Application Of Individual Protection Functions; Power Swing Detection And Blocking (Psb); Biphase Power Swing Characteristic - GE MiCOM P40 Agile Technical Manual

P44x/EN AP/Hb6
(AP) 5-86
4

APPLICATION OF INDIVIDUAL PROTECTION FUNCTIONS

4.1

Power Swing detection and blocking (PSB)

Power swings are caused by a lack of stability in the network with sudden load fluctuations.
A power swing may cause the two sources connected by the protected line to go out of step
(loss of synchronism) with each other.
The power swing detection element may be used to selectively prevent when the measured
impedance point moves into the start-up characteristic from a power swing and still allows
tripping for a fault (fault evolving during a power swing). The power swing detection element
may also be used to selectively trip once an out-of-step condition has been declared.
Power swings are oscillations in power flow which can follow a power system disturbance.
They can be caused by sudden removal of faults, loss of synchronism across a power
system or changes in direction of power flow as a result of switching. Such disturbances can
cause generators on the system to accelerate or decelerate to adapt to new power flow
conditions, which in turn leads to power swinging. A power swing may cause the impedance
presented to a distance relay to move away from the normal load area and into one or more
of its tripping characteristics.
4.1.1 Power Swing Detection
A power swing is characterized by:
• A 3 successive impedance points in start-up zone of the biphase characteristic,
• A slow variation of current,
• A slow variation of voltage.
On the contrary a fault is characterized by a rapid (instantaneous) and "exaggerated"
variation of current.
Power Swing detection uses a ΔR (resistive) and ΔX (reactive) impedance band which
surrounds the entire biphase fault trip characteristic.
Figure 59: Biphase power swing characteristic
A power swing is detected when all 3 phase to phase impedances have remained within the
ΔR for at least 3 acquisition samples (5 ms at 50Hz) and have taken longer than 5 ms to
reach the trip characteristic.
More precisely, a power swing is detected and declared if:
• At least one phase-phase impedance is within the start-up zone after having crossed
the power swing band in more than 5 ms.
Application Notes
MiCOM P40 Agile P442, P444