The BE1-47N has the ability to detect negative

sequence voltage levels of this magnitude.

Undervoltage and voltage balance relays have tradition

ally been applied for the protection of induction motors

from operating with one phase open. These relays may

not reliably detect this condition due to the back emf of

the motor on the open phase. However, an induction

motor, with a starting current of 6 per unit, will generate

a negative sequence voltage of 16% if fully loaded when

a fuse blows. The negative sequence voltage will be

somewhat reduced if the motor is not fully loaded. The

sensitivity of the BE1-47N and its insensitivity to fre

quency will provide reliable protection for motors.

Motor losses and current unbalance increase with the

negative sequence voltage level. The increased loss,

due to negative sequence voltage, is not a function of

motor load but is independent. A machine operating

with 3.5% negative sequence voltage will have its stated

losses increased by 25%. A blown fuse on a power factor

correction capacitor bank can result in a negative se

quence voltage increase. The increase in motor losses

can be costly.

The BE1-47N should be applied to protect motor buses

from a open phase. It can also be applied to protect

critical individual motors, static and non-rotating loads

from the effects of negative sequence voltage.

A choice of time delay characteristics allows the relay to

respond in the desired manner for a wide variety of

transient and fault conditions.

The BE1-47N may also be used to provide over/

undervoltage protection. A separate time delay is uti

lized to prevent shutdown of equipment for minor volt

age dips and to permit sequential operation when the

relay is being used in a supervisory capacity.