High Voltage Distribution System

8/10/2019 High Voltage Distribution System

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Single Phase Transformers

in

H. V. Distribution Systems


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Nature of Rural Loads

Loads in rural India are predominantlypumpsets used for lift irrigation

These loads have low p.f., low load

factor

Load density is low due to dispersal of

loads

Existing system is to lay 11 KV lines,employ 3 phase DTRs 11kv / 433 volts

and lay long LT lines


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Nature of Rural Loads (Contd.)

To fetch a load of one pump set of 5 HP

(4 kw) ; two or three L.T. spans are to

be laid

On each DTR 63 or 100 KVA 20 to 30such pump sets are connected. If used

for domestic services about 100

consumers can be connected

They run for about 1500 Hrs in an year

of 8760 hours.


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Disadvantages experienced with LVDS

Poor tail end voltages

High quantum of losses

Frequent jumper cuts and fuse blow outs

Motor burn outs almost twice in each cropping

period of 100 days

DTR failures due to frequent faults

Loss of standing crops due to inordinatedelays in replacement of failed DTRs


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Solution ? H V D S ?

To improve quality of supply and reduce

losses HVDS is recommended

11 KV lines are extended to as nearer to

the loads as possible and erect small size

single phase transformers 5, 10 or 15 KVAand release supply with NO or least LT line

Aim at LTlesssystem starting from Less

LT

Unavoidable short LT lengths to be covered

by insulated wires like ABC (Aerial Bunched

Cables)


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Technical Superiority of HVDS

For the distribution of same power, the

comparison of voltage drop, losses etc., with100 as base is illustrated below

Parameter Single Phase 6.3

kv / 433 V HVDS

Conventional 3

phase LVDSCurrent (A) 11 100

Losses (kw) 8.5 100

Voltage drop 12.7 100


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Technical Superiority of HVDS

Smaller size conductors can be employed

Excellent voltage profile

Reduced losses

No frequent fuse blow outs

Negligible transformer failures

Two or three consumers get effected against

30 if DTR fails (even 100 domestic)

Very easy and quick replacement


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HVDS Single phase - Irrigation

Good quality single phase motors areavailable

High yield of water as pump set

efficiency is high

Single phase motors are capacitor

startand capacitorrun

Starters not required Built in capacitor


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Additional advantages of HVDS

Unauthorised hooking of loads is not possible as

LT lines are short and insulated

System power factor improves (0.95) causing

easy reactive power control

As only two or maximum (3) pump sets are

connected on each DTR ; the consumers assumeownership and responsibility

High quality of power supply earns total

consumer satisfaction


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Questions & Critical issues

frequently faced on HVDS

A. Whether HVDS is for future areas to be

electrified or to convert existing LVDS?

B. Can HVDS & LVDS coexist in the same area?

C. What is the linkage between load density andtype of Distribution System

D. Economics & payback period

E. Policy on procurement of single phase

transformers


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A&B

H.V.D.S. to be implemented straight away

where new villages are being electrified inview of its technical superiority

Where 3 phase pump sets are in use HVDS can

be implemented by converting existing LT

lines for 11 KV

Even three Nos. smaller size single phase

transformers can be used for providing three

phase LT supply capacity (3Xindividual

capacity)


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A&B (Contd.)

Single phase transformers 6.3 kv / 233

Volts can be manufactured with single

or two bushings

Three single phase transformers can be

connected with HVs in star or delta


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nN

Aa

Bb

Cc a

nA B

C

cb

Star Star Vs. Delta - Star


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Comparison

Star Star Delta Star

Vector group connections

outside

Vector group connections

outside

Single HV bushing Two 11 kv bushings

Graded insulation on HV Entire HV winding to beinsulated for 11 kv

Current rating is high and

hence more copper

Current in HV is less in

delta and hence less

copper


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(C) Linkage with current density

In Metro areas with high load densities ashigh as 20 MW per sq km due to rise

multistoried complexes enough load can

be met with practically no LT

In smaller urban areas, single phase

transformers can be employed selectively

for single phase as well as three phase


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(C) Linkage with current density (Contd.)

Even if one limb fails, single phaseloads on that phase can be distributed

on the other two and the failed unit can

be replaced very quickly as it is easy to

transport and erect

In the case of 3 phase large capacity

transformers, entire unit is to be

replaced and down time is high


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(C) Linkage with current density (Contd.)

In rural areas of low load densitiesHVDS using one or three Nos. single

phase transformers can be employed

without any hesitation

Rural loads even village habitat portion

are too low and mostly single phase

In villages getting electrified afresh;

the load densities are bound to be too

low


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(D) Economics

Cost of three Nos. single phasetransformers of capacity K is equal to a

three phase transformer of capacity (3K)

Cost of employing three single phase

transformers is 1.3 times the cost of a 3phase transformer

There is no difference in no load losses

and full load losses between one 3 phasetransformer of 3 K and three Nos. single

phase transformer of K


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(D) Economics (Contd.)

However current for same capacity istoo low at 11 KV compared to LT

For 100 KVA current is 5 Amps at 11 KV

and 140 Amps at LT Line losses get reduced in the ratio

52:1402(25:19600)

Hence highly economical

(E) Usage of three Nos single phase against one


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(E) Usage of three Nos. single phase against one

three phase transformer in urban localities

The schemes being implemented inmany rural areas are mostly such as

Kutir Jyothi and A Lamp for each

house do not need high capacity

transformers.

There are single 5, 10, 15 / 16 capacity

transformers also which can be used

advantageously in these light loadareas

(E) U f th N i l h i t


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This has many advantages as follows

Capacities of single phase units can be so

selected to avoid laying LT lines as these

units are available in ratings from 5 KVA to

15 KVA

Single phase loads can be connected on

individual single phase transformers duly

dividing them.

(E) U f th N i l h i t


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In respect of extremely few three phaseloads with connected loads of 4 kw or

above (very rare in rural areas) three

single phase transformers of smaller

capacities can be employed.

The loads are too small that they cannot

contribute to high unbalances.

(E) Usage of three Nos single phase against one


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In the event of one phase unit givingtrouble, the loads can be distributed on

the other two phase units and the

defective unit can be taken out easily

Transport, replacement is very easy and

can be done much faster.

In fact a rolling stock of 4% can be

maintained at each distribution sectionoffice for faster replacement

PROS & CONS i R t t i i ti


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PROS & CONS in Restructuring existing

LVDS to HVDS

99.99% customers avail supply at 415 / 240Volts thus operational performance of LV

network is key to customer services

Losses in Indian Power System are around

20%. LV system is responsible for high lossscenario as LV line losses are 6 times of

target limit and 3 times maximum

tolerable limit. Switchover to HVDS alone

can bring losses to international norms.

PROS & CONS in Restr ct ring e isting


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LVDS to HVDS

Power loss for transmission of equal loadin LVDS (415V) and HVDS (11000V) lines

are in ratio 13:1

Maximum permissible voltdrop between

DSS and customer premises is 10%. Hencecompliance with IE rule. 56 on voltage

drop is difficult and very expensive in

LVDS whereas it is simple in HVDS



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LVDS to HVDS

The investigation of typical LV feeders in

LVDS indicate that 75% of LV feeders havevoltdrop above 5% and is the cause of high

losses whereas in HVDS losses on LV line

are insignificant.

The current for distribution of same power

in L.V.D.S. is high and existing conductors

get loaded beyond economic loading

limits. It can be avoided by switch over to

HVDS



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LVDS to HVDS

The monitoring of feeders in LVDS is

difficult compared to HVDS as number of

feeders to be monitored is in ratio of 60:1

Unauthorised tapping of LV lines is simpleand rampant in LVDS whereas it is very

difficult in HVDS

ABC cables with tough insulation areindigenously available

PROS & CONS i R t t i i ti


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LVDS to HVDS

3 Phase HVDS

The work involved in restructuring

distribution work are

Conversion of existing low voltage lines to

single phase 2 wire HV lines

Replacement of existing three phase

distribution transformers with smallcapacity single phase transformers

Utilisation of existing three phase motors.


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HIGH VOLTAGE DISTRIBUTION SYSTEM

IN

APSPDCL


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Existing LT Distribution of KOTTUR - SS-I

39 Agl Services3.6 km LT Line


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Existing LT Distribution of Murakambattu - SS-II

24 Agl Services

3.0 km LT Line


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Existing LT Distribution of PatnamSS II

9 Agl Services

1 no Poultry Service

1.59 km LT Line


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Existing LT Distribution of Bangaru PalemSS IV

38 Agl Services

3.3 km LT Line


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Present LT Distribution system consists of 3 phase distributiontransformer with a capacity of 100 KVA in rural areas which

feeds supply to all the consumers through 3 phase 4 wire LT

network.

DISADVANTAGES OF EXISTING SYSTEM

Lengthy LT Lines.

Voltage drop at the consumer end.

High I2R losses .

Frequent motor burn-outs due to low voltage and consequent

expenditure on repairs.Transformer failures-expenditure towards repairs and

inconvenience to the consumers.

Existing LT Distribution Network

Continue


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Damage to standing crops, due to delay in

replacement of failed distributiontransformers.

Fluctuations in voltages due to more

number of consumers connected under thistransformer (say 25 to 30 consumers).

Nobody owns the transformer since

everybody thinks that others will take care ofthe transformer.


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CALCULATION OF LT LINE LOSSES

Continue

Electronic meters fixed on the LV Side of the

distribution transformers

All Agricultural Services provided with

electronic energy meters.

Energy sent out from the transformer measured.

During the same period energy consumed by the

Agricultural consumers measured .Losses worked out.


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Sl.No Particulars Kottur-ss I Murakkombattu

ss II

1 Crop pattern Sugarcane,

paddy

Coconut , mango garden, paddy and part

of the land cultivated by sugarcane.

2 Length of LT

lines

3.6Km 3.0 Km

3 No. of Pump sets 39 24

4 Connected Loads 179.5 HP 130 HP

5 No. of days 13 days 14 days

6 Input 4290 units 3059 units

7 Output 3490.4 units 2638 units

8 Loss of units 799.6 units 421 units

9 % of line loss 18.63% 13.76%

ORIGINAL 100 KVA DTR VOLTAGE &LINE LOSS COMPARISON


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Sl.No Particulars Patnam-ss Bangarupalem ss

1 Crop pattern Sugarcane-

90% paddy

&G.nut

Sugar cane,Paddy,Coconut,Mango

Garden

2 Length of LT

lines

1.59Km 3.3 Km

3 No. of Pump sets 9 38

4 Connected Loads 72.5 HP+2.25

KW

130 HP

5 No. of days 40 days 19 days

6 Input 17672 units 6152 units

7 Output 14700 units 5149 units8 Loss of units 2972 units 1003 units

9 % of line loss 16.82% 16.30%

ORIGINAL 100 KVA DTR VOLTAGE &LINE LOSS COMPARISON


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As seen from the previous table results the LT line

losses are more in LT distribution network.

To overcome this,HVD 3Ph system is introduced by

A.P.S.P.D.C.L to maintain better voltages andreliability of supply.


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Existing LT 3Phase 4 wire line

on support

Same support with HVD System

Conversion of existing LT 3ph 4w Line into HT Line


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HVD SYSTEM

Original 3ph 100KVA Dist.Transformer replaced

with 11KV.CTPT set

3ph 15KVA Dist.Transformer erected

under HVDS to cater 2 to 3 services


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H.T. and L.T Layout of HVD System.KOTURU-SS-I

39 Agl Services

3.6 km LT Line

2.6 km converted to HT

1.0 km LT Line

11 Nos 15 kVA DTRs


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H.T and L.T layout of HVD System Murakambattu SS I1

24 Agl Services3.0 km LT Line2.04 km converted to HT0.96 km LT Line10 Nos 15 kVA DTRs


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H.T. and L.T Layout of HVD System.Patnam SS-II

9 Agl Services

1.59 km LT Line


8 Nos 15 kVA DTRs


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H.T and L.T layout of HVD System Bangaru Palem SS IV

38 Agl Services

3.3 km LT Line


0.8 km LT Line

9 Nos 15 kVA DTRs


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HVD SYSTEM

Existing LT Lines converted into HV Lines by replacing

L T 3-Phase crossarm by 11KV . V crossarm

Replacement of 3 number L T pininsulators with 3 number 11KV pin

insulators.

Replacement of 3 number LT shackles with 3 number 11KV strain

insulators .

Erection of additional supports where ever clearances are inadequate.

Erection of smaller capacity 3 phase distribution transformer of 15 KVA

capacity for every 2 to 3 pumpsets.

Connection of existing pumpsets from the newly erected 15KVA

distribution transformers with airbunched cable .


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Calculation Of HT Line Losses in HVD System

11 KV CT PT set erected in place of existing 100

KVA Distribution Transformer

Readings taken simultaneously at CT PT set and at

all pump sets.

Losses worked out.

Continue


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Sl.No Particulars Kotturu SS-I Murakkambattu ss-II

1) No 15KVA distribution

transformer erected

11 nos 10 nos

2) No of days 15 days 13 days

3) INPUT 5310 units 3926 units

4) OUTPUT 5019.2 units 3712.2 units

5) Losses 290.8 units 213.8 units

Continue


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Sl.No Particulars Kotturu ss-I Murakambatt

u ss-II

6) % of line losses

on HVDS

5.47% 5.44%

7) % of line losson earlier LT

Distribution

System

18.63% 13.76%

8) % Net

reduction in

line losses

13.16% 8.32%


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Sl.No Particulars Patnam SS-II Bangarupalem ss-II

1) No 15KVA distribution

transformer erected

8 nos 9 nos

2) INPUT 1299 units 334 units

3) OUTPUT 1229 units 321.4 units

4) Loss of units 69.7 units 12.6 units

Continue


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Sl.No Particulars Patnam ss-II Bangarupalem

ss-II

5) % of line losses on

HVDS

5.30% 3.77%

6) % of line loss on

earlier LT

Distribution

System

16.82% 16.30%

7) % Net reduction

in line losses

11.52% 12.53%


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Comparison between LT System with HVD System

Particulars LT HVDS

Length of HT

lines- 2.6Km

Length of LTlines

3.6 Km 1 Km

No of Distribution

transformers100 KVA1 no/.. 15KVA- 11 no/..

Voltage at tail end 350 volts 420 volts

% line losses 18.63% 5.47%

KOTTURU SS-I


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Voltage at tail end

350

420

300

320

340

360

380

400

420

440

Voltageat

tailend

Series1

Series2

Tail end Voltage in LT System

Tail end Voltage in HVD System


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% Line losses

18.63%

5.47

0.00%

2.00%

4.00%

6.00%

8.00%

10.00%

12.00%

14.00%

16.00%

18.00%

20.00%

% line losses

%L

inelo

sses

% Line losses before HVD System

% Line losses after HVD System


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Particulars LT HVDS

Length of HT

lines- 2.04Km

Length of LT

lines3.6 Km 0.96 Km

No of Distribution



% line losses 13.76% 5.44%

MURAKAMBATTU SS-II 100 KVA


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Murakambattu SS II 100 KVA

430

375

340

350

360370

380

390

400

410

420

430

440

Voltage at tail end

Voltageattailend

Series1

Series2


Tail end Voltage in HVD System


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Murakambattu SS II 100 KVA

13.76%

5.44%

0.00%

2.00%4.00%

6.00%

8.00%

10.00%

12.00%

14.00%

16.00%

% line losses

%

Linelosses


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Particulars LT HVDS

Length of HT

lines- 1.59 Km

Length of LT

lines 1.59 Km -

No of Distribution



% line losses 16.82 % 5.30%

PATNAM SS-II 63 KVA


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Patnam SS II 63 KVA

340

420

340

350

360370

380

390

400

410

420

430

440

Voltage at tail end

Voltageattailend

Series1

Series2



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Patnam SS II 63 KVA

16.82%

5.3%

0.00%

2.00%

4.00%

6.00%

8.00%

10.00%

12.00%

14.00%

16.00%

% line losses

%L

in

elosse


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The New version of HVDS system is an extension of

HVDS work executed at previous locations.The H.T

line losses in previous systems is 5.3%. An effort

has been done to further reduce the H.T line losses

by adopting following methods.

1. Reinforcement of existing LT net work of 7/2.59

ACSR conductor with 55 sqmm conductor.

2.Providing of required rated capacitors at eachagricultural services.

NEW VERSION OF HVDS SYSTEM

Bangaru Palem SS-IV 100 KVA


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Particulars LT HVDS

Length of HT

lines- 2.5 Km

Length of LT

lines

3.3 Km 0.8 Km

No of Distribution



% line losses 16.30 % 3.77%

Bangaru Palem SS-IV 100 KVA with reinforcement of

conductor and installing rated capacitors.


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Particulars

HVDS with

existing

conductor

HVDS with

Reinforcement ofconductor and rated

capacitors

Voltage at tail

end420 volts 430 volts

% line losses 5.31 % 3.77%

Bangaru Palem SS-IV 100 KVA.

Comparison between HVDS with existing conductorand HVDS with reinforcement of conductor and

installing rated capacitors


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Bangaru Palem SS IV 100 KVA

320

430

340

350

360

370

380

390

400

410

420430

440

Voltage at tail end

Volt

ageattailend

Series1

Series2

Tail end Voltage in LT SystemTail end Voltage in HVD System


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Bangaru Palem SS IV 100 KVA

16.30%

3.77%

0.00%

2.00%

4.00%

6.00%8.00%

10.00%

12.00%

14.00%

16.00%

% line losses

%

Line

losses


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ADVANTAGES OF HVD SYSTEM

The registered customers will feel ownership and take responsibility and

not allow others to meddle with the L.T. Network.

Prevention of unauthorized loads by the consumers themselves since the

distribution transformer may fail if loaded beyond its capacity.

Failure will be minimal because of no over loading and no meddling of L.T

Lines.

In the event of equipment failure only 2 or 3 customers will get affected

instead of 25 to 30 customers in original system.

High quality of supply since there is practically no voltage drop.

Less burnouts of motors because of good voltage and less fluctuations.

Continue


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Considerable reduction in line losses and consequent

savings in power purchase cost

Since Losses are reduced considerably ,Power can be

supplied to additional loads without any further

investment on infrastructure.

No additional generation capacity needed for giving

new loads due to reduction in power drawals.

Accidents due to touching of snapped conductors

reduced due to the fact that the breaker trips atsubstation since the line is at 11 KV potential.


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Interaction with the consumers by CMD/APSPDCL& JMD

(vigilance)A.P. Transco on 01.10.2002 at Doddipalle


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Interaction with the consumers by CMD/APSPDCL& JMD

(vigilance)A.P.Transco on 01.10.2002 at Murakambattu SSII

Consumers opined that

The motors are drawing less current and hence life span of

motor has increased.The rate of motor burnouts are also reduced.

The motors running smoothly without hissing noise.

The transformer failures are almost avoided.

Theft of energy eliminated since the consumers will not allow

others to pilfer from their Distribution Transformer.

Interruptions have been minimized and quality of supply

assured.

Due to reliability of supply ,2 crops can be raised and can

increase the productivity.


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Documents

High Voltage Distribution System