Basler Electric BE1-50BF Breaker Failure Relay

DESCRIPTION

BE1-50BF Breaker Failure Relays are three-phase, solid state relays designed to provide protection and

security for the power system against failure of the monitored breaker.

Breaker failure relaying is the use of a current monitoring relay to determine whether or not current

continues to flow into a faulted circuit some time after a circuit breaker has been instructed to interrupt the

circuit. In the event that current continues to flow into the faulted circuit (after a defined period of time has

elapsed sufficient for the breaker to have interrupted the current), then the circuit breaker is considered to

have failed, and steps must be initiated to trip the next set of breakers up stream in the power system. The

back up scheme must be designed to isolate both the faulted circuit and the failed breaker.

Following are several reasons why a breaker fails to clear a fault:

• Trip circuit can be open (broken wire, blown fuse, open trip coil).

• Interrupting mechanism can stick, leaving a single phase of a three-phase circuit connected.

• Interrupter can flash-over due to the loss of dielectric strength through contamination or damage.

• Operating mechanism can fail to operate.

Breaker failure relays detect these conditions and initiate contingency or back up procedures.

Typically, breaker failure protection is applied to transmission and sub transmission systems. However,

breaker failure protection may be applied to any portion of the power system where failure of a circuit

breaker to operate properly could result in severe system damage or instability.

Trip Timing

Within the relay are two timers that control operation of the device. Timer 1 defines the delay time between

recognition of the breaker trip signal and the interrogation of the current monitoring circuits for the presence

of current. Adjustment range for this timer is 18 to 500 milliseconds.

At the same time that timer 1 is initiated, the control timer is also initiated. Figure 1-1 illustrates the trip

timing relationships. The purpose of the control timer is to increase security by limiting the response time

of the relay to a short period following any given attempt to interrupt the breaker. The control timer also

terminates the closure of the BF output relays, and breaks the seal of the seal-in circuit (if used).

Breaker failure initiate (BFI) input seal-in is selected by closing printed circuit board switch S1-3 (refer to

Section 2 for location and Section 3 for logic block diagram). This selection may be required when current

from an isolated weak source cannot be depended on to maintain the minimum signal level to the protective

relays initiating the BFI input. Such a condition can occur when the fault voltage is depressed to zero. The

seal-in feature may also counteract contact bounce.

An optional supervisory contact input to the BE1-50BF relay may be specified. When the supervisory

contact input is specified, a third timer (timer 2) is built into the relay. Timer 2 (plus associated circuitry

together with the supervisory contact) duplicates the corresponding features of the timer 1 system. This

addition allows different breaker failure times for different types of failures.

As an example, it might be desirable to use a shorter tripping time if the breaker mechanism fails to operate

(all three breaker poles failed to clear the fault). If the mechanism did operate, but only one of the poles

failed to clear, a longer breaker failure time might be appropriate. This protection can be provided by

connecting the BFI input in series with a 52a contact of the breaker to the supervisory contact input and

setting the delay on timer 2 shorter than timer 1. If the breaker mechanism failed to operate, the breaker

failure relay would be controlled by timer 2. If the breaker mechanism did operate, timer 2 would (in time)

reset and the breaker failure relay would be controlled by timer 1.

This scheme (BFI in series with 52A to supervisory input) allows for 52A or current supervision of the BF

timers 1 and 2. If 52A supervision is desired, switch S1-7 would be closed. Refer to Section 3 block diagram

for logic details.