Science.
All rights reserved.
Corresponding Author:
Matias F. Bulacio,
Department of Electronics,
Facultad de Ingenieria, UBA,
Av. Paseo Colon 850, C1063ACV, Buenos Aires, Argentina.
Email: mbulacio@fi.uba.ar
1. INTRODUCTION
Induction motors are widely used at industry for motion control system due to their low cost and the
relative low frequency of maintenance [1]. Anyway, a severe failure in such systems can cause significant
economic losses due to the stop of production for long time spans. Because of that, many research works are
focused on developing reliable ways for motor control diagnosing their conditions and performance (sensing
motor parameters), and protecting them (keeping the mechanical and thermal conditions within acceptable
limits) [2]-[4]. Statistics show that annual down times of 0.5% to 4% may be expected [5]. When it is
necessary to regulate the motor speed, VSDs are used, which command the motor with adjustable frequencies
and voltages using different Pulse Width Modulation (PWM) techniques [6]-[7].
VSDs sometimes require received control and diagnosis information both from the monitoring
station and the motor [8]-[11]. This communication is commonly done using industrial communication
protocols which need additional wires that can increase the system cost, and many times may be difficult or
even impossible to install due to the inaccessibility to the place where the motors are mounted [12]. In some
cases long cables need to be used, with lengths from a few hundred meters to a kilometer, between the motor
and its driver [12]-[13]. Examples of these are underground pump driving motors, heaters used in industry
and mines, and wind generators [8].

IJPEDS ISSN: 2088-8694 
Motor Command and Supervision Using the Magnetic Components of the Insulation .... (Matias F. Bulacio)
205
Also, these motor drives, integrate protection functions against overload, short circuit between
phases and insulation faults, among others. The main causes of motor failure are the variation of the feeding
phase voltages, mechanical overloads, and problems produced by inadequate or faulted electrical installations
[3],[4],[14]. Other causes may include the aging of the motor or eventual adverse environmental conditions.
Most of these events lead to an increase of the current and to a subsequent rise of motor temperature. An
unacceptable overheating of the motor could damage the insulation of the windings taking the motor out of
service [4],[14],[15]. The high dv/dt, characteristic of PWM VSDs, is a source of further stress and
deterioration of the insulation.
There are many works, such as [8]-[11],[13], in which the power lines feeding the motor are used as
communication channel to transmit commands and diagnose information. In this work, in addition of
profiting of the power lines as a communication channel, the magnetic components of the insulation fault
protection system (commonly used in VSDs) are used as communication coupling devices. This approach
implies the difficulty of transmitting and detecting signals with the common mode noise injected by the high
voltage PWM signals. The inductive coupling proof to be the more reliable in PWM networks [8], but the
communication signals are injected in common mode to be able of insulation fault detections.
Due to the fact that the signal injection is in common mode, the communication channel and the
noise are studied for this particular scheme using the ABCD transmission matrix of the system components
as in [13]. Based on the communication channel model obtained, an FSK system was designed, implemented
and tested. A 10 kbps communication over a length of 125 m of 4 x 6 mm2
ETIX cable was successfully
achieved. Also, the system was tested successfully with 8 sections of PI circuit (representing 125 m each
section) emulating the behavior of 1 km of the same cable.
2. PROTECTION AND COMMNAD SYSTEM
2.1. Basic Protection Scheme
Basic protection functions are commonly integrated in VSDs, such as insulation fault detection.
These systems are generally implemented as differential relays [16],[17], which are conceptually based on a
property of single-phase and three-phase systems, which states that in absence of insulation faults the sum of
the line currents must be null. This scheme switches-off the motor whenever a zero sequence current in the
feed lines appears.
As stated in [18] if the differential protection scheme is built using small-cores transformers, two
transformers are required. One injects a high frequency zero sequence current to be detected by the second
one only if an insulation fault occur. This scheme is shown in Figure 1.
DIFFERENTIAL
DETECTION
TRANSFORMER
HOMOPOLAR
SENSING
R
S
T
INDUCTION
MOTOR
INJECTOR
DIFFERENTIAL
INJECTION
TRANSFORMER
Figure 1. Injection and detection signal scheme for insulation fault detection
The signal injection circuit will not produce a high-frequency circulating current as long as the
motor does not have a neutral connection, which is the usual case. In this situation, the secondary of the
differential current detection transformer presents no induced voltage. The signal will be effectively injected
and detected when a ground or neutral fault occurs because that only the homopolar current could produce a
net flux in the transformer core to induce a detectable secondary voltage. If the neutral terminal is accessible
to the operator, both line-to-ground and line-to-neutral faults can be discriminated between each other by
using two detection circuits and passing the neutral wire through one of the detection transformer cores.

 ISSN: 2088-8694
IJPEDS Vol. 8, No. 1, March 2017 : 204 – 212
206
2.2. Communication Signal Coupling using the Magnetic Components of Insulation Fault Protection
System
The previous section introduced the use of current transformers for motor protection against
insulation faults. The following describes the use of the magnetic components as coupling devices interfacing
with the power lines to inject and recover commands, without losing the capacity of insulation fault
detection. Depending on the specific application, there are two possible communication system schemes.
One corresponds to the case where the data flow is between the supervision system and the variable
speed drive (Figure 2). Under these conditions, if the inverter has a filter at the input (which usually has), the
flowing currents do not have a high harmonic distortion, which is the most favorable case for setting the
communication. On the other hand, a more adverse scenario is present when the communication is stablished
between the motor and the inverter (Figure 3), due to the high voltage PWM signal presence on the power
lines, which pollute the communication media and degrade the signal to noise ratio. In this scheme the motor
could be sending diagnosis information to the supervision system, such as motor winding temperature,
vibration, etc.
Monitoring
station
Induction
motor
Energy
Data
Motor drive
Commands
Transmitter Receptor
Figure 2. Inverter-Motor remote command
Monitoring
station
Induction
motor
Energy
Data
Motor drive
Transmitter
Receptor
Sensing
Figure 3. Motor parameters remote sensing
In order to allow the communication to the monitor system, an FSK modulation and demodulation
scheme was implemented using an FPGA and ASIC (Application Specific Circuit) which implements the
demodulator by Switched Capacitor technique [19]. Both the injection and detection signal circuit use the
magnetic components of the insulation fault protection system, as coupling interfaces to the power lines. As
concluded in [8] the inductive coupling interface is the more reliable.
Figure 4 shows the system when used to send and receive diagnosis information from the motor to
the inverter. This scheme is the most interesting because their requirements, given that the communication
must be set in the presence of the PWM signal. The dv/dt filter at the inverter output is optional and it is not
needed to set the communication, but to protect the induction motor against surge waves because of long
cables.
2.3. Communication Channel Modelling
In all data transmission system, it is customary to analyze the media which transport the
communication signals and the existing noise to properly design the communication system.

207
MOTOR
DRIVE
COMMON MODE FILTER
INDUCTION MOTOR
FPGA
A3P250
Tx
SW. CAP.
DEMODULATOR
FPGA
AFS600
Rx
Figure 4. Injection and recovering data scheme in PWM network. The power cable is connected between the
injection and detection current transformers
The communication scheme of Figure 4 can be represented by the general communication model
shown in Figure 5. The model consists of the impulsive response of the channel communication media, and
the additive noise at the receiver end. According to this simple model, the signal at the receiver end can be
written as:
( ) ( ) ( ) ( ) (1)
where s(t) is the injected signal by the transmitter, h(t) is the impulsive response of the media and n(t) is the
noise at the receiver end.
Transmitter
Channel
Communication
h(t)
Receiver
Noise n(t)
s(t) r(t)
Figure 5. General channel model
In general PLC systems are difficult to model due to the multiple paths that the signal can take. In
the case of the communication between the motor and the inverter the scheme is simpler because the
components of the system are well defined. As the injected signal is homopolar, the common mode
impedance of each component must be modeled. In this section, the channel communication is studied,
obtaining the frequency response between the sender and the receiver, by the ABCD transmission matrix
method as in [13].
All the components that integrate the whole system are described by their own transmission matrix,
and then, the chain rule is applied in order to obtain the complete transfer characteristic. As shown in
Figure 4, the signal is injected by the transmitter through the inductive coupling at the motor side. Then, the
data travel through the power lines to the receiver end, where the inductive coupling of the receptor
demodulates the information. Additionally, in parallel with the motor and the inverter (if no dv/dt filter is
connected) there are common mode impedances (series RC) that allow the homopolar current to flow.
Figure 6 shows the coupling interface at the transmitter and receiver ends. The injection current
transformer is commanded by a push-pull circuit. Notice that the receiver current transformer is connected to
the Switched Capacitor demodulator. All the impedance models of each component of the communication
system were modelled by the transmission matrixes that respond to the next equations, depending whether
the impedance be connected in series or parallel with the signal path:
( ) ( ) (2)

 ISSN: 2088-8694
208
( ) ( ) (3)
Then applying the chain rule, the total transmission matrix is obtained between the transmitter and
receiver. The individual transmission matrix connection is shown in Figure 7. The total quadripole
transmission matrix connection is also shown in the same figure. Each transmission matrix of the Figure 7a
corresponds to:
Tpi: Injector’s parallel impedance transmission matrix.
Tsi: Injector’s series impedance transmission matrix
Tm: Motor’s and parallel leakage’s impedance transmission matrix.
Tc: Cable’s transmission matrix.
Tfi: Inverter’s and parallel leakage’s impedance transmission matrix.
Tsd: Detector’s series impedance transmission matrix.
Tsp: Detector’s parallel impedance transmission matrix.
Finally, in Figure 8, the frequency response of channel communication between the motor and the
inverter modelled and measured is plotted taking into account that:
(4)
The measurement setup includes a function generator with 50 ohms output impedance and a regular
oscilloscope. The sinusoidal frequency of the signal at the function generator was varied between 10 kHz-1
MHz and the injected and detected signal was measured. The discrepancy in the model and measurement
around the frequency corners is due to the sensibility of the oscilloscope (mV signal was measured for that
frequencies).
Transmitter
Receiver
Power Lines
Injected Signal Detected signal
Figure 6. Transmitter and Receiver coupling interface
Ug Tpi
Zg
Ui ZL
+
-
Tsi Tm Tc Tfi Tsd Uo
+
-
Tpd
Ug
Zg
Ui
Ii
ZL
Io
Uo
A B
C D
+
-
+
-
(a) (b)
Figure 7. (a) Chain transmission matrix Communication channel model between the motor and the inverter.
(b) Quadripole model through the ABCD transmission matrix excited by a generator with impedance Zg and
connected to a load ZL

209
Figure 8. Communication channel frequency response between the motor and the inverter to the frequency
band of 10kHz-1MHz
2.4. Noise Characterization
As important as model the communication channel is to characterize the source of noise in the
media. In [20] the authors say that the power lines do not conform an AWGN channel. Also, in [21] it is
argued that the noise sources are as diverse as colored noise, narrow band noise and periodic and aperiodic
impulsive noise. In inverter fed power lines the main cause of noise is the high voltage PWM signal.
The inverter output IGBTs has high dv/dt variations. The usual switching frequency varies between
2-20 kHz. The level of detected noise at the receiver end will depend on the connection or not of the dv/dt
filter at the output of the inverter. The Figure 9 shows the PWM signal measured between a phase and ground
and it’s PSD. Also the PSD of the detected noise is plotted for no filter at the inverter output connected. The
switching frequency is 10 kHz. Figure 9.c shows how the noise detected because of the PWM signal is
severely diminished by the communication channel.
(a)
(b)
(c)
Figure 9. (a) PWM signal measured at the inverter output (b) PSD of PWM signal and (c) PSD of the PWM
noise detected at the receiver end

 ISSN: 2088-8694
210
3. EXPERIMENTAL RESULTS
The laboratory experimental setup is represented in Figure 10. A 0.4kW Hitachi VFD was connected
to a 0.18kW Siemens induction motor, through a 125 m 4x6 mm2
ETIX power cable. The FSK modulator
and demodulator implemented were coupled through the coupling interface shown in Figure 6. Also the RC
network at the motor and inverter ends was connected in order to provide a path to the communication
signals. As shown in Figure 10 there is no need to connect a dv/dt filter at the inverter output to establish a
proper communication.
In Figure 11 the insulation fault protection measurement are presented. Abrupt leakage impedance
was connected and the detected rectified and the alarm signals were measured. The delay of the insulation
fault detection can be seen in Figure 11, and it is of the order of 5 µs, which not only allow human [22] and
motor protection but also protection of the IGBT modules as well.
Then the communication system tests were performed to show the no influence of the PWM signal
to recover the injected commands in the power lines. Three motor commands were implemented in the
prototype which are forward, reverse and stop commands. Figure 12 show the detected signal and
demodulated bit for a 0-1-0 bit sequence. Figure 13 show the transmitted and demodulated bit for the three
commands implemented with the inverter on.
As can be seen in Figures 12 and 13 the bit rate obtained is 10 kbps. The same bit rate was achieved
in the laboratory setup with the PI sections circuits that emulates a 1 km of 4 x 6 mm2
ETIX power cable.
The cable electrical parameters were obtained by finite element method (FEM) simulation of the geometry of
the cable provided by the manufacturer.
Injection circuit
VARIABLE
SPEED
DRIVE
INDUCTION MOTOR
FPGA
A3P250
Tx
FPGA
AFS600
Protection Rx
CH B
CH A
CH A CH B
CH A CH B
CH A
CH A GND
SW. CAP.
DEM.
Leakage
CH A
CH B
Alarm
CH A
Figure 10. Laboratory experimental setup for protection and power line communication test
Figure 11. Insulation fault protection measurement
Figure 12. Communication system measurements

211
(a)
(b)
(c)
Figure 13. Received commands in the PWM network (a) Forward (b) Reverse (c) Stop
4. CONCLUSION
In this work, magnetic components of the insulation fault protection system, commonly used in
VSDs, were used as coupling interfaces to the power lines in order to achieve a communication through
them. A 10 kbps communication over a 125 m length of cable and over a 1 km pi-section circuit that emulate
the behavior of the same cable was successfully achieved with the laboratory prototype. Also, both protection
and communication functions can simultaneously work. A channel communication and noise model for the
common mode injection scheme over the 10 kHz – 1 MHz band was obtained.
The insulation fault detection delay is of the order of few µs, which not only allow human and motor
protection but of the IGBT modules of the inverter as well. The apparently weakest point of the system is
maybe it’s bigger advantage with respect of the other works, and it is the injection and detection common
mode signal. If one or even two wires of the power line fails (cutoff) the system can warn the monitoring
system by establishing communication through the remaining wire.
ACKNOWLEDGEMENTS
This work is a PhD Thesis supported by the Peruilh Grant awarded by the Facultad de Ingeniería of
the Universidad de Buenos Aires and by the “UBACYT 20020130100840BA” research subsidy from the
same university.
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2005.

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BIOGRAPHIES OF AUTHORS
Matias F. Bulacio was born in Buenos Aires, Argentina, in 1984. He received the B. E. degree
in electrical engineering from the University of Buenos Aires in 2011 and he is currently
finishing his Ph.D.. Since 2013, he has been instructor at the Department of Electrical
Engineering in Basic Electronics. He had an UBA (2011) and Peruilh (2011-2016) scholarships
to realize his PhD directed by H. E. Tacca at the “Laboratorio de Control de Accionamientos
Traccion y Potencia, LABCATYP”, Facultad de Ingenieria, Universidad de Buenos Aires.
Hernan E. Tacca was born in Argentina on December 15, 1954. He received the B.E. degree in
electrical engineering from the University of Buenos Aires (Argentina), in 1981 and the M.S.
and Ph.D. degrees from the University of Sciences and Technologies of Lille (France) in 1988
and 1993, respectively. In 1998 he received the Doctorate degree from the University of Buenos
Aires. Since 1984, he has been with the Faculty of Engineering of the University of Buenos
Aires, where he is currently full Professor and engaged in teaching and research in the areas of
industrial electronics. His research interest are in the field of SMPS, UPS, battery chargers, soft-
switching techniques and microcontroller control of power converters.

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