Capacitor duty switching contactor
If contactors are used for switching of capacitor ,the capacitor must be completely discharged by means of resistance or discharging chokes.
When capacitor are switch ON depending on the phase angle at the instant of switch ON sever current peaks may occur.
Drawbacks: Welding of contactor
Erosion of contacts
Protective measures: The effective capacitor-load switching capabilities of a.c. contactors & their service life can be increased by following measure.
•Choke coils: The transient condition which is caused when switching in on an existing capacitive load may be damped if an air cored inductance of at least 6 micro Henry connected in parallel connecting leads between the capacitors
Fig. Choke
•Pre-charge resistor: Connect precharge resistance in parallel with capacitors.
fig.capacitor duty contactor
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