InteliPro, SW version 1.0, ©ComAp – May 2011
InteliPro Application Guide
2-12
The following image shows the conditions of activation of Directional Overcurrent protection in
InteliPro – i.e. critical angles between voltage and current, given the voltage is placed at the 0°angle:
90°
The setting is done using the setpoints in the group DOC.
Neutral Voltage Displacement (NVD, ANSI 59N)
NVD protective function is used in medium or high voltage systems with isolated or indirectly grounded
zero-point. Under healthy conditions of the system, the sum of the three phase-to-earth voltages
should balance to zero. When an earth-fault occurs, it does not cause a short-circuit, because of the
isolation of the system in the zero point. However, the fault provides connection of one phase with
earth what represents hazard for the system safety (ground-fault in any other phase would then mean
a phase-to phase short-circuit, phase-to-ground voltage of the other phases may fluctuate to multiples
of its nominal, providing increased stress to the isolation system, etc). One of the effects of the fault is
a rise in the neutral voltage, so called neutral voltage displacement. This neutral voltage displacement
is measured in a specific "open-delta" connection of voltage transformers, shown in the chapter
Voltage and current inputs. In some cases, it is required to clear the fault by tripping the appropriate
circuit breaker. However, the NVD protection itself does not allow detecting the location of a fault and
for this reason it is sometimes used only for providing an earth-fault alarm.
It is possible to set whether the NVD contributes to the common trip of the relay or uses its own
separate output for signalization of the NVD alarm. The setting is done using the setpoints in the group
NVD.
Directional power (ANSI 32)
InteliPro provides two stages of power protections, both of them allowing setting of either overreaching
the preset limit or underreaching it. This way, all of the following protections are realized:
- Mains reverse power (protection of unintentional export)
- Generator reverse power (protection of motoric operation)
- Minimum import underreaching (timely trip in case of unintentional export approaching)
0°
-90°
DOC>
Trip area
150°
Base angle
-135°
-60°
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