Power Switching Applications for High Voltage Relays
High voltage power switching applications are those which require the relay to make and/or break the load. In most applications, it is important to know the highest potential fault current which could be encountered and how many times the relay or contactor will be required to clear the fault since this will determine the relay or contactor which should be selected.
Load switching in AC circuits is much easier on the relay due to the natural arc extinction which occurs as the current passes through zero. Because of this, relay ratings are usually much higher when switching AC circuit loads.
Switching of direct current loads creates special problems for relays. Many traditional relays and contactors have difficulty interrupting loads above 48 Vdc. Kilovac has a broad product line of relays, contactors, and power controllers which have been specially designed to handle the problems of DC switching. When load switching must be done at voltages above 1000 volts, refer to the power switching curve on the product data pages or the below graphs for relay families. For specific recommendations, call us on our Application Hot Line at 1-800-253-4560.
Higher current affects relay ratings more than higher voltage. There are no hard and fast rules which can be used to develop a relay's electrical life rating given voltage and current switching specifications. Once again, experience and thorough testing in the actual circuit are the best ways to establish relay life and reliability. Figure 24 illustrates the operating characteristic determined experimentally for one family of power switching products.
Typical Hot Switching Resistive Load-Life Characteristics K41A, K43A, K81A Relays
Figure 24
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