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
