Application - ABB RELION REX640 Technical Manual

Section 4
Protection functions
4.8.4.6
980
in the DT mode, the OPERATE output is activated. If a drop-off situation occurs, that
is, a power factor improves and exceeds the Start reset value in the direction as defined
by Dir start reset value before the operate delay is exceeded or either magnitude of all
three phase current or voltages goes below Current block value and Voltage block
value respectively, the timer reset state is activated. The reset timer depends on the
Reset delay time setting.
The Timer 1 calculates the start duration value START_DUR, which indicates the
percentage ratio of the start situation and the set operating time. The value is available
in the Monitored data view.
Timer 2
Once activated, the Timer 2 activates the alarm timer. The timer characteristic is
according to DT. When the alarm timer has reached the value set by Alarm delay time
in the DT mode, the ALARM output is activated. If a drop-off situation occurs, that is,
a power factor improves and exceeds the Alarm reset value in the direction as defined
by Dir alarm reset value before the alarm delay is exceeded or either magnitude of all
three phase current or voltages goes below Current block value and Voltage block
value respectively, the timer reset state is activated. The reset timer depends on the
Reset delay time setting.
Blocking logic
There are three operation modes in the blocking function. The operation modes are
controlled by the BLOCK input and the global setting in Configuration/System/
Blocking mode which selects the blocking mode. The BLOCK input can be controlled
by a binary input, a horizontal communication input or an internal signal of the
protection relay's program. The influence of the BLOCK signal activation is
preselected with the global setting Blocking mode.
The Blocking mode setting has three blocking methods. In the "Freeze timers" mode,
the operation timer is frozen to the prevailing value, but the OPERATE output is not
deactivated when blocking is activated. In the "Block all" mode, the whole function is
blocked and the timers are reset. In the "Block OPERATE output" mode, the function
operates normally but the OPERATE output is not activated.

Application

The MPUPF function can be used to detect loss of excitation or for power factor
correction. Synchronous motors are mostly operated at leading power factor and its
operation as lagging power for extended period can be used an indication of an out-of-
step condition possibly caused by under or loss of excitation. To detect such a
situation, the relay is typically set to operate when the current into a motor lags more
than 30 degrees, that is, a power factor goes below +0.87 lagging.
The function provides alarm facility which can be used as an early indication that the
power factor is moving outside the allowable range; therefore the Alarm value setting
should be set higher than the Start value. The delay time for alarm should also be set
as low as possible, only long enough to prevent spurious activation of the output.
1MRS759142 C
REX640
Technical Manual