ACKNOWLEDGEMENTS
The ‘Hand Book’ covers the Code of Practice in Protection Circuitry including
standard lead and device numbers, mode of connections at terminal strips, colour
codes in multicore cables, Dos and Donts in execution. Also principles of various
protective relays and schemes including special protection schemes like differential,
restricted, directional and distance relays are explained with sketches. The norms of
protection of generators, transformers, lines & Capacitor Banks are also given.
The procedures of testing switchgear, instrument transformers and relays are
explained in detail. The close and trip, indication and alarm circuits for variety of
Circuit breakers indicating ferrule numbers are also included. All relevant
information and circuit diagrams necessary for trouble shooting are also given.
We have more than 25 years experience, each in protective relaying and
included a lot of information by way of original contribution apart from collection of
useful information from a large number of reference books, manuals of
manufacturers, etc. and it is hoped that this Hand Book will serve as a useful guide
for all practicing Engineers.
1. Code of Practice
1.1 Standard number for devices
1.2 Types of Panels
1.3 Protective Relay – Connection & Zones of Protection
1.4 Norms of Protection for Generator, Transformers & Lines
1.5 Current Transformers
1.6 Voltage Transformers
1.7 Energy Meters
1.8 Synchronising Panel
2. Generator and their Protection
3. Transformers and their Protection
4. Distance Relays in A.P.System, relay indications & their Meanings
5. Busbars – Arrangements & Protection
6. O/L & E/F relays
7. Circuit Breakers
8. Station Battery
9. Earthing Practices
10. Excitation & Voltage Regulation.
CODE OF PRACTICE
CODE OF PRACTICE : PROTECTION
1.00 Circuitry
1.01 The entire wiring of circuitry for indications, alarms, metering and protection should be permanent wiring.
1.02 There is no place for temporary wiring or adhocism in Relay circuitry.
1.03 The leads should be identified by ferrules near terminals.
1.04 Every lead should end at a terminal point and no junctions by twisting is allowed. If two wires are to be terminated at same terminal they may be connected at two different terminals and a loop provided.
1.05 The wiring should be by copper leads for C.T secondaries for all cores (i.e.) metering as well as protection.
1.06 The wiring should be by copper leads for PT secondaries also wherever they are intended for protection.
1.07 The copper lead for 1.05 & 1.06 above should be stranded but not single lead type.
1.08 Aluminum leads can be used for indication, alarms and PT secondaries for metering but stranded wires only are to be used. However where PTs are employed for commercial metering, stranded copper wires are to be used.
1.09 The terminations should be lugged by ring shape ‘O’ lugs. ‘U’ shape lugs should be avoided.
1.10 For CT Secondary terminations, two nuts with one spring washer and two flat washers to be compulsorily used.
1.11 The terminal strips should be stud type with nuts and not screw-in-type.
1.12 Wherever two batteries are available, the primary protection and back-up protection should be from different batteries.
1.13 Where there is only one battery at a Power Substation, the primary and back-up protections
should be given D.C supply through two individual circuits with independent fuses run from D.C bus.
1.13A When CBs have two trip coils, both main protection and backup protection will energise both the trip coils.
1.14 D.C and A.C supplies should not be taken through different cores of the same cable.
1.15 Independent D.C cables should be run to every equipment in the yard and looping of D.C
supply either in the yard or in the control room from one equipment to the other is not permitted.
1.16 The D.C yard lighting for emergency lighting should be through independent cables and not mixed up with protection and other circuitry.
1.17 For indications, alarms, annunciations, controls (closing coil, trip coil, etc. negative (-ve) is always given direct and positive (+ve) is supplied only ‘on commands’ like close, trip, relay trip, etc.
1.18 Where D.C protection supply is at 24 volts or 32 volts, the battery units should be very near the equipment and not in the control rooms.
1.19 In cases of 1.18 above, each tripping units (24 volts or 32 volts battery with charger) should not be used for more than two circuit breakers or equipment.
1.20 Standard colour codes for leads in control cable of different sizes should be as denoted on the cover page.
1.21 The lead numbers are also standardised as follows so that any MRT Engineer can easily identify the purpose for which the lead is connected by noting the lead number.
1.22 CTs with 1 amp secondary rating should be used compulsorily where meters, protective
devices etc. are remotely situated with reference to equipment.
1.23 The CT ratios available and adopted with number of cores shall be displayed on each panel
as follows: (with underlined position as adopted).
400 - 200 - 100 / 1-1-1
1.24 Wherever CT cores are not used “SHORTING LOOPS” should be provided near CT secondary
terminals and not in marshaling boxes or at panels.
1.25 The Cable entries near equipment, marshaling boxes and panels should be by use of appropriate size glands.
1.26 The Wiring inside the panels should be clear and neatly fastened avoiding loose wires.
1.27 All wires not in use should not only be disconnected but removed from panels.
1.28 PT secondaries should have group MOCBs with D.C alarm. Fuses at different panels should not be used.
1.29 Few cells from a battery of cells should not be used for separate low voltage D.C circuits. D.C
- D.C converters only should be employed utilising full D.C voltage of the entire battery as
input.
Official
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