Areva MiCOM P441, Technical Manual

Page: 165 / 636

Relay Description P44x/EN HW/E33
MiCOM P441/P442 & P444 Page 37/44
4.7.2 Line in one pole open condition (during single-pole trip)
In this case, the power swing only occurs on two phases. A power swing is detected if:
•
At least one single-phase impedance is within the start-up zone after having crossed
the power swing band in more than 5ms.
•
The two impedance points have been in the power swing band for more than 5 ms.
NOTE: During an open-pole condition, the P44x monitors the power swing on
two single-phase loops. No external information is needed if the
voltage transformers are on the line side. If the voltage transformers
are on the bus side, the «pole discrepancy» signal should be used.
The «pole discrepancy» input represents a «one-circuit-breaker-pole-
open» condition.
4.7.3 Conditions for isolating lines
If there is a power swing, it may be necessary to trip and disconnect the two out-of-step
sources. There are various tripping and blocking options available that are used to select if
the line is tripped for power swings or not.
The selective blocking of remote zones allows the P44x to separate the network near the
electrical zero by tripping zone 1 only. Therefore, in the example given in figure 15, the relay
D trips out.
A
B
Electrical
Zero
C D E F
P3039ENa
Relay set for out-of-step tripping,
zone 1.
FIGURE 15 - SELECTIVE PROTECTION BLOCKING
4.7.4 Tripping logic
Depending on the blocking or unblocking selected, the P44x will trip or block as the swing
(stable or unstable) passes through the zones.
NOTE: If selected, tripping will occur if the impedance stays in any zone
longer than its time delay.
There is a master unblocking timer that is used to override any blocked zone (unblocking
time delay). This is used to separate the sources (open the breaker, 3-phase trip) in the
event that a block was taking place, and the impedance remained in the blocked zone for a
relatively long time. This would be indicative of a serious overcurrent condition as a result of
too great a power transfer after a disturbance (a power swing that does not pass through or
recover). If the impedance point moves out of the start-up characteristic again before the
time delay expires, a trip is not issued and the adjustable time delay is reset.
Unblocking the Zones Blocked due to Faults
In order to protect the network against a fault that may occur during power swing, blocking
signals can be stopped when current thresholds are exceeded. The adjustable unblocking
current thresholds are
•
A residual current threshold equal to 0.1 In + (kr x Imax(t)).
•
A negative-sequence current threshold equal to 0.1 In + (ki x Imax(t)).
•
A phase current threshold: IMAX.