Current Protection: Voltage Controlled Overcurrent (51V) - 7Sr22; Figure 3.2-1 Logic Diagram: Voltage Controlled Overcurrent Protection - Siemens 7SR21 Manual

3.2 Current Protection: Voltage Controlled Overcurrent (51V)
– 7SR22
Voltage controlled overcurrent is available in the 7SR22 relay.
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 Operation of the VT Supervision function.
51V Element
Enabled
Disabled
51V VTS Action
Off
&
Inhibit
VT Fail
V
L1
V
L2
V
L3

Figure 3.2-1 Logic Diagram: Voltage Controlled Overcurrent Protection

©2010 Siemens Protection Devices Limited
I
L1
I
L2
I
L3
&
51V Setting
c
V
12
<
V
23
<
V
31
<
7SR21 & 7SR22 Argus Description of Operation
Control Voltage
51-n Multiplier
c
c
x IL1 51-n Setting
c
x IL2 51-n Setting
c
x IL3 51-n Setting
V
12
V
23
V
31
L1
See
L2
Delayed
Overcurrent
(51-n)
L3
Chapter 1 Page 27 of 71