Alstom SHPM 101, Service Manual

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SERVICE MANUAL R5888C
QUADRAMHO Chapter 2
Page 1 of 74
Section 1. INTRODUCTION
The Quadramho protection scheme, has been designed to satisfy the demand for a
cost effective distance relay for medium and high voltage transmission and
distribution lines. The relay is a high performance full scheme design having many
advantages over the switched relays traditionally used in this application.
Three zones of protection are incorporated, each having separate measuring
elements for each type of phase and ground fault. The full scheme arrangement
uses 18 comparators, eliminating the need for starting relays and switching
circuits, thereby providing better reliability and faster operating times.
For short line applications involving strong sources of power infeed, quadrilateral
ground fault characteristics for all three zones can be specified, ensuring adequate
tolerance to arcing and tower footing resistance. Alternatively, partially cross
polarised mho characteristics with strong resistive expansion for Zone 1 and 2 and
a lens-shaped Zone 3 characteristic may be specified. Synchronous polarising (an
advanced digital memory system) is provided to allow correct response to three
phase close-up faults.
Quadramho contains interfacing and scheme logic to allow signalling between
relays at the ends of a transmission line, via a signalling channel, for rapid
clearance of faults anywhere within the whole of the protected section of line.
Several different tripping schemes are incorporated in the relay, selectable by
switches on the front panel. Integral tripping relays give three pole or single and
three pole tripping, as required, and other relays are present for interfacing with a
signalling channel, auto-reclose equipment, remote alarms, fault recorder and fault
locator. Optical isolators are used for input signals such as from the signalling
channel. Visual indications are provided by 10 light emitting diodes.
Either busbar or line voltage transformers can be used and these can be either
capacitor VT or electromagnetic types. The design is highly tolerant of saturated
current transformers, so that the CT requirements are moderate.
The distance relay has inbuilt continuous self-monitoring and periodic self-testing
features designed to announce a failure of the relay or its supplies.
A comprehensive injection and test monitoring system simplifies commissioning,
routine testing, and fault finding operations on the relay. The system permits the use
of programmable portable test equipment so that on-site testing can be performed
by personnel who do not have detailed training on distance relays.
Quadramho owes its high performance and compact size to a new type of
comparator is physically implemented as a ULA (uncommitted logic array)
integrated circuit. This comparator is used in conjunction with input filters to give
fast and accurate operation even under conditions of noisy and harmonically
distorted waveforms commonly encountered in power distribution systems.