Current Protection: Voltage Controlled Oc (51V); Figure 3.2-1 Logic Diagram: Voltage Controlled Overcurrent Protection - Siemens 7SR224 Technical Manual

3.2

Current Protection: Voltage Controlled OC (51V)

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
I
I
I
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
L1
L2
L3
&
51V Setting
c
V
12
<
V
23
<
V
31
<
7SR224 Argus Description of Operation
Control Voltage
V
12
V
23
V
31
51-n Multiplier
c
c
L1
x IL1 51-n Setting
c
See
L2
Delayed
x IL2 51-n Setting
Overcurrent
c
(51-n)
L3
x IL3 51-n Setting
Chapter 1 Page 22 of 70