Analysis of failed distribution transformers and application of low voltage arresters

Technical Report · Thu Jun 01 04:00:00 EDT 1995

OSTI ID:376838

Goedde, G L ^[1]; Plummer, C W ^[2]

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1. Cooper Power Systems, Franksville, WI (United States)
2. Cooper Power Systems, Pewaukee, WI (United States)

Cooper Power Systems was contracted by EPRI in 1987 to perform a feasibility study on reducing distribution transformer basic insulation level. The project goal was to examine the economics of removing insulation from distribution transformers. The study was done with the help of Wisconsin Power and Light (WP&L). At the time the protective margins of distribution arresters were adequate but not excessive. Most of the economics could be realized in the costs of accessories such as replacing the 125kV BIL transformer bushings with the high volume 95kV BIL bushing. After the project`s completion, discussions with WP&L led to transformer tear downs to determine why their transformers were failing. Their method of protection was to use a cross arm mounted primary arrester in parallel with a fuse cutout and the transformer. Prior to the WP&L tear downs the utility industry was aware of secondary surge failures at Florida Power Corporation where more than half of the non-interlaced transformer failures were due to low side current surges. The analysis of WP&L failed transformers indicated a high failure rate due to secondary surges of both interlaced and non-interlaced transformers. Additional tear downs at midwest and southeastern utilities provided similar results.

• Research Organization: Electric Power Research Inst., Palo Alto, CA (United States); CK and Associates, Albany, CA (United States)
• OSTI ID: 376838
• Report Number(s): EPRI-TR--104581; CONF-9311343--
• Country of Publication: United States
• Language: English

Related Subjects

24 POWER TRANSMISSION AND DISTRIBUTION
CONTROL
EQUIPMENT PROTECTION DEVICES
FAILURES
POWER SYSTEMS
SURGES
TRANSFORMERS