Mains pro 1.6.1 Global Guide
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LED f and the output f Sig (page 65) moves to fault-indicating position immediately. If the frequency keeps out
of limits for the delay of the appropriate stage, TRIP (page 31) is issued. As the frequency returns back within
limits, the LED and f Sig (page 65) 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 overfrequency and underfrequency protective stages provide possibility of setting 2 levels with
independent delay assigned to each level.
Note: MainsPro measures frequency on the phase L1 only, therefore frequency measurement will be distorted
in case that a fault occurs in this phase.
In order to prevent from unwanted frequency oscillation around the overfrequency, respective underfrequency
limits, there is a possibility to set up a frequency hysteresis. The principle is shown in the pictures below. After
overfrequency situation, frequency must decrease under the hysteresis limit to clear the fault. After
underfrequency situation, frequency must exceed the hysteresis limit to clear the fault.
Image 8.3 Frequency hysteresis for overfrequency
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