(1) Description of Operation 7SR224
©2009 Siemens Protection Devices Limited Page 53 of 66
5.2 VT SUPERVISION (60VTS)
1 or 2 Phase Failure Detection
Normally the presence of negative phase sequence (NPS) or zero phase sequence (ZPS) voltage in a
power system is accompanied by NPS or ZPS current. The presence of either of these sequence
voltages without the equivalent level of the appropriate sequence current is used to indicate a failure
of one or two VT phases.
The 60VTS Component setting selects the method used for the detection of loss of 1 or 2 VT phases
i.e. ZPS or NPS components. The sequence component voltage is derived from the line voltages;
suitable VT connections must be available. The relay utilises fundamental voltage measurement
values for this function.
The element has user settings 60VTS V and 60VTS I. A VT is considered to have failed where the
voltage exceeds 60VTS V while the current is below 60VTS I for a time greater than 60VTS Delay.
3 Phase Failure Detection
Under normal load conditions rated PPS voltage would be expected along with a PPS load current
within the circuit rating. Where PPS load current is detected without corresponding PPS voltage this
could indicate a three phase VT failure. To ensure these conditions are not caused by a 3 phase fault
the PPS current must also be below the fault level.
The element has a 60VTS V
PPS
setting, an 60VTS I
PPS
Load setting and a setting for 60VTS I
PPS
Fault. A VT is considered to have failed where positive sequence voltage is below 60VTS V
PPS
while
positive sequence current is above I
PPS
Load and below I
PPS
Fault level for more than 60VTS Delay
then a VT failure will be detected.
External MCB
A binary input can be set as Ext_Trig 60VTS to allow the 60VTS Delay element to be started from an
external MCB operating.
Once a VT failure condition has occurred the output is latched on and is reset by any of the following:-
Voltage is restored to a healthy state i.e. above V
PPS
setting while NPS voltage is below V
NPS
setting.
Ext Reset 60VTS A binary or virtual input, or function key and a VT failure condition no
longer exists.
Inhibit 60VTS A binary or virtual input.
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