Residual Current; Negative Sequence Current; Phase Current Threshold; Power Swing Unblocking (Unblocking Of The Relay For Faults During Power Swing) - GE MiCOM P40 Agile Technical Manual

Application Notes
MiCOM P40 Agile P442, P444
locations on the power system can be designed as split points, where circuit breakers will trip
3 phase in to stabilize.
Power swing blocking is automatically removed after "unblocking 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 indicate 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.
Note:
4.1.5

Power Swing unblocking (unblocking of the relay for faults during power swing)

If a fault occurs while the power swing blocking algorithm is on going the Power Swing
blocking algorithm is unblocked so that the protection relay can protect from the occurring
fault (by tripping).
• The relay operates normally for any fault occurring during a power swing
4 fault detection criteria can unblock the "Power Swing blocking":
• Residual Current (IN> status setting) criterion:
This allows tripping for earth faults occurring during a power swing
0.1 In + (kr x Imax(t))
If Residual current condition is true for more than 40ms, then Power Blocking is
unblocked.
• Negative Sequence Current (I2> status setting) criterion:
This allows tripping for phase to phase faults occurring during a power swing.
0.1 In + (ki x Imax(t))
If Negative Sequence Current condition is true for more than 40ms, then Power
Blocking is unblocked.
• ∗
kr = an adjustable coefficient for residual or zero sequence current (3I0),
ki: = an adjustable coefficient for negative sequence current (I2),
Imax(t): maximum instantaneous current detected on one phase (A, B or C),
In: nominal current
• Phase current threshold (ImaxLine> status setting) criterion:
This allows tripping for 3 phase faults occurring during a power swing.
• Delta I criterion ('Delta I status' setting)
This allows tripping for 3 phase faults occurring during a power swing even if the fault
current is lower than ImaxLine>
• condition 1: There is an exaggerated Delta I
• condition 2: There is an absence of current variation on biphases loop.
If there is a delta exaggerated current (condition1 = true) and there is an absence of
variation of current (condition 2 = true) for more than 100ms then Power Swing blocking is
unblocked.
If there isn't any delta exaggerated current (condition1 = false) and there is an absence of
variation of current (condition 2) for more than 200ms then Power Swing blocking is
unblocked.
Power Swing Blocking can be disabled (for distribution systems). Power Swings
should not happen at Distribution voltage levels.
∗
∗
Where:
P44x/EN AP/Hb6
(AP) 5-89