protection are measured on the protected generator output terminals side (HV-
side), then invertion is necessary (InvertCTCurr = Enabled), provided that the
CT’s actual direction complies with ABB recommendations, as shown in Table 29.
8.6 Loss of excitation LEXPDIS
(40)
SEMOD156735-1 v3
8.6.1 Identification
SEMOD158930-2 v3
Function description IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Loss of excitation LEXPDIS
SYMBOL-MM V1 EN-US
40
8.6.2 Application
SEMOD151271-4 v6
There are limits for the loss of excitation of a synchronous machine. A reduction of the
excitation current weakens the electromagnetic coupling between the generator rotor
and stator, hence, the external power system. The machine may lose the synchronism
and starts to operate like an induction machine. Then, the reactive consumption will
increase. Even if the machine does not lose synchronism it may not be acceptable to
operate in this state for a long time. Loss 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 even the iron core.
A generator connected to a power system can be represented by an equivalent single
phase circuit as shown in figure 145. For simplicity the equivalent shows a generator
having round rotor, (X
d
≈X
q
).
Section 8 1MRK 502 071-UUS A
Impedance protection
302 Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
Application manual
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