Loss Of Excitation Lexpdis (40) - ABB Relion Technical Manual

1MRK 502 048-UUS A
7.3
7.3.1
7.3.2
7.3.3
Technical manual

Loss of excitation LEXPDIS (40)

Identification
Function description
Loss of excitation
Functionality
There are limits for the low excitation of a synchronous machine. A reduction of the
excitation current weakens the coupling between the rotor and the stator. The machine
may lose the synchronism and start to operate like an induction machine. Then, the
reactive power consumption will increase. Even if the machine does not loose
synchronism it may not be acceptable to operate in this state for a long time. Reduction of
excitation increases the generation of heat in the end region of the synchronous machine.
The local heating may damage the insulation of the stator winding and the iron core.
To prevent damages to the generator it should be tripped when excitation becomes too
low.
The impedance measurement is used for LEXPDIS function. Its operating characteristic
is designed as two zone, offset mho circles and a directional element restrain line.
Function block
LEXPDIS (40)
I3P* TRIP
V3P* TRZ1
BLOCK TRZ2
BLKTRZ1 PICKUP
BLKTRZ2 PU_Z1
PU_Z2
XOHM
XPERCENT
ROHM
RPERCENT
ANSI0700031-1-en.vsd
ANSI0700031 V1 EN
Figure 70: LEXPDIS (40) function block
Impedance protection
IEC 61850 IEC 60617
identification identification
LEXPDIS
SYMBOL-MM V1 EN
Section 7
ANSI/IEEE C37.2
device number
40
<
167