Basler Electric BE1-87G Variable Percentage Differential Relay

The BE1-87G is a single or three-phase solid-state variable percentage

differential relay designed to provide selective, high-speed, differential

protection for generators, motors, and shunt reactors.

ADVANTAGES

• Single or three-phase relays available.

• Variable percentage characteristic.

• Low operating burden.

• Balancing impedance in CT inputs provides excellent security

during external faults or other transients.

• High speed operation.

• Seven sensitivity settings cover the range of 0.1 to 1.6A

or 0.02 to 0.32A.

• Pickup accuracy within ±5% of the operate characteristic.

• Qualified to the requirements of- IEEE C37.90.2 for Radio Frequency

Interference (RFI)- IEEE C37.90.1-1989 for Fast Transient and Surge Withstand

Capability- IEC 255-5 and ANSI/IEEE C37.90 for Impulse and Dielectric tests.

• UL recognized per Standard 508. UL File #E97033.

• Gost R certified per the relevant standards of Gosstandart of Russia.

• Five year warranty.

APPLICATION

BASIC PRINCIPLES

Differential relaying is the most selective form of fault

protection that may be applied to the individual

elements, or zones, of ac power systems. Various

types of differential relays and relaying systems have

evolved to take advantage of the differential principle.

The BE1-87G is a single or three-phase solid-state

variable percentage differential relay designed to

provide selective, high-speed differential protection

for generators, motors, and shunt reactors.

The selectivity of differential relaying is based on the

ability of the relay to distinguish between an internal

fault (within the protected zone) and an external fault.

Under normal operating conditions the current into

the protected zone equals the current out of the

protected zone with a net operating current equal to

zero. Internal faults upset this balance and result in a

difference between the input and output currents.

External faults have relatively little effect on the

balance, because the current in still equals the

current out of the protected zone. Therefore, by

comparing the currents on both sides of the protected

element or zone and detecting when these currents

are not equal, a differential relay acts to isolate the

element or zone from the system.

The BE1-87G typically trips a lockout relay (86), which

in turn trips the generator breaker and, when present,

the field and/or neutral breakers.

RESTRAINT CHARACTERISTICS

At high current levels, the inevitable difference in the

saturation characteristics between current transform

ers requires a compensating decrease in relay

sensitivity. The design of the BE1-87G provides a

restraint factor that is proportional to input current.

Specifically, the BE1-87G compares the two sensed

currents (in and out) to determine which is less. This

lower current level becomes the restraining current.

The difference between the two sensed currents (I0

) is compared to a reference established by the sensitivity

setting and adjusted by an amount proportional to the

restraining current. (The typical ratio is given in the

formula on page 3.) This makes the BE1-87G more

sensitive to low current internal faults, for which the

relay should operate, and less sensitive to external

faults with high levels of through current for which the

relay should not operate.