Kunal

. Transformers consist of two or more coils of conducting material, such as wire, wrapped

around a core (often made of iron). The magnetic field produced by an alternating current in

one coil induces a similar current in the other coils

TYPES OF TRANSFORMER ------Power transformers

Laminated core

Laminated Core Transformer

This is the most common type of transformer, widely used in appliances to convert mains voltage to low voltage to power electronics

Widely available in power ratings ranging from mW to MW Insulated lamination minimizes eddy current losses Toroidal

Toroidal Transformer

Toroidal transformers compared to EI core transformers:

Lower external magnetic field Smaller for a given power rating Higher cost in most cases, as winding requires more complex and slower equipment Less robust

Autotransformer

An autotransformer has only a single winding, which is tapped at some point along the

winding. AC or pulsed voltage is applied across a portion of the winding, and a higher (or

lower) voltage is produced across another portion of the same winding

Polyphase transformers

Example of Y Y Connection

For three-phase power, three separate single-phase transformers can be used, or all three

phases can be connected to a single polyphase transformer. The three primary windings are

connected together and the three secondary windings are connected together

Resonant transformers

A 25 kV flyback transformer being used to generate an arc.

A resonant transformer operates at the resonant frequency of one or more of its coils and

(usually) an external capacitor. The resonant coil, usually the secondary, acts as an inductor,

and is connected in series with a capacitor.

Oil cooled transformer

For large transformers used in power distribution or electrical substations, the core and coils

of the transformer are immersed in oil which cools and insulates. Oil circulates through ducts

in the coil and around the coil and core assembly, moved by convection

Cast resin transformers

Cast-resin power transformers encase the windings in epoxy resin. These transformers

simplify installation since they are dry, without cooling oil, and so require no fire-proof vault

for indoor installations. The epoxy protects the windings from dust and corrosive

atmospheres

Instrument transformers

Current transformers

Main article: Current transformer

Current transformers used in metering equipment for three-phase 400 ampere electricity supply

A current transformer (CT) is a measurement device designed to provide a current in its secondary coil proportional to the current flowing in its primary. Current transformers are commonly used in metering and protective relays in the electrical power industry where they allow safe measurement of large currents, often in the presence of high voltages

Voltage transformers

Voltage transformers (VT) or potential transformers (PT) are another type of instrument transformer, used for metering and protection in high-voltage circuits. They are designed to present negligible load to the supply being measured and to have a precise voltage ratio to accurately step down high voltages so that metering and protective relay equipment can be operated at a lower potential. Typically the secondary of a voltage transformer is rated for 69 V or 120 V at rated primary voltage, to match the input ratings of protective relays.

Pulse transformers

A pulse transformer is a transformer that is optimised for transmitting rectangular electrical pulses (that is, pulses with fast rise and fall times and a relatively constant amplitude). Small versions called signal types are used in digital logic and telecommunications circuits, often for matching logic drivers to transmission lines.

Parallel operation of transformer-----

Parallel transformers

Most transformers installed in parallel have the same kVA, turn ratios, and impedances,

which can make it difficult for power engineers in industrial and commercial facilities to

understand circulating currents and load sharing.

conditions necessary for parallel operation

All paralleled units must be supplied from the same network. The inevitable circulating

currents exchanged between the secondary circuits of paralleled transformers will be

negligibly small providing that:

Secondary cabling from the transformers to the point of paralleling have approximately equal lengths and characteristics

The transformer manufacturer is fully informed of the duty intended for the transformers, so that:- The winding configurations (star, delta, zigzag star) of the several transformers have the same phase change between primary and secondary voltages

Sub Station Main Functions & Classification----

An electrical substation is an assemblage of electrical components including busbars,

switchgear, power transformers, auxiliaries etc. These components are connected in a definite

sequence such that a ckt. can be switched off during normal operation by manual command

and also automatically during abnormal conditions such as short-ckt.

Basically an electrical substation consists of number of incoming ckt. and outgoing ckt.

connected to a common Bus-bar systems. A substation receives electrical power from

generating station via incoming transmission lines and delivers elect. power via the outgoing

transmission lines.

“Substation is integral part of a power system and form important links between the generating station, transmission systems, distribution systems and the load points.”

Secondary Distribution

Secondary substation - Vilalonga VLG 66/20 kV

Distribution Substation

Circuit Breaker & Types of Circuit Breaker----A switch that automatically interrupts the flow of electric current if the current exceeds a preset limit, measured in amperes. Circuit breakers are used most often as a safety precaution where

excessive current through a circuit could be hazardous. Unlike fuses, they can usually be reset

Sulfur hexafluoride (SF6) high-voltage circuit-breakers

A sulfur hexafluoride circuit breaker uses contacts surrounded by sulfur hexafluoride gas to quench the arc. They are most often used for transmission-level voltages and may be incorporated into compact gas-insulated switchgear. In cold climates, supplemental heating or de-rating of the circuit breakers . For example, a 22/10 rating.

This rating means that the meter pack has a 22 kAIC tenant breaker, feeding a 10 kAIC loadcenter with 10 kAIC branches

EARTHING GROUNDING-----Earthing and Grounding are basically same  in concept. Difference between Earthing and Grounding is one of the most confused and misunderstood concepts. The importance of grounding in commercial and industrial installations can never be underestimated. Circuits of machines are grounded to provide an effective return path from the machines to the power source. There are many benefits of grounding to owners of buildings. These include maximum equipment protection, reducing shock hazard, and cost savings which accrue by avoiding machine servicing. Confusion arises with interchangeable terms such as earthing, grounding and bonding are used in these contexts.

Transmission lines----In communications and electronic engineering, a transmission line is a specialized cable designed to carry alternating current of radio frequency, that is, currents with a frequency high enough that their wave nature must be taken into account. Transmission lines are used for purposes such as connecting radio transmitters and receivers with their antennas, distributing cable television signals, and computer network connections.

Explanation

Ordinary electrical cables suffice to carry low frequency AC, such as mains power, which reverses direction 100 to 120 times per second (cycling 50 to 60 times per second). However, they cannot be used to carry currents in the radio frequency range or higher, which reverse direction millions to billions of times per second, because the energy tends to radiate off the cable as radio waves, causing power losses. Radio frequency currents also tend to reflect from discontinuities in the cable such as connectors, and travel back down the cable toward the source. These reflections act as bottlenecks, preventing the power from reaching the destination.

Types of transmission line include ladder line, coaxial cable, dielectric slabs, stripline, optical fiber, and waveguides.

History

Mathematical analysis of the behaviour of electrical transmission lines grew out of the work

of James Clerk Maxwell, Lord Kelvin and Oliver Heaviside. In 1855 Lord Kelvin formulated

a diffusion model of the current in a submarine cable. The model correctly predicted the poor

performance of the 1858 trans-Atlantic submarine telegraph cable. In 1885 Heaviside

published the first papers that described his analysis of propagation in cables and the modern

form of the telegrapher's equations.

Applicability Applicability In many electric circuits, the length of the wires connecting the components can for the most part be ignored. That is, the voltage on the wire at a given time can be assumed to be the same at all points

introduction

The Bihar State Electricity Board (BSEB) functions as a single entity looking after generation, transmission and distribution in the state. While the state government announced plans to unbundle the board into six companies in early 2006, there has been no progress so far.

Bihar Electricity Regulatory Commission has approved T&D losses at 38%, 35%, 32% and 29% for FY-09, FY-10, FY-11 & FY-12 respectively. BSEB had T&D losses of almost 42.61 per cent in 2006-07.

As of March 31, 2005, the total transmission line length in the state was 4,681 ct. km. Of this, 132 kV lines accounted for 78 per cent. The board's total transformer capacity was 3,745 MVA. BSEB had 49 EHV substations as of March 31, 2005, including 44 at the 132 kV level.

BSEB functions as an integrated entity responsible for generation, transmission and distribution of electricity in the state. Recently, the new state government announced plans for unbundling the board.

Transmission Network Details

Transmission Network Transformer Capacity (MVA)

2000-01 2001-02*

2002-03 2003-04

2004-05

CAGR (%)

220 kV NA 1,200.0 1,200.0 1,200.0 1,400.0 5.3**

132kV NA 2,080.4 2,080.4 2,080.4 2,345.2 4.1**

Total 4,034.5 3,280.4 3,280.4 3,280.4 3,745.2 -1.8

% change - -18.7 - - 14.2 -

Transmission Line Length (ckms)

2000-01 2001-02 2002-03 2003-04

2004-05

CAGR (%)

400 kV 235.0 75.0 75.0 75.0 75.0 -24.8

220 kV 1,584.0 1,113.0 1,113.0 957.0 957.0 -11.8

132 kV 4,275.0 3,500.0 3,500.0 3,648.7 3,648.7 -3.9

Total 6,094.0 4,688.0 4,688.0 4,680.7 4,680.7 -6.4

% change - -23.1 - -0.2 0.0 -

Number of Substations (ct. km)

2000-01 2001-02 2002-03 2003-04

2004-05

CAGR (%)

220 kV - - 4 4 5 11.8

132 kV - - 43 44 44 1.2

Total - - 47 48 49 2.1

% change - - - 2.1 2.1 -

 (MVA)

2000-01

2001-02

2002-03

2003-04

2004-05

Number 26 26 9 9 9

Total capacity (MVA)

2,135 2,135 559 559 559

Step-down Transformers

2000-01

2001-02

2002-03

2003-04

2004-05

Number 442.4 102.0 102.0 102.0 125.0

Total capacity (MVA)

4,600.0 3,500.0 3,600.0 3,280.4 3,745.5

Transmission Losses (%)

2000-01

2001-02

2002-03

2003-04

2004-05

2005-06

2006-07

T&D losses 30.0 38.2 38.0* 36.7* 38.9* 38.56 42.61

Transmission Expenditure (Rs million)

- - - 2003-04

2004-05

Expenditure on new transmission projects

- - - 380.0 2,870.0

Key Planned Projects

Physical target 2000-06

Transmission line plan (ct. km)

220 kV 337.0

132 kV 1,408.0

Transformer capacity plan (MVA)

220 kV* 946.0

Ongoing Projects Under Rashtriya Sam Vikas Yojana

Transmission system strengthening schemes (as on January 2006)

SL Name of Scheme Associated Transmission Line

Remarks

1 132/33 KVNew Bhabhua Substation

LILO of 132 KV Dehri-Karmnasa Line at Bhabhua

Operational.

2 132/33 KVNew Bikramganj Substation

LILO of 132 KV Dehri-Dumraon Line at Bikramganj

Power-Flow started.

3 132/33 KVNew Sasaram Substation

LILO of 132 KV Dehri-Kudra-Karmnasa Line at Sasaram

Load-Flow started.

4 132/33 KVNew Bihta Substation

132 KV Khagaul-Bihta Operational.

5 132/33 KVNew Banka Substation

132 KV Sabour-Banka Power-Flow started.

6 132/33 KVNew Barh Substation

LILO of 132 KV Biharsharif-Hathidah Line at Barh

Power-Flow started.

7 33/11 KVBanianpur Substation

33KV S/C Siwan-Banianpur

Complete. Down-Linking arrangements under progress.

8 132/33 KVNew Udakishanganj Substation

132 KV Saharsa-Udakishanganj

March'2006.

9 132/33 KVNew Jaynagar Substation

132 KV Pandaul-Madhubani-Jaynagar-Phulparas

March'2006.

10 132/33 KVNew Madhubani Substation

March'2006.

11 220/132 KVDarbhanga Substation

220 KV D/C Muzaffarpur-Darbhanga

March'2006.

12 132/33Vaishali Substation

132 KV Muzaffarpur-Vaishali

Test charged. Down-Linking arrangements under progress.

13 132/33 KVNew Forbesganj Substation

132 KV Kishanganj-Forbesganj-Kataiyaa

March'2006.

14 132/33 KVNew Sheetalpur Substation

LILO of 132 KV Hajipur-Chapra at Sheetalpur and 132 KV Vaishali-Sheetalpur

March'2006.Land acquisition delayed.

15 132/33 KVDhaka Substation

132 KV D/C Motihari-Sitamarhi-Dhaka

March'2006.

16 220/132 KVGopalganj Substation

220 KV D/C Muzaffarpur-Gopalganj

March'2006.

17 132/33 KVPhulparas Substation

132 KV Phulparas-Supaul-Saharsa

March'2006.

18 132/33 KVSupaul Substation

LILO of 132 KV Purnea-Dalkhola at Kishanganj

March'2006.

Sub Transmission Schemes (as on January 2006)

SL Name of Scheme Total Scope Present Status

1 220/132 KV GSS 2 Gopalganj: March'2006Darbhanga: March'2006

2 132/33 KV GSS 15 Bhabhua, Bihta, Sasaram, Barh, Banka, Bikramganj, GSS are availing power. Vaishali: Control room & Downlinking arrangement under progress. Quarters at GSS yet to be completed.Jainagar, Dhaka: March,2006 Madhubani: March,2006 Supaul: March, 2006Sheetalpur: March’2006

3 33/11 KV PSS 1 Complete down-linking arrangement under progress.

4 220 KV Line (2 Nos.)

168 Kms -

CAPACITY OF TRANSFORMERS IN GRID SUB-STATION (132 kV & above) (as on March 2005)

SL Sub-Station Voltage Transformers Nos. CapacityRatio (MVA) (MVA)

A 220 kV. Grid Sub-Station1 Bodh Gaya 220/132 150 3 4502 Dehri - on-Sone 220/132 100 1 150

220/132 50 13 Biharsharif 220/132 150 2 300

4 Fatuha 220/132 100 2 2005 Khagaul 220/132 100 2 200

Total 11 1300B 132 kV. Grid Sub-Station1 Chandauti 132/33 20 2 40

132/33 15 1 15132/25 12.5 2 25

2 Bodh Gaya 132/33 20 2 403 Sonenagar 132/33 50 1 50

132/33 25 1 25132/25 20 1 20132/25 13.5 1 13.5

4 Karmnasa 1132/33 20 2 40132/25 20 1 20132/25 12.5 1 12.5

5 Jehanabad 132/33 20 1 206 Rafiganj 132/33 20 2 407 Dehri-on-sone 132/33 20 1 20

132/33 50 1 508 Biharsharif (Baripahari) 132/33 20+50 2 709 Hathidah 132/33 20 1 20

132/33 9.4 1 9.410 Lakhisarai 132/33 20 2 4011 Jamui 132/33 20+10 2 3012 Sheikhpura 132/33 10 1 1013 Nawada 132/33 20 2 4014 Jamalpur 132/33 20 2 4015 Sultanganj 132/33 7.5 1 7.5

20 1 2016 Sabour 132/33 20 3 6017 Dumraon 132/33 20 2 4018 Arrah 132/33 20 2 4019 Patna (Jakkanpur) 132/33 50 2 100

132/33 15 1 15132/33 20 1 20

20 Khagaual 132/33 50 3 15021 Fatuha 132/33 20 3 6022 Mithapur 132/33 50 2 10023 Purnia 132/33 20 3 6024 Saharsa 132/33 20 1 2025 Khagaria 132/33 20 1 20

132/33 10 1 1026 Naugachhia 132/33 20 1 20

132/33 10 1 1027 Muzaffarpur 132/33 50 2 10028 Sitamarhi 132/33 20 2 4029 Samastipur 132/33 20 2 4030 Pandaul 132/33 20 2 4031 Hajipur 132/33 20 2 4032 Chapra 132/33 20 1 20

132/33 12.5 1 12.533 Siwan 132/33 20 2 4034 Motihari 132/33 20 2 40

132/33 12.5 1 12.535 Bettiah 132/33 20 1 2036 Ramnagar 132/33 20 1 2037 Kataiya 132/33 20 2 4038 Rajgir (Defective) 132/33 20 1 20