ABB RELION REX640 Technical Manual page 1164

Protection and control

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Protection related functions

Figure 660: Functional module diagram

Level detector 1

The measured phase currents are compared phasewise to the set

the measured value exceeds the set

exceeding of the value to the start, retrip and backup trip logics. The parameter

should be set low enough so that breaker failure situations with small fault current

or high load current can be detected. The setting can be chosen in accordance with

the most sensitive protection function to start the breaker failure protection.

Level detector 2

The measured residual current is compared to the set

measured value exceeds the set

exceeding of the value to the start and backup trip logics. In high-impedance

earthed systems, the residual current at phase-to-earth faults is normally much

smaller than the short circuit currents. To detect a breaker failure at single-phase

earth faults in these systems, it is necessary to measure the residual current

separately. In effectively earthed systems, also the setting of the earth-fault current

protection can be chosen at a relatively low current level. The current setting should

be chosen in accordance with the setting of the sensitive earth-fault protection.

Start logic is used to manage the starting of Timer 1 and Timer 2. It also resets the

function after the circuit breaker failure is handled. On the rising edge of the START

input, the enabling signal is sent to Timer 1 and Timer 2. Typically, the START input is

activated when any protection function operates and trips the circuit breaker.

The Start logic module is reset depending on the settings

failure trip mode as shown in

resetting is possible only after 150 ms from the activation of Start logic. This time is

for ensuring correct operation in case of oscillation in the starting signal.

Current value , the level detector reports the

Current value Res , the level detector reports the

. In all cases in

Current value . If

Current value Res . If the

CB failure mode and CB

, however, the

Technical Manual

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