Power Electronics

AC/DC Sensitive Earth-Leakage Relay

Littelfuse, Inc. announced its new EL731 AC/DC Sensitive Earth-Leakage Relay, which can detect ground currents,even in resistance-grounded electrical systems,all the way down to 0 Hz. This makes it ideal for protecting variable-frequency drives (VFDs) that may operate at low speeds, during which AC current approaches DC. The EL731 relay provides complete range of ground-fault protection in VFDs from 0 to 15000 Hz in one device, saving cost and panel space compared to other relays.

Unlike any relay previously available, the EL731 uses a patented approach that enables the relay to detect the location of ground faults and makes it equally useful for AC, mixed AC/DC, and DC systems, including low-voltage 6-pulse VFDs commonly used on motors up to 250 hp. It can reliably protect a variety of applications including conveyor belts, cranes, compressors, pumps and mixers found in demanding environments such as mining, oil sands operations, chemical plants, food processing, and other industrial facilities.

The new relay is ideal for protecting VFDs operating in resistance-grounded electrical systems, which are growing in popularity because of their ability to reduce arc-flash hazards. The on-board ground-fault protection that comes with VFDs is generally not sensitive enough to detect a ground fault in resistance-grounded systems.

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.

Littelfuse Inc.
Part Number: EL731

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