Current Protection: Voltage Controlled Overcurrent (51V) - 7Sr12; Figure 3-4 Logic Diagram: Voltage Controlled Overcurrent Protection - Siemens 7SR12 Argus Manual

3.1.4 C
URRENT
Voltage controlled overcurrent is only available in relays with four current inputs.
Each shaped overcurrent element 51-n Setting can be independently controlled by the level of measured
(control) input voltage.
For applied voltages above VCO Setting the 51-n element operates in accordance with its normal current setting
(see 3.1.3). For input Ph-Ph control voltages below VCO Setting a multiplier (51-n Multiplier) is applied to
reduce the 51-n pickup current setting.
51-n Multiplier is applied to each phase independently when its control phase-phase voltage falls below VCO
Setting. The voltage levels used for each phase over-current element are shown in the table below. Relays with a
Ph-N connection automatically calculate the correct Ph-Ph control voltage.
Current Element
The Voltage Controlled Overcurrent function (51V) can be inhibited from:
VCO VTSAction: Inhibit
51V Element
Enabled
Disabled
51V VTS Action
Off
Inhibit
VT Fail

Figure 3-4 Logic Diagram: Voltage Controlled Overcurrent Protection

©2017 Siemens Protection Devices Limited
P : V
ROTECTION OLTAGE
I
L1
I
L2
I
L3
Operation of the VT Supervision function.
&
&
51V Setting
c
V
12
V
L1
V
23
V
L2
V
31
V
L3
7SR11 & 7SR12 Description Of Operation
C O
ONTROLLED VERCURRENT
Control Voltage
51-n Multiplier
c
c
<
x IL1 51-n Setting
c
<
x IL2 51-n Setting
c
<
x IL3 51-n Setting
(51V) - 7SR12
V
12
V
23
V
31
L1
See
L2
Delayed
Overcurrent
(51-n)
L3
Chapter 1 Page 35 of 88