Toshiba GRL100-701B Instruction Manual page 177

supervision function (VTFS) as a measure against such incorrect operation. When the VTFS
detects a VT failure, it blocks the following voltage dependent protections instantaneously. In 10
seconds, it displays the VT failure and outputs an alarm.
• Zone 1-3 and R distance protection
• Directional earth fault protection
• Command protection
Resetting of the blocks above and resetting of the display and alarm are automatically performed
when it is confirmed that all three phases are healthy.
A binary input signal to indicate a miniature circuit breaker trip in the VT circuits is also
available for the VTFS.
Scheme logic
Figure 3.3.5.1 shows the scheme logic for the VTFS. VT failures are detected under any one of
the following conditions and then a trip block signal VTF is output.
VTF1: The phase-to-phase undervoltage element UVFS or phase-to-earth
undervoltage element UVFG operates (UVFS = 1 or UVFG =1) when the three
phases of the circuit breaker are closed (CB-AND = 1) and the phase current change
detection element OCD1 does not operate (OCD1 = 0).
VTF2: The residual overcurrent element EFL does not operate (EFL = 0), the residual
overvoltage element OVG operates (OVG = 1) and the phase current change
detection element OCD1 does not operate (OCD1 = 0).
In order to prevent detection of false VT failures due to unequal pole closing of the circuit
breaker, the VTFS is blocked for 200 ms after line energisation.
The trip block signal VTF is reset 100 milliseconds after the VT failure condition has reset.
When the VTF continues for 10s or more, an alarm signal VTF-ALM is output.
Further, the VT failure is detected when the binary input signal (PLC signal) EXT_VTF is
received. The binary input signal requires the time coordinated with Zone 1 operation and reset.
If not, the time can be adjusted by the PLC function.
This function can be enabled or disabled by the scheme switch [VTF1EN] or [VTF2EN] and has
a programmable reset characteristic. When set to "ON", the latched operation for VTF1 is reset
by reset of UVFS/UVFG element, and that for VTF2 is reset by reset of OVG element. Set to
"OPT-ON" to reset the latched operation when OCD1 or EFL operates.
The VTFS can be disabled by the PLC signal VTF_BLOCK.
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