Undervoltage Unit; Mode Of Operation; Settings - GE MLJ1000 Manual

3.3 UNDERVOLTAGE UNIT

Besides the undervoltage described in and linked with the synchronism unit, there is an independent
unit which has various undervoltage and overvoltage functions to allow for the closure of the circuit
breaker in dead lines and/or bus situations (see figure 1).

3.3.1 Mode of Operation

The modulus are calculated from the line and bus voltage phasors and then compared with the
settings. For each voltage two different levels can be set.
If the voltage is below the set undervoltage level, the corresponding line or bus is said to be dead. If the
voltage is above the set overvoltage level, the line or bus is said to be live.
There can be three different situations of undervoltage: live line and bus (LLLB), dead line and live bus
(DLLB), or dead bus and live line (LLDB). By choosing settings we are able to make the undervoltage
unit operate in any of these situations.
Similar to what has been stated in the case of the synchronism unit, if the Manual input is activated, in
order for the undervoltage units to operate, it is necessary to also activate the Enable input. However,
as opposed to the synchronism check unit, this undervoltage unit has no time delay whatsoever.

3.3.2 Settings

The undervoltage unit has the following assigned settings:
3-1: VL↑:
3-2: VL↓:
3-3: VB↑:
3-4: VB↓:
4-2: DLDB ON-OFF:
4-3: DLLB ON-OFF:
GEK - 105560
Level of voltage present in line (live line: LL).
Range: from 40 to 245 in steps of 1.
Units: volts
Default value: 50
Level of voltage absent in line (dead line: DL).
Range: from 10 to 180 in steps of 1.
Units: volts
Default value: 30
Level of voltage present in bus (live bus: LB).
Range: from 40 to 245 in steps of 1.
Units: volts
Default value: 50
Level of voltage absent in bus (dead bus: DB).
Range: from 10 to 180 in steps of 1.
Units: volts
Default value: 30
Activation condition: dead line and bus (DLDB).
Range: Enabled or disabled.
Units: --
Default value: OFF (Disabled)
Activation condition: dead line with live bus
(DLLB).
Range: Enabled or disabled.
Units: --
Default value: OFF (Disabled)
14