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4.7.2
Three-phase underexcitation protection 40
4.7.2.1
Identification
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Three-phase underexcitation protection
UEXPDIS
X<
40
4.7.2.2
Function block
TRIP
PICKUP
V_C_CA
V
1
BLOCK
40
EXT_LOS_DET
V_A_AB
V_B_BC
I_C
I
1
I_A
I_B
GUID-AC8833E9-5E4E-4783-9A78-64350BD0ADD8 V1 EN
Figure 345:
Function block
4.7.2.3
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.
4.7.2.4
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.
Section 4
1MAC059074-MB A
Protection functions
696
615 series ANSI
Technical Manual
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