InteliPro, SW version 1.0, ©ComAp – May 2011
InteliPro Application Guide
2-11
Time overcurrent with voltage control and restraint (ANSI 51V)
The voltage control of time overcurrent assures that the protection is blocked in case that the
measured voltage is above the level set by the setpoint I> V: I> V Control.
The voltage restraint function is a modification of the IDMT overcurrent protection. It uses the same
mechanism of the delay calculation according to the IDMT trip curve, but the delay is further adjusted
according to the measured voltage:
This protection functionality uses the fact that voltage in the point of short-circuit drops to zero or very
low values and with growing distance from the fault, it increases up to the mains nominal voltage
value. Thus, increased sensitivity to the short-circuits localization and protection coordination is
provided. The setting is done using the setpoints
in the group I> V.
Neutral overcurrent (ANSI 50N, ANSI 51N)
To allow measurement of the neutral overcurrent, the plug-in module Relay Card CT2-REL2 is
necessary. The protection stage allows to set up instantaneous neutral overcurrent or IDMT
overcurrent, similar to the mains overcurrent protective functions. The setting is done using the
setpoints group EFC.
Current unbalance (ANSI 46)
The current unbalance protection is used to avoid unballanced load in the point of mains connection.
The setting is done using the setpoints in the setpoint group I Unb.
Directional overcurrent (DOC, ANSI 67)
DOC is sensitive for location of the fault with relation to the measurement point. This way, directional
protection is capable to detect whether the fault happened "in front of it" or "behind". Directional
overcurrent protection, applied in the point of generator connection to mains, is considered a loss of
mains protection, however it does not substitute the traditional loss of mains protections like Vector
shift or ROCOF. The typical application is a generator running in parallel to mains with its own load
consumption (e.g. peak shaving, soft transfer stand-by, or other applications). The generator is usually
used to support the local consumption with no export to the mains. In case of mains transition into an
island mode, the generators, running in parallel with the islanded area, would start to supply its
complete consumption, generating current in opposite direction. DOC protection is used to avoid this
situation, and trip the generator from the islanded mains, combining the overcurrent protection
together with its directional character. Compared to the "reverse power protection", DOC protection
detects also reactive currents from the given angle zone, what allows better sensitivity for tripping.
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