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	Details	Relay Type
Differential	1. Unbiased, with series stabilising resistor	CAG 34 FAC 34
	2. Biased differential	DDG 31
Transverse Differential	For machine with split phase winding	CAG 34 FAC 34
Over current	1. Inverse time	CDG 31
	2. Inverse time, voltage controlled	CDV 62
Stator Earth-fault	1. Inverse time delay for generator earthed through a distribution transformer	VDG 14
	2. For generator earthed through a resistance or solidly earthed and generator is connected to the system via delta-star transformer	CAG 14
Standby Earth-fault	For generator directly connected to system	CDG 11
Rotor Earth-fault	Instantaneous, generally connected for alarm	VAEM 21 VME
Field Failure	To protect against prolonged asynchronous operation. Used in conjunction with a timer and an auxiliary relay	YCGF
Instantaneous over voltage	For over voltage protection of generator	VAGM 22 VTIG
Time delayed over voltage	For over voltage protection of generator	VDG 11 VTU VAU
Negative phase sequence	To detect sustained unbalance condition, relay characteristics to match machine withstand characteristic	CDN CTN
Overload	To detect sustained overload of the machine	CTU 12 CTLM 11
Reverse Power	1. Primary protection against motoring	WCD 11
	2. Protection of diesel generators against motoring where motoring power is relatively high	CCUM WDG
Backup distance	To provide backup protection against uncleared system faults	YCG 15AA+VAA31 +VAT or VTT
Forward under power interlock	Interlock against overspeed	WCD 12
Pole slipping	Protection against pole slipping	ZTO 11
Rotor temperature	To monitor rotor high temperature	DZT 4

Table 2 – Generator-Transformer

Protection	Details	Relay Type
Differential	Biased, for overall phase and earth fault of the generator and generator-transformer	DTH 31/32
Over current	Inverse time phase and earth fault protection	CDG 31
Restricted earth fault	For earth fault in transformer winding	CAG 14
Standby earth fault	For back-up protection	CDG 11
Overfluxing	For protection of transformer against over excitation	GTT
Buchholz	Protection against insipient fault in the transformer	OBGM
Winding temperature	Protection, control and indication	TTT & CTTT

Table 3 – Power Transformer Protection

Protection	Details	Relay Type
Differential	Biased, for phase and earth fault protection in the transformer winding	DDT DTH
Over current	1. Non-directional inverse time	CDG
	2. Directional, inverse time	CDD
Restricted earth fault	For faults in transformer winding	CAG 14 FAC 14
Backup earth fault	1. Non-directional inverse time	CDG 11
	2. Directional, inverse time	CDD 21
Buchholz	For incipient fault in the transformer	OBGM
Time delayed earth fault	To protect the neutral earthing resistor and to provide backup protection	CDG 12
Temperature	Protection, control and indication	TTT & CTTT
Voltage regulating relay and line drop compensator	For use with ON load tap changers for automatic regulation of voltage	VTJC&CIJC AVE4 & CAD
Overfluxing	For protection against over excitation	GTT

Table 4 – Auto Transformer

Protection	Details	Relay Type
Differential	Unbiased, over main winding only	CAG 34 FAC 34
Differential	Biased, over all windings	DTH 31 DTH 32
Over current	Inverse time, phase and earth fault protection, non-directional or directional	CDG 31 CDD 21
Restricted earth fault	For earth fault in transformer winding	CAG 14 FAC 14
Buchholz	Protection against incipient faults in transformer	OBGM
Winding temperature	Protection, control and indication	TTT & CTTT
Voltage regulating relay and line drop compensator	For use with ON load tap changers for automatic regulation of voltage	VTJC&CIJC AVE4 & CAD
Overfluxing	For protection against over excitation	GTT

Table 5 – Unit Transformer

Protection	Details	Relay Type
Differential	Biased, for phase and earth fault protection in the transformer winding	DDT 32 DTH 31
Over current	Inverse time, phase and earth fault protection without or with high set	CDG 61 CDG 31
Restricted earth fault	For earth fault in transformer winding	CAG 14 FAC 14
Neutral displacement	For detection of earth fault where low voltage system is insulated	VDG 14
Buchholz	Protection against incipient faults in transformer	OBGM