4.7
Impedance protection
4.7.1
Three-phase underexcitation protection UEXPDIS
4.7.1.1
Identification
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Three-phase underexcitation pro-
tection
UEXPDIS
X<
40
4.7.1.2
Function block
Figure 373: Function block
4.7.1.3
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, if desired.
4.7.1.4
Operation principle
The function can be enabled and disabled with the
Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of UEXPDIS can be described using a module diagram. All the
modules in the diagram are explained in the next sections.
Protection functions
1MRS757644 H
720
620 series
Technical Manual