Vt Supervision (60Vts); Figure 5-3 Logic Diagram: Total Harmonic Distortion Supervision Element (81Thd) - Siemens 7SR10 Argus Series Manual

81THD
Enabled
Disabled
81THD
81THD- Inrush
L1 81HBL2
Action
Off
Inhibit
L2 81HBL2
L3 81HBL2
Figure 5-3
5.4

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 VPPS setting, an 60VTS IPPS Load setting and a setting for 60VTS IPPS Fault. A VT
is considered to have failed where positive sequence voltage is below 60VTS VPPS while positive sequence
current is above IPPS Load and below IPPS Fault level for more than 60VTS Delay.
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 VPPS setting while NPS voltage is below VNPS setting.
Ext Reset 60VTS
Inhibit 60VTS
©2018 Siemens Protection Devices Limited
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81THD
Measurement
IL1
IL2
IL3
Logic Diagram: Total Harmonic Distortion Supervision Element (81THD)
A binary or virtual input, or function key and a VT failure condition no longer
exists.
A binary or virtual input.
81THD Setting
c
81THD Delay
c
>
c
>
c
>
7SR10 Description of Operation
≥1
General Pickup
≥1
81THD
Chapter 1 Page 64 of 77