3BDH000741R1 CTI121-P Ex ABB Controller module main control board circuit board

Description

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 = 0 for a total phase error  of 10′ is
P = 0.03   = 0.03  10 = 0.3% [%; 1; min]
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 reactive 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
leaking steam valves is avoided. To prevent false tripping in the
case of steam turbines, the reverse power function is enabled by
auxiliary contacts on the main steam valves of the prime mover.