Hazards Causes and Types of Transformer Core Multi point Ground Faults
Hazards of Multi-point Core Ground Faults
A transformer core must not have multi-point grounding during normal operation. An alternating magnetic field around the winding induces parasitic capacitances between windings, core, and shell. Live windings couple through these capacitances, creating a core floating potential relative to ground. Uneven distances between components cause potential differences; when high enough, they spark. This intermittent discharge degrades transformer oil and solid insulation over time.
To prevent this, the core and shell are reliably connected to share the same potential. However, two or more core/metal component ground points form a closed loop, causing circulation and local overheating. This decomposes oil, reduces insulation performance, and in severe cases, burns core silicon steel sheets—leading to major main transformer accidents. Thus, main transformer cores must use single-point grounding.
Causes of Core Ground Faults
Key causes include: grounding plate short circuits from poor construction/design; multi-point grounding from accessories or external factors; metal debris left in the transformer; and burrs, rust, or welding slag due to shoddy core processing.
Types of Core Failures
Six common types:
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