Drying out of Switchgear

In this article, drying of switchgear is given by the Megger. The switchgear equipment is dried out before used in the system.

Insulation Resistance

  • A 1000 V megger is used for measurement of insulation resistance, for higher rating motorized megger of 2.5 kV shall be used.
  • The switchgear equipment first dried out before it is switched when

Insulation Resistance of switchgear

Insulation Resistance

Voltage Rating

< 1 Mega ohm

Rated 1000 V

100 Mega ohm

Rated voltage above 1000 V and up to including 33 kV

1000 Mega ohm

Rated voltage above 33 kV


Drying out of switchgear 

  • It is noted that continuously apply heat for a considerable time so as to dry out moisture. 
  • It is recommended to takes insulation resistance periodically during drying out period. 
  • It is generally found that at the beginning of drying out, moisture is redistributed. 
  • The value of insulation resistance becomes minimum after some time and stability this value for some time, after that its value increases and reaches its maximum value. 
  • This value is generally much greater than value specified in above table.
  •  The switchgear equipment is safer to put into service when the insulation resistance has been reached.

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