Journal of Scientific & Industrial Research

Vol. 62, May 2003, pp 473-490

Energy Efficiency Improvement of Electrical Transmission Distribution Networks

M Siddhartha Bhatt

Central Power Research Institute, Energy Research Centre, Sreekariyam, Tri vandrum 695 017

Recei ved: I 8 October 200 I ; accepted: 3 I December 2002

The mean utility T & D efficiency in India is 78.8 per cent while the mean T & D efficiency in private networks is 87 .3 per cent. The mean capacity loss in utility T & D networks is 20.6 per cent while in private networks it is 10.6 per cent. In both , utility and private T & D networks, conductors/cables followed by transformers are the main elements causing the losses. In this paper the strategies for improvement in T & D efticiency, minimizing the capacity losses and improvement in power quality, are presented. The results of experimental work on systems are al so presented in the form of curve fits. The main suggestions are centered on upgrading operating voltage, automation , network re-confi guration , operational optimization, demand management , and system moderni zation .

Introduction

Electrical transmission and distribution (T & D) systems are significant links between the production and the utilization sectors. The networks cover the utility (or utility T & D system) and the private networks (which are located inside the end user' s premises). The process of transfer of electrical energy from the generating stations to the end users, results in quality, quantity , and capacity losses . Quality losses are those associated with poor quality of power at the user's end-mainly voltage drop, waveform distortion, the presence of harmonics, low frequency, and unbalance in phase voltages/currents. Quantity losses are the energy losses in cables/conductors, transformers, joint losses, and earth leakage losses. Capacity losses are those leading to the underrating of the power transfer capacity of system due to the low power factor, low voltage and low frequency which lead to sub-optimal performance of the electrical network.

In the developed countries the energy efficiency of utility T & D systems are in the range 92 per cent and 97 per cent of the generated power. The energy efficiency of the private networks is in the range 97

Present address: Central Power Research Institute, Sir C V Raman Road , Bangalore 560 080

and 99.5 per cent of the input energy . The situation is different in many developing countries . The energy efficiency in the utility T & D systems varies between 52 per cent and 85 per cent. The energy efficiency in the private networks range from 65 to 94 per cent'. Thus, nearly 20 to 50 per cent of the generated energy in the power stations is dissipated as energy losses in the overall T & D system. The energy losses can be classified as inherent losses in the system, losses due to non-optimal operation and commercial losses (those emanating from erroneous metering, accounting errors, and illegal extraction) .

In India the installed capacity, which was 1362 MW in 1947 has risen to around 110 GW in 2002. The general growth curve is given in Figure 1. In the coming five decades the installed power is likely to be around 400 GW. The trend in the T & D efficiency curve is given in Figure 2 . The T & D efficiency, which was 85.6 per cent during 1947, has dropped to 78 per cent during 200 I. The trend indicates that the T & D efficiency in the next five decades is likely to be around 78 per cent unl ess corrective measures are taken to increase it. The energy losses are around 100 TWh/y .

The case of Romania 2 which was successful in improving the utility T & D efficiency from 70 per cent to 94 per cent within a decade, projects

474 J SCI IND RES VOL 62 MAY 2003

3!: 500 -,--- ----- ----------,

" ;: 400 -.~ 300 c.. co " 200

"0

100

I - - I

.S1 iii -I/)

c O ~--~==~----~----------~ 1940 1960 1980 2000 2020 2040

Years

Figure 1- Growth of installed capacity in India

8G

*114 ,,:; u c OJ

~ 82

"' o

~ 80

78

7G L _. _ _ ___ - --------'

1940 1960 1980 2000 2020 2040 2060

Year

Figure 2 - T & D efficiency of utility systems in India

2060

optimism for many countries where these losses are high . Janick' has reviewed the options for investment in the T & D sector for improving energy efficiency and recommended that investment be mounted to reduce the network losses. In this paper the various losses are quantified, their origin is traced and ways of minimizing these are proposed .

Utility T and D Systems

Structure of the Systems and Problems

The Indian power sector is composed of five independent grids each handling between 15,000 and 30,000 MW of electric power. Each of the grids are furth er divided into State Electricity Boards or Regional Power Corporations which form the basic units for which the T & D efficiencies are computed . There are twenty-five such sub-systems for which the performance is evaluated _ Transmission is primari Iy AC based with trunk lines (800 kV or 400 kV), inter state grid lines (250 kV or 400 kV), main feeders (220 k V) and secondary feeders (132 k V, 1 10k V or

66 kV). It is stepped down to 33 kV, II kV or OA15 kY. Distribution is at 11 kV and OA 15 kV through three phase systems of nominal frequency 50 Hz. Cornmon conductors for transmission systems are ACSR (aluminum conductor with stee l reinforcement) and AAAC (all aluminum alloy conductor) of 500-700 mm2

. Cables are used in very limited areas because the cost ratio between conductors and cables is around IS: I. Oil filled cables of 400 kV and 275 kV and XLPE (cross­linked polyethylene) cables of 132 kV and 275 kV are in use only for 0.8 per cent of the network.

There are around 1.7 million distribution transformers (11 kV/OAI5 kV) of 50-1600 kVA with an average size of 75 kVA(4J• 92 per cent of these are oil filled, 6 per cent are of dry type and the balance 2 per cent is of amorphous core/copper 4 .

The HT distribution networks (II kV) are mainly a collection of open radial networks . The majority (around 80 per cent) of the 11 kV lines are overhead copper conductors (12 kV grade) . Overhead lines are composed of open wire, flat mounted formations with reinforced cement concrete pole support. The balance of 20 per cent of the lines are underground/overhead 3 core sheathed cables (12 kV grade) with aluminum/copper conductors and PVC/XLPE/paper insulation .

The bulk of the LT (OA15 kV) distribution lines (around 75 per cent) are overhead copper conductors of I kV grade. The balance of 25 per cent of the lines are 3Y2 core armored sheathed underground/overhead cables (I kV grade) of aluminum/copper conductors and PVC/XLPE insulation .

For both, HT and LT (OAI5 kV) distribution networks, bare overhead conductors are used because of their low cost (only 20-25 per cent of that of cables), ease of fault location and ease of maintenance. Cables are preferred in congested/ urban/dangerous locations, where safety and space are important considerations. Table I gives the length of the various lines in the total network.

The quality losses manifest themselves in the form of low voltage, low frequency, voltage unbalance, current, imbalance, and harmonic distortion. Capacity losses are basically caused by low voltage, low frequency, and grid disintegration . Active power shortage causes low frequency while reactive power shortage leads to low voltage. Supply

BHATT': ENERGY EFFICIENCY IMPROVEMENT OF ELECTRICAL TRANSMISSION 475

Table 1- Lengths of HT and LT lines in the total network (installed capacity: 110 GW)

SI No. Voltage level Line length (Gm)

01 800 kV/lOOO kV/HVDC 0.006

02 400 kV 0.06

03 220 kV 0.24

04 132 kV 0.17

05 66 kV 0.06

06 33kV 0.42

07 II kV 2.10

08 Total HT lines 3.056

09 Total L T (415/230 V) lines 4.230

induced disturbances are voltage dips, voltage fluctuations, harmonics, DC components, and voltage unbalance. High frequency disturbances include voltage spikes, lightning surges, and radio frequency signals.

The power transferred through an AC transmission line is not controllable in a strictly axiomatic sense. The magnitude of the voltage difference, the sine of the phase angle differences and the transfer impedance govern the power transmitted on an AC line. This lack of dynamic controllabi lity results in the following problems:

(i) The grid tends to be unstable when the voltages and frequency are on the brink of the cutout limit. Each grid has 4-5 members who have set under-frequency relays at 47.8 Hz with a time delay between 05- 1.5 s. When LT, low frequency occur the islanding schemes operate . This often leads to grid disintegration . Due to under frequency, member states get separated from the grid. Inadequate communication and inadequate automation for act ive control also add to grid disintegration. Frequent tripping of 400 kV1200 kV tie and trunk lines on power swing and load encroachment causes further separation of the systems. Once separation occurs, tie-up takes long time because of mismatch of frequency and voltageS.

(i i) The thermal (conventional coal) to hydel capacity ratio is 70:30. During dry seasons when hydel generation is low and when agricultural loads are high, severe low voltage

problems are experienced . The line voltages drop up to 75 per cent of the nominal va lue.

(iii) High reactive generation caused by overloading the generating units leading to their being forced to reduce their active generation causing further dip in frequency.

(iv) Tripping of auxiliaries in thermal power plants due to low voltage.

The other problems facing the utility T & D systems are as follows:

(i) While in many industrialized countries like the UK the ratio of the HT to LT line length is around 5: 1, this ratio is only 0.1 to 0.8 in India. The design of Indian T & D systems is different from that in Europe and the US. In these countries, the HT lines (II kV) are drawn right up to the load point and then stepped down through transformers of 5 to 100 kVA in a decentralized mode 6. In India the step down from HT (II kV) to LT (0.415 kV) takes place in centralized transformers of 50 to 1600 kV A and subsequently distributed through the L T network. Long lengths of L T (0.4] 5 kV) lines and too many voltage transformations cause energy losses .

(ii) Investment in power distribution (20 per cent of the total investment in the power sector) is not commensurate with the ll1crease 111

generation capacity.

(iii) Poor equipment quality, no preventive maintenance of lines, and poor/ loose joints causes energy losses. There are over 500 transformer manufacturers and many use inferior materials and processes.

(iv) The annual transformer replacement rate is 8-35 per cent due to high failure rates (7-25 per cent). The average replacement rate is 13 per cent as compared to 1-3 per cent in the developed countries . The average life of a transformer is around 7-8 y 4 . A detailed analysis of failures of distribution transformers indicates that nearly 40 per cent of the transformers have failed due to over load, 40 per cent failed due to over voltage and 10 per cent due to aging. The baiance of failures are on account of various reasons such as lightning hits, damage to tanks, bushings , clamps, and structures.

476 J SCIIND RES VOL 62 MAY 2003

(v) Over/under loading of transformers, ad hoc si zing and routing of lines leads to network saturation and energy losses.

(vi) The sale price of electrical energy for the different sectors is varied . If unit production price of 1.0, the sale price is 1.30 for industrial sector, 1.25 for the commercial sector, 1.00 for the urban domestic sector, 0 .50 for the rural domestic sector and 0.15 for the agricultural sector. The incentives for efficient use of energy are lost in the low priced sectors .

(vii) Organizational structures are not bifurcated into generation/transmission/distribution agencIes as a result of which energy accounting is rather difficult.

Harmonics, a significant quality index, cause distortion of power frequency voltages, nuisance tripping of relays, misfiring of thyristors and interference with te lephone lines 7. Harmonics in the present context refer to non-fundamental frequency (multiples of 50 Hz) currents, which flow in the power system due to the nature of the loads . Harmonic currents flow from non-linear load towards the lowest impedance, which is usually the power generator. Harmonics are caused by equipment which draw current in short pulses only during the peak of the sine wave resulting in super imposition of high frequency harmonics on the fundamental 50 Hz frequency. Some sources of harmonics are non-linear loads (ferromagnetic devices, rectifiers, diode­capacitor input power supply, thyristor devices, solid state power converters, static power converters, variable speed drives, thyristor driven locomotives), furnaces (electric arc and induction), electronic equipment (medical equipment, computers), and welding transformers.

The effects of harmonics on the T & D system components are as follows:

(i) On capacitors - Overheating due to harmonic distortion of line voltage, frequent failure , capacitors for a resonant circuit with inductive elements in the system which will create an increase in voltage across the capacitors 8 .

Harmonics cause series resonance leading to high voltage distortion and parallel resonance leading to voltage distortion and telephone interference. Since the impedance of the capacitors is inversely proportional to the

frequency, a capacitor will have lower impedance at high frequencies. Hence, even a small voltage of higher frequency will lead to a substantial flow of current, which overloads the capacitor and ultimately leads to failure.

(ii) On transmission system - additional trans­mission losses due to increased currents and harmonic voltage drops across the circuit impedance. Harmonics affect corona inception and extinction levels and are a function of the peak to peak voltages. It is thus possible that the root mean square voltage will be within limits, whereas the peak voltage will be above the inception level9

.

(iii) Power cables - harmonic current heating due to skin effects and proximity effects. Cables involved in system resonance may be subject to voltage stresses, which can lead to insulation failure.

(iv) Harmonics distort the operating characteristics of relays especially digital relays.

(v) Transformers - While current harmonics increase the copper losses the voltage harmonics lead to increased iron losses. Heat generation due to increased losses associated with eddy currents and hysterisis in transformer cores and skin effects in windings . A delta-star 3-phase transformer can cause additional heating feeding star connected branch circuits. Because the third harmonic current and succeeding odd multiple of this harmonic do not have any cancelling effect but an additive effect, when this neutral current reaches the transformer secondary it goes back into the delta primary where it circulates causing additional heat generation .

(vi) Neutral conductors - Third harmonics and multiples do not cancel but add together in neutral conductors.

(vii) Electrical panels - Heat generation or damage due to heat, hot spots in the neutral bus bars and buzzing sounds .

(viii) Motors - Heating causes additional rotating magnetic fields. Most commonly found harmonics for an induction motor is 51h

harmonic. The magnetic field associate with 51h harmonic is backward rotating and will attempt to run the motor in the backward

BHA IT: ENERGY EFFICIENCY IMPROVEMENT OF ELECTRICAL TRANSM ISSION 477

direction reducing efficiency and possible over heating.

The above problems are primari ly respons ible for the quality and quantity losses in the uti lity T & D systems.

Results and Discussions

The data related to losses are fitted to curves of the following form:

AI Type I: Y = Ao X

BIX Type II: Y = Bo e

.. . (1 )

. . . (2)

.. . (3)

The coefficients for the various fits are given in subsequent tables .

Overall Network-energy Considerations

Table 2 gives a typical break-up of the losses in the uti lity T & D system. It is seen that the distribution system accounts for over 80 per cent of the energy losses. Equipment-wise, conductors and cables account for 60 per cent of the energy losses, transformers 24 per cent and misce llaneous elements account for 3 per cent of the losses.

Figure 3 gives the variation of the T & D efficiency with the length of the transmission lines for the various State Electricity Boards for the past 2 y. It can be seen from Figure 3 that the T & D efficiency is almost independent of the length of the transmiSSion line, which implies that the conductor/cable losses (in the transmission segment of the network) do not form a major fraction of the losses.

Table 2 - Energy losses in the uti lity T & D systems

SI No. Particulars of losses

Technical losses

01 33 kV to 1000 kV

Conductor/cable losses

Transformer losses

Miscell aneous losses

Total losses: 33 kV-IOOO kV

02 I I kV to 33 kV segments

Conductor/cable losses

Transformer losses

Miscellaneous losses

Total losses: II kV -33 kV

03 L T (415 V & 230 V) segments

Conductor/cable losses

Transformer losses

Miscell aneous losses

Total losses in LT (415 V & 230 V)

04 Total technical losses

Commercial losses

05 Unaccounted (commercial) losses

06 Total T & D losses

07 Utility T & D efficiency

2.65

0.90

0.05

4.30

1.00

0.10

5.80

3.20

0.50

All India

Energy loss (per cent)

3.60

5.40

9.50

18.50

02.70

21.20

78.80

Developed countries

2.45

0.70

0.05

2.50

0.60

0.30

0.30

0.50

0.30

3.20

3.40

1.10

7.70

0.10

7.80

92.20

478 J SCI IND RES VOL 62 MAY 2003

Figure 4 gives the effect of distri bution line lengths on the T & D efficiency fo r vari ous State Elec tricity Boards fo r the past 2 y. It is seen that as the distribution line length is increased, the T & D efficiency is increased . Thi s is because most systems are overloaded. W hen the distribution line length is increased the level of loading in the T & D system decreases thereby increas ing the effic iency.

Figure 5 shows the sensiti vity of the T & D effic iency to the rat io of the HT to LT line length for vari ous State E lectricity Boards for the past 2 y. It is seen that as the ratio is increased the T & D effi c iency is also increased.

~ ;;; 100 1 g 90 ~ • .~ 80~ __ · · -''-_~''''·-''-o_o _ _ _ _ o -,-~-- •• I

~ ~~ r.=. ___ o_o ___ ~ _ __ _

c.!S 50 J.-. '--~i - -- ---,-~---.---,

o 0.2 0.4 0.6 0 .8

Transmission line length, Gm

Figure 3-Variation of ulility T& D efficiency wi th transmission line length

~ 90 -, 0 ° >. • 0

.~ 80 f~ oo~ -

() 70 ---~-----------!E" •

II) ,

c.!S • c 60 C' ° .. --.

I- 50 ° . - --.-----,------.---

o 0.1 0.2 0.3 0.4 0.5

Distribution line length, Gm

Figure 4- Varial ion of ulili ty T&D efllciency with distribulion line length

~ 90 1 0_ 85 ° ~ 80 0--"- 0 0 0 ° .!........~ ___ _

~75 L. -~~ --­:§70 l~~o ~ 65 - • - - ----c 60 1 ____ _ c.!S 55 -'--t_o _ _ __ __ -.-___ __ _ I- 50 +--

o 0.2 0.4 0.6 0.8

Ratio of HT to L T line length

Figurc 5-Variation ofT& D efficiency wi th ratio of HT to LT li ne length

The three main segments of end use of e lectrical energy are the industrial, agricultural, and domestic energy consumption. The total of the three is taken as 100 per cent. The effec t of each of these end-use sectors, viz., industri al, agricultural and domestic on T & D effic iency for vari ous State E lectricity Boards fo r the past 2 y is given in Figures 6-8 respecti ve ly. The T & D efficiency improves with increased percentage of industrial energy consumpti on. It also increases with increased agricultural energy consumpti on, in contrast to the observation that the low T & D effic iencies are caused mainly because of excess ive suppl y of energy the agricultural sector

() 80 ___ ______ _ ... ~..L.. ___ _

C • ° : 90 ~ :0

:§ 70 p '_ .:.-~-~. - .. 0 _

~ 60 i----~-----;---------·--·---05 . i l

I- 50 ~---~------r------,-.----_,

o 20 40 130 80

Industrial energy consumption, %

Figure 6- Variation of ut ility T & D efficiency with percentage of industrial energy consumption

?!- 90 l >; ~ . • •

~ 80 ..1<1"'-. -, _.===;.========-::==~o~==:;_.~. ==::.=::::=- -~ 70 : Q)

C 01:1 I-

60 j. 50 -r----... ----=---- .. --~---..,-.---

o 10 20 30 40 50

Agricultural energy consumption, %

Figure 7-Varialion of utili ty T& D efficiency with percentage of agricultural energy consumption

90 "' ~ . :-: ;;;80 -: - .. ~-'~ .. ~

Cu i .... • 01:1 ~ 70 II ~ _.- .. - .. _-.-I- 'u . --.~-------.

!E 60 ,---- .----Q)

----_._-. 50 +-- --....,.....:: -'-,--_._--,- -----,

o 20 40 60 80

Domestic energy consumption, %

Figure 8- Variation of util ity T&D efficiency with percentage of domes tic cnergy consumpt ion

BHAIT: ENERGY EFFICIENCY IMPROVEMENT OF ELECTRICAL TRANSMISSION 479

with subsidized charges. When the percentage of domestic energy consumption increases the T & D effici ency decreases because of excessive LT lines.

The coefficients in the curve fits related to energy losses in the overall network are given in Table 3.

Overall Network-quality Considerations

Table 4 gives the quantification of capacity losses in the system. The capacity reduction is in the range of 16-47 per cent of the rated capacity of the system. The mean capacity reduction is around 21 per cent.

In the developed countries the loss of availability of LT systems is 2-3 hly , while in the developing countries it is 600-700 h/y . The total number of interruptions in developed countries is ] 0-12/y as against 500 interruption sly in the developing countries. The quality can be improved by reducing the consumer no power complaints (L T) to around 200-30011000 customers/y. The number of inter­ruptions at the HT (11 kV) level must be reduced to 50/1000 customers/y . The number of interruptions on account of transformer LT fu se must be below 601100 km, transformer HT fuse must be below 5/100 km, substation breakers must be lower than SOl I 00 km and line sectionalizing cut outs must be less than 10/100 km.

The coefficients III the curve fits related to quality losses in the overall network are given III

Table 5.

Conductors and Cables

Conductors are the single most important cause of energy losses in the utility networks . Acceptable total transmission line losses are around 50 kW/km. These are mainly the ohmic heating losses. The corona losses are in the range 0-20 kW/km. Normally, these are only 2-3 per cent of the total energy losses averaged over the year. These are significant during bouts of bad weather such as heavy rain. Corona losses are also sensitive to fluctuations in transmission voltages 10 .

In distribution systems the ohmic losses in HT (II kV) cables are 37.9-76.6 kW/km for cables embedded in ground and 26.7-88.1 kW/km for cables in free air(II). The losses in LT cables are 42.8-75.7 kW/km for installations in ground and 26.1-86.4 kW/km for those in free airll . The res istance of HT cables is in the range of 0.07-0.87 Q/km and

Table 4 - T & D capacity losses in utility grids.

SI No. Particulars Quality loss (per cent of rated capacity)

Worst Best Mean case case value

01 Low voltage 23.72 3.64 4.55

02 Low frequ ency 4.86 0.97 1.04

03 Low power factor 19.00 12.00 15 .00

04 Total capacity losses 47 .58 16.6 1 20.59

05 Capacity factor (per cent) 52.42 83.39 79.4 1

Table 3 - Coenicients in the curve fit for parameters related to overall utility T & D network -energy losses

SI No. Particulars Constants

Eq No. I Ao A[

01 X: Operating voltage [0.415 - 400 kV) 2.80738 -0.1723 Y: T & D operating cost considering unit cost at 400 kV [Range: 1.0 - 2.4)

Ec; No.3 Co C [ C2

02 Y: Utility T & D eftlciency [50 - 100 per cent)

X: Transmission line length [0.1- 0.8 Gm) 74.7604 -0.0423 0.0

03 X: Distribution line length [0 - 0.4 Gm) 69.2492 48.8926 -36 .0849

04 X: Ratio of HT to L T line length [0 -1 .0) 66.08 17 12.3086 3.06240

05 X: Industria l energy consumpti on 66.7804 0.21570 0.0

[0 - 80 per cent of total consumption]

06 X: Domestic energy consumption 85.8442 -0.6597 0.00512 [0 - 70 per cent of total consumption)

07 X: Agricultural energy consumpti on 72.2461 0.0 1425 0.0 [0 - 50 per cen t of total consumption)

480 1 SCI INO RES VOL 62 MAY 2003

inductance is in the range 0.28-0.40 mH/km. For LT

(OA I5 kV) cables the resistance is 0.06-1.54 Q/km and inductance is 0.24-0.28 mH/km.

The coefficients in the curve fits related to energy losses in conductors and cables are given 111

Table 6.

Transjo nne rs

Transformers are the second most important cause of energy losses in the utility T & D networks. Over the last century the iron loss at 50 Hz has decreased from 2.5 W/kg to 0.8 W/kg due to developments in grain oriented silicon steel and through reduced thickness of laminations from 0.50 mm to 0.15 mm. Further reduction is possible through developments in amorphous metal core transformers.

The overloading of transformers has been a major problem. For economically optimal connection of transformers of equal capacity, the load factor of the transformer, above which a new unit must be added into the circuit, is given by,

LF = [(N/5)(N-I)] 112,

where N (> I) is the number of transformers. The ratio of the on load loss (copper loss) to the no load loss (iron loss) is taken as 5: I.

The low life of transformers is another teething problem. The total annual demand for new transformers is 20 per cent of the existing number of units (new capacity addition: 6.5 per cent and replacement of o ld units: 13 per cent) . The average life of a transformer is around 7-8 y. Transformer life due to aging caused by overload and over voltages can be determined by the Monsinger's rule l2 as,

where Lei IS the design life (25 y), f..T is the average temperature rise above the normal operating temperature.

The coefficients in the curve fits related to energy losses in transformers are given in Table 7 .

Miscellaneous Line Elements

Pablal 3

has brought out the losses in network elements such as switchgear and switches. The power losses in miscellaneous line elements are given in Table 8.

Remedial Action-energy Considerations

The remedial measures for improving the energy efficiency of utility T & D systems are discussed as various options.

Table 5 - Coeffic ients in the curve fit for parameters related to overall utility T & 0 network -quality considerations

SI. No. Particulars

Eq. No. I

X: Operating voltage [0.415-400 kV]

01 Y: No . of interruption sly [2-500]

02 Y: Present availability [0.9200-0.9995]

03 Y: Expected availabi lity from improved system [0.9980-1.0]

04 Y: Minimum energy losses in capacitor at full capacity [0.25-53 WI kVAr]

05 Y: Allowable total harmonic distortion (per cent)

06 X: Capacity factor of 6 k V Ar capacitor [0-100 per cent of rating in k V A,.] Y: Energy losses in capacitor [0-6000 WI kV A,.]

07 X: Capacitor si ze [0-30 kVA,.]

08

09

Y: Energy losses in capacitor at full capacity [28-430 WI kVArl

Eq. NO.3

X: Ambient temperature above 18 °C (6T=0-25 0c) Y: Underrated Load factor of transformer (0.8-1.0)

X: Energy efficiency of the T & 0 system (utility + private) (60-90 per cent) Y: Greenhouse emission index (kg of C02/kWh supplied to the system) (25)

1.0

3.34177

Constants

Au

396.3930

0.9389

0.9980

52.5950

15.5090

6025.4400

430.0940

CI

-0.008

-0.02375

AI

-0.8121

0.0124

0.0003

-0.89026

-0.5510

-1.2226

-0.79740

0.0

0 .0

BHATT: ENERGY EFFICIENCY IMPROVEMENT OF ELECTRICAL TRANSM ISSION 481

Tab le 6 - Coeftlcients in the curve tit for parameters related to overall utility T & 0 network - cables and conductors

SI. No. Particulars Constants

Eq . No. I Ao AI

X: Operating voltage [0.4 15-400 kVl

01 Y: Reactance of underground cables [0.2-0.4 ~Q/mml 0.46 188 -0.0599

X: Cross section al area of cable (mm2)

02 Y: Power transferred by LT cables in free air (kW/mm2) 12. 1829 -0.3646

03 Y: Power transferred by HT cables in free air (kW/mm2) 10.4870 -0.3441

04 Y: Power transferred by LT underground cables (kW/mm2) 18.9100 -0.4359

05 Y: Power transferred by HT underground cables (kW/mm2) 13.6440 -0.3832

06 Y: Resistance - L T cables CQhnm2/k m) 29.379 -1.9926

07 Y: Resistance - HT cables (Q/mm2/km) 8.7408 -1.7407

08 Y: Inductance - L T cables (mHhnm2/km) 0.3075 -1.0407

19 Y: Inductance - HT cables (mHhnm2/km) 0.3084 - 1.0264

X: Power rating (0-600 kW)

10 Y: Resistance - L T cables (Q/kW Ikm) 1632.00 -2.5529

II Y: Resistance - HT cables (Q/kW/km) 289.70 -2.2807

12 Y: Inductance - L T cables (Q/kW Ikm) 0.3801 -1.0612

13 Y: Inductance - HT cables (Q/kW/km) 0.4302 -1.0448

Eq . No.2 Bo 8 1

X: Operating voltage (0.415-400 kV )

14 Y: loint resistance [2-150 ~Ql 190.78 1 -0.0 1279

15 Y: Reactance of overhead conductors [0.2-0.4 ~Q/mml 0.08027 0.00249

16 X: Cable operating voltage (11-132 kV)

Y: Economical transmission capacity (10-400 MV A/circuit) 7.45490 0.0298

Eq. No.3 Co C I C2

X: Ln of cross sectional area of cable (mm2)

Y: Ohmic losses in:

17 LT-cables in free air (kW/mm2/km) 2.3488 -0.3963 0.0

18 HT-cables in free air (kW/mm2/km) 2.0264 -0.3522 0.0

19 LT-underground cables (kW/mm2/km) 3.6015 -0.62950 0.0

20 HT-underground cables (kWhnm2/km) 2.5880 -0.45935 0.0

X: Ln of power transferred by cable (kW)

Y:

21 LT- cables in free air (kW/kW/km) 0.8365 -0.1152 0.0

22 HT- cables in free air(kW/kW/km) 0.5460 -0.11 19 0.0

23 LT-underground cables (kW/kW/km) 1.2704 -0. 1876 0.0

24 HT-underground cab les (kW/kW/km) l.i419 -0.1660 0.0

482 1 SCI IND RES VOL 62 MAY 2003

Table 7 - Coefficients in the curve fit for parameters related to overall utility T & D network - transformers

SI. No. Particulars

Eq. No. I

X: Distribution transformer rating [25-1600 kVA)

Y variable:

o I No load power loss in 11/0.43 kV transformers [1.9-5.0 W/kV A)

02 Full load power loss in 11/0.43 kV transformers [10-30 W/kV A]

03 Power loss in CRGO transformers [2.0-4.0 W/kV A]

04 Power loss in amorphous metal core transformers [0.3-3.5 W/kVA]

05 No load loss in standard transformers [1.5-8 W/kV A]

06 No load loss in energy efficient transformers [1-6 W/kV A]

07 No load loss in highly energy efficient transformers [0.5-5 W/kVA)

X: Distribution transformer load factor [0.8-2.0)

08

09

10

Y variable: Power loss in :

Standard transformers [8-50 W/kV A]

Energy efticient transformers [5-25 W/kVA]

Highly energy efficient transformers [4- 18 W/kV A)

X: Induction tlux density (T)

Y variable: Iron losses at 50 Hz in:

II CRGO steel of 0.35 mm (0.7-1.8 W/kg)

12 Hi-B grade silicon steel of 0.30 mm (0.5-1.2 W/kg)

13 Hi-B grade silicon steel 01'0.23 mm (0.4- 1.1 W/kg)

14 Hi-B DR grade silicon steel 01'0.23 mm (0.4-1.1 W/kg)

15 Hi-B grade silicon steel of 0.15 mm (0.35-0.90 W/kg)

16 Laser treated Hi-B grade Si steel of 0.15 mm (0.35-0.90 W/kg)

17 Amorpholls metall ic glass alloy silicon steel 01'0.025 mm (0.2-0.3 W/kg)

18 X: Thickness of transformer lamination (mm) Y: 1.0 - Stacking factor (dimensionless, 0- 1)

Eq Nu. 2

18 X: Hot spot temperature abuve 98 °C

19

20

21

22

Y: Permissible safe operating period of distribution transformer without impairing life (dimensionless: 0-1)

Eq No.3

X: Voltage level of oi l filled transformer (primary/secondary) (0.4 15-66 kY)

Y: Insulation resistance measured after I minute at 30°C ( 100-500 MQ)

X: Temperature difference above 30 °C (5-40 °C)

Y: Correction factor for insulation resistance (dimensionless; 1.2-5.0)

X: Load factor of transformer (dimension less: 0-2)

Y: Efficiency ratio (11/11m", ) of transformer (dimension less : 0.95-1.0)

X: Silcon content in transformer core steel (0-5 per cent)

Y: Saturation induction flux density (T)

CII

12 1.78

1.1405

0.9543

2.1540

Constants

12.212

60.858

5.4788

5.4830

13 .00

9.9596

10.220

11.860

6.5882

4 .564 1

0.3142

0.3106

0.2644

0.1985

0.2199

0.1600

0.0954

0.012 1

BII

1.0994

C 1

6 .5502

0.0137

0.080

-0.046

-0.2654

-0.2458

-0.1488

-0.3905

-0.2794

-0.3 178

-0.4038

2.0564

2.0217

1.9650

2.8825

2.1126

2.2079

2.7005

2.3570

2.4674

2.8356

-0.8524

BI

-0.1193

C2

-0.0123

0.002

-003425

0.0

BHA1T: ENERGY EFFICIENCY IMPROVEMENT OF ELECTRICAL TRANSMISSION 483

Table 8-Power losses in miscellaneous network elements

SI. No. Particular

01 Switchgear: 132 kV and above

02 Switchgear: 33 kY and 66 kY

03 Switchgear: L T

04 HT and L T energy meters (excluding CTs, PTs and CYTs)

05 Load breaker switches

06 LT bus bars

07 L T ferrous tension clamps

08 LT aluminum tension clamps

Conductors and Cables

Power loss (per cent of

transferred power)

0.001-0.008

0.005-0.020

0.130-0.340

0.300-0.600

0.003-0.030

0.050-0.500

0.0009-0.0014

0.00004-0.00008

The remedial measures for conductors and cables are as follows:

(i) AAACs though costly are superior to ACSRs from the point of durability, ohmic losses and strength to weight ratio. In a coastal location, after 2 y, the decrease in electrical conductivity of AAACs was only 1.9-3.4 per cent as compared to 14-15 per cent for ACSR.

(ii) Aerial bunched cables (ABC) for 11 kV and LT overhead lines are inherently cheaper than underground lines. I I kV EPR single core cables are more resistant than XLPE. Single cores offer easier handling, jointing and greater flexibility. An alternative is the 11 kV ABCs .

(iii) High temperature superconductors have now been proven on a 31 m nitrogen cooled line at 12.5 kV and 1250 A14. These reduce line losses by 40-50 per cent and hold promise for the future.

(iv) Single wire earth return system (SWER) for remote low loaded locations and where no load addition is expected over the next lOy or so. This is 40 per cent economical, has a high power factor (0.95) and results in low level of outages as compared to the conventional 3 phase system. The limitations are that the maximum ground return current is 8 A, power transfer is limited to 3 kW/km and creates possibility of radio interference if used haphazardly .

Transformers

The remedial measures are as follows:

(i) Transformer capacity, location, and loading must be optimized. Transformers must be shifted nearer to load centres.

(ii) The specifications and criterion used for procurement of transformers need to be changed. The transformer efficiency and reliability need to be used as key parameters in vendor evaluation.

(iii) The The total owning cost (TOC) calculations, which is practiced universally must also include the failure rate of the transformers. Typically, an improvement of 0.5 per cent in the failure rate justifies a 10 per cent increase in capital cost of the transformer4

.

(iv) There must be incentive for manufacturers to improve their manufacturing processes and products. For example the insulation drying process (hot air/resistance heatinglinfrared heating/thermic fluid heating in vacuum! airlinert gas) the oil filling process (ambient/degassed oill under vacuum) .

(v) Energy efficient transformers with a life of 25 y (or 200000 h) and capable of withstanding up to 170 per cent overload (for 4 h stretching for 25 per cent of the operating life), must be installed while meeting the total annual demand.

(vi) Economic optimization evaluation techniques must be used for decision support on installation and sizing of new units .

(vii) Replacement/redeployment of over/under loaded transformers to maintain a load factor of around 80 per cent can result in minimum losses6

.

(viii) Amorphous metal core distribution transformers may be used on a wider scale. These are 25 per cent costlier and reduce no­load losses by 30 per cent of that of cold rolled grain oriented (CRGO) transformers . Their limitation is that the induction flux density is limited to 1.3 T .

(ix) Oil-free cable wound power transformers have been successfully used for primary voltages between 36 kV and 145 kV and power ratings up to 150 MV A 15. These reduce transformer losses by 30 per cent.

484 J SCI IND RES VOL 62 MAY 2003

Upgrading Network Voltages

A high potential for energy savings has been envisaged for operating the system at higher operating voltages. The techniques, which have been successful, are as follows :

(i) Upgradation of network voltages - Con­version of LT lines to HT lines will result in reduction of conductor losses in the LT segments by 76 per cent and pays back period within 3 y. One of the criterion suggested is to have LT for demands below 50 kVA, 11 kV for 50 kVA to 1.5 MVA, 33 kV for 1.5 MVA to 5 MV A and 132 kV or 220 kV for demands above 5 MV A 16. Another criterion is that the individual load should be less than 25 per cent of the transformer and line capacity. When the capacity on the transformer and lines exceed 75 per cent, new capacity must be added to the system. The HT to LT ratio should be

. I· dl6 progressive y lIlcrease .

(ii) LT less HT distribution system - There are a large number of distribution transformers with long LT feeders where line losses are high and possibility of theft exists. The LT less HT distribution system involves locating the distribution transformers near load points and connecting loads directly to transformers as in Western countries.

(iii) Increasing the number of taps off the transmission system.

(iv) Lower number of voltage reductions and increased 33 kV transmission.

A lternative Transmission Systems

Promising alternative transmission systems are as follows:

(i) Decentralized HVDC systems can reduce peak power by 20 per cent and energy losses by 30 per cent.

(ii) Multi-phase transmission could be considered as viable alternative to the 3 phase transmission 17. For example, 6 phase, 400 kV line can lead to better transmission efficiency and lower capital cost.

(iii) Modular back to back HVDC communication using capacitors, tuned AC filters, compact HT switch gear, metering and modular I · I 18 t lynstor va ves .

Network Re-configuration

At present, very little attention is being given to network re-configuration. Constant network re­configuration has been shown to be very effective in reducing line losses. Situations, which call for a network re-configuration, are as follows:

(i) Rerouting and redistribution of feeders among sub-stations and adding new links.

(ii) Network growth - Controlling the develop­ment of the electrical network by over sizing conductors and adding parallel feeders 6.

(iii) Rating equipment at its optimal settings -Overrated or under rated settings calls for a reconfiguration.

(iv) Conversion of radial feeders to ring main units (RMUs) by introducing several open points with proVISIOn for alternative feed by switching and which can be configured handle the load.

(v) Provision for changing the open points to enable re-configuration of RMUs .

(vi) New connections must be given only after loads are balanced on transformers and tail end voltage is regulated.

Automation

Manual switching/remote control/automation have their advantages and disadvantages. A combination of these must be used in the automation schemes to minimize capital cost. The various areas for automation are as follows:

(i) Remote controlled load management systems like rural area distribution, automation and control system (RADAC) in segments where the losses are quite high.

(ii) Supervisory control and data acquisition system (SCADA) may be used for partial network and portable electronic data loggers may be used for rest of the network.

(iii) Automation of shunt capacitor operation: Use of automatic switched capacitors with SF6/vacuum type switches for repeated switching duty at I I Kv / 33 kV/66 kV sub­stations. These would lead to savings in transformer losses by 75 k Wh/k V A/Y 19.

(iv) Computerization of energy flow at the sub­station level.

BHAlT: ENERGY EFFICIENCY IMPROVEMENT OF ELECTRICAL TRANSMISSION 485

Operational Optimization

This involves optimizing network loading by the following methods :

(i) Balancing of loads on phases by shifting of single-phase loads and limiting of unbalance in L T segments to within 2 per cent.

(ii) If load is shared between two equal feeders in the ratio of 75 per cent to 25 per cent, the loss will be 25 per cent more than if the load is shared equally between the two. Thus, unequal loading may be identified and equalized.

(iii) Minimizing local metering errors by cross checks/audits through metering at sub-stations and at important feeders .

(iv) Setting of taps of interconnecting transformers.

(v) Sectionalizing of lines.

Maintenance and Good Practices

Some of the practices, which have resulted III

improved performances, are as follows:

(i) Maintenance of EHV (400 kV) systems by hot line washing20 and live line maintenance can mllllmize partial discharges, surfaces discharges, hot clamps, welding of joints and bad bimetallic contacts.

(ii) Changing the conductors of some 400 kV lines that have a high corona related loss.

(iii) Re-conditioning of loss III efficiency transformers .

(a) End user meters can be ensured to be free of manufacturing defects, tampering, bypassing, shock, mal-operation , non­calibration, and with defective current/ potential transformers.

(b) Replacement of electro-mechanical meters by electronic meters, automatic reading meters, pre-paid card meters (accuracy class: 0.5 per cent), or remote meters .

(c) Use of fixed CT ratios through software.

(d) Fitting of distribution transformers and main feeders with programmable overload controllers and electronic meters .

(e) Periodic planned maintenance of lines, sub-stations and transformers.

(f) Minimizing manufacturing defects in switch gear, distribution transformers, bus bars, cables and conductors.

(g) Implementing performance guarantees for 5 y of trouble free operation can ensure quality control.

(h) Change over of dead end snubbing clamps of cast iron by those of aluminum.

Demand Management.

Demand management plays a major role in ensuring a high T & D efficiency. Some of the areas of interest are:

(i) Radio tele-switching of agricultural and non­time specific rural industrial loads 2 1.

(ii) Locating generation closer to load centres. Large loads get located near urban centres far away from the generating stations because of other infrastructural advantages. The larger loads can be located near the generating stations by offer of special incentives and infrastructure.

(iii) Cogeneration by locating the heating loads near the generating stations, which can minimize condensation of steam and dispersal of heat (through cooling towers or directly to river/sea water).

(iv) Distributed cogeneration from sugar mills can improve the rural power profiles.

(v) Development of biogas energy systems as a substitute to grid electric supply for stationary mechanical and lighting loads will minimize the use of isolated and long LT lines.

(vi) Introduction of pumped storage hydro plants of ] 000-2000 · MW/grid with operating capacity of 4-6 h at a time one way.

(vii) Promoting of solar water heaters to reduce the morning electrical heating load demand for bath water.

(viii) Designing a fair tariff structure giVing importance of fairness towards both active and reactive components.

There is potential for increasing the T & D efficiency from the present level to as high as 90 per cent through implementing the above measures.

486 J SCI IND RES VOL 62 MAY 2003

Remedial Action-Quality Considerations

Harmonics

The limit of harmonics is 10 per cent for total harmonic distortion and for individual harmonic it is 8 per cent of fundamental. The techniques for minimizing of harmonics:

(i) Elimination/modification of sources.

(ii) Installation of voltage harmonic filters by end users and by the power suppliers.

(iii) PF capacitors on electrically weak systems often cause resonance and harmonic current magnification when associated with Thyristor controlled loads. These capacitors must be de­tuned by use of series connected reactors that render the combined LC circuit resonance inductive at the lowest principal frequency and above.

Capacitors

Normally addition of capacitive compensation does not keep pace with the growth in the active power demand. Inadequate addition (capacities 35 per cent MV Ar support by generators) by grid members (proportional to their stipulated share) leads to low voltage. The measures suggested for power factor and voltage profile improvement are as follows :

(i) Shunt Capacitors (LT end) - Power factor correction near load centres is preferable. Leasing of LT shunt capacitors in highly loaded rural networks has been very rewarding. Typical case is of Bhiwani where the load is composed of 0.3 million power loomsn . The Electricity Board on a nominal monthly rent leased the capacitors for 5 y. It was seen that the voltage improved by 10-12 V the over loading tripping rate was reduced to 30 per cent of the original value, the energy losses were reduced by 30 per cent, the failure rate of induction motors reduced by 50 per cent and the productivity of each loom increased by 12 per cent.

(ii) Shunt Capacitors (HT side) - Installation of II kV pole mounted automatically switched capacitors with on-off control. Alternatively, switched LT capacitors(231, are designed to provide variable reactive compensation in 3 to 4 steps. While the former have the advantage

of lower failure rates, they run the risk of over compensation . The latter provide better control and improve the power factors from 0.70 to 0.99 with voltage improvement of 8-10 per cent and capacity improvement of 30 per cent. Line losses reduced by 22 per cent from 2.734 W/kW/km to 1.634 W/kW/km. The requirement of capacitors is 0.36 kV AlkV A of distribution transformer capacity. SF6/vacuum type capacitor switches are more suitable for repetitive cyclic duty.

(iii) Series Capacitors (HT end) - The negative reactance of a series capacitor compensates the inductive voltage drop in transmission lines thereby resulting in better receiving end voltage. Series capacitors are used to effectively regulate power flow between two parallel feeders, for increasing loading capacity of a line and for flicker control besides reducing ohmic losses in the feeders . The fear of sub-synchronous resonance gave a set back to the above method. However, many solutions for timely detection and de-tuning of sub-synchronous resonance are now available. By providing 70 per cent series compensation on an 80 km 220 kV line reduced the loss by 2.2 MWI 6. In another line of 400 kV the power transfer increased from 580 MW to 610 MW by providing 40 per cent series

. 16 compensation .

Miscellaneous Line Elements

The measures are as follows:

(i) Automatic voltage boosters are transformers, which sense the load current and generate additional voltage, which is added to the existing system voltage thereby regulating the tail end voltage of the transmission system. These are also used in traction applications where there are heavy bursts of power demand.

(ii) By installation of equipment like air circuit breakers, high rupture capacity fuses, mlIII ature circuit breakers, high density polyethylene boards and molded core circuit breakers in highly loaded belts, the annual average fuse call rate has been reduced from about 1200/y to around 80/y (ref. 24) .

BHATT: ENERGY EFFICIENCY IMPROVEMENT OF ELECTRICAL TRANSMISSION 487

Automation

The suggested measures for automation with the objective of improving the power quality are as follows:

(i) Low frequency is caused by inadequate capacity addition, stochastic nature of hydro generation, coal shortages, forced outages of generating units, inadequate load shedding, maximum simultaneous drawl of central share by grid members and grid indiscipline by members 5. Frequency control can be achieved by accurate real time balancing of the generation and consumption based on past trends as well as the current operating dynamics.

(ii) Introduction of automatic on-load tap changers for maintenance of secondary voltages can provide temporary relief but in the long run result in higher primary losses.

(iii) Introduction of SCADA for monitoring of quality parameters could lead to tracing the origin of the loads, which wreck power quality .

(iv) Automation of shunt capacitor operation IS already discussed under quantity losses.

Operational Optimization

The operational optImIzation for quality improvement is as follows:

(i) Capacity can be improved by increasing the design temperature of the conductor. For example, in a 220 kV Zebra ACSR the power transfer capacity can be increased by 12 per cent if the operating temperature is increased by \0 0c.

(ii) Urban distribution system must be inter connected to increase reliability with provision for varying the open point.

Demand Management

The measures under demand management for capacity improvement are as follows:

(i) Control of load curve-Remote controlled agricultural load management with signal receivers can be achieved by identifying all transformers catering to agricultural loads . Signal receivers are to be coupled with electro-mechanically operated LT circuit

breakers installed on the transformers . The transformers can be divided into three groups and cyclically charged to stabilize the load curve. Industrial users may be asked to segregate loads to essential (25 per cent) and non-essential (75 per cent) . Using remote control switching using a ripple control system from a central location , only the non­essential loads may be de-energized in the event of a power cut.

(ii) Programmed cyclic load shedding 26.

(iii) Frequency linked tariff for drawl of central share 26.

(iv) Reactive power tariff for grid members 26.

(v) Co-generation from the existing industries, which are presently generating only process steam. The additional capacity of equipment can be used for reactive support as well.

(vi) Solar PV lighting systems.

Private Distribution Systems

Description

The private distribution network refers to systems, which are within the user's premises. A study has been conducted on around 20 distribution networks and the results are presented below.

Results and Discussions

Energy Efficiency

A study of the vanatlOn of the network efficiency with the monthly energy input of the plant shows that there is virtually no dependence of the network efficiency on the size of the installation . Also the size of the installation has very little effect on the transformer losses or the cable/conductor losses.

Table 9 gives the energy losses in the private networks. The significant losses are those of cables (32 per cent), transformers (25 per cent) and joints (15 per cent). The network efficiencies range from 66 per cent to 94 per cent. The mean efficiency is 87.27 per cent.

The remedial measures for improvement in energy efficiency of private distribution networks are as follows:

(i) Cyclic de-energization and voltage control of distribution transformers.

488 J SCI IND RES VOL 62 MAY 2003

(ii) Network re-configuration through rerouting and trimming of line lengths .

(iii) Relocation of heavy loads to reduce line losses .

(iv) Replacement of line elements causmg excessive fR losses such as capaci tors, bus bars, etc.

(v) Changeover to low loss joints.

Quality and Capacity Losses

Table 10 gives the capacity losses in the private networks . It is seen that the capacity reduction is around 5-17 per cent of the input power. The capacity

is reduced primarily because of low voltage and low power factor, and low frequency and transformer losses . The load on the private T & D networks is on ly 20-30 per cent. As a result of this, grid related variables such as supply voltage and frequency do not strongly affect the private networks.

The private T & D networks are bi lled on the basis of a maximum demand component and the energy charges. If the maximum demand is not reached, this is not a cause for concern and capacity losses can be ignored . But if the maximum demand is exceeded, remedial measures suggested are as fo llows:

Table 9 - Energy losses in private T & D networks

SI No. Particu lars of losses Units Per cent Worst case Best case Mean value

01 Transformer losses per cent 7.82 1.34 3.19

02 Cable/conductor 12R losses per cent 9.94 1.59 4.10

03 Inadequate reactive power compensation per cent 1.27 0.11 0.42

04 Joint I2R losses per cent 4.02 0.61 1.91

05 Low voltage per cent 0.59 0.04 0.16

06 3-pahse load unbalance per cent 0.26 0.02 0.13

07 Unbalance in conductors of parallel cables per cent 0.19 0.01 0.08

08 Inadequate configuration of cables per cent 0. 16 0.01 0.07

09 Harmonics per cent 0.79 0.12 0.40

10 Earth leakage per cent 1.93 0.06 0.69

11 Total network losses per cent 34.10 6.10 12.73

12 Network efficiency per cent 65.90 93.90 87.27

Table 10 - Capacity losses in private T & D networks

SI No. Particulars of losses Units Per cent Worst case Best case Mean value

01 Inadequate reactive power compensation per cent 6.13 1.82 2.76

02 Low voltage per cent 4.27 0.50 2.18

03 Low frequency per cent 0.96 1.20 0.73

04 Transformer losses per cent 3.93 1.85 3.81

05 Joint I2R losses per cent 0.64 0.01 0.25

06 3-phase voltage unbalance per cent 0.70 0.02 0.63

07 3-pahse load unbalance per cent 0.25 0.01 0. 12

08 Unbalance in conductors of parallel cables per cent 0. 17 0.01 0.08

09 Inadequate contiguration of cables per cent 0.02 0.0 1 0.01

10 Harmonics per cent 0.03 0.01 0.01

II Earth leakage per cent 0.08 0.01 0.01

12 Total network capacity losses per cent 17.18 5.45 10.59

13 Network capacity factor per cent 82.82 94.55 89.41

BHATI: ENERGY EFFICIENCY IMPROVEMENT OF ELECTRICAL TRANSMISSION 489

(i) Capacitive Compensation-Installation of devices with built-in provision for maintaining near-unity power factor. Typically automatic switchable capacitor banks in binary fashion are ideal for power factor control.

(ii) Improved secondary voltages by correct position of tap changers as short term measures.

Conclusions

The mall1 conclusions of this study are as follows :

(i) Though agricultural power IS highly subsidized, increased percentage of energy consumption in this sector does not increase the T & D losses .

(ii) The distribution segment of the utility T & D system accounts for over 80 per cent of the T & D losses. Equipment-wise conductors account for 60 per cent of the energy losses in the entire network.

(iii) There is potential for increasing the utility T & D efficiency from around 78 per cent to 90 per cent through measures such as upgrading voltage levels , system automation, network re­configuration, operational optimization, good maintenance practices, and system modernization.

(iv) With the proliferation of computers and electronic equipment, harmonics is one of the nascent quality problems, which can wreck havoc on the network unless controlled at an early stage.

(v) Capacity reduction in the utility T & D networks can be minimized from around 21 per cent to around 5 per cent by ensuring that voltage, frequency , and power factor are within limits. The measures suggested fall under improvement in power factor, network re-configuration , operational optimization, demand management, and system modernization .

(vi ) The major sources of energy losses in private T & D networks are cables (32 per cent), transformers (25 per cent) and joints (15 per cent).

:vii) The energy efficiency III private T & D networks is around 87 per cent and can be

improved to around 95 per cent by minimizing idling losses in transformers through cyclic de­energization of low loaded transformers, reconfiguration of lines, relocation of heavy loads, and use of low loss joints .

(viii) The mean capacity losses in private networks are of the order of 11 per cent, primarily because of low voltage, low power factor, low frequency, and transformer losses . However, since the loading on private networks is only around 20-30 per cent, the effect of the grid related variables is not as serious as in utility T & D networks.

(ix) The T & D problem should be viewed in its totality- quality, quantity and capacity for both utility networks and private networks, in order to devise ways of successfully reducing the losses.

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490 J SCI IND RES VOL 62 MAY 2003

II Heinhold L & Stubbe R, Power cables and their applications, Part 2 (Seimens AG, Berlin) 1993.

12 Hochart B, Power transformer handbook (Butterworths) London, 1987.

13 Pabla A S, Electric flower distribution system (Tata McGraw Hill , New Delhi) 1992.

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Abbreviations Used A(),A 1

AAAC

ABC

AC

ACSR

Bo,BI C Q,C 1,C2

C RGO

CT

CVT

DC E HV

EPR

HT

HVDC

L LF

-Constants in curve fits

-All a luminum alloy conductor

-Aer ia l bunched cables

-Alte rnating current

-Aluminum co nduc tor w ith s teel re inforcement

-Constants in curve fits

-Constants in curve fits

-Cold rolled gra in o ri ented

-Curre nt transforme r

-Capac itance voltage transformer

-Direct c urrent -Ex tra hi gh voltage (400 kV and above)

-Ethyle ne polypropylene rubber

-Hig h te nsion (vo ltages II kV a nd above)

-High vo ltage direct current

-Operating life (y)

-Load fact or (dimensionless, 0-1)

20 Raghavan M S S, Ramanamurthy K C V & Rao N S M, A few strategies in conservation of energy, AARO Tech J (India ),l(1 ) ( 1993) 23-26.

2 1 Sexana R K, Initiati ves taken by rural e lectrillcati on corporation in energy conservati on, CIR E (India) News , 2 & 3 (September 1996) 20-22.

22 Rao S T, Demand side management and electricity end use effi ciency-The need of the hour in today ' s power crisi s, ClRE (India) News, 2 & 3 (September) 1996 , 8-14.

23 ABB Reactive power compensation (ABB Power Sys tems, AB , S-72 I, 64 Vasteras , Sweden, NR-sOO-028 E) 1993, 1-24.

24 Khare P N, Reliability of urban di stri but ion system, Electric India , 39(9)( 1999) 15-18 .

25 Bhatt M S, Energy eftici ency and greenhouse emi ssion burden from coal fired electri c power plants- A case study of the Indian power sector, EneI' Sourc, 22 (2000) 6 11 -23.

26 Narasimhan S L, & Aggarwal A K, Status of transmission and di stribut ion system in India- Programme and techniques for reduction of losses, J Int Assoc Electric Generat Transllliss Distribut {Aj i'o Asian Region}, 1 (4) (1994) 177-186.

LT -Low tensi on (voltages of OAI5 kV and 240 V )

N -Number o f tra nsform e rs

PT -Potential transform er PVC -Po ly vinyl chloride

RADAC -Rura l area distribution , automation and co ntro l

RMU SCADA

SWER

T T&D

-Ring ma in unit

-S upervisory control and data acqu is iti o n sys te m -S in gle wire earth re turn system

-Temperature (0C)

-Transmiss ion a nd di s tribution

TOC -Total owning cost

X -Independe nt variable

XLPE -Cross linked poly ethylene

Y -Depend ent vari able

Subscripts r -Reactive (s in <jl componen t)

d -Design