Current Protection: Voltage Controlled Overcurrent (51V); Figure 3.2-1 Logic Diagram: Voltage Controlled Overcurrent Protection - Siemens 7SR224 Description & Operation

3.2 C P
URRENT
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
I
L2
I
L3
The Voltage Controlled Overcurrent function (51V) can be inhibited from:
VCO VTSAction: Inhibit
51V Element
Enabled
Disabled
51V VTS Action
Off
&
Inhibit
VT Fail
V
L1
V
L2
V
L3
Figure 3.2-1
©2009 Siemens Protection Devices Limited
: V
ROTECTION OLTAGE
V
12
V
23
V
31
Operation of the VT Supervision function.
&
51V Setting
c
V
12
V
23
V
31
Logic Diagram: Voltage Controlled Overcurrent Protection
C O
ONTROLLED VERCURRENT
51-n Multiplier
c
c
<
x IL1 51-n Setting
c
<
x IL2 51-n Setting
c
<
x IL3 51-n Setting
(1) Description of Operation 7SR224
(51V)
L1
See
L2
Delayed
Overcurrent
(51-n)
L3
Page 23 of 66