Electrokinetic effects in power transformers

Technical Report · Sun Nov 01 00:00:00 EST 1992

OSTI ID:6807642

Nelson, J K; Lee, M J; Salon, S J ^[1]

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1. Rensselaer Polytechnic Inst., Troy, NY (United States). Dept. of Electric Power Engineering

Electrokinetic effects such as static electrification can cause catastrophic failures in large forced-oil-cooled power transformers. Experimental and analytical studies confirm that surface charges can significantly impact dielectric integrity. The project team used a closed-loop oil circulation system and full-scale models of power transformer cooling duct structures to conduct controlled experiments. They measured charge density in the oil-resulting from flow through these structures-as a function of flow rate, temperature, ac voltage stress, moisture, and duct types. In addition, they constructed models so that the spatial distribution of electrostatically induced currents and stresses could be determined. They developed a finite-element computer program to study the complex voltage distribution in the models and in two transformer winding examples. A special test cell was used to examine the impact of surface charge on creep strength of transformer pressboard. Static electrification in power transformer duct structures is aggravated by flow rate, temperature, presence of collars, and ac energization; and it is mitigated by increasing oil moisture content. Shell-form model structures exhibit more charge generation than disk-type core-form winding ducts under corresponding conditions. Partial discharges were detected in one shell-form model but only under the worst conditions. These discharges were not energetic enough to produce visible damage. Preliminary finite-element analysis indicates that surface charge has more impact on cumulative stress in a shell-form geometry than in a core-form disk winding.

• Research Organization: Electric Power Research Inst., Palo Alto, CA (United States); Rensselaer Polytechnic Inst., Troy, NY (United States). Dept. of Electric Power Engineering
• Sponsoring Organization: EPRI; Electric Power Research Inst., Palo Alto, CA (United States)
• OSTI ID: 6807642
• Report Number(s): EPRI-TR-101216
• Country of Publication: United States
• Language: English

Related Subjects

24 POWER TRANSMISSION AND DISTRIBUTION
42 ENGINEERING
INSULATING OILS
CHARGE TRANSPORT
TRANSFORMERS
CHARGE DENSITY
COOLING SYSTEMS
DIELECTRIC PROPERTIES
ELECTRIC FIELDS
ELECTRICAL INSULATION
ELECTROSTATICS
FAILURES
FINITE ELEMENT METHOD
FLOW RATE
POWER SUBSTATIONS
POWER SYSTEMS
RELIABILITY
CALCULATION METHODS
ELECTRICAL EQUIPMENT
ELECTRICAL PROPERTIES
EQUIPMENT
NUMERICAL SOLUTION
OILS
ORGANIC COMPOUNDS
OTHER ORGANIC COMPOUNDS
PHYSICAL PROPERTIES
240200* - Power System Networks
Transmission & Distribution- (1990-)
426000 - Engineering- Components
Electron Devices & Circuits- (1990-)