|
Relays Home > Kilovac Home > Power Switching Applications for High Voltage Relays > Capacitive Discharge or Make-Only Power Switching
Capacitive Discharge or Make-Only Power SwitchingOne of the most common applications for high voltage relays is the charge and discharge of a high voltage capacitor. Since this normally involves "make-only" power switching, Kilovac SF-6 gas-filled relays generally offer superior performance to vacuum relays. In order to select the proper relay, you must determine the peak current and RC time constant in addition to the normal parameters of voltage, contact configuration, etc. The RC time constant is the time it takes for the capacitor to discharge 63% of its stored electrical charge. Virtually all electrical charge will be discharged in 5 RC time constants. The RC time constant is simply the product of the circuit resistance and capacitance. For example, a circuit discharging an 8 microFarad capacitor through 100 ohms of series resistance will have an RC time constant of 800 microseconds. (R X C)= 100 X .000008 = .0008 or 800 microseconds It is often difficult to specify the proper relay for capacitive discharge applications because of the many potential variables. It is especially important in these applications to conduct tests to determine which relays are suitable and their reliability. |