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3 Determination of Relay Settings
3.1 Information Required For The Setting Calculations
To match a distance protection relay to a feeder the following data must be known:-
•
Positive sequence of the feeder Z
•
Zero sequence impedance of the feeder Z
•
Length of protected feeder
•
Maximum and minimum fault current infeed at relaying point
•
Current transformer ratio
•
Voltage transformer ratio
•
Impedance of adjacent lines which are partially or wholly included within the Zone 2, 3 or 4
•
The position, rating and reactance of any power transformers connected to the system within the zone 3
forward and reverse impedance reach.
•
Fault current infeeds at tee-off points or remote substations
•
Fault clearance time on circuits within the Zone 2 and Zone 3 and Zone 4 impedance reaches
•
Maximum load current
•
Phase angle of line impedance
•
Maximum residual capacitance current at the relaying points for earth faults in adjacent circuits
•
Minimum residual current available to operate the earth fault detector
3.2 Distance Protection Settings
The first settings in the menu are common for all zones. The relay will use a time-stepped scheme by default. All
relay schemes are detailed in Section 3 of this manual.
3.2.1 Overall Settings.
The first settings made in the distance protection menu apply to all zones of protection. The CT secondary, is
set as set as 1A, 2A or 5A depending on the CT rating. The line angle is the angle of the positive sequence
impedance of the feeder.
3.2.2 Residual Compensation Settings.
The Zone reach settings for each zone of protection are made in terms of the positive sequence impedance of
the transmission line. To allow the earth fault comparators to correctly take account of the fault loop impedance,
the ratio of voltage to current is multiplied by a factor of K
which may be determined from the following equation;
Settings made on the relay are:
EF Comp Z0/Z1 ratio. This is simply the ratio between the zero and positive sequence impedances. It ranges
between 0 – 10 in 0.01 steps.
EF Comp Z0 Angle. This is simply the angle of the zero sequence impedance. It is set from 0-355° in 5° steps.
The relay automatically calculates the residual compensation from these two settings.
©2011 Siemens Protection Devices Limited
ohm/km
1
ohms/km
0
+1, where K
N
⎛
1
⎜ ⎜
=
K
N
3
⎝
7SG164 Ohmega 400 Series Applications
is the Residual Compensation Factor,
N
⎞
Z
⎟ ⎟
−
0
1
Z
⎠
1
Chapter 7 Page 4 of 8
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