When the mains voltage/frequency has returned, some hystereses can be adjusted. The Multi-line 2 controller has four separate
hystereses which are located in menu 7090. The first hysteresis is for the “low voltage limit”. If the mains “low voltage” is set at 90 %
(7063), the Multi-line 2 will start the “Automatic Mains Failure” sequence when the voltage is lower than 90 % of the nominal voltage.
By default, the hysteresis is set at 0 % (7091), which means, in this example, that when the voltage has increased above 90 %, it is
allowed to feed the load from the grid again. If the hysteresis had been set at 2 %, it would not be allowed to go back to grid until the
mains voltage had increased above 92 %.
If, for example, the “mains low voltage” was set at 85 % and the hysteresis was set at 20 %, the calculation would imply that it was
not allowed to go back to grid operation until the mains voltage was 105 %. The Multi-line 2 controller can be 100 % of nominal at
the most. This is the same for “mains high voltage” and both frequency limits. The hysteresis can be at 100 % nominal at the most.
Conditions for breaker operations
The breaker sequences react depending on the breaker positions and the frequency/voltage measurements.
The conditions for the ON and OFF sequences are described in the tables below.
Breaker close conditions
Sequence
Condition
GB ON, direct closing
Running feedback
Generator frequency/voltage OK
MB open
MB ON, direct closing
Mains frequency/voltage OK
GB open
GB ON, synchronising
Running feedback
Generator frequency/voltage OK
MB closed
No generator failure alarms
MB ON, synchronising
Mains frequency/voltage OK
GB closed
No generator failure alarms
Breaker open conditions
Sequence
Condition
GB OFF, direct opening MB open
MB OFF, direct opening
Alarms with fail classes:
Shut down or Trip MB alarms
GB OFF, deloading MB closed
MB OFF, deloading
Alarms with fail class:
Trip and stop
DESIGNER'S HANDBOOK 4189341275A EN Page 63 of 196
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