Problem Definition



Transformer Theory

Test Circuit




One major problem in the electric power industry is effectively protecting large transformers from inter-winding faults. The current equipment being used to protect large transformers from these faults often doesn’t trip until significant damage has been done to the transformer.
exploding transformer
We want to avoid the above scenario. For a movie of the exploding transformer, click here.

Our project will help to test a new method for detecting inter-winding faults on energized power transformers.

Our objective is to specify a transformer that can be configured to simulate an inter-winding fault and design a safe laboratory setup. Data will then be taken during several fault simulations. This data will be used to determine how sensitively a microprocessor-based relay can be set to detect inter-winding faults.

Transformer Theory

A large power transformer cannot easily be removed from its location and replaced.  Most power transformers are built in Europe and are then shipped to North America by barge.  This construction and transportation process can take as long as three years.  As a result of this long lead-time and the fact that many large transformers cost several million dollars, the protection of transformers is of high priority.  Unfortunately, the current methods for detecting inter-winding faults on energized power transformers are not always accurate or reliable.
    One of the current methods for detecting internal faults is by use of a device called a Buchholz relay. 
buchholz relay
When interwinding faults occur, the heat from the arc causes gas to be produced in the oil.  This slow accumulation of gas in the oil causes a float to close a set of alarm contacts in the relay.  However, overheating and other operating conditions can cause the Buchholz relay to issue an alarm signal as well.  This means, that the transformer is either left in service and assumed to be healthy, or is isolated and tested.  If a damaged transform
er is misdiagnosed and left in service, the internal fault can grow and eventually destroy the transformer.  Likewise, if an undamaged transformer is taken out of service, money is lost due to the outage.

    If there were a way to safely test energized power transformers, power engineers could accurately determine the condition of a transformer, and electric utilities could save a lot of time and money in the event of an internal fault.

Top of page | Background | Outcomes | Needs | Specs | Constraints

Project Outcomes
The main objective of this project is to test the sensitivity of micro-processor based relays to inter-turn faults on power transformers.  In order to accomplish this goal, a test bench will need to be built such that an inter-winding fault can be simulated safely without causing damage to the transformer or to people in the laboratory.

Top of page | Background | Outcomes | Needs | Specs | Constraints






Prioritized and rated with *.
*** = critically important need.

Design protection algorithm for detecting inter-turn faults.

Transformer can have a short circuit placed on it.

Transformer can be short-circuited by various percentages of the windings.
Transformer’s short circuits can be a low percentage of the winding.
Short circuit fault can be safely created.
Short circuit fault can be easily created.

Transformer can be tested safely.
Transformer operates safely in its electrical circuit.
Transformer is protected from additional shorting.
Transformer’s temperature can be tested.
Transformer’s flux can be tested.

Test ben
ch can be operated safely.
Test bench operates safely in its electrical circuit.
Test bench is protected from overheating.
Test bench promotes safety.

Test bench is designed well.
Test bench labels are accurate.
Test bench wiring is easy to understand.
Test bench looks professional.

Transformer can be used in a variety of ways.
Transformer can be used with specified power.
Transformer can be used in dry air.
Transformer can be immersed in oil.
Transformer can be connected in any configuration of delta or wye.

Top of page | Background | Outcomes | Needs | Specs | Constraints

Target Specifications  (Initial Specs)
  • Specify and order a transformer
  • Set up a circuit to short-circuit and test the transformer
  • Show how sensitively protection can be set to detect inter-turn faults
Transformer Specifications:
  • 50/50/5.0 kVA
  • 240/240/24 Volts
  • Taps from turns at 2%, 4%, 8% and 10% of the winding. 
  • 3-phase
  • Put taps on one leg
  • Thermocouples to measure heat
  • Search coils to measure flux
Safety Concerns:
  • Safely short circuit transformer when there is a huge current running through a small number of turns. Possible solutions include current transformers, switches, fuses, and circuit breakers.
  • Transformer must not be ruined.
  • Students and the surrounding environment must remain safe during all testing.
  • We need at least ten duty cycles to read a measurement.
Top of page | Background | Outcomes | Needs | Specs | Constraints
  • Transformer should not be ruined.
  • Transformer should have 50kVA wire rating but 25kVA core size.
  • Leads to take measurements need to be kept as short as possible to limit flux.
  • Short circuits need to be able to be created easily and safely. Wiring from transformer to test bench and test bench to measurement equipment.
  • Cost of transformer should remain near $5,000.
Top of page | Background | Outcomes | Needs | Specs | Constraints
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Last updated: 4/25/07.
University of Idaho, Moscow, Idaho.