ABB RELION REB500 Technical Manual page 96

Section 5
Bay protection functions
IEC19000442 V1 EN-US
Figure 38: Power swing blocking
The voltage and current input variables are passed on to the evaluation system. The criterion
for pick-up of the power swing blocking function is the continuous variation of (U × cosϕ),
which corresponds to the variation of real power in relation to current amplitude (P = I × U ×
cosϕ). The value of (U × cosϕ) is determined after every zero-crossing of the current. A
blocking signal is generated, as soon as a repetitive variation of the value of (U × cosϕ) is
detected, that is, a variation must be detected at least three times to count as a power swing.
Two periods are needed to detect the faster power swings up to a frequency of 8 Hz. The
power swing blocking function does not pick up during a fault, because the variation of (U ×
cosϕ) in relation to time only occurs once and at a much higher rate than the function's
operating range.
Slow swings are evaluated over five periods by a second system. At its lowest operating limit,
this system detects a frequency of 0.2 Hz.
Together the two systems cover a range from 0.2 to 8 Hz and no setting is required during
commissioning.
The blocking signal PSB is maintained for as long as the distance protection function is in the
picked-up state. The power swing blocking function is only effective for the symmetrical three-
phase condition and cannot block the distance function for asymmetrical faults (phase-to-
ground and phase-to-phase faults).
A blocking signal is not issued, if the zero-crossings of the cur-rent signal occur at relatively
irregular intervals, because considerable differences between the zero-crossing intervals are a
clear indication of a fault on the power system. Phase jumps in the current wave form occur at
90
E1 U
U
E1
Indep endent of:
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U  
cos


U  cos
I

E2
- relay location
- relay characteristics
- relay settings
1MRK 505 406-UEN B
E2
18000037-IEC19000442-1-en.vsdx
Bay protection functions REB500
Technical manual