Application - ABB RELION REX640 Technical Manual

1MRS759142 C
4.2.5.6
REX640
Technical Manual
Timer 1
Once activated, the Timer activates the START output. The timer characteristic is
according to DT. When the operation timer has reached the value set by Operate delay
time in the DT mode, the OPERATE output is activated. If a drop-off situation occurs,
that is, a fault suddenly disappears before the operating delay is exceeded, the timer
reset state is activated. The reset time depends on the Reset delay time setting.
The binary input BLOCK can be used to block the function. The activation of the
BLOCK input deactivates all outputs and resets the internal timers.
Timer 2
Once activated, the Timer 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 fault suddenly disappears before the alarm delay is exceeded, the timer reset state is
activated. The reset time depends on the Alm reset delay time setting.
The binary input BLOCK can be used to block the function. The activation of the
BLOCK input deactivates all outputs and resets the internal timers.

Application

The rotor circuit of synchronous machines is normally isolated from the earth. The
rotor circuit can be exposed to an abnormal mechanical or thermal stress due to, for
example, vibrations, overcurrent and choked cooling medium flow. This can result in
the breakdown of the insulation between the field winding and the rotor iron at the
point exposed to excessive stress. If the isolation resistance is decreased significantly,
this can be seen as an earth fault. For generators with slip rings, the rotor insulation
resistance is sometimes reduced due to the accumulated carbon dust layer produced by
the carbon brushes. As the circuit has a high impedance to earth, a single earth fault
does not lead to any immediate damage because the fault current is small due to a low
voltage. There is, however, a risk that a second earth fault appears, creating a rotor
winding interturn fault and causing severe magnetic imbalance and heavy rotor
vibrations that soon lead to a severe damage.
Therefore, it is essential that any occurrence of an insulation failure is detected and
that the machine is disconnected as soon as possible. Normally, the device is tripped
after a short time delay.
A 50/60 Hz voltage is injected via the injection device REK 510 to the rotor field
winding circuit of the synchronous machine as shown in
voltage is 100 V AC via the coupling capacitors. A coupling capacitor prevents a DC
current leakage through the injection device.
Section 4
Protection functions
Figure 265. The injected
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