Alstom MiCOM P545 - 3.1.3 Teed feeder example

Application Notes P54x/EN AP/La4
MiCOM P543, P544, P545 & P546
(AP) 6-51
AP
When a Star/Delta software interposing CT is chosen, no additional account has to be taken
for the
3 factor which would be introduced by the delta winding. This is accounted for by
the relay.
Phase Correction Example
:
Using the same transformer as shown in Figure 15 it is now necessary to correct for the
pha
se shift between the HV and LV windings.
The transformer connection shows that the delta connected high voltage line current leads
the low voltage line current by 30°. To ensure that this phase shift does not create a
differential current, the phase shift must be corrected in the LV secondary circuit. The LV
relay software interposing CT is effectively a winding replica of the main power transformer.
It not only provides a +30° phase shift, but also performs the necessary function of filtering
out any LV zero sequence current component.
Hence, the HV relay setting requires no phase shift or zero sequence current filtering (as HV
winding is delta connected). The LV relay setting requires phase shifting by +30° and also
requires zero sequence current filtering (as LV winding is star connected).
Set: HV = Yy0
LV = Yd11 (+30°)
It is important when considering the software ICT connection, to account for both the phase
shift and zero sequence current filtering. For example, with the transformer in Figure 15, it
woul
d have been possible to provide phase compensation by applying Yd1 and Yy0 settings
to the HV and LV relays respectively. Although this provides correct phase shift
compensation, no zero sequence current filtering exists on the LV side and hence relay
maloperation could occur for an external earth fault.
3.1.3 Teed feeder example
10 Km
P543 P543
P543
Ch 1
Ch 2
Ch 1
Ch 2
Ch 2
Ch 1
1200/5
End C
275 kV
45 Km 30 Km
End B
275 kV
End A
275 kV
4000/5
Digital communication link
Digital communication link
Digital communication link
Steady State Charging Current = 0.58 A/Km Overhead Line
4000/5
P1502ENc
Figure 16 Typical teed feeder application
If there are not VT inputs connected, P54x relays have not facilities to account for charging
line current, therefore the setting Is1 must be 2.5 times the steady state charging current.
If VT inputs are connected, there is a facility to overcome the effect of charging current.
As mentioned before, it is necessary to enter the positive sequence susceptance value.