APPLICATION

PURPOSE

The BE1-47N is designed to protect three-phase ma

chines against damage caused by phase failure, reverse

phase sequence phase unbalance, undervoltage and

overvoltage.

The BE1-47N responds to the negative sequence voltage

which results from a fault or misconnection on a balanced

three-phase system.

The BE1-47N detects reverse phase connection of lines,

transformers, motors, generators, and synchronous con

densers and is often applied in automatic transfer schemes

to assure connection of proper phase rotation as well as

voltage conditions. The Negative Sequence Voltage Re

lay is recommended for all important buses supplying

motor loads. When used in motor protection, the relay will

provide protection by preventing start-up of the motor for

open phase or reverse phase conditions and by tripping

the motor off-line for phase unbalance, undervoltage or

overvoltage conditions.

Negative sequence voltage is the result of any unequal

phase condition. This can be due to unequal single-phase

loads on the system or unequal transformer impedances

between the phases. A 1% – 2% negative sequence level

can normally be expected in an industrial supply. Any

significant increase above this level is an indication of a

power service problem that could lead to serious plant

problems. The BE1-47N has the ability to detect negative

sequence voltage levels of this magnitude.