Slide 1
Thesis Defense
By Saad.M.Saad
Advised ByDr. Abdelsalam ElhaffarANALYSIS OF TRADITIONAL
ANDIMPROVED TRANSFORMER DIFFERENTIALPROTECTIVE RELAYS
1
ContentsIntroductionBackgroundProblem StatementDesign,
Experiments & ModelingConclusionReferences
9/9/20142
Transformer: Function principle and equivalent
circuit11/24/2015
3
Causes of Transformer Failures11/24/2015
4Transformer failures cause about 100 millions in England Only,
and its happen for couple of kinds of Faults and failure:INTERNAL
FAULTS Incipient faults Overheating Over-fluxing Overpressure
Active faults Short circuit in wye connected windings Short
circuits in delta windings Phase-to-phase faults Turn-to-turn
faults Core faults Tank faults
Causes of Transformer Failures11/24/2015
5Winding failures 51%Tap changer failures 19%Bushings failures
9%Terminal board failures 6%Core failures 2%Miscellaneous failures
13%
Differential protection can detect all of the types offailures
above
Power Transformer Differential Protection Differential
protection is one of the most reliable and popular techniques in
power system protection.
In 1904, British engineers Charles H. Merz and Bernard Price
developed the first approach for differential
protection.11/24/2015
6
Transformer Differential Protection special qualities Angle
shifting N30 due to vector group (0 N 11) for 3-phase transformers.
Different current values of the CT- sets on the high voltage side
(HV) and on the low voltage side (LV) Zero sequence current in case
of external faults will cause differential current Transformer-tap
changer, magnetising current Transient currents: Inrush ,
CT-saturation
Relay Characteristics11/24/201582.0
8.09.03.0
7.02.5Slope 1Slope 2IDiff>
0
1.04.05.03.06.001.00.52.01.5
xTripBlock
TotalCT-errorTap-changerMagnet.current
Example: Transformer with Tap changer
Current Mismatch Caused the Transformation Ratio and by
Differing CT RatiosDeltaWye Transformation of CurrentsCT
Saturation, CT Remanence, and CT ToleranceInrush Phenomena and
Harmonic Content AvailabilityOver Excitation PhenomenaSwitch Onto
Fault concernsChallenges to Understanding TransformerDifferential
Protection11/24/2015
9
Inrush Phenomena and Harmonic Content Availability11/24/2015
10
Inrush Phenomena and Harmonic Content Availability11/24/2015
11
Inrush Phenomena and Harmonic Content Availability11/24/2015
12residual flux worst-case conditions result in the flux peak
value attaining 280% of normal value
point on wave switching
number of banked transformers
transformer design and rating
system fault level
System Impedance, and X/R ratio of the system
CT Saturation, CT Remanence, and CT Tolerance11/24/2015
13
Background and History of Differential Protection of Power
Transformer
11/24/2015
14The first solution to this problem was to introduce an
intentional time delay in the differential relay by I. T.
Monseth.
desensitize the relay for a given time, to override the inrush
condition by E. Cordray.
Using all the harmonics to restrain the tripping signal.
Using 2nd and 5th harmonic for restraining or blocking
Background and History of Differential Protection of Power
Transformer
11/24/2015
15
Problem Statement11/24/2015
16In order to provide a high security for differential
protection in case of switching power transformer.
Inrush current still cause relay failures.
Trip signal can be initiated due to DC component with long time
decay.
Continuous failures of relay to recognize inrush current will
cause unwanted long duration interruptions.
Research Contribution11/24/2015
17suggested technique prevents the relay from tripping using DC
component restraining combined with 2nd & 5th Harmonic
blocking.
Suggest improvement in the existing setting for the relay
installed in the grid to increase the security of those relays
during switching of power transformer.
Design Analysis, Experiments & Modeling11/24/2015
18Event recorded in 27/12/2012 at 11:34 AM:Primary Currents of
Power Transformer
Design, Experiments & Modeling9/9/201419Event recorded in
27/12/2012 at 11:34 AM:Binary Output of the Relay
Design, Experiments & Modeling9/9/201420Event recorded in
27/12/2012 at 11:34 AM:Harmonics Contents at 0.0 time
Design, Experiments & Modeling9/9/201421Event recorded in
27/12/2012 at 11:34 AM:Harmonics Contents at Tripping time
Design, Experiments & Modeling9/9/201422MethodologyDC
Harmonic Restraining2th harmonic Blocking
Design, Experiments & Modeling9/9/201423Methodology
IRT = K(Iw1 + Iw2)
Iop > SLP*IRT + K5 I5 And Iop > K2 I2
Where IRT is Restraining CurrentIop is Differential CurrentSLP
is Slope Characteristic of the Relay
Design, Experiments & Modeling9/9/201424Using Discrete
Fourier TransformationDiscrete Fourier series representation of
periodic sequence
The discrete Fourier series coefficients
Relay Modeling9/9/201425Simulation of power system with Proposed
Relay Methodology
Relay Modeling9/9/201426Simulation of power system with Proposed
Relay Methodology
Relay Modeling9/9/201427DFT :Using Full Wave Cycle Discrete
Fourier Transform Method with eight samples per cycle
Discrete Fourier Transform Block in Simulink
Relay Modeling9/9/201428Single Line Diagram of Simulated
System
Design, Experiments & Modeling9/9/201429Simulation of power
system with Proposed Relay Methodology
Case 1: Normal Switching ( at different angles)Case 2: External
Three & single phase FaultsCase 3: Single Line to Ground
FaultCase 4: Double Line FaultCase 5: Double Line to Ground
Fault
Design, Experiments & Modeling11/24/2015
30Simulation of power system with Proposed Relay MethodologyCase
1: Normal Switching ( at 0 angle)
Primary Currents at Zero angle
Design, Experiments & Modeling11/24/201531Simulation of
power system with Proposed Relay MethodologyCase 1: Normal
Switching ( at 0 angle)
Restraining Current in phase A
Design, Experiments & Modeling11/24/201532Simulation of
power system with Proposed Relay MethodologyCase 1: Normal
Switching ( at 0 angle)
Differential, 2nd,DC Currents in phase A
Design, Experiments & Modeling11/24/201533Simulation of
power system with Proposed Relay MethodologyCase 1: Normal
Switching ( at 45 angle)
Primary Currents at Zero angle in phase A
Design, Experiments & Modeling11/24/201534Simulation of
power system with Proposed Relay MethodologyCase 1: Normal
Switching ( at 45 angle)
Restraining Current in phase A
Design, Experiments & Modeling11/24/201535Simulation of
power system with Proposed Relay MethodologyCase 1: Normal
Switching ( at 45 angle)
Differential, 2nd,DC Currents in phase A
Design, Experiments & Modeling11/24/201536Simulation of
power system with Proposed Relay MethodologyCase 1: Normal
Switching ( at 90 angle)
Primary Currents at 90 angle
Design, Experiments & Modeling11/24/201537Simulation of
power system with Proposed Relay MethodologyCase 1: Normal
Switching ( at 90 angle)
Restraining Current in phase A
Design, Experiments & Modeling11/24/201538Simulation of
power system with Proposed Relay MethodologyCase 1: Normal
Switching ( at 90 angle)
Differential, 2nd,DC Currents in phase A
Design, Experiments & Modeling11/24/201539Simulation of
power system with Proposed Relay MethodologyCase 2: External Three
phase Faults
Primary Currents of Power Transformer
Design, Experiments & Modeling11/24/201540Simulation of
power system with Proposed Relay MethodologyCase 2: External Three
phase Faults
Signal Trip
Design, Experiments & Modeling11/24/201541Simulation of
power system with Proposed Relay MethodologyCase 4: Double Line
Fault
Primary Currents of Power Transformer
Design, Experiments & Modeling11/24/201542Simulation of
power system with Proposed Relay MethodologyCase 4: Double Line
Fault
Signal Trip
Design, Experiments & Modeling11/24/201543Simulation of
power system with Proposed Relay MethodologyCase 5: Double Line to
Ground Fault
Primary Currents of Power Transformer
Design, Experiments & Modeling11/24/201544Simulation of
power system with Proposed Relay MethodologyCase 5: Double Line to
Ground Fault
Signal Trip
Design, Experiments & Modeling11/24/201545Summary of all
tested casesCase TypeRelay ResponseTrip signalrelease time(m
sec)LoadedUnloadedInrush CurrentRestrainNo Trip SignalSingle Line
to GroundTrip11.220External Three phase FaultRestrain/TripNo
TripSignalNo Trip SignalDouble Line FaultTrip7.56.2Double Line to
GroundTrip2021
Design, Experiments & Modeling11/24/201546Summary :
Fast in Operation and make no delay in case of faults.
security (no false trips).
distinguish between in inrush and other types of faults.
No need for system impedance Value and reduce measurement in the
relay
11/24/2015
47Suggested SettingExisting Setting:
Function ValueIDIFF Pickup0.20 I/In01 Slope characteristic0.25
I/In02 Slope characteristic0.50 I/In02nd Harmonic Content15%Cross
Blocking for 2nd Harmonic3 Cycle5th Harmonic Content30%Trip without
Delay7.5 I/In0
Relay Testing11/24/2015
48Tests done by injection the recorded event again to relay
.
Transplay the event by (OMOCRON 257 6output).
To analyze suggested setting through faults, Power System Model
by ATP/EMTP environment.
Relay Testing Results11/24/2015
49
No load Test of power transformerCurrent TransformerF/I
curve
Relay Testing Results11/24/2015
50Relay Setting Tested:ParametersIDIFFCross blocking2nd
contentCase 10.253 Cycle15 %Case 20.255 Cycle15 %Case 30.2515
Cycle15 %Case 40.255 Cycle10%Case 50.253 Cycle12%Case 60.2720
Cycle15%Case 70.2720 Cycle20%Case 80.2720 Cycle25%
Relay Testing Results11/24/201551Results for Each Suggested
Setting :ParametersInrushSLGCase 1TripTrip at 20 msCase 2TripTrip
at 30 msCase 3TripTrip at 20 msCase 4TripTrip at 20 msCase
5TripTrip at 19 msCase 6OFFTrip at 300 msCase 7OFFTrip at 400
msCase 8OFFTrip at 20 ms
Relay Testing Results11/24/201552Conclusion
Inrush Current Events usually had a 2nd harmonic magnitude
between 20-25 % in first 2 Cycles.
Cross Blocking function give suppress trip signal in case of
inrush current with high DC components.
Most fault current has 2nd harmonic content lower than 19%.
DC component in inrush current could lead to relay
misoperation.
ReferencesGerhard Ziegler Numerical Distance protection Second
Edition, GmbH, GWA,Sandro Gianny Aquiles Perez Modeling Relays for
Power System Protection Studies A Thesis For the Degree of Doctor
of Philosophy in the Department of Electrical Engineering
University of Saskatchewan Saskatoon, Saskatchewan Canada by
Copyright Sandro G. Aquiles Perez, July 2006.E. Sortomme, S. Arun
G. Phadke, James S. Thorp Computer Relying for Power Systems Second
Edition A John Wiley and Sons, Ltd., Publication. Copyright
2009MATLAB, the language of technical computing, Version
7.6.0.324(R2008a), 1984- 2008, The MathWork.INC.H. Dommel, EMTP
Reference Manual, Bonneville Power Administration 1986. E. A.
Klingshirn, H. R. Moore, and E. C. Wentz, Detection of faults in
power transformers, AIEE Transactions, pt. III, vol. 76, pp. 8795,
Apr. 1957.I. T. Monseth and P. H. Robinson, Relay Systems: Theory
and Applications. New York: McGraw Hill Co., 1935.R. E. Cordray,
Percentage differential transformer protection, Electrical
Engineering, vol. 50, pp. 361363, May 1931S. E. Zocholl, A. Guzmn,
and D. Hou, Transformer modeling as applied to differential
protection, in 22nd Annual Western Protective Relay Conference,
Spokane, WA, Oct. 2426, 1995.11/24/201553
Thank you11/24/201554
