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Application Guide for English Electric Relays English Electric had virtual monopoly in the electricl protective relays in India. Even now, in these times of digital architecture and computer communication with relays, you'll be surprised to find so many of these old electromechanical relays happily in service. The sensitivity and reliability of them are legendary, prompting the maintenance engineers not to part with them. The brand name has changed many times over the years, to GE, Alstom and now to Areva T&D, but the quality which lies at the base remains rock solid. Here's an application guide for the relays. The following tables provide recommended common applications for protection of various apparatus/systems. Specific application problem not included in the tables may be referred to the manufacturer. For the sake of completeness, the following tables include some standard imported relays available with the company’s UK associates.

Table 1 - AC Generator Protection Protection Differential Transverse Differential Over current

Details 1. Unbiased, with series stabilising resistor 2. Biased differential For machine with split phase winding 1. Inverse time

2. Inverse time, voltage controlled 1. Inverse time delay for generator earthed through a distribution transformer Stator Earth- 2. For generator earthed through a fault resistance or solidly earthed and generator is connected to the system via delta-star transformer Standby Earth- For generator directly connected to fault system Rotor EarthInstantaneous, generally connected for fault alarm To protect against prolonged asynchronous operation. Used in Field Failure conjunction with a timer and an auxiliary relay Instantaneous For over voltage protection of generator over voltage Time delayed over voltage Negative phase sequence Overload

For over voltage protection of generator To detect sustained unbalance condition, relay characteristics to match machine withstand characteristic To detect sustained overload of the machine

Relay Type CAG 34 FAC 34 DDG 31 CAG 34 FAC 34 CDG 31 CDV 62 VDG 14 CAG 14 CDG 11 VAEM 21 VME YCGF VAGM 22 VTIG VDG 11 VTU VAU CDN CTN CTU 12 CTLM 11

Reverse Power

1. Primary protection against motoring 2. Protection of diesel generators against motoring where motoring power is relatively high

Backup distance

To provide backup protection against uncleared system faults

YCG 15AA+VAA3 1 +VAT or VTT

Interlock against overspeed

WCD 12

Protection against pole slipping

ZTO 11

To monitor rotor high temperature

DZT 4

Forward under power interlock Pole slipping Rotor temperature

WCD 11 CCUM WDG

Table 2 – Generator-Transformer Protection Differential Over current Restricted earth fault Standby earth fault Overfluxing Buchholz Winding temperature

Details Biased, for overall phase and earth fault of the generator and generatortransformer Inverse time phase and earth fault protection

Relay Type

For earth fault in transformer winding

CAG 14

For back-up protection

CDG 11

For protection of transformer against over excitation Protection against insipient fault in the transformer Protection, control and indication

DTH 31/32 CDG 31

GTT OBGM TTT & CTTT

Table 3 – Power Transformer Protection Protection Differential Over current

Details Biased, for phase and earth fault protection in the transformer winding 1. Non-directional inverse time

Relay Type DDT DTH CDG

2. Directional, inverse time

Backup earth fault

1. Non-directional inverse time

CDD CAG 14 FAC 14 CDG 11

2. Directional, inverse time

CDD 21

Buchholz Time delayed earth fault

For incipient fault in the transformer To protect the neutral earthing resistor and to provide backup protection

OBGM

Temperature

Protection, control and indication

Voltage regulating relay and line

For use with ON load tap changers for automatic regulation of voltage

Restricted earth fault

For faults in transformer winding

CDG 12 TTT & CTTT VTJC&CIJ C AVE4 &

drop compensator Overfluxing

CAD For protection against over excitation

GTT

Table 4 – Auto Transformer Protection

Details

Differential

Unbiased, over main winding only

Differential

Biased, over all windings

Over current

Inverse time, phase and earth fault protection, non-directional or directional

Restricted earth fault

For earth fault in transformer winding

Buchholz

Protection against transformer

Winding temperature Voltage regulating relay and line drop compensator Overfluxing

incipient

faults

in

Relay Type CAG 34 FAC 34 DTH 31 DTH 32 CDG 31 CDD 21 CAG 14 FAC 14 OBGM

Protection, control and indication

TTT & CTTT

For use with ON load tap changers for automatic regulation of voltage

VTJC&CIJ C AVE4 & CAD

For protection against over excitation

GTT

Table 5 – Unit Transformer Protection Differential Over current Restricted earth fault Neutral displacement Buchholz

Details Biased, for phase and earth fault protection in the transformer winding Inverse time, phase and earth fault protection without or with high set For earth fault in transformer winding For detection of earth fault where low voltage system is insulated Protection against incipient faults in transformer

Relay Type DDT 32 DTH 31 CDG 61 CDG 31 CAG 14 FAC 14 VDG 14 OBGM