Experimental determination of the effects of steep front-short duration surges on 25 kVA pole mounted distribution transformers
Nineteen standard commercial, 7200-volt, 25-kVa distribution transformers were tested to determine vulnerability of their insulation systems to steep front-short duration (SFSD) surges. These transformers were tested both with and without surge arresters using the high voltage pulser at the Maxwell Laboratories, San Diego, CA. The open circuit pulser test voltages were 400 kV, 500 kV, 800kV, and 1000kV. These voltages exhibited an approximately 60 ns rise time and aproximately 2000 ns to half value. The voltage was applied to the transformer under test through a 400-Ohm series resistor. This series resistor represented the distribution line surge impedance. Standard lightning impulse tests for this voltage class of distribution transformers were conducted prior to the steep front surge tests to verify insulation integrity, and were repeated following the steep-front surge tests to ascertain if an insulation failure had occurred in the tested transformer due to the steep-front impulse. Failed transformers were disassembled to evaluate failure modes. It was determined that no insulation failures occurred on any transformers tested that were protected by surge arresters mounted directly on the transformer. An external flashover of the high voltage bushing occurred in some cases when the transformer was not protected by a surge arrester, but the bushing sparkover was not always sufficient to protect the transformer. Unprotected transformers failed at voltages around 250 kV to 300 kV peak. The failure mode was usually an internal flashover/puncture between the first few turns of the outer layer of the high voltage winding and the low voltage winding or, sometimes, to an inner layer of the high voltage winding. 10 refs., 10 figs., 1 tab.
- Research Organization:
- Westinghouse Electric Corp., Pittsburgh, PA (USA). Advanced Systems Technology Div.; Oak Ridge National Lab., TN (USA)
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 7002485
- Report Number(s):
- CONF-880701-2; ON: DE88009056
- Resource Relation:
- Conference: IEEE Power Engineering Society summer meeting, Portland, OR, USA, 24 Jul 1988
- Country of Publication:
- United States
- Language:
- English
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