Frequency hysteresis for underfrequency
Voltage unbalance (ANSI 47)
The voltage unbalance is evaluated in case that amplitude difference between any 2 phases
overreaches the preset limit V Unb: V Unb. It refers to the amplitude unbalance of the measured
voltage.
Floating average overvoltage
The floating average overvoltage protection provides continuous 10 minutes long measurement of
either phase-to-neutral or phase-to-phase voltage (depending on the Voltage Setup parameter
setting). In case that the measured voltage exceeds the set limit, an immediate trip is issued. The limit
Avg V> is in the setpoints group U<>.
"Loss of mains" protections
InteliPro provides two different methods for fast evaluation of loss of mains (LOM), into which the generator
operates:
- Vector shift
- Rate Of Change Of Frequency
The loss-of-mains protections setpoints are in the group LOM.
Vector shift (ANSI 78)
Vector shift is one of the LOM protections. It provides very fast detection of mains failure (in units or
tens of ms), based on the principle of shift of the synchronous generator displacement angle. The
displacement angle is an angle between magnetic field of a rotor and the rotating magnetic field of the
stator winding and relates strongly to the load of the generator. In case that this load changes, the
displacement angle immediately changes by a "jump". Compared to the frequency decrease, which
probably also occurs, this jump is an immediate phenomena and is detected as a shift of the
measured voltage sine curve - Vector shift or Vector jump. Depending on the preset limit in degrees
[°],itallowsimmediatedisconnectionofveryfastfailuresandthuspreventionofsevere damages
which could not be prevented within the delay of frequency or voltage protections.
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