Blocking logic
There are three operation modes in the blocking function. The operation modes are
controlled by the BLOCK input and the global setting in Configuration> System>
Blocking mode which selects the blocking mode. The BLOCK input can be controlled
by a binary input, a horizontal communication input or an internal signal of the
protection relay's program. The influence of the BLOCK input signal activation is
preselected with the global
Blocking mode
setting.
The
Blocking mode
setting has three blocking methods. In the "Freeze timers"
mode, the operation timer is frozen to the prevailing value, but the OPERATE output
is not deactivated when blocking is activated. In the "Block all" mode, the whole
function is blocked and the Timers are reset. In the "Block OPERATE output" mode,
the function operates normally but the OPERATE output is not activated.
The “Freeze timers” mode of blocking has no effect during the inverse
reset mode.
4.4.1.5 Timer characteristics
The operating curve types supported by PHPTOV are:
Table 430: Timer characteristics supported by IDMT operate curve types
Operating curve type
(5) ANSI Def. Time
(15) IEC Def. Time
(17) Inv. Curve A
(18) Inv. Curve B
(19) Inv. Curve C
(20) Programmable
4.4.1.6 Application
Overvoltage in a network occurs either due to the transient surges on the network
or due to prolonged power frequency overvoltages. Surge arresters are used to
protect the network against the transient overvoltages, but the relay's protection
function is used to protect against power frequency overvoltages.
The power frequency overvoltage may occur in the network due to contingencies
such as:
• The defective operation of the automatic voltage regulator when the generator is
in isolated operation.
• Operation under manual control with the voltage regulator out of service. A
sudden variation of load, in particular the reactive power component, gives
rise to a substantial change in voltage because of the inherent large voltage
regulation of a typical alternator.
• Sudden loss of load due to the tripping of outgoing feeders, leaving the
generator isolated or feeding a very small load. This causes a sudden rise in
the terminal voltage due to the trapped field flux and overspeed.
If a load sensitive to overvoltage remains connected, it leads to equipment damage.
Protection functions
1MRS758755 C
424 REC615 & RER615
Technical Manual
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