Download Transformer Testing Station

Transformer Testing Station
Determining Sensitivity of a Relay
to Inter-turn Faults on an
Energized Power Transformer
Sponsored by:
Schweitzer Engineering Laboratories, Inc.
Transformer Testing Station
Team
• Jacob Pomeranz
• Jared Mraz
• Eevi Maki
• Mentor: Normann Fischer (SEL)
• Advisor: Dr. Joe Law
Transformer Testing Station
Catastrophic Transformer Failure!
Transformer Testing Station
Background
• Inter-turn faults can destroy large power
transformers
• Large transformers can cost millions of
dollars
• New transformers can take up to 3 years
for delivery
• Existing protection methods are not
effective
Transformer Testing Station
Current Protection Methods
• Buchholz relays
– Operated by gas
accumulation
– Can issue alarm
signals for non-fault
conditions
Transformer Testing Station
Current Protection Methods
• Transfer Function Method
– Effective for detecting faults
– Transformer must be de-energized
Transformer Testing Station
Needs
• Determine the sensitivity of a
microprocessor-based relay to inter-turn
faults on an energized power transformer.
• Develop a protection scheme for detecting
inter-turn faults
Transformer Testing Station
Specifications
• Determine how sensitively protection can
be set to detect inter-turn faults
• Specify and order a 3-phase transformer
• 55kVA transformer with taps being over as
few turns as possible
Transformer Testing Station
Transformer Specifications
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•
•
•
•
55kVA
240/240/25 Volts
3-phase
Thermocouples to measure temperature
Search coils to measure flux
Transformer Testing Station
Transformer Specifications
• Taps at 1,2,3, and 5 turns on primary
winding
• Windings rated for three times nominal
current
Transformer Testing Station
Safety Concerns
• Transformer must not be damaged or
destroyed.
• Laboratory personnel and surrounding
environment must remain safe during all
testing.
Transformer Testing Station
Accomplishments
• Transformer has been ordered
• Low-voltage fault tests have been
conducted on an existing transformer
• Preliminary design for shorting circuit is
operational
Transformer Testing Station
Goals
• Explore detection of inter-turn faults on an
energized power transformer
• To write a technical paper for presentation
at WPRC
• Prevent damage to equipment and team
members
Transformer Testing Station
Existing Test Circuit
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•
•
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Constructed to develop testing methods
Shorting circuit is low capacity
15 kVA transformer
Variac used to limit voltage and fault
currents
Transformer Testing Station
Final Test Circuit Design
• Shorting circuit will be high capacity
• Leads for test circuit as short as possible
to reduce inductance
• 55kVA Transformer and shorting
mechanism enclosed for safety
• Fusing must clear fault quickly to prevent
damage
Transformer Testing Station
Existing Test Circuit
Transformer Testing Station
Existing Test Circuit
Transformer Testing Station
Existing Test Circuit
Transformer Testing Station
Test Circuit
Existing
transformer
• 15kVA
• Coils rated 36A
• Shortable windings
Transformer Testing Station
Test Circuit
SEL-421Relay
• Event recorder
• Measures currents
• Event reports exported to PC for analysis
• Setup will be similar for final test circuit
Transformer Testing Station
Short
Circuit
• Contactor rated
600A
• Fuses used to clear
fault
• High ampacity
cable and bus bar
for final design
Transformer Testing Station
Initial Test Results-Test 1
V A (k V ) V B (k V ) V C (k V )
IA (A ) IB (A ) IC (A )
IA (A )
IB (A )
IC (A )
V A(k V )
V B (k V )
V C (k V )
10
0
-1 0
0 .0 1 0
0 .0 0 5
-0 .0 0 0
-0 .0 0 5
-0 .0 1 0
2 .5
5 .0
7 .5
C y c le s
1 0 .0
1 2 .5
1 5 .0
Transformer Testing Station
D ig it a ls
V A ( k V ) V B ( k V ) V C ( I kA V( A) ) I B ( A ) I C ( A )
Initial Test Results-Test 2
IA ( A )
IB ( A )
IC ( A )
V A (k V )
V B (k V )
V C (k V )
10
5
0
-5
-1 0
0 .0 1 0
0 .0 0 5
- 0 .0 0 0
- 0 .0 0 5
- 0 .0 1 0
50P1
0 .0
2 .5
5 .0
7 .5
C y c le s
1 0 .0
1 2 .5
1 5 .0
Transformer Testing Station
Initial Test Results
Figure 3. Current flowing in shorting mechanism Vs. Phase Voltage
y = 4.5136x - 1.609
30
25
Current (Amps)
20
15
10
5
0
0
1
2
3
4
5
-5
Voltage (Volts)
6
7
8
9
10
Transformer Testing Station
Budget
Initial Budget
Motor Contactor
Current Transformers
Misc. Equipment
$12,376
-$ 585
-$ 678
-$ 100
Transformer
-$ 9,376
Remaining Budget
$ 1,637
Transformer Testing Station
Plan
• Additional work with 15kVA transformer
– Gather data relating fault currents to phase voltage
– Determine relation between fault and load currents
– Obtain fuse elements capable of protecting transformer
Transformer Testing Station
Plan
• Final design for shorting mechanism
completed before transformer arrival
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–
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Additional detailed fault current modeling
Thermal analysis for conductor sizing
Size fuses to clear fault within 2-3 cycles
Safe enclosure designed for fuse bank
Transformer Testing Station
Plan
• Test bench design
– Need to obtain dimensions from transformer
manufacturer
– Bench must be functional and aesthetically
pleasing
Transformer Testing Station
Plan
• Final testing with 55kVA transformer
– Fault signature not as apparent in phase
quantities
– Filtering with MathCAD relay model
necessary to determine fault signature
– Results used to design special differential
protection scheme
Transformer Testing Station
Any Questions?
http://seniordesign.engr.uidaho.edu/2006_2007/teamprotection/