4.7.3.2 Function block
Figure 563: Function block
4.7.3.3 Functionality
The three-phase underexcitation protection function UEXPDIS is used to protect the
synchronous machine against the underexcitation or loss of excitation condition.
The protection is based on the offset-mho circular characteristics on the impedance
plane. The function calculates the apparent impedance from the machine terminal
voltages and currents. If the impedance vector enters the offset-mho circle, the
function gives the operating signal after a set definite time. The operating time
characteristics are according to definite time (DT).
This function contains a blocking functionality. It is possible to block the function
outputs, timer or the function itself.
4.7.3.4 Analog channel configuration
UEXPDIS has two analog group inputs which all must be properly configured.
Table 945: Analog inputs
Input Description
I3P Three-phase currents
U3P Three-phase voltages
See the preprocessing function blocks in this document for the possible
signal sources.
There are a few special conditions which must be noted with the configuration.
Table 946: Special conditions
Condition Description
U3P connected to real measurements The function can work with one voltage chan-
nel connected (
Phase Sel for Z Clc
set to "A
or AB", "B or BC" or "C or CA"), if the setting
Impedance Meas mode
is set to "1Phase-to-
earth" or "1Phaseto- phase".
The function requires that at least two (the
third voltage will be derived) or all three volt-
age channels are connected if
Impedance
Meas mode
is set to "3Phase-to-earth",
"3Phase-to-phase" or "Pos sequence".
Protection functions 1MRS759142 F
1016 REX640
Technical Manual
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