D30 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL 8-1
D30 Line Distance Protection System
Chapter 8: Application of settings
Application of settings
This chapter provides example(s) of use.
8.1 Application guidelines
8.1.1 Overview
This chapter provides general application guidelines for stepped distance, overcurrent, and pilot protection. Where
relevant, design details and performance characteristics of the D30 are given to facilitate the process of setting the relay
for a given application.
8.1.2 Impact of memory polarization
The D30 uses a memorized positive sequence voltage as a polarizing signal in order to achieve dependable operation for
forward faults and secure non-operation for reverse faults.
The dynamic shift of the characteristic ensures improved directionality, but it also means that if a backup function is
required for a reverse fault on the bus, then it is appropriate to reverse Zone 3 so that a time delayed backup function can
be obtained. As mentioned earlier, it can be beneficial to also avoid extremely large reach settings by setting a remote
backup so that it is reverse looking. This strategy is beneficial if the reduced reach enhances the discrimination between
the load and fault conditions.
8.1.3 High set overcurrent elements
Especially at low SIR values, fast fault clearance times can be seen as extremely important, from both system stability, and
equipment damage viewpoints. The high-set overcurrent element, when set appropriately, can be extremely useful in
achieving these goals. It helps the setting calculations if the system impedances are reasonably well known.
Set the overcurrent pickup to the greater of the following values:
• The maximum infeed seen by the relay, for a close in reverse fault
• The maximum fault level seen by the relay for a fault at 100% of the protected line
The maximum error of the phase overcurrent elements is below 2%. Use a safety factor of 1.25 to account for relay errors
and system impedance uncertainty.
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