single phase transformers in h. v. distribution systems

1

Single Phase Transformers

in

H. V. Distribution Systems

2

Nature of Rural Loads

• Loads in rural India are predominantly pumpsets 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

3

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 30 such 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.

4

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 inordinate delays in replacement of failed DTRs

5

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 KVA and release supply with NO or least LT line

• Aim at “LT less” system starting from “Less LT”

• Unavoidable short LT lengths to be covered by insulated wires like ABC (Aerial Bunched Cables)

6

Technical Superiority of HVDS• For the distribution of same power, the

comparison of voltage drop, losses etc., with 100 as base is illustrated below

Parameter Single Phase 6.3 kv / 433 V HVDS

Conventional 3 phase LVDS

Current (A) 11 100

Losses (kw) 8.5 100

Voltage drop 12.7 100

7

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

8

HVDS – Single phase - Irrigation

• Good quality single phase motors are available

• High yield of water as pump set efficiency is high

• Single phase motors are ‘capacitor start’ and ‘capacitor run’

• Starters not required

• Built in capacitor

9

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 assume ownership and responsibility

• High quality of power supply earns total consumer satisfaction

10

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 and type of Distribution System

D. Economics & payback period

E. Policy on procurement of single phase transformers

11

A&B

• H.V.D.S. to be implemented straight away where new villages are being electrified in view 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)

12

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

13

nN A

aB b C

c a

n A B Ccb

Star – Star Vs. Delta - Star

14

Comparison

Star – Star Delta – StarVector group connections outside

Vector group connections outside

Single HV bushing Two 11 kv bushings

Graded insulation on HV Entire HV winding to be insulated for 11 kv

Current rating is high and hence more copper

Current in HV is less in delta and hence less copper

15

(C) Linkage with current density

• In Metro areas with high load densities as high 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

16

(C) Linkage with current density (Contd.)

• Even if one limb fails, single phase loads 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

17

(C) Linkage with current density (Contd.)

• In rural areas of low load densities HVDS 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

18

(D) Economics

• Cost of three Nos. single phase transformers 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 3 phase transformer

• There is no difference in no load losses and full load losses between one 3 phase transformer of 3 K and three Nos. single phase transformer of K

19

(D) Economics (Contd.)

• However current for same capacity is too 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

20

(E) Usage of three Nos. single phase against one three phase transformer in urban localities

• The schemes being implemented in many 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 load areas

21


• 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.

22


• In respect of extremely few three phase loads 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.

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• In the event of one phase unit giving trouble, 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 section office for faster replacement

24

PROS & CONS in Restructuring existing LVDS to HVDS

• 99.99% customers avail supply at 415 / 240 Volts 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 loss scenario 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.

25


• Power loss for transmission of equal load in LVDS (415V) and HVDS (11000V) lines are in ratio 13:1

• Maximum permissible voltdrop between DSS and customer premises is 10%. Hence compliance with IE rule. 56 on voltage drop is difficult and very expensive in LVDS whereas it is simple in HVDS

26


• The investigation of typical LV feeders in LVDS indicate that 75% of LV feeders have voltdrop 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

27


• 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 simple and rampant in LVDS whereas it is very difficult in HVDS

• ABC cables with tough insulation are indigenously available

28


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 small capacity single phase transformers

• Utilisation of existing three phase motors.

29

HIGH VOLTAGE DISTRIBUTION SYSTEM

IN

APSPDCL

31

Existing LT Distribution of KOTTUR - SS-I

39 Agl Services3.6 km LT Line

32

Existing LT Distribution of Murakambattu - SS-II


33

Existing LT Distribution of Patnam – SS II

9 Agl Services1 no Poultry Service1.59 km LT Line

34

Existing LT Distribution of Bangaru Palem – SS IV


35

Present LT Distribution system consists of 3 phase distribution transformer 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…

36

•Damage to standing crops, due to delay in replacement of failed distribution transformers.

•Fluctuations in voltages due to more number of consumers connected under this transformer (say 25 to 30 consumers).

•Nobody owns the transformer since everybody thinks that others will take care of the transformer.

37

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.

38

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

39

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 units

8 Loss of units 2972 units 1003 units

9 % of line loss 16.82% 16.30%

ORIGINAL 100 KVA DTR VOLTAGE &LINE LOSS COMPARISON

40

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 and reliability of supply.

41

Existing LT 3Phase 4 wire line on support

Same support with HVD System

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

42

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

43

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

39 Agl Services3.6 km LT Line2.6 km converted to HT1.0 km LT Line11 Nos 15 kVA DTR’s

44

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


45

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

9 Agl Services1.59 km LT Line1.59 km converted to HT8 Nos 15 kVA DTR’s

46

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


47

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 .

48

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…

49

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…

50

Sl.No Particulars

Kotturu ss-I

Murakambattu ss-II

6) % of line losses on HVDS

5.47% 5.44%

7) % of line loss on earlier LT Distribution System

18.63% 13.76%

8) % Net reduction in line losses

13.16% 8.32%

51

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…

52

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%

53

Comparison between LT System with HVD System

Particulars LT HVDS

Length of HT lines

- 2.6Km

Length of LT lines

3.6 Km 1 Km

No of Distribution transformers

100 KVA –1 no/..

15KVA- 11 no/..

Voltage at tail end

350 volts 420 volts

% line losses 18.63% 5.47%

KOTTURU SS-I

54

Voltage at tail end

350

420

300

320

340

360

380

400

420

440

Vol

tage

at t

ail e

nd

Series1

Series2

Tail end Voltage in LT System

Tail end Voltage in HVD System

55

% 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

ine

los

se

s

% Line losses before HVD System

% Line losses after HVD System

56

Particulars LT HVDS

Length of HT lines

- 2.04Km

Length of LT lines

3.6 Km 0.96 Km


100 KVA –1 no/..

15KVA- 10 no/..

Voltage at tail end

385 volts 430 volts

% line losses 13.76% 5.44%

MURAKAMBATTU SS-II 100 KVA

57

Murakambattu SS II 100 KVA

430

375

340

350

360

370

380

390

400

410

420

430

440

Voltage at tail end

Vo

lta

ge

at

tail

en

d

Series1

Series2


Tail end Voltage in HVD System

58

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

% L

ine

loss

es

59

Particulars LT HVDS

Length of HT lines

- 1.59 Km

Length of LT lines

1.59 Km -


63 KVA –1 no/..

15KVA- 8 no/..

Voltage at tail end

340 volts 420 volts

% line losses 16.82 % 5.30%

PATNAM SS-II 63 KVA

60

Patnam SS II 63 KVA

340

420

340

350

360

370

380

390

400

410

420

430

440

Voltage at tail end

Vo

lta

ge

at

tail

en

d

Series1

Series2


61

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

ine

loss

es

62

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 each agricultural services.

NEW VERSION OF HVDS SYSTEM

Bangaru Palem SS-IV 100 KVA

63

Particulars LT HVDS

Length of HT lines

- 2.5 Km

Length of LT lines

3.3 Km 0.8 Km


100 KVA –1 no/..

15KVA- 9 no/..

Voltage at tail end

320 volts 430 volts

% line losses 16.30 % 3.77%

Bangaru Palem SS-IV 100 KVA with reinforcement of conductor and installing rated capacitors.

64

Particulars HVDS with existing

conductor

HVDS with Reinforcement of

conductor and rated capacitors

Voltage at tail end

420 volts 430 volts

% line losses 5.31 % 3.77%

Bangaru Palem SS-IV 100 KVA.

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

installing rated capacitors

65

Bangaru Palem SS IV 100 KVA

320

430

340

350

360

370

380

390

400

410

420

430

440

Voltage at tail end

Vo

lta

ge

at

tail

en

d

Series1

Series2

Tail end Voltage in LT SystemTail end Voltage in HVD System

66

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

% L

ine

loss

es

67

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…

68

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 at substation since the line is at 11 KV potential.

69

Interaction with the consumers by CMD/APSPDCL& JMD (vigilance)A.P. Transco on 01.10.2002 at Doddipalle

71

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.

single phase transformers in h. v. distribution systems

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