7SR224 Argus Description of Operation
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
Control Voltage
I
L1
V
12
I
L2
V
23
I
L3
V
31
The Voltage Controlled Overcurrent function (51V) can be inhibited from:
VCO VTSAction: Inhibit
Operation of the VT Supervision function.
V
L1
51V Setting
c
&
51V Element
Enabled
Disabled
<
<
<
V
L2
V
L3
51V VTS Action
Off
Inhibit
See
Delayed
Overcurrent
(51-n)
VT Fail
&
51-n Multiplier
c
V
12
V
31
V
23
c
x IL1 51-n Setting
c
x IL2 51-n Setting
c
x IL3 51-n Setting
L3
L2
L1
Figure 3.2-1 Logic Diagram: Voltage Controlled Overcurrent Protection
©2010 Siemens Protection Devices Limited
Chapter 1 Page 22 of 70