1. Transformer Testing Station
Determining Sensitivity of a Relay
to Inter-turn Faults on an
Energized Power Transformer
Sponsored by:
Schweitzer Engineering Laboratories, Inc.

2. Transformer Testing Station
Team
Jacob Pomeranz
Jared Mraz
Eevi Maki
Mentor: Normann Fischer (SEL)
Advisor: Dr. Joe Law

3. Transformer Testing Station
Catastrophic Transformer Failure!
Jared-
This is a worst case scenario of what we are protecting against…
Even the protection methods in place on this transformer failed.
Most internally damaged transformers won’t blow up in such a fashion, but it is still a risk.
Oil type shown above.

4. 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
Jared-
We are essentially building a laboratory setup for conducting testing for 3-phase transformers. The type of transformer needed for our research is not available off the shelf, therefore a custom desging was needed for the project (refer to slide)
Mention fault current magnitudes involved in testing.

5. Transformer Testing Station
Current Protection Methods
Buchholz relays
Operated by gas accumulation
Can issue alarm signals for non-fault conditions
Jared-
We are essentially building a laboratory setup for conducting testing for 3-phase transformers. The type of transformer needed for our research is not available off the shelf, therefore a custom desging was needed for the project (refer to slide)
Mention fault current magnitudes involved in testing.

6. Transformer Testing Station
Current Protection Methods
Transfer Function Method
Effective for detecting faults
Transformer must be de-energized
Jared-
We are essentially building a laboratory setup for conducting testing for 3-phase transformers. The type of transformer needed for our research is not available off the shelf, therefore a custom desging was needed for the project (refer to slide)
Mention fault current magnitudes involved in testing.

7. 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
Jared-
We are essentially building a laboratory setup for conducting testing for 3-phase transformers. The type of transformer needed for our research is not available off the shelf, therefore a custom desging was needed for the project (refer to slide)
Mention fault current magnitudes involved in testing.

8. 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

9. Transformer Testing Station
Transformer Specifications
55kVA
240/240/25 Volts
3-phase
Thermocouples to measure temperature
Search coils to measure flux
These are some of the notable features of the custom transformer. The specifications shown here differ somewhat from the original specifications requested by the client. This was due to practical design constraints…(initial coil ratings-full or rated, window size, volts per turn, etc) Ended up choosing rated*4 for the coil sizing.
Mention that transformer is dry-type
Learning process-
Delivering an initial spec sheet
Explaining project to sales manager to get his opinion on design
Trying to explain the protection that will be put in place, etc.
Dealing with a design engineer, holding our ground, being assertive.

10. Transformer Testing Station
Transformer Specifications
Taps at 1,2,3, and 5 turns on primary winding
Windings rated for three times nominal current
These are some of the notable features of the custom transformer. The specifications shown here differ somewhat from the original specifications requested by the client. This was due to practical design constraints…(initial coil ratings-full or rated, window size, volts per turn, etc) Ended up choosing rated*4 for the coil sizing.
Mention that transformer is dry-type
Learning process-
Delivering an initial spec sheet
Explaining project to sales manager to get his opinion on design
Trying to explain the protection that will be put in place, etc.
Dealing with a design engineer, holding our ground, being assertive.

11. Transformer Testing Station
Safety Concerns
Transformer must not be damaged or destroyed.
Laboratory personnel and surrounding environment must remain safe during all testing.
This is an integral part of the project
-Dealing with high current magnitudes, even for a short time, can be very dangerous. If a fault is left on the transformer for too long, the transformer could be destroyed. Precautions will be taken to protect the transformer.
-If an arc were to hit someone in the lab, or a fuse casing were to explode, someone could be seriously injured.

12. 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
To date, the custom transformer has been ordered. This part of the project was given high priority due to the long lead time of weeks.
Some low-voltage laboratory work has been done with an existing 15kVA transformer in the power lab. These tests have aided in the design and setup of the test circuit (relay, etc)
Short circuit mechanism is functional for the 15kVA transformer. Will need increased current carrying capacity for final design.

13. 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
If all the tests are successful and all the data has proven that the relay algorithm works we will be writing a technical paper to be presented next fall at the Western Protective Relay Conference. This is the biggest protection conference in North America.
If any of the equipment is damaged before all the tests are complete the project could be a failure. This is why one of our major goals is to make sure no damage occurs.

14. Transformer Testing Station
Existing Test Circuit
Constructed to develop testing methods
Shorting circuit is low capacity
15 kVA transformer
Variac used to limit voltage and fault currents
This is the 15KVA transformer that some initial test have been completed on.
It has shorting taps 5% or 10%
We can also configure as Delta or Y configuration, which our transformer will also be able to do
This transformer does not have a tertiary winding and the custom built transformer will

15. 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
This is the 15KVA transformer that some initial test have been completed on.
It has shorting taps 5% or 10%
We can also configure as Delta or Y configuration, which our transformer will also be able to do
This transformer does not have a tertiary winding and the custom built transformer will

16. Transformer Testing Station
Existing Test Circuit
This is the 15KVA transformer that some initial test have been completed on.
It has shorting taps 5% or 10%
We can also configure as Delta or Y configuration, which our transformer will also be able to do
This transformer does not have a tertiary winding and the custom built transformer will

17. Transformer Testing Station
Existing Test Circuit
This is the 15KVA transformer that some initial test have been completed on.
It has shorting taps 5% or 10%
We can also configure as Delta or Y configuration, which our transformer will also be able to do
This transformer does not have a tertiary winding and the custom built transformer will

18. Transformer Testing Station
Existing Test Circuit
This is the 15KVA transformer that some initial test have been completed on.
It has shorting taps 5% or 10%
We can also configure as Delta or Y configuration, which our transformer will also be able to do
This transformer does not have a tertiary winding and the custom built transformer will

20. Transformer Testing Station
Test Circuit
Existing
transformer
15kVA
Coils rated 36A
Shortable windings
One disadvantage to the 15kVA transformer was the rating of its coils. This transformer could easily be burnt up if the team isn’t careful.
This transformer wouldn’t give us the sensitivity that was necessary for this project so after group consensus we decided to order the 55kVA transformer.

21. 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
The SEL 421 Relay will be used to get data from the tests that will be conducted.
There are settings in the relay that allow you to start an event report when a primary current hits a certain level. Calculations and small voltage tests are done to figure out how much current will be needed to start an event, but we also don’t want to set it to low to trip when a fault is not applied.
The event files from the relay will be analyzed through a program called SEL 5601 software. This allows us to see what element picked up the fault and how long it took the fault to clear.

22. Transformer Testing Station
Short Circuit
Contactor rated 600A
Fuses used to clear fault
High ampacity cable and bus bar for final design
There are several important aspects to the design of the shorting circuit. Preliminary calculations show that the fault current will be in the 1000’s of amps depending on the amount of the winding that is shorted.
The motor contactor is used to close the shorting circuit which simulates an arcing fault. The contactor is rated for 200A per phase, which gives a 3-phase steady state rating of 600A. Currents up to 5 times this rating can be sustained for a few cycles during inrush currents for motor starting applications.
Eventually, a bus bar will be connected to one of the taps on the transformer…
The fuses will have to be sized according to the predicted current in the short circuit such that the fault is cleared in a timely manner

23. Transformer Testing Station
Initial Test Results-Test 1

24. Transformer Testing Station
Initial Test Results-Test 2

25. Transformer Testing Station
Initial Test Results

26. Transformer Testing Station
Budget

27. 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

28. Transformer Testing Station
Plan
Final design for shorting mechanism completed before transformer arrival
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

29. Transformer Testing Station
Plan
Test bench design
Need to obtain dimensions from transformer manufacturer
Bench must be functional and aesthetically pleasing

30. 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

31. Transformer Testing Station
Any Questions?