Page 77 - Electrical Equipment Handbook _ Troubleshooting and Maintenance

TRANSFORMER COMPONENTS AND MAINTENANCE

4.6 CHAPTER FOUR

Low-Voltage Bushing
Hand Hole
High-Voltage Bushing
Pressure Relief Device

Cover Lifting Eye

Lifting
Lug
Radiator Bracing
Sealed
Tank
No-Load
Tap Change

Tank Core & Coil
Bracing Assembly

Grounding Pad
Jacking
Pads

FIGURE 4.3 Cutaway view of a power transformer.

4. High-voltage winding. It has a larger number of turns, and its conductor has a smaller
diameter than the low-voltage winding conductor. The high-voltage winding is usually
wound around the low-voltage winding (only cooling ducts and insulation separate the
windings). This is done to minimize the voltage stress on the core insulation.
5. Tank. It houses the windings, core, and oil. It must be strong enough to withstand the
gas pressures and electromagnetic forces that could develop when a fault occurs.
6. Oil. It is a good-quality mineral oil. It provides insulation between the windings, core,
and transformer tank. It also removes the heat generated. The oil is specially refined,
and it must be free from impurities such as water, inorganic acid, alkali, sulfur, and
vegetable and mineral oil.
Note: Some transformers use Askarel, which is nonflammable insulating and cooling
medium, instead of insulating oil. It gives good fire protection, which is a significant
advantage when the transformer is located inside a building. However, Askarel con-
tains polychlorinated biphenals (PCBs). They have been linked to cancer-causing sub-

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