MainsPro G99TT 1.0.0 Global Guide
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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 67) 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 G99TT measures frequency on the phase L1 only, therefore frequency measurement will be
distorted in case that a fault occurs in this phase.
To avoid any unwanted oscillation around the underfrequency or overfrequency limit, 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
Image 8.4 Frequency hysteresis for underfrequency
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