Three-Phase Underexcitation Protection 40 - ABB 615 series Technical Manual

Section 4
Protection functions
4.7.2
4.7.2.1
4.7.2.2
4.7.2.3
4.7.2.4
696

Three-phase underexcitation protection 40

Identification
Function description
Three-phase underexcitation protection
Function block
40
TRIP
I_A
PICKUP
I_B
I_C
I
1
V_A_AB
V_B_BC
V_C_CA
V
1
EXT_LOS_DET
BLOCK
GUID-AC8833E9-5E4E-4783-9A78-64350BD0ADD8 V1 EN
Figure 345: Function block
Functionality
The three-phase underexcitation protection function 40 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 trip
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 "Enable" and "Disable".
The operation of 40 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<
1MAC059074-MB A
ANSI/IEEE C37.2
device number
40
615 series ANSI
Technical Manual