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 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 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

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?