Littelfuse's EL731 AC/DC Sensitive Earth-Leakage Relay protects VFDs that operate at low speeds
Littelfuse's EL731 AC/DC Sensitive Earth-Leakage Relay is designed to detect ground currents, even in resistance-grounded electrical systems, down to 0 Hz. The EL731 is made for protecting variable-frequency drives (VFDs) that may operate at low speeds, during which AC current approaches DC. The EL731 relay is engineered to provide ground-fault protection in VFDs from 0 to 15000 Hz in one device.
The EL731 is built to detect the location of ground faults and is designed for AC, mixed AC/DC, and DC systems, including low-voltage 6-pulse VFDs commonly used on motors up to 250 hp. The EL731 can be installed in place of an existing ground fault relay without replacing the current transformer. Two CTs are required for the entire frequency range, or one CT can be used for only low- or high-frequency detection. The relay has a temperature input, metering capabilities, password protected alarm and trip settings. Ethernet communications port is optional.