7SR210 & 7SR220 Description of Operation
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5.2 VT Supervision (60VTS) – 7SR22
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, virtual input, function key or remote data Comms.
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