Thursday, December 8, 2011

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

2 comments:

  1. Thanks for sharing these useful power tips.Keep sharing useful information like this.
    Medical Hospital Furnitures

    ReplyDelete
  2. Thank you for sharing this valuable information

    ReplyDelete