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! 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.

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.

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.

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.

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.

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 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.

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.

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.

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 12-14 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.

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.

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

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

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

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

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

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.

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.

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

Transformer Testing Station Initial Test Results-Test 1

Transformer Testing Station Initial Test Results-Test 2

Transformer Testing Station Initial Test Results

Transformer Testing Station Budget

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 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/