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TRANSMISSION AND DISTRIBUTION

Alok Tripathi (04) Amit Kumar Singh (08)

Amit Kumar Yadav (07) Angel Priy Tarzan (09)

CONTENTS Single Line Diagram

Components of an Electrical Power System

Types of Power Lines

HV Power Line Components

Substations

Losses

Major Challenges and Bottlenecks

Electrical Networks

SINGLE LINE DIAGRAM (SPECIFICATION)

• 500 MW Generating Station – 11kV/220/400 kV

• 220 kV Transmission Substation - 220kV/132kV/66kV

• 66kV Distribution Substation – 66kV/11kV

• Pole Mounted Substation – 11kV/415V

Components of an Electrical Power System

Step-down

transformer &

switchgear

Step-up transformer

& switchgear

Distribution lines

Lighting

Heating

Appliances

Power Station

Substation

Substation

System Loads

Transmission Lines

TYPES OF POWER LINES High Voltage(HV)

Medium Voltage(MV)

Low Voltage(LV)

Power Statio

n

Substation

Substation

Transformer

System Loads

STANDARD VOLTAGESClassification

Range Standard Levels

LV < 1 kV 415V (3-phase)240V (1-phase)

MV 1kV – 100 kV 3.3kV, 6.6kV, 11kV, 33kV, 66kV

HV >100 kV 132kV, 275kV,400kV, 750kV

Transmission Way’s

• Transmission can be done by 1.Overhead lines and 2. Underground lines. Transmission mode can be HVDC or HVAC

depending upon the requirement.

HVDC SYSTEM

Rectifier - SE (AC to DC)Inverter - RE (DC to AC)Converter - heart of HVDC system operation

ADVANTAGES OF HVDC TRANSMISSION

• These systems are economical for bulk power transmission over long distance (550Km).

• The DC system is cheaper as it requires only two conductor instead of three and hence cost on insulator become less.

• Low line loss.• Less line insulation.

Disadvantages of HVDC Transmission

• The overall cost increases for line lengths below 550 Km because of additional requirement of converters, filters etc.

• Step-up and Step-down is not possible.

SUBSTATION

SUBSTATION- OVERVIEW

An electrical substation is a subsidiary station of an electrical generation, transmission and distribution system where voltage is transformed from high to low, or the reverse, or other many important functions.

SUBSTATION EQUIPMENT• CT and PT• Circuit Breakers• Isolator• Power Transformer• Switches• Bus Section• Surge Arrestors• Current Limiting Reacators• Relays and Protective Devices

CT AND PT: TO STEP DOWN THE CURRENT FOR MEASUREMENT /PROTECTION AND TO STEP DOWN THE VOLTAGE FOR MEASUREMENT /PROTECTION.

CIRCUIT BREAKER: AUTOMATIC SWITCHING DURING NORMAL OR ABNORMAL CONDITIONS.

ISOLATOR: DISCONNECTION OF CIRCUIT UNDER NO LOAD CONDITION.

POWER TRANSFORMER: TO STEP UP OR STEP DOWN THE VOLTAGE AND TRANSFER POWER FROM ONE A.C VOLTAGE TO ANOTHER AT THE SAME FREQUENCY.

LIGHTNING ARRESTER: TO DISCHARGE LIGHTNING AND SWITCHING OVER VOLTAGES.

BATTERY BANKS: TO MAINTAIN THE D.C SUPPLY CONTINUILY DURING A.C SUPPLY FAILURE

CONTROL AND RELAY PANEL : TO SOUND AN ALARM OR TO CLOSE THE TRIP CIRCUIT OF BREAKER SO AS TO DISCONNECT A COMPONENT DURING ABNORMAL CONDITIONS (OVER LOAD, UNDER VOLTAGE, UNBALANCED LOAD, SHORT CIRCUITS).

Station Transformer: To supply of A.C power for charging the batteries and provides D.C control supply.

Bus Section: For connecting incoming and outgoing circuits.

TYPE OF SUBSTATION

Transmission Substation

Distribution Substation

Collector Substation

Switching Substation

LOSSES (TRANSMISSION & DISTRIBUTION)

In India, average T & D losses, have been officially indicated as 27-35 percent of the electricity generated.However as per sample studies carried out by TERI, losses have been estimated to be as high as 50 percent in some states.

The impact of theft is not limited to loss of revenue, it alsoeffects power quality resulting in low voltage and voltage dips.

According to Electric Power Research Institute (EPRI) of the USA Transmission and Distribution Losses (Power), the losses in various elements of the T&D system usually are of the order

Distribution linesSub-transmission system & step-down to distribution voltage levelStep downto sub-transmission voltage levelStep-up transformers & EHV transmission system

COMPONENTS OF T&D LOSSES

T & D Losses

Technical losses

Transmission losses

Sub-transmissio

n losses

Distribution losses

Commercial losses

PilferageErrors in meter

REASONS FOR HIGH TECHNICAL LOSSES

Inadequate investment on transmission and distribution, particularly in sub-transmission and distribution.Haphazard growth of sub-transmission and distribution system with the short-term objective of extension of power supply to new areas.Too many stage of transformations.

Poor quality of equipment used in agricultural pumping in rural areas, cooler air-conditioners and industrial loads in urban areas.

Too many stage of transformations.

MEASURES FOR REDUCING TECHNICAL LOSSES

Short term measures

Identification of the weakest areas in the distribution system and improving them so as to draw the maximum benefits of the limited resources.

Reducing the length of LT lines by installations of additional distribution transformers.

Installation of shunt capacitors for improvement of power factor.

MEASURES FOR REDUCING TECHNICAL LOSSES

Long term measures

Compilation of data regarding existing loads, operating conditions, forecast of expected loads etc.

Preparation of long-term plans for phased strengthening and improvement of the distribution systems along with associated transmission system.

Estimation of the financial requirements for implementation of the different phases of system improvement works.

REASONS FOR COMMERCIAL LOSSES

Tampering the meter readings by mechanical jerks, placement of powerful magnets or disturbing the disc rotation with foreign matters.Stopping the meters by remote control.Bypassing the meter.Errors in meter reading and recording.Improper testing and calibration of meters.Hooking or tapping the bare conductors of L.T. feeder or tampered service wires.

MEASURES FOR REDUCING COMMERCAL LOSSES

Set up vigilance squads to check and prevent pilferage of energy.Severe penalties may be imposed on those tampering with the meter seals.

Installation of tamper-proof meter boxes and use of tamper-proof numbered seals.

Providing adequate meter testing facilities. A time bound program should be chalked out for checking the meters, and replacement of defective meters with tested meters.

WEAK LAWS IN INDIAChina's power thief

A power thief in China, an electrician from the Fujian Province was charged with helping residents, restaurants and companies steal electricity.

The offender was caught red-handed while tampering with a meter, it was found that he had helped filch electricity worth over 2,40,000 Yuan ($29,989).

The Chinese court sentenced the offender to 10 years rigorous imprisonment, while the local police separately fined the beneficiaries.

In India anyone caught stealing electricity can be imprisoned for up to three years or fined or both under the Electricity Act.

T&D LOSSES IN RESTRUCTURED SEBSThe reforming states that were reporting T&D losses of around twenty percent before restructuring process suddenly reported higher losses.Orissa reported 23 percent loss, after restructuring, T&D loss were shown to be51 percent.

AP where these losses were of the order of about 25 percentbefore restructuring, later estimated losses around 45 percent after restructuring.

Haryana estimated its losses at 40 percent and Rajasthan at 43 percent against earlier level of 32 percent and 26 percent respectively.

Major Challenges & bottlenecks in the

field of power in India

THE REAL PROBLEMS IN THE SECTOR1)No basic design constraints are followed ,due to various reasons beyond the control of utility companies.

2)No real account of transmission and distribution losses.

3)No authority for curbing the theft of energy.

4)Poor standards in choosing the major equipments and materials.

5)Priorities based on Political interferences.

6)Free electricity for political/ruling power advantages.

7)Lack of real management principles and tactics.

BOTTLENECK AT PLANNING LEVEL•Basis - Power systems planning and optimization studies by CEA.

•Formulation of individual projects by SEBs.

•Project costing over Rs. 1000 crores requires CEA techno- economic clearance.

•All power projects require several other clearances from various ministries and departments of Federal and State Governments.

•Final clearance by Planning Commission for state sector projects and Federal cabinet for central sector projects.

•All central sector projects require cabinet approval following approval of Public Investment Board (PIB)

MAJOR WEAKNESS OF PLANNING SYSTEM

•Traditional approach of meeting demand through new capacity additions.

•Bureaucratic delays in obtaining various clearances.

•Lack of coordinated planning of generation and transmission.

•Inadequate investments in transmission system main cause for increase in T&D losses and poor quality of power supply.

•Distribution plans formulation lacks systematic planning .

• Adhoc expansion of distribution systems results inhigh losses,low reliability andfrequent interruptions.

SOLUTION - POWER PLANNING•CEA/ministries to streamline procedures and develop a time bound program for clearances.

•Generation and transmission planning be done simultaneously not sequentially .•No bias in allocation of resources between generation and transmission projects.

•Improve performance of distribution systems throughefficient operation and management of existing systems andscientific system planning for future load growth.

•Increasing shortage of resources calls for integration of both supply and demand management (energy efficiency and conservation).

BOTTLENECK - FINANCIAL•Financial planning by Annual Plans and budgets.

•Inclusion of a project in Plan, guarantee to cover costs despite time/cost overruns

•However, uncertainty about funds that would actually flow during different years of Plan.

•Capital structure of boards not sustainablePrimarily debt based - heavy interest burden.Declining financial health of States adversely affects fund availability.Poor liquidity position of boards - capital resources diverted for working capital.

SOLUTION - FINANCE•Financial viability of boards crucial for growth.

•At least 20% of capital expenditure be financed by board's internal resource generation.

•Rationalized tariffs, cost control and complete financial discipline in operations of boards.

BOTTLENECKS

OPERRATIONS & MAINTENANCE

Application of Scientific & professional approach :

Needs more attention:

• due to minimum educational standard

• due to lack of training

• due to less involvement

• due to less awareness of financial implications of

actions

BOTTLENECK - TARRIF

•Reason for deteriorating financial health of SEBs - average revenue realized less than average cost of generation and supply.

•Excessive political interference in setting tariffs - guided by socio-political considerations than economic objectives .

•Tariffs for agriculture sector most subsidized - average cost of supply and revenue differ by 80- 100% in states.

SOLUTION - TARRIF

•Transparency in tariff revision exercises.

•Tariffs in short run be based on normative efficient cost and marginal costs in long run.

•All electricity sales metered - flat rate abolished.

•Cross-subsidization limit within consumer categories. •Establishment of National Power Tariff Board at center with five Regional Tariff Boards.

BOTTLENECK-MANAGEMENT AND OPERATION OF SEBS

•Excessive interference by states in day-to-day management of boards.

•Board members appointed by State Government.

•State Electricity Consultative Council to advise SEBs on policies, planning, and review progress - ineffective.

•SEBs caught in day-to-day operational problems such aspower interruptionscoal receiptmaintenance of key equipmentbilling and collection problems etc.

SOLUTION - MANAGEMENT AND OPERATION OF SEBS

•Improving generation efficiencies of existing facilities.

•Reducing transmission and distribution losses through.

•Rational utilization of excess staff ,enhance skills of personnel.

•Reducing revenue outstanding ,take actions against defaulters.

•Improving reliability and quality of power supply.

•Incentives be linked to overall performance score instead to PLF or losses

Commercialization of Boards•Converting Boards into corporations.

•Separation of generation, transmission and distribution functions.

•Privatization of distribution and generation.

•Rural electrification to be separated from boards operations and converted into cooperatives.

•Prices for electricity generation to be fixed by market forces rather than regulation.

•Statutory regulatory body for overseeing transmission and distribution operations.