Page 24 - 4587

UNIT 4
MOST COMMON CONTRIBUTING
FACTORS IN INSULATION FAILURE

1 Learn the meaning of the following words, word-
combinations and word groups:

Frequent, failure, electrical equipment, degradation, breakdown,
flashover, insulation, liquid, solid, organic, inorganic, air-cooled
electrical machinery, moisture, crack, seep into, short-circuit,
adjacent, wire, loop, magnetic flux, suck into, heating, cooling,
cycle, dryer, decrease, rate, absorb.

2 Read and translate Text 1:
Text 1

Degradation and Breakdown
The most frequent failure in electrical equipment is the
degradation and breakdown (flashover) of the insulation. Electrical
insulation can be liquid or solid, organic or inorganic.
Organic insulation material consists of: enamels, varnishes,
resins, or polymers that are applied to the steel surface to provide
high inter-laminar (between windings) resistance as found on most
air-cooled machinery and some oil-immersed transformers.
Larger transformers are oil-filled with pure mineral oil to
provide higher insulation capability and more effective heat
dissipation when equipped with external radiators, fans and
pumps. Physical insulation inside these transformers is often in the
form of oil-impregnated paper wrapped around the conductors.
Inorganic insulation material can include a combination of:
• Magnesium oxide,
• Silicates,
• Phosphates, and
• Ceramic powder.
This type of insulation is usually heat-treated into the surface of
the steel and is less common than organic insulation.
No matter what the type of insulation, the two most common
contributing factors in insulation failure are moisture and heat.

23