ABB RELION 620 Series Technical Manual page 724

Section 4
Protection functions
4.7
4.7.1
4.7.1.1
4.7.1.2
4.7.1.3
4.7.1.4
718
Impedance protection
Three-phase underexcitation protection UEXPDIS
Identification
Function description
Three-phase underexcitation protection
Function block
GUID-1D165D41-1EE8-4AF4-A3F5-E688F97850DB V1 EN
Figure 363: Function block
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.
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.
IEC 61850 IEC 60617
identification identification
UEXPDIS X<
1MRS757644 F
ANSI/IEEE C37.2
device number
40
620 series
Technical Manual