Setting Guidelines; General - ABB RELION 650 Series Applications Manual

Section 7
Impedance protection
fault divided by the IED current. For the IED at C, the impedance on the high voltage side U1
has to be transferred to the measuring voltage level by the transformer ratio.
Another complication that might occur depending on the topology is that the current from one
end can have a reverse direction for fault on the protected line. For example, for faults at T the
current from B might go in reverse direction from B to C depending on the system parameters
(see the dotted line in figure 63), given that the distance protection in B to T will measure
wrong direction.
In three-end application, depending on the source impedance behind the IEDs, the impedances
of the protected object and the fault location, it might be necessary to accept zone 2 trip in
one end or sequential trip in one end.
Generally for this type of application it is difficult to select settings of zone 1 that both gives
overlapping of the zones with enough sensitivity without interference with other zone 1
settings, that is, without selectivity conflicts. Careful fault calculations are necessary to
determine suitable settings and selection of proper scheme communication.
Fault resistance
The performance of distance protection for single phase-to-earth faults is very important,
because normally more than 70% of the faults on transmission lines are single phase-to-earth
faults. At these faults, the fault resistance is composed of three parts: arc resistance,
resistance of a tower construction, and tower-footing resistance.The resistance is also
depending on the presence of earth shield conductor at the top of the tower, connecting
tower-footing resistance in parallel. The arc resistance can be calculated according to
Warrington's formula:
=
Rarc
EQUATION1456 V1 EN-US
where:
L
I
In practice, the setting of fault resistance for both phase-to-earth
RFPP should be as high as possible without interfering with the load impedance in order to
obtain reliable fault detection.
7.1.3

Setting guidelines

7.1.3.1

General

The settings for Distance measuring zones, quadrilateral characteristic (ZMFPDIS) are done in
primary values. The instrument transformer ratio that has been set for the analog input card is
used to automatically convert the measured secondary input signals to primary values used in
ZMFPDIS .
The following basics must be considered, depending on application, when doing the setting
calculations:
114
×
28707 L
1.4
I
represents the length of the arc (in meters). This equation applies for the distance protection zone 1.
Consider approximately three times arc foot spacing for the zone 2 and wind speed of approximately
50 km/h
is the actual fault current in A.
1MRK 505 363-UEN A
GUID-83E3E475-3243-4308-9A91-B8DD9B47C276 v3
(Equation 56)
RFPE and phase-to-phase
GUID-BA20D421-4435-44CA-A6E9-743E461F8C59 v2
Application manual
IP14962-1 v1