Settings Of Protection Function - ABB REG670 Applications Manual

1MRK 502 071-UEN -
7.2.4.2
7.2.4.3
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual

Settings of protection function

Operation: The operation of the high impedance differential function can be switched
On or Off.
U>Alarm: Set the alarm level. The sensitivity can roughly be calculated as a certain
percentage of the selected Trip level. A typical setting is 10% of U>Trip This alarm
stage can be used for scheme CT supervision.
tAlarm: Set the time delay for the alarm. A typical setting is 2-3 seconds.
U>Trip: Set the trip level according to the calculations (see examples below for a
guidance). The level is selected with margin to the calculated required voltage to
achieve stability. Values can be within 20V - 400V range dependent on the
application.
SeriesResistor: Set the value of the used stabilizing series resistor. Calculate the value
according to the examples for each application. Adjust the resistor as close as possible
to the calculated value. Measure the value achieved and set this value for this
parameter.
The value shall always be high impedance. This means for example,
for 1A circuits say bigger than 400 ohms (400 VA) and for 5 A circuits
say bigger than 100 ohms (2500 VA). This ensures that the current
will circulate and not go through the differential circuit at through
faults.
That the settings of U>Alarm, U>Trip and SeriesResistor must be
chosen such that both U>Alarm/SeriesResistor and U>Trip/
SeriesResistor are >4% of IRated of the used current input. Normally
the settings shall also be such that U>Alarm/SeriesResistor and
U>Trip/SeriesResistor both gives a value <4*IRated of the used
current input. If not, the limitation in how long time the actual current
is allowed to persist not to overload the current input must be
considered especially during the secondary testing.
T-feeder protection
In many busbar arrangements such as one-and a half breaker, ring breaker, mesh
corner, there will be a T-feeder from the current transformer at the breakers up to the
current transformers in the feeder circuit (for example, in the transformer bushings).
It is often required to separate the protection zones that the feeder is protected with one
scheme while the T-zone is protected with a separate differential protection scheme.
The 1Ph high impedance differential HZPDIF function in the IED allows this to be
done efficiently, see Figure 63.
Section 7
Differential protection
159