The American Petroleum Institute (API) has launched a great new initiative - to share standards online! Even though most of their standards are available illegally on the Net, that's not the way we should be working with. Now, anyone can register (for free) at http://publications.api.org and can API standards in the following categories.
1. Safety and fire protection
2. Exploration and production
3. Refinery equipment
4. Pipeline operation
5. Petroleum measurement
6. Marketing
The documents are available on a special format that can be viewed only with RealRead Viewer (also provided online). There is no provision for saving the file. You can read the full standard online and if you want to copy it, you have to buy it. The purpose of this offering "is to provide the public with access to key industry standards,
particularly those standards that are safety-related or have been incorporated into
federal regulation".
I wish all standard-making bodies imitate this noble initiative from API.
Bureau of Energy Efficiency assigns star-ratings to various equipments to help consumers identify energy efficient units among the vast array of products. Here is a list of items for which star rating is available.
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
Recently, I had the good fortune to attend a training program on ETAP, conducted by Mr. P Nandakumar, a reputed freelance consultant and trainer of ETAP. The software is a superb tool for analyzing power systems of any complexity, but often it throws some counter-intuitive errors, which is difficult to analyze for the novice. This post is a collection of such common errors and the easiest solutions to them.
1. 1.Error 2002 – The system has no energized branches
This is a common error while using ETAP for the first time, blocking out all calculations. Even though you might’ve added many elements to the layout, ETAP requires some elements, like a cable, line or transformer which has a non-zero impedance value. A circuit breaker helps to add more interconnected branches, but won’t solve the issue. If a transformer cannot be included in your diagram, you have to add a new bus and connect it using a short cable (say, 25 sq.mm, 50 m length) as shown below. This may be labeled dummy, if you like, and won’t affect the calculations in any way. This simple trick will save you from unnecessary hold up (about 1 hour, in my case!!)
