ABB Relion 620 Series - Page 788

Phase angle of the
compensated unbalance
current (degrees)
Phase and branch of the
element failure
Counters to be incremented
+45...+75 Phase-B branch 1 COUNT_BR1_B
+15...+45 Phase-A branch 2
Phase-B branch 1
COUNT_BR2_A
COUNT_BR1_B
After Alarm delay time has elapsed, the corresponding counter value is incremented
based on the magnitude of the unbalance current. If I_AMPL_COMP is less than
1.5 times the set
Alarm value , the counter is incremented by one. Furthermore,
if I_AMPL_COMP is between 1.5 and 2.5 times the set Alarm value , the counter is
incremented by two and so on.
Normally, the setting
Alarm value is about 0.1 percent lower than the
value of the unbalance current which is caused by one faulty element.
This setting value has to be chosen carefully because a slightly lower
value may lead to a situation where the counters show more failures
than the actual. Too high setting leads to a situation where a fault is not
detected.
The counter values COUNT_BR1_A, COUNT_BR2_A, COUNT_BR1_B, COUNT_BR2_B,
COUNT_BR1_C and COUNT_BR2_C are available in the monitoring data view.
The total number of element failures in double-Y-connected capacitor banks,
FAIL_COUNT, is available in the monitored data view.
The ALARM output is activated, when the value of FAIL_COUNT exceeds the setting
Element failure limit .
The counter values can be reset via CUBPTOC counters which is located under the
Clear menu.
Level detector 2
The calculated compensated unbalance current I_AMPL_COMP is compared to the
set Alarm start value . If the I_AMPL_COMP exceeds the set Alarm value the Level
detector 2 sends enabling signal to the Alarm control module.
Alarm control
Depending on the Alarm mode setting, the alarm stage operation is according to
“Normal mode” or “Element counter mode”.
In the “Normal mode” the time characteristic is according to DT. When the
alarm timer has reached the value set by Alarm delay time , the ALARM output is
activated. If the fault disappears before the alarm activates, the alarm timer is reset
immediately.
The “Element counter mode” is used to detect faulty elements of the capacitor bank
and count the number of element failures in each branch and line. On activation, this
module increments the corresponding element failure counters after the set
Alarm
delay time has elapsed.
Blocking logic
There are three operation modes in the blocking function. The operation modes
are controlled by the BLOCK input and the global setting Configuration > System >
Blocking mode, which selects the blocking mode. The BLOCK input can be controlled
Protection functions
1MRS757644 H
788 620 series
Technical Manual