9424200996 17-1
BE1-11m Loss of Excitation - Reverse Var Based (40Q) Protection
17 • Loss of Excitation - Reverse Var
Based (40Q) Protection
The loss of excitation - reverse var based (40Q) element monitors total reactive power (vars).
Element logic connections are made on the BESTlogic™Plus screen in BESTCOMSPlus® and element
operational settings are configured on the Loss of Excitation - Reverse var Based (40Q) settings screen
in BESTCOMSPlus. A summary of the logic inputs and outputs and operational settings appears at the
end of this chapter.
BESTCOMSPlus Navigation Path: Settings Explorer, Protection, Power, Loss of Excitation - Reverse
var Based (40Q)
HMI Navigation Path: Settings Explorer, Protection, Settings Group x (where x = 0 to 3), Power
Protection, Reverse var 40Q
Element Operation
The loss of excitation element operates on excessive var flow into the machine, indicating abnormally low
field excitation. Operation of synchronous motors drawing reactive power from the system can result in
overheating in parts of the rotor that do not normally carry current. The 40Q pickup response is shown in
Figure 17-1.
Figure 17-1. 40Q Pickup Response
Bus CT Configuration
On protection systems equipped with two sets of CTs, the 40Q element can monitor CT circuit 1 or CT
circuit 2. The CT source is selected on the Sensing Transformers settings screen in BESTCOMSPlus.
Pickup and Trip
The Pickup output occurs first, followed by the Trip output.
Pickup
The Pickup output becomes true when the calculated reactive power increases above or decreases
below the threshold established by the Pickup setting. In BESTlogicPlus, the Pickup output can be
connected to other logic elements to annunciate the condition, control other elements in logic, and start
the fault recorder (logic element FAULTTRIG).
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