RXETB 1 operates in case of fuse failure in one or two phases of a three-phase system or if the voltage in one phase drops below 40 % of rated voltage and the other two phases have rated voltage. Fuse failure in all three phases is unlikely to occur, therefore the RXETB 1 relay is sufficient in most cases.
The measurement principle is based on a comparison between the neutral point of the voltage transformer and an internal neutral point derived from the three phases. When a voltage difference is detected, the two output relays, each with one change-over contact, operates.
By a knob at the front, the operation can be set to be delayed up to 10 seconds. During operation, a red LED is lit at the front of the relay.
Unbalanced phase-to-phase connected loads is not a problem due to the high remaining voltages. If the relay operates because of a voltage drop in one phase, it will reset when the voltage exceeds 75 % of rated voltage.
- Detects single- or two-phase fuse failures
- Is used together with fuses only
- Detects voltage unbalance in a three-phase group
- Settable operate time delay 0-10 s
- Operation is indicated by a red LED
- Used to give delayed alarm of fuse failure in ac supply circuit e.g. to synchronizing and energy metering equipment