Smart Grid and Renewable Energy, 2012, 3, 159-164
http://dx.doi.org/10.4236/sgre.2012.33023 Published Online August 2012 (http://www.SciRP.org/journal/sgre)
159
New “Intellectual Networks” (Smart Grid) for Detecting
Electrical Equipment Faults, Defects and Weaknesses
Alexander Yu. Khrennikov
Federal Grid Company of United Energy System, Moscow, Russia.
Received November 3rd, 2011; revised May 10th, 2012; accepted May 17th, 2012
ABSTRACT
The most important elements of “intellectual networks” (Smart Grid) are the systems of monitoring the parameters of
electrical equipment. Information-measuring systems (IMS), which described in this paper, were proposed to use to-
gether with rapid digital protection against short-circuit regimes in transformer windings. This paper presents an appli-
cation’s experience of LVI-testing, some results of the use of Frequency Response Analysis (FRA) to check the condi-
tion of transformer windings and infra-red control results of electrical equipment. The LVI method and short-circuit
inductive reactance measurements are sensitive for detecting such faults as radial, axial winding deformations, a twist-
ing of low-voltage or regulating winding, a losing of winding’s pressing and others.
Keywords: Intellectual Networks; Smart Grid; Monitoring System; Electrical Equipment; Information-Measuring System;
Frequency Response Analysis; Transformer Winding Fault Diagnostic; Low Voltage Impulse Method;
Short-Circuit Inductive Reactance Measurement
1. Introduction
Joint Stock Company “Federal Grid Company of United
Energy System” is the operator of the United National
Electrical Network of Russia. Extent of the electrical
power transmission lines is 121.7 thousand km, the quan-
tity of substations is 805, the class of voltage 220 - 750
kV. The five-year investment program in 2010 was for
the first time affirmed the program of company, which
foresees the building of 73 new substations.
“Modernization must bear the innovation nature,
which assumes passage to the existing energy technolo-
gies of XXI century”—says Mr. Sergey Shmatko, Min-
ister of power electrical engineering of Russia. The real-
ized by Federal Grid Company passage to “clever power
engineering” (Smart Grid) will make it possible not only
substantial to change today’s energy landscape, but also
will give pulse to the development of electrotechnical
industry, the mastery of new technologies and electrical
equipment by plants and by scientific design institutes, it
will fill by the practical sense of the development of
Russian scientists.
It was declared on the passed in June 2011 Saint-Peters-
burg International Economic Forum, that the result of the
conversions, conducted today by Federal Grid Company,
must become the creation of the components of “intel-
lectual networks” (Smart Grid), which can solve the ex-
isting tasks of the power electrical engineering branch, to
increase the effectiveness of its work and to create condi-
tions for increasing the competitive ability of the econ-
omy of Russia on the basis of the new innovation solu-
tions and technologies.
2. Information-Measurin g System for
Control of Inductance Value
Transformer’s Winding
The most important elements of “intellectual networks”
(Smart Grid) are the systems of monitoring the parame-
ters of electrical equipment.
The residual winding’s deformations of power trans-
formers during short circuits will appear practically in-
stantly, without leaving time to analysis the results of the
diagnostic measurements, and requiring as it is possible
to rapidly switch off, with the purpose of averting or re-
ducing repairing of electrical equipment in the future.
Information-measuring systems (IMS), which described
in this paper, were proposed to use together with rapid
digital protection against short-circuit regimes in trans-
former windings. The instantaneous and average values
of inductance were calculated. This calculation showed
that IMS, using for inductance value (L) control, allowed
to decrease failure volume and expenditures for renova-
tion repairing at transformer manufacturer.
Scheme of IMS for the control of transformer’s wind-
ing state in service of transformer’s winding in service

New “Intellectual Networks” (Smart Grid) for Detecting Electrical Equipment Faults, Defects and Weaknesses
160
without switching off from the network is depicted in
Figure 1 [1-4].
3. Algorithm of Information-Measuring
Systems (IMS)
The algorithm of IMS’s work is the following. The con-
tinuous control of the winding’s state of the controlled
power transformer is ensured by a constant determination
of the significance of inductance’s deviation from the
base value of inductance, which is taken from the block
of the base inductance.
During the work of the three-phase controlled power
transformer (T) for the three-phase resistive load (Load)
is made the measurement of the value of primary voltage
U1 by measuring converters primary voltage (high-voltage
transformers TV1).
Signal from the converters was entered to the entrance
of the block of bringing the primary voltage to the sec-
ond. In this block the value of the primary voltage, which
is corrected to the second, is calculated:
1
1
t
U
U
K

 (1)
where Kt—known given value of the transformation ratio
of power transformer.
Signals from the measuring converters of second volt-
Control
block
protection
b
loc
k
ТV2
CТ
А
В
С
В
ТV1
Т
Hz
Load
di/dt
Uaverage
L0

L Laverage
Lj
Ljmeas. U*
U1*
iR
R0
Figure 1. Information-measuring system for control of transformer’s windings state in service.

New “Intellectual Networks” (Smart Grid) for Detecting Electrical Equipment Faults, Defects and Weaknesses 161
age (voltage transformers TV2) and signals from the
output of the previous block were entered to the entrance.
In the block of calculation of voltage difference, which
corrected to the second side, is determined:
1
UUU 

2
(2)
where U2—the value of second voltage, measured by
converters TV2.
The calculation is produced in the assigned time inter-
val in the block of calculation of voltage’s average value:


2
average 2
jj
ut ut
u 

1
(3)
where
j
u
—value between corrected to the second side
voltages on the transformer; t1 and t2—temporary bounda-
ries of partition’s interval.
In the block of calculation of the current derivation is
calculated the increase of the current in the assigned time
interval:


2
21
jj
j
it it
di dttt


1
(4)
ij—value of current in the secondary winding of con-
trolled transformer, measured by current converters (cur-
rent transformers CT).
In the block of calculation of inductance the instanta-
neous value of inductance is determined in the assigned
time interval:

average
meas.j
j
u
Ldi dt 

(5)
where average—average value of voltage, u
j
didt —va-
lue of current derivation.
Equation (5) can be obtained from Ohm’s law for the
magnetic circuit:
Li

 (6)
Further using expressions:
;
d
uL
dt i

, (7)
we obtain dLdiidL

.
Disregarding second term (L = const), we have with
the linear characteristic of the medium:
di
uL
dt
 (8)
which is analogous to (5).
In the block of bringing the value of inductance to the
nominal frequency the instantaneous value of inductance,
with corrected to the nominal frequency, is calculated:
meas.
meas.
nom.
jj
f
LL f  (9)
where: meas.
f
—measured by frequency converter value
of the frequency (Hz), nom.
f
—nominal value of the fre-
quency. —instantaneous value of inductance.
meas .j
In the following block the average value of inductance
during each period is calculated:
L
average
1
N
j
j
LL

N (10)
In the block of calculation of deviation is produced the
comparison of Laverage value during the period with the
base L0 value and their difference is calculated:


average 0
0
100%LL
LL

 (11)
average —the average value of inductance during the
period;
L
L0—the base value of transformer inductance, deter-
mined by calculations also according to the results of
preliminary experiment.
In the case of the beginning of winding deformations,
and also in the case of winding turn-to-turn internal short-
circuit the value of inductance L is developed to increase,
or to decrease from this period to next period that ac-
companies the irreversible destruction of the controlled
power transformer’s windings.
Then the signal from the control block enters to the
protection block (rapid digital protection), where signal
to switch off in high-voltage circuit breaker (B) is formed.
And then Information-measuring system and connected
with it protection block stopped the process of winding
destruction [1-4].
4. Short-Circuit Testing of Power
Transformers and LVI Method for
Detecting Transformer’s Winding
Deformations
Power transformers are one of the basic parts in the cir-
cuitry of power transmission and delivery. Therefore the
interest to perfection of the power transformers’ fault
diagnostic methods is being increased. The repairing of
power transformers and other electrical equipments are
carried on, using diagnostic measurement results [5-7].
Infra-red control was used for detecting electrical
equipment’s faults, defects and weaknesses.
There are main causes of power transformer winding
faults: high-voltage bushing damage, breakage of wind-
ing insulation after long time service factors and partial
discharge intensity, insufficient electrodynamic winding
strength during short-circuits.
LVI-testing, FRA and short-circuit inductive reactance
measurements are sensitive to detecting such transform-
ers winding faults as buckling, axial shift and others. 180
units of 25 - 240 MVA 110 - 500 kV power transformers

New “Intellectual Networks” (Smart Grid) for Detecting Electrical Equipment Faults, Defects and Weaknesses
162
were checked by low voltage impulse (LVI) method. A
few power transformers were detected with winding de-
formations after short-circuit with aperiodical short-circuit
current. The block 80 MVA 110 kV transformer had se-
rious amplitude and frequency LVI LV1-LV2 winding
oscillogram differences after generator side short-circuit.
The low-voltage (LV) winding FRA spectrum of 80
MVA 110 kV transformer changed after short-circuit.
22 units of power transformers extending in capacity
range from about 25 MVA to over 666 MVA and in
voltage range from 110 kV to 750 kV were tested at
short-circuit at Togliatti Power Testing Laboratory dur-
ing 1983-1995. The application of LVI method and mea-
surement of inductive reactance deviation allowed to
detect a twisting of low-voltage winding and radial
winding’s deformations at tests of the 400 MVA and a
250 MVA block power transformers [4-9].
The damage of regulating winding was detected at the
short-circuit tests of link 167 MVA/500 kV/220 kV and
125 MVA/220 kV/110 kV autotransformer at Power Test-
ing Laboratory. The regulating winding was untwisted at
short-circuit tests of 25 MVA railway transformer. The
windings of 160 MVA metallurgical transformer were
pressed off during these tests. Deformations of turns
were detected at the electrodynamic tests of 666 MVA
power transformer for the Hydroelectric Power Station.
5. An Example of Transformer’s Winding
LVI-Testing
The LVI method is very sensitive to small local changes
of winding mechanical condition: turn-to-turn and coil-
to-coil capacitances, mutual inductances between trans-
former windings. The LVI oscillogram, which contains
basic resonance frequencies of transformer winding, is a
“fingerprint” or state of transformer. Generally, windings
of large power transformers have three basic resonance
frequencies. Frequency Response Analysis (FRA) showed
presence of 110 kHz, 320 kHz and 550 kHz frequencies
for 250 MVA/220 kV transformer. An amplitude of these
resonance frequencies changed 1.3 - 2 times after detec-
tion of radial buckling in LV winding at short-circuit
tests (Figure 2) [10-12].
Inductive reactance deviation was Xk = +1% in this
case.

The axial shift and damage of pressing system with
short-circuit to iron core were detected in the B phase LV
internal winding of 250 MVA/220 kV transformer after
short-circuit tests (Figure 3). Inductive reactance devia-
tion was Xk = +20% on the B phase. 
Radial buckling in MV 220 kV winding (a) and in HV
500 kV winding (b) of 167 MVA/500 kV/220 kV auto
transformer after three short-circuits in service is in the
Figure 4.
125 MVA/220 kV/110 kV autotransformer was switched
Figure 2. Typical example of deformation due to radial
buckling in the A phase LV internal winding of 250 MVA/
220 kV transformer (

Xk = +1%).
(a)
(b)
Figure 3. Example of deformation due to axial shift (a) and
damage of pressing system with short-circuit to iron core (b)
in the B phase LV internal winding of 250 MVA/220 kV
transformer (

Xk = +20%).

New “Intellectual Networks” (Smart Grid) for Detecting Electrical Equipment Faults, Defects and Weaknesses 163
off by gas relay protection after internal short-circuit at
the substation in service. The tank of autotransformer
was not deformed (Figure 5). Serious deformations and
turn-to-turn internal short-circuit were detected in MV
110 kV winding, regulating winding and LV winding by
LVI-testing, short-circuit inductive reactance measure-
ments and iron core losses methods. LVI oscillograms of
MV 110 kV winding, including turns of regulating wind-
ing (a), and oscillograms of LV winding (b) are in the
Figure 6. The LVI amplitude-frequency differences of C
phase from A and B phases are noticeable. The short-
circuit inductive reactance differences of C phase from A
and B phases are Xk = –11.6% in MV-LV winding
regime, and Xk = –7% in HV-LV winding regime.
The main goal of diagnostic investigation of 125 MVA/
220 kV/110 kV autotransformer was to define the possi-
bility of repairing. On the basis of results of this diagnostic
investigation there was planed the substitution of auto-
transformer [8,10-15].


6. Application of FRA Method
The block 80 MVA 110 kV transformer had serious
MV
(a)
HV
(b)
Figure 4. An example of radial buckling in MV 220 kV
winding (a) and in HV external 500 kV winding (b) of 167
MVA/500 kV/220 kV autotransformer after three short-
circuits at 500 kV substation in service.
Figure 5. 125 MVA/220 kV/110 kV autotransformer after
internal short-cirat at 220 kV substation.
(a)
(b)
Figure 6. LVI oscillograms of MV 110 kV winding, in-
cluding turns of regulating winding (a), and oscillograms of
LV winding (b) of 125 MVA/220 kV/110 kV autotrans-
former after internal short-circuit at 220 kV substation,
illustrating amplitude-frequency differences of C phase .
amplitude and frequency LVI-changes in the LV1-LV2
winding oscillogram differences after generator side
short-circuit at Heat Electric Power Station. The FRA
signal spectrum of 80 MVA 110 kV transformer changed
after short-circuit. The original 300 kHz, 500 kHz, 700
kHz resonance frequencies disappeared and a new 400
kHz, 800 kHz resonance frequencies appeared. The FRA
spectrum analysis of 80 MVA 110 kV transformer’s
LV-windings detected axial electrodynamic deformations
[4,9-11,13,15].
Diagnostics experience was showed that the trans-
former plant documentation should be included: normo-
grams of LVI-testing, FRA spectrum, data bases of par-
tial discharge technique, normograms of infra-red diag-
nostics (for first models) during heat testing, data bases
of winding pressure by vibration measurements of trans-
former. Short-circuit reactance measurements (Zk) and
LVI-testing should be carried out together. The necessity
of LVI-normograms of all new manufactured transformer
with capacity over 2.5 MVA, which are produced at the
transformer manufacturers, is caming. It’s necessary for
data bases of the mechanical winding conditions for the
future LVI-testing at the energy system after probable
short-circuit. The first examples are normograms of
LVI-testing of 125 MVA 220/110 kV.
Autotransformer, 250 MVA/110 kV transformer for
the Heat Electric Power Station, which carried out after
repair with the winding change at the transformer manu-
facturer. The normograms of LVI-testing of new 6.3
MVA/110 kV transformer were recorded. LVI-testing is
necessary for all transformers after short-circuits, for new

New “Intellectual Networks” (Smart Grid) for Detecting Electrical Equipment Faults, Defects and Weaknesses
164
transformers, for transformers after repairs at all energy
systems [4,9,10,15].
7. Conclusions
The most important elements of “intellectual networks”
(Smart Grid) are the systems of monitoring the parame-
ters of electrical equipment.
The residual winding’s deformations of power trans-
formers during short circuits will appear practically in-
stantly, without leaving time on the analysis of the results
of the diagnostic measurements, and requiring as it is
possible to rapidly switch off, with the purpose of avert-
ing or reducing repairing of electrical equipment in the
future.
Information-measuring systems, which described in
this paper, were proposed to use together with rapid
digital protection against short-circuit regimes in trans-
former windings.
At the beginning of winding deformations, and also in
the case of winding turn-to-turn internal short-circuit the
value of inductance L is developed to increase, or to de-
crease.
Information-measuring system and connected with it
protection block stopped the process of winding destruc-
tion.
The low voltage impulse testing is a very sensitive and
reliable method of deformation’s detections of transformer
windings. The LVI oscillograms is a “fingerprint” of
transformer.
This winding “fingerprint” is defined by major reso-
nance frequencies (a winding spectra). The 250 MVA
220 kV winding transformer’s spectra contained a 110
kHz, 320 kHz and 550 kHz frequencies, which are
changed 1.3 - 2 times after the mechanical radial winding
deformations. The LV-winding FRA spectrum of 80
MVA 110 kV transformer changed after short-circuit.
The original 300 kHz, 500 kHz, 700 kHz resonance fre-
quencies disappeared and a new 400 kHz, 800 kHz reso-
nance frequencies appeared.
REFERENCES
[1] A. Yu. Khrennikov, “Control and Protection Device of
Transformer Windings against Deformation at Short Cir-
cuits,” Patent of Russian Federation, No. 2136099, Bulle-
tin No. 24, 1999.
[2] A. Yu. Khrennikov, O. A. Shlegel and S. I. Lurie, “Con-
trol and Protection Device of Transformer Windings
against Deformation at Short Circuits in Service,” Patent
of Russian Federation, No. 2063050, Bulletin No. 18,
1996.
[3] A. Yu. Khrennikov, “Measuring Device of the Inductive
Transformer Short-Circuit Impedance,” Patent of Russian
Federation, No. 96110718А, 1998.
[4] A. Yu. Khrennikov, “Complex Diagnostic Modeling of
Technical Parameters of Power Transformer-Reactor
Electrical Equipment Condition,” Ph.D. Thesis, Samara
University, Samara Oblast, 2009.
[5] A. Yu. Khrennikov and O. A. Shlegel, “Extra High Volt-
age Transformer Short Circuit Steadiness Test Results
and Their Effect on Calculations and Design,” Reports of
9th International Power System Conference, St. Peters-
burg, Vol. 2, 1994, pp. 1-121.
[6] T. Fogelberg and R. S. Girgis, “ABB Power Transformers:
A Result of Merging Different Technologies with Pros-
pects for Significant Future Advancements,” Interna-
tional Simposium “Electrotechnics 2010”, Moscow, Vol.
1, 1994.
[7] V. Balakrishnan, “A Study of Short-Circuits in Large
Power Transformers,” Elect rical In dia, Vol. XXIX, No. 4,
1989.
[8] W. Lech and L. Tyminski, “Detecting Transformer Wind-
ing Damage—The Low Voltage Impulse Method,” Elec-
trical Review, No. 18, 1966.
[9] W. J. McNutt, W. M. Johnson, R. A. Nelson and R. E.
Ayers, “Power Transformen Short-Circuit Strength—Re-
quirements, Design, and Demonstration,” IEEE Trans-
actions on Power Apparatus and Systems, No. 8, 1970, pp.
1955-1969. doi:10.1109/TPAS.1970.292780
[10] R. Malewski, A. Yu. Khrennikov, O. A. Shlegel and A. G.
Dolgopolov, “Monitoring of Winding Displacements in
HV Transformers in Service,” Reports of CIGRE Working
Group 33.03, Padua, 4-9 September 1995.
[11] A. Yu. Khrennikov, “Short-Circuit Performance of Power
Transformers. Test Experience at Samaraenergo Co. and
at Power Testing Station in Togliatti, including Fault Di-
agnostics,” Reports of CIGRE Study Commitee 12 Trans-
formers, Budapest, 14-17 June 1999.
[12] A. Yu. Khrennikov, “Power Transformer’s Fault Diagnos-
tics at SAMARAENERGO Co., including FRA/LVI Me-
thod,” Reports from School of Math, and System Engi-
neering, Vaxjo University, Småland, No. 43, 2000.
[13] A. Yu. Khrennikov, “Short-Circuit Performance of Power
Transformers. Transformer Testing Experience for Re-
liability’s Increase of Electric Power Supply,” Reports of
CIGRE Colloquium, Comitee A2, Moscow, 19-24 June
2005.
[14] A. Yu. Khrennikov, V. G. Goldshtein and A. A. Sklad-
chikov, “The Analysis of a Condition of Overhead Lines
of Power Transmission 6 - 500 kV,” Power Plants, No. 5,
2010.
[15] A. Yu. Khrennikov and V. G. Goldshtein, “The Technical
Diagnostics, damages and Resource of Power and Meas-
urement Transformers, Reactors,” Energo Atomizdat, 2007,
319 p.