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 pickup and backup trip logics. In high-impedance grounded systems, the
residual current at phase-to-ground faults is normally much smaller than the short circuit
currents. To detect a breaker failure at single-phase ground faults in these systems, it is
necessary to measure the residual current separately. In effectively grounded systems,
also the setting of the ground-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 ground-fault protection.
Start logic
The start logic is used to manage the starting of the timer 1 and timer 2. It also resets the
function after the circuit breaker failure is handled. On the rising edge of the PICKUP
input, the enabling signal is send to the timer 1 and timer 2.
Function resetting is prevented during the next 150 ms. The 150 ms time elapse is
provided to prevent malfunctioning due to oscillation in the starting signal.
In case the setting Pickup latching mode is set to "Level sensitive", the 50BF is reset
immediately after the PICKUP signal is deactivated. The recommended setting value is
"Rising edge".
The resetting of the function depends on the CB failure mode setting.
• If CB failure mode is set to "Current", the resetting logic further depends on the CB
failure trip mode setting.
Section 5 1MAC059074-MB A
Protection related functions
774 615 series ANSI
Technical Manual
To Next Page
Loading...
