Mains pro 1.6.1 Global Guide
33
8 Protective features
The following protective functionalities, referred also by their ANSI number, are available in MainsPro unit:
8.1 ANSI 59 Overvoltage, ANSI 27 Undervoltage 33
8.2 Floating 10 minutes average overvoltage 34
8.3 ANSI 81H Overfrequency, 81L Underfrequency 34
8.4 ANSI 47 Voltage unbalance and angle asymmetry 36
8.4.1 Voltage unbalance 36
8.4.2 Positive sequence undervoltage, Negative sequence overvoltage 36
8.5 ANSI 78 Vector shift 37
8.5.1 Measuring principle 38
8.6 81R Rate Of Change Of Frequency (ROCOF) 39
8.7 Phase rotation, incorrect phase polarity 39
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8.1 ANSI 59 Overvoltage, ANSI 27 Undervoltage
The RMS value of measured voltage is compared with the preset limit of overvoltage or undervoltage. When any
of the preset limits is over/underreached, the appropriate LED signal is issued by LED U and the output U Sig
moves to fault-indicating position immediately. If voltage of in the given phase keeps out of limits for the delay of
the appropriate stage, TRIP (page 31) is issued. As the voltage returns back within limits in all measured
phases, the LED and U Sig (page 64) output stop to signal the fault state immediately, regardless of whether
TRIP (page 31) was issued or not or Fault reset (page 32) was performed or not. Both overvoltage and
undervoltage protective stages provide possibility of setting 2 levels with independent delay assigned to each
level.
In order to prevent from unwanted voltage oscillation around the overvoltage, respective undervoltage limits,
there is a possibility to set up a voltage hysteresis. The principle is shown in the pictures below. After
overvoltage situation, voltage must decrease under the hysteresis limit to clear the fault. After undervoltage
situation, voltage must exceed the hysteresis limit to clear the fault.
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