Degradation and decomposition

The most common faults in electrical equipment are degradation and breakdown (flashover) of insulating materials. Electrical insulation can be liquid or solid, organic or inorganic.

The 2 most common influencing factors of motor insulation failure

Organic insulating materials include: enamel, varnish, resin or polymer, coated on the steel surface to provide high interlayer (between winding) resistance, which is common in most air-cooled machinery and some oil-immersed transformers Can be found.

Larger transformers are filled with pure mineral oil, which can provide higher insulation and more effective heat dissipation when equipped with external radiators, fans and pumps. The physical insulation inside these transformers is usually in the form of oil-impregnated paper that wraps the conductors.

Too much water

On air-cooled motors, the moisture content in the air is very important. As the insulating material ages, fine wire cracks appear in the insulating material. Moisture can seep into these cracks and short-circuit the circuit between adjacent turns of wire.

Although the voltage between the turns is small, when they are short-circuited together, a closed magnetic flux loop is formed, which causes a large amount of current to flow in the short-circuit loop. This usually damages the motor, so it must be removed and re-wound/replaced.

On oil-cooled machinery (for example, transformers), moisture can only be detected by conventional oil samples. In the continuous process of the transformer heating and cooling cycle, moisture will be sucked into the oil through the oil expansion vent.

For oil-filled transformers, it must be noted that only a small amount of water is required to greatly reduce the insulation value of the oil. Only 30 parts of water per million parts of oil will reduce the insulation capacity by 50%.

Temperature is too high

On air-cooled motors, prolonged high temperature will cause thermal aging. This causes the insulation to become brittle. As mentioned earlier, the ultimate failure may be caused by moisture penetration or physical contact of conductors.

In oil-filled transformers, this effect is called insulation aging. Chemical aging occurs faster at high temperatures, and the loss of insulation life increases almost exponentially with temperature.

Obviously, it is important to maintain daily operating temperature records and ensure that all electrical equipment is kept at a lower ambient temperature.