Low insulation

Factors that affect insulation 

1) Moisture

• Leakage current increases

2) Dust, oil, deposits on end of winding and connections

• Cause insulation burn out overtime
• Reduce heat dissipation, dust clog 
• Ventilation duct and restrict free flow of air
• Increase machine temperature and cause thermal degradation on insulation.
• Oil vapors forms and attract dust

3) Insulation deteriorate with age.

Precaution 

• Keep motor clean and cool, keeping dry.
• insulation resistance is measured between the insulated conductors and earth and between conductor
• The insulation resistance is measured by the equipment known as megger

• the equipment to be tested for insulation resistance must be disconnected from the live power supply and the supply to be locked down to prevent any accidents.

Procedure 

• short the 2 probe of megger and turn the handle to megger. Pointer show zero
• with probe apart reading is infinity
• switch the power off to the equipment 
• disconnect the motor phase from connection, and do measurement between earth and phase.
• Insulation serve as a guide to indicate health of the electrical machinery

Insulation resistance is the ability to resist the current flow

Low reistance cause electrical shock, fire, short circuit