Power Swing Load Blinding Boundary - GE MiCOM P40 Technical Manual

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The PSB Unblock dly timer is common to all elements.

The PSB Unblock dly is used to time the duration for which the swing is present. The intention is to allow the

distinction between a stable and an unstable swing. If after the timeout period the swing has still not stabilised, the

block for selected zones can be released (unblocking), giving the opportunity to split the system. If no unblocking is

required, set to maximum (10 s).

There is a further timer associated with the PSB function. This is the PSB Reset Delay timer. This timer is provided to

maintain the power swing detection for a period after the superimposed current detection (ΔI) has reset. ΔI

naturally tends to zero twice during each power swing cycle (around the current maxima and minima in the swing

element). A short time delay ensures continued PSB pick-up during these ΔI minima.

The PSB Reset Delay is used to maintain the PSB status when DI naturally is low during the swing cycle (near the

current maxima and minima in the swing envelope). A typical setting of 0.2s is used to seal-in the detection until DI

has chance to appear again.

The WI Trip PSB setting determines what will happen if a power swing is detected whilst the Weak Infeed (WI)

tripping feature is being used and the WI condition is present for longer than the WI Trip Delay time. If Blocking

is selected, the weak infeed operation will be disabled for the duration of the swing. If Delayed Unblock is

chosen, the weak infeed element block will be removed after drop off timer PSB Unblock dly has expired, even if

the swing is still present. This allows system separation when swings fail to stabilise. In Allow trip mode, the

weak infeed element is unaffected by power swing detection.

POWER SWING LOAD BLINDING BOUNDARY

If the product has load blinding enabled, the following applies for phase-to-phase loops:

Impedance values, which are inside the load blinder boundaries and close to it for more than one cycle, are

indicative of a power swing. The power swing region is represented by the shaded area in the following diagram.

P446SV-TM-EN-1

Chapter 10 - Power Swing Functions