Multi-Ended Line Differential Protection; Basic Principles And Algorithm Design For Multi-Ended Differential Protection; Fault Discrimination - GE P4A Technical Manual

P54A/B/C/E
2.2

MULTI-ENDED LINE DIFFERENTIAL PROTECTION

Current differential protection has been used for many years to protect the transmission lines and distribution
feeders. Previous protection relays could protect 2 or 3 ended schemes, but these products introduce multi-ended
differential protection, which can protect lines or cables up to maximum of six terminals with sub-cycle for up to 4-
ended schemes, and 1.25 cycle for 5 or 6 ended schemes.
The multi-ended differential protection scheme has the following features:
● Sample based RMS differential implementation proved by large amount of validations, where differential
protection with sample based RMS algorithm is faster than a Fourier based algorithm, used in earlier
products. Additionally, it is not affected by frequency variation, so a frequency tracking block is not
necessary for sample based RMS differential protection.
Enhanced multi-ended differential protection algorithm has a fault discriminator to differentiate between
●
external and internal faults. This works even during CT saturation, eliminating the need for a separate CT
saturation detection algorithm.
Scalable for many topologies up to 6 terminals and 4 junctions.
●
Multi-ended differential protection algorithm also implements a charging current compensation feature.
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The technique used for charging current compensation is more accurate, especially for longer line
applications
The same dual slope differential characteristics as the P540D products.
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Key functions for each product are described below:
P54A compact (40TE), economical line differential protection without VT inputs, offering non-directional
●
backup protection.
● P54B compact (40TE), economical line differential protection with directionalised back-up protection and
inbuilt reclosing and check synchronism.
P54C transmission-class 1/3-pole tripping line differential protection with backup protection and inbuilt
●
reclosing and check synchronism (built from today's P543 hardware).
● P54E transmission-class 1/3-pole tripping line differential protection with back-up protection and inbuilt
reclosing and check synchronism with a large number of binary I/O for traditional hardwired schemes (built
from P545 hardware).
Multi-ended line differential relays are not compatible with the conventional line differential MiCOM Agile relays.
2.3 BASIC PRINCIPLES AND ALGORITHM DESIGN FOR MULTI-ENDED DIFFERENTIAL
PROTECTION
The basic principles of the multi-ended differential protection are presented here.
2.3.1

FAULT DISCRIMINATION

To understand the basic principle of differential protection, we must first consider the ideal circumstances of a
multi-ended system--in order to examine the characteristic differences between internal and external faults, from
which the discriminative criteria of the protection is generated, see below.
The following assumptions are made:
● The capacitive current due to the equivalent shunt capacitance of lines are neglected.
The load current is assumed to be zero.
●
● Unbalanced parameters, unbalanced measurements, CT saturation, etc, are neglected.
P54xMED-TM-EN-1
Chapter 6 - Current Differential Protection
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