42121760 5 2 DPR Development of Schemes

Power Finance Corporation Ltd.(A Govt. of India Undertaking)

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Project Development, DPR Preparation, Appraisal and Schemes ImplementationDistribution Reform, Upgrades and Management (DRUM) Training Program

Development of Schemes

Source: MECON

VOLTAGE REGULATION

OBJECTIVE

The basic objective of strengthening and improvement of sub Transmission-system is to ensure quality and reliability of supply to the consumers, along with bringing down the technical losses to an optimal minimum value and phase the system expansion to match the growing power demand in the area under study.

Today consumers have become more aware of electricity supply quality. Appliances used today by consumers are more sensitive than earlier. Quality power supply is necessity of today. By quality power supply we mean voltage regulation with in a limit laid by Bureau of Indian Standard, Power Supply should be free from harmonics which affects the equipment life adversely and increase the energy loss.

In order to improve the sub-transmission and distribution system to provide reliable and quality power supply to consumers. It is necessary to take up strengthening and improvement of the system in a scientific and methodical manner.

Why Voltage Regulation?

Performance of electrical equipment is affected by variation in voltage, current and frequency of supply power. There are many appliances available today which are in common use of consumer which are very sensitive to voltage, current and frequency. For example a microwave oven is frequency sensitive equipment where as tube light is voltage sensitive and a filament bulb is current sensitive. In industry annealing is very precise process which is current sensitive process where as the performance of drive motors depends on the availability of voltage at their terminals and AC drives are frequency sensitive. Among these examples variation in frequency & current is least recognized parameter by common consumers but it is the voltage which is much talked by people. A tube-light stop glowing as soon as the voltage dips a certain level and it is quickly notices by people.

Among voltage, current and frequency it is the voltage which is quantifiable, measurable and easily controllable by utilities. Controlling frequency variation is not in the hand of utility. This is why an electrical power supply network is design and developed taking the voltage variation at different level/ section.

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What is Voltage Regulation?

By Voltage regulation we mean the voltage drop between sending end to receiving and due to resistance, reactance, skin effect etc. BIS has specified the range of permissible/ acceptable voltage at consumer end. Today consumers/ industries are using electronic equipment in large numbers which are voltage sensitive. So quality power is the necessity of today.

Sending End Voltage – Receiving End VoltageVoltage Regulation =

Sending End Voltage

E1 – E2

= - E1

Where E1 = Sending End VoltageE2 = Receiving End Voltage

For example Sending End Voltage = 440 Voltage Receiving End Voltage = 420 Voltage

440 - 420Than % voltage regulation x 100 = 4.5%

440

The voltage drop in 33 kV and 11 kV feeders should not exceed 5% at the farthest end under peak load conditions and normal system operation regime. However, under system exigencies e.g. outage of transformer / line, voltage variation at various voltage levels with on load tap changing at power transformer if necessary shall be maintained with in the following limits:

Above 33 kV (-) 12.5% to (+) 10%Up to 33 kV (-) 9.0% to (+) 6%Low voltage (-) 6% to (+) 6%

To develop new network or to renovate existing system to achieve above voltage variation limit following tools are used.

1. KVA – KM2. Software available for network analysis like – POWERNET, ETAP, DINIS,

POWERGEN NETWORK, MI-POWER etc.

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The selection of conductor size should be based on studies using software and the economic analysis by considering capital cost and capitalization of losses. Till computer software facilities are established in the circle, kVA- KM concept as explained may be used to decide the size of conductor and distribution planning.

Tools for calculating regulation of power distribution lines. KVA-KM methodology is very commonly used tools for calculating voltage regulations of lines.

250 kVA

0.2 KM 100 kVA 0.1 KM 160 kVA

0.05 KM 0.3 KM 1.0 KM 0.5 KM 1.5 KM 2.0 KM 315 kVA 0.1 KM 100 kVA 0.2 KM 100kVA 25 kVA 0.1 KM 0.05 KM 0.05 KM 63 kVA 0.05 KM 100kVA 100kVA 200kVA 0.05 KM

Sending End Receiving End 0.5 KM 1.5 KM 2.0 KM 1.0 KM 325 kVA 610 kVA 513 kVA 315 kVAkVA-KM = 2 X 315 + 1.5 X 828 + 0.5 X 1438 + 1 X 1763

= 630 + 1242 + 719 + 1763 = 4354

KVA-KM X P.F 4354 X 0.85% Regulation = --------------------- = ------------------ = 3.464 % D.F X RC 1.2 X 838

Where P.F = Power FactorD.F = Diversity FactorR.C = Line Regulation Constant

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Regulation constant for commonly used ACSR conductors are given in following table:

Sl. No. Size & Name of conductor KW-Km for 1% voltage drop at p.f. 0.8 at 33 kV

1. 7/3.35 mm ACSR Rabbit 107082. 7/4.09 mm ACSR Raccoon 137503. 6/4.72 mm + 4/1.57 mm ACSR Dog 16267

Sl. No. Size & Name of conductor KW-Km for 1% voltage drop at p.f. 0.8 at 11 kV

1. 7/2.11 mm ACSR Squirrel 6172. 7/2.59 mm ACSR Weasel 8383. 7/3.35 mm ACSR Rabbit 1219

Sl. No. Size & Name of conductor KW-Km for 1% voltage drop at p.f. 0.8 at 450 Volt

1. 7/2.21 mm AAC GNAT 1.142. 7/3.10 mm AAC ANT 1.983. 7/2.11 mm ACSR Squirrel 0.904. 7/2.59 mm ACSR Weasel 1.225. 7/3.15 mm ACSR Rabbit 1.80

Some Important FactorsLoad FactorThe load factor can be defined as the ratio of the energy consumed during a given period to the energy which would have been used it the maximum load has been maintained through out that period.

Energy consumed during 24 hoursLoad Factor = -------------------------------------------------

Maximum load recorded x 24 hours

Average LoadAlso Load Factor = --------------------------

Maximum Load

Power FactorPower Factor is defined as the ratio of active power to apparent power.

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kW Active Power

kVAR Reactive Power

kVA Apparent Power

φ




KW (True Power)Power Factor = Cos φ = ---------------------------------------------

KVA (Apparent Power)

What are the effects of low power factor?

Low power factor results in:• Poor Voltage Regulation• Increase in Maximum Demand• Increased loading in customer’s cable/ transformer

Why does Power Factor become low?

• Presence of large number of Induction Motors• Highly loaded induction motors

How to Improve Power Factor?

• Installation of Static Capacitors• Installation of Static VAR Compensator

Variation of Maximum Demand with Change in Power Factor (pf)

100MD at Unity pf = ----------------- = 100 kVA

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100MD at 0.95 pf = ----------------- = 105.26 kVA i.e. 5.25% Increase

0.95

100MD at 0.90 pf = ----------------- = 111.11 kVA i.e. 11.11% Increase

0.90

Advantage of improvement in power factor is the reduction in monthly Maximum Demand Charges.

Diversity Factor

Diversity Factor is the ratio of the maximum non coincident demand over a period to maximum diversified demand over the same period.

Maximum non-coincident demand = sum of individual maximum demand of various load over a particular period.

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Maximum diversified demand = Maximum demand of the group of loads over a particular period.

P1, max + P2, maxDiversity Factor = -----------------------------

PC, max

Sum of maximum demand of individualDiversity Factor = -------------------------------------------------------

Maximum load connected to system

Voltage Regulation Improvement Tools

• Bifurcation of lines• Reconductoring• Use of higher Size conductor• Use of AAAC conductor in place of ACSR Conductor• Improving power factor• Diversifying the load• Setting of new substation near load centre

Bifurcation of Lines

Long length transmission line have more voltage drop due to I2R loss because with the increase of length resistance increases so it is preferable to have short transmission line by furcating the existing long transmission line or creating a new feeder from primary sub-station.

Reconductoring

The another method of improving voltage regulation is by replacing old conductor with one size higher new conductor. The main constraint in this method is taking shut down. So a good planning is very essential before taking up reconductoring.

Replacing ACSR & AAAC

All aluminum alloy conductor have better conductivity than aluminum conductor steel reinforced though it is costlier.

Improving Power Factor

Voltage at receiving end bear less power due to use of induction motors is large number in industries as well as for pumps for irrigation purpose. This can be improved by use of capacitors of proper rating near the load to compensate the reactive power requirement.

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Diversity the Load

Voltage regulation can be improved by incoming consumers to use electrical power in different time. For example the industrial consumers can be asked to use power during night. PHED can use pumps in warning house. For this utility can fixed different tariff for different hours.

Setting New PSS

By setting new PSS instead of stretching 11 kV lines too long can improve voltage regulation with increase of consumers the length of 11 kV lines have also increase to cater the consumers located at for distance. So by carrying out proper survey of load a new PSS can be installed near load centre which in turn will provide better voltage to consumer.

Network Development

The Distribution System planning involves setting of sub-station routing of feeders and many other decisions relating to both location and amounts of capacity additions. Therefore the distribution forecast refers to fore cast of geographical locations as well as quantum of future load growth. The three steps procedures involved in distribution load forecast are:

• Analysis of past trends of growth in electricity demand.• System load forecast via forecast for the entire area.• Spatial / small area load forecast. Divide the utility service area into sufficient large

number of small areas and the forecast for each small area.

To renovate the existing network we must know the following data :

• Length of present network• Single line diagram of network• The voltage regulation of the system• Type and size of conductor used• Consumer profile• Emergency supply requirement if any• The existing capacities of PSS

To develop new power supply network or to renovate the existing power supply network, one should know the following information/ data.

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Consumer Profile

Consumer profile includes type of the consumer, connected loads of consumer, specific requirement of consumer, consumer may be of the following types.

• HT Consumers• Domestic Consumer• LT Industrial Consumers• PHED Loads• Street Lighting Loads• Agriculture Consumers

Peak Demand

It is the highest average kVA recorded during any one demand interval with in the month. The demand intervals are normally 30 minutes, but may vary from utility to utility from 15 minutes to 60 minutes. The demand is measured using a trivector meter/ digital energy meter.

Area Profile

It includes latitude, altitude, population, wind speed, snow fall, rain fall, seismic intensity, solar radiation, floods etc.

Existing Network details incase of renovation and modernization i.e.

i) Capacities of existing GSS, PSSii) SLD of existing networkiii) Length of the linesiv) Details of conductors i.e. size & materialv) Land availabilityvi) Accessibility of road & rail

* Following points are taken care while developing network:

• Non coincident peak demands at the individual 33/11 kV sub-station would be used in the load flow studies for assessing the adequacy and reinforcements required to sub-transmission lines. However for the system below 33 kV diversities shall be taken into account.

• Non coincident peak demands at the individual 33/11 kV Sub-station would be used in the load flow studies for assessing the adequacy and reinforcements required to sub transmission lines. However, for the system below 33 kV diversities shall be taken into account.

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• The voltage drop in 33 kV and 11 kV feeders should not exceed 5% at the farthest and under peak load condition and normal operation regime.

• Adequate power supply at normal voltage shall be available from main grid sub-station (GSS) to meet the system demand. In case of outage of one transformer the other transformer should be of sufficient capacity to meet the system requirement alone.

• Every 33/11 kV Sub-station may have preferably at least two incoming feeders from two different sources from reliability consideration.

• The loading of lines should preferably be kept as per economic loading level of the particular conductor.

• The 11 kV feeders shall generally not be long under normal condition. It possible it should not be exceeded beyond 15 Km.

• The power factor of the system would preferably be not less than 0.95 at 11 kV level.

• The preferred transformer capacity for primary Sub-station (i.e. 66/11 kV or 33/11 kV) should be of 5 MVA, 6.3 MVA, 8 MVA, 10 MVA, 16 MVA and 20 MVA for Urban Area and 1, 1.6, 3.15, 5 MVA for Rural Area.

• As a guideline, the conductors / cables indicated below could be preferred.

Rated System Voltage

Conductor Type

33 kVACSR Panther, Wolf, Dog or equivalent AAAC. 3 Core XLPE cables of 150, 185, 240, 300 and 400 sq.mm

11 kV

ACSR Dog, Raccoon, Rabbit or equivalent AAAC. Equivalent Aerial Bunched Cable (ABC), 3 Core XLPE cables of sized 120, 150, 185, 240 & 300 sq.mm

LT

ACSR Dog, Raccoon, Rabbit AAC, Ant, Grasshopper, Wasp or equivalent Aerial Bunched Cable (ABC) 3½ Core or 4 Core, PVC Cables of 95, 120, 150, 185, 240, 300 sq.mm

The separate 33/11 kV feeders shall be laid for major industrial consumers.

• Maximum Demand of up to 100 kVA to be supplied at low voltage

• Maximum Demand of between 100 kVA and 1500 kVA to be supplied at 11 kV

• Maximum Demand between 1.5 MVA and 5 MVA to be supplied at 33 kV

• Maximum Demand of more than 5 MVA to be supplied at 66 kV (or higher voltage)

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Maximum fault level

• 33 kV System – 750 MVA

• 11 kV System – 350 MVA (Urbans)– 250 MVA (Rurals)

• LT System – 40 MVA

ECONOMIC LOSS LEVELS

Sl. No. System Components Levels for peak power losses

Target Level (%)

Max. Tolerable(%)

1. Step up Transformer and EHV Transmission System

0.5 1.00

2. Transformation to inter-mediate voltage level, transmission system & step down to sub-transmission voltage level

1.50 3.00

3. Sub-transmission system and step down to distribution voltage level

2.25 4.50

4. Distribution lines and service connections 4.00 7.00

TOTAL POWER LOSS 8.25 15.50

CONCLUSION

As discussed in preceding sides it is clear that to develop and analyze a electrical sub-transmission and distribution system, it is equally important to take care of all component of network like voltage, current, frequency, all factors affecting the calculation to decide the rating and capacity of equipment. kVA- Km tool to calculate voltage regulation of transmission line, the power triangle to calculate the kVAR required to improve the power factor. The diversity factor to know the pattern of the connected load. Voltage regulation is taken as indicator of power supply quality as it quantifiable, measurable and controllable by utility.

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42121760 5 2 DPR Development of Schemes

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