CCBRBRF Operation principle - Arc protection - Motor protection - Feeder protection - Back-up protection - Technical Manual - REX610 Protection and control - Relion Protection and Control - 1.2 - IEC - ANSI - 19.04.2024

The function can be enabled and disabled with the Operation setting. The corresponding parameter values are "On" and "Off".

The operation of CCBRBRF can be described using a module diagram. All the modules in the diagram are explained in the next sections. Also further information on the retrip and backup trip logics is given in sub-module diagrams.

Level detector 1

The measured phase currents are compared phasewise to the set Current value. If the measured value exceeds the set Current value, the level detector reports the 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 Current value Res. If the measured value exceeds the set Current value Res, the level detector reports the 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

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 CB failure mode and CB failure trip mode as shown in Table 1. In all cases in Table 1, however, the 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.

In addition, the function is immediately reset if:

• Start latching mode is set to "Level sensitive", and the START signal is deactivated. The recommended setting value is "Rising edge".
• The BLOCK input is activated.

Timer 1

Once activated, the timer runs until the set Retrip time value has elapsed. The time characteristic is according to DT. When the operation timer has reached the value set with Retrip time, the retrip logic is activated. A typical setting is 0...50 ms.

Timer 2

Once activated, the timer runs until the set CB failure delay value has elapsed. The time characteristic is according to DT. When the operation timer has reached the set maximum time value CB failure delay, the backup trip logic is activated. The value of this setting is made as low as possible at the same time as any unwanted operation is avoided. A typical setting is 90 - 150 ms, which is also dependent on the retrip timer.

The minimum time delay for the CB failure delay can be estimated as:

It is often required that the total fault clearance time is less than the given critical time. This time often depends on the ability to maintain transient stability in case of a fault close to a power plant.

Timer 3

This module is activated by the CB_FAULT signal. Once activated, the timer runs until the set CB fault delay value has elapsed. The time characteristic is according to DT. When the operation timer has reached the maximum time value CB fault delay, the CB_FAULT_AL output is activated. After the set time, an alarm is given so that the circuit breaker can be repaired. A typical value is 5 s.

Retrip logic

Timer 1 activates Retrip logic, which can be used to give a retrip signal TRRET for the main circuit breaker. The operation of Retrip logic depends on the settings CB failure mode and CB fail retrip mode as shown in Table 2.

Once activated, TRRET remains active for the set Trip pulse time or until the reasons for activation are reset. TRRET is also reset if CB_FAULT_AL or BLOCK is activated.

Backup trip logic

Timer 2 activates Backup trip logic, which gives a backup trip TRBU for the upstream circuit breaker if the main circuit breaker fails to clear the fault. Backup trip logic is also activated if the timer-enabling signal from the Start logic module (rising edge of the START input detected) and CB_FAULT_AL are both active.

The operation of Backup trip logic depends on the settings CB failure mode and CB failure trip mode as shown in Table 3.

Once activated, TRBU remains active until the set Trip pulse time or until the reasons for activation are reset. TRRET is also reset if BLOCK is activated.