Alstom MiCOM P546 - 1.22.4 Delta directional decision (Distance option only)

Operation P54x/EN OP/La4
MiCOM P543, P544, P545 & P546 (OP) 5-57
OP
1.22.4 Delta directional decision (Distance option only)
On fault inception, delta quantities are generated, and it is then simple for the relay to
determine the direction of the fault:
Forward fault -
Delta V is a decrease in voltage, and so is in the negative sense;
whereas delta I is a forward current flow and so is in the positive
sense. Where delta I and delta V are approximately in
antiphase
, the fault is forward. The exact angle relationship for
the forward fault is:
V / I = - (Source impedance, Zs)
Reverse fault -
Delta V is a decrease in voltage, and so is in the negative sense;
delta I is an outfeed flowing in the reverse direction, so that too is
in the negative sense. Where delta I and delta V are
approximately in phase, the fault is reverse. The exact angle
relationship for the reverse fault is:
V / I = (Remote Source impedance Zs’ + ZL)
Where ZL is protected line impedance and Zs’ source impedance behind the relay.
An RCA angle setting in the relay allows the user to set the center of the directional
characteristic, according to the amount the current will nominally lag the reference delta
voltage. The characteristic boundary will then be  90 degrees either side of the set center.
Note: Distance zone directionalizing shares the same characteristic angle
setting used for Delta directional comparison protection, but uses fixed
operating thresholds: V=0.5V and I=4%In. In distance applications,
if the fault V is below the setting of 0.5V, a conventional distance line
ensures correct forward/reverse polarizing. This is not true for Delta
directional aided schemes where sufficient V must be present, for
tripping to occur.
The directional criteria for delta directional decisions are given below:
Directional forward
-90o < (angle(I) – angle(V+180
o
) – RCA) < 90
o
Directional reverse
-90
o
> (angle(I) – angle(V+180
o
) – RCA) > 90
o
In order to facilitate testing of the Distance elements using test sets which do not provide a
dynamic model to generate true fault delta conditions, a Static Test Mode setting is provided.
This setting is found in the COMMISSIONING TESTS menu column. When set, this
disables phase selector control and forces the relay to use a conventional (non-delta)
directional line.