SURGE CAPACITORS WITHOUT INTERNAL DISCHARGE RESISTORS
Motors or Generators equipped with Surge Capacitors that have
internal discharge resistors will have a lower insulation resistance
reading during I/R testing. This is because of the internal discharge
resistors being connected in parallel to the capacitor frame ground.
The resistors provide a low resistance path to ground which causes
the total motor or generator system resistance to be lowered to
typically between 3 – 4 megohms. The discharge resistors are
molded inside the capacitor assembly and therefore cannot be
removed. Insulating the Surge Capacitor assembly itself from
ground will correct the insulation readings but it is not
recommended because the Surge Capacitors need to be grounded
to operate properly.
To eliminate the low insulation resistance readings a Surge
Capacitor assembly must be used that does not have internal
discharge resistors. These type of Surge Capacitors are available
from manufacturers such as GE and ABB for all operating
voltages, but need to be special ordered without the discharge
resistors. Note: These type surge capacitors need to be manually
discharged with a ground strap during the normal lock and tag out
procedure before working on the equipment.