Thermal Overload Protection of Power （热过载保护的权力）.pdf

Thermal Overload Protection of Power Transformers – Operating Theory and Practical Experience Rich Hunt, M.S., P.E. Michael L. Giordano B.S., P.E. Senior Field Application Engineer Electrical Engineer NxtPhase TD Corporation. Distribution Engineering Design Northeast Utilities Systems Presented at the th 59 Annual Protective Relaying Conference Georgia Tech Atlanta, Georgia th th April 27 – 29 , 2005 Thermal Overload Protection of Power Transformers – Operating Theory and Practical Experience Rich Hunt, M.S., P.E. Michael L. Giordano B.S., P.E. Senior Field Application Engineer Electrical Engineer NxtPhase TD Corporation. Distribution Engineering Design Northeast Utilities Systems Introduction TRADITIONAL methods of protecting power transformers use functions based on measured current and voltage. These functions are useful in detecting short circuits and other transient electrical fault events in the transformer. However, for liquid-immersed power transformers, the temperature of the winding hot-spot is the important factor in the long-term life of the transformer. The insulating oil temperature is dependent on the winding temperature, and is used to indicate the operating conditions of the transformer. Many numerical transformer protection relays available today include protection functions that operate on insulating oil temperatures, calculated lo