Introduction - GE D30 Instruction Manual

9 APPLICATION OF SETTINGS
9 APPLICATION OF SETTINGS 9.1APPLICATION GUIDELINES
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.
As explained, 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 may
be obtained. As mentioned earlier, it may be beneficial to also avoid extremely large reach settings by setting a remote
backup so that it is reverse looking. This strategy can be beneficial if the reduced reach enhances the discrimination
between the load and fault conditions.
Especially at low SIR values, fast fault clearance times may be seen as extremely important, both from system stability, and
from 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.
The overcurrent pick up should be set to the greater of the following values:
1. The maximum infeed seen by the relay, for a close in reverse fault.
2. 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%. A safety factor of 1.25 should be used to account for
relay errors and system impedance uncertainty.
If CT saturation is an issue such as close to a generation where long lasting dc components are likely to saturate the CTs, it
should be noted that the instantaneous overcurrent elements require 1.33 cycle of data to operate for a multiple of pickup of
1.01. For higher multiples of pickup, the relation between the multiple of pickup and the amount of data required for opera-
tion before complete CT saturation is approximately linear. For example, for a multiple of pickup of 4, approximately 1.33 /
4 = 0.332 of power cycle is required by the phase instantaneous overcurrent element to operate. The above information
should not be confused with the operating time, which includes some inherent delays such as a trip rated output contact.
GE Multilin D30 Line Distance Protection System
9.1 APPLICATION GUIDELINES

9.1.1 INTRODUCTION

9.1.2 IMPACT OF MEMORY POLARIZATION
9.1.3 HIGH SET OVERCURRENT ELEMENTS
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