EMR-5000
IM02602012E
For activating this function, the parameter »
VRestraint« has to be set to active in the parameter set of the
corresponding overcurrent element I[x].
The
51V protection function restrains operation which reduces pickup levels. This allows the User to lower the pickup
value of the
51V protection function with the corresponding phase input voltage (phase-to-phase or phase-to-ground,
depending on the setting of »
Measuring Channel« within the current protection module). When the minimum fault
phase current is close to the load current, it may make the phase time overcurrent protection coordination difficult. In
this case, an undervoltage function may be used to alleviate this situation. When the voltage is low, the phase time
overcurrent pickup threshold may be set low accordingly, so that the phase time overcurrent protection may achieve
adequate sensitivity and better coordination. The device uses a simple linear model to determine the effective pickup
by characterizing the relationship between the voltage and the phase time overcurrent pickup threshold.
Once the voltage restraint protection function is activated, the effective phase time overcurrent pickup threshold will be
the calculated Pickup% times the phase time overcurrent pickup setting. The effective pickup threshold must be within
the setting range allowed and, if it is less, the minimum pickup value will be used.
That means:
Vmin = 0.25*Vmax;
•
Pickup%min = 25%;
•
Pickup% = 25%, if V <= Vmin;
•
Pickup% = 1/Vmax*(V - Vmin) + 25%, if Vmin < V < Vmax;
•
Pickup% = 100%, if V >= Vmax;
The tripping curves (characteristic) will not be influenced by the voltage restraint function.
If the voltage transformer supervision is activated, the voltage restraint overcurrent protection element is blocked in
case of m.c.b. trip to avoid false trippings.
www.eaton.com
556
Pickup%
VRestraint max
25% VRestraint max
25%
100%
V
