ABB REG316 4 Series Operating Instructions Manual page 213

REG 316*4 1MRB520049-Uen / Rev. F
Phase compensation
This setting is for correcting the phase error between the v.t's
and c.t's, which have a considerable adverse influence on the
measurement of active power at low power factors.
Example 2
The active power error at rated current and a power factor of
cos j = 0 for a total phase error d of 10' is
D P = 0.03 ´ d = 0.03 ´ 10 = 0.3%
This is an error which is not negligible at a setting of 0.5%.
The total error corresponds to the difference between the v.t.
and c.t. errors. The case considered in this example of full reac-
tive current (100%) would scarcely occur in practice, but currents
from about 80% are possible.
Application as reverse power protection
The reverse power function is used primarily to protect the prime
mover. It is necessary for the following kinds of prime mover:
steam turbines
·
Francis and Kaplan hydro units
·
gas turbines
·
diesel motors.
·
Two reverse power functions are used for prime movers with
ratings higher than 30 MW, because of their importance and
value.
The reverse power function has two stages. The setting is half
the slip power of the generator/prime mover unit and is the same
for both stages.
The first stage has a short time delay and is intended to protect
against overspeeding during the normal shutdown procedure. By
tripping the main circuit-breaker via the reverse power function,
the possibility of overspeeding due to a regulator failure or leak-
ing steam valves is avoided. To prevent false tripping in the case
of steam turbines, the reverse power function is enabled by aux-
iliary contacts on the main steam valves of the prime mover.
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