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
Voltage drop
12.7

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
Whether HVDS is for future areas to be electrified or to convert existing LVDS?
Can HVDS & LVDS coexist in the same area?
What is the linkage between load density and type of Distribution System
Economics & payback period
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. Star – Star Vs. Delta - Starn N A a B b C c

14. Comparison Star – Star Delta – Star 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
(E) Usage of three Nos. single phase against one three phase transformer in urban localities
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. (E) Usage of three Nos. single phase against one three phase transformer in urban localities
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.

23. Transport, replacement is very easy and can be done much faster.
(E) Usage of three Nos. single phase against one three phase transformer in urban localities
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. PROS & CONS in Restructuring existing LVDS to HVDS
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. PROS & CONS in Restructuring existing LVDS to HVDS
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. PROS & CONS in Restructuring existing 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 simple and rampant in LVDS whereas it is very difficult in HVDS
ABC cables with tough insulation are indigenously available

28. PROS & CONS in Restructuring existing 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 small capacity single phase transformers
Utilisation of existing three phase motors.

29. HIGH VOLTAGE DISTRIBUTION SYSTEMIN
APSPDCL

31. Existing LT Distribution of KOTTUR - SS-I
39 Agl Services
3.6 km LT Line

32. Existing LT Distribution of Murakambattu - SS-II
24 Agl Services
3.0 km LT Line

33. Existing LT Distribution of Patnam – SS II
9 Agl Services
1 no Poultry Service
1.59 km LT Line

34. Existing LT Distribution of Bangaru Palem – SS IV
38 Agl Services
3.3 km LT Line

35. Existing LT Distribution Network
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.
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
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.
Continue…

38. ORIGINAL 100 KVA DTR VOLTAGE &LINE LOSS COMPARISON
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
units
2638 units 8
Loss of units
799.6 units
421 units 9
% of line loss
18.63%
13.76%

39. ORIGINAL 100 KVA DTR VOLTAGE &LINE LOSS COMPARISON
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
% of line loss
16.82%
16.30%

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. Conversion of existing LT 3ph 4w Line into HT Line
Same support with HVD System
Existing LT 3Phase 4 wire line on support

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 Services
3.6 km LT Line
2.6 km converted to HT
1.0 km LT Line
11 Nos 15 kVA DTR’s

44. H.T and L.T layout of HVD System Murakambattu SS I1
24 Agl Services
3.0 km LT Line
2.04 km converted to HT
0.96 km LT Line
10 Nos 15 kVA DTR’s

45. H.T. and L.T Layout of HVD System.Patnam SS-II
9 Agl Services
1.59 km LT Line
1.59 km converted to HT
8 Nos 15 kVA DTR’s

46. H.T and L.T layout of HVD System Bangaru Palem SS IV
38 Agl Services
3.3 km LT Line
2.5 km converted to HT
0.8 km LT Line
9 Nos 15 kVA DTR’s

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. No 15KVA distribution transformer erected 11 nos 10 nos
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
units
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. No 15KVA distribution transformer erected 8 nos 9 nos
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
KOTTURU SS-I
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%

54. Tail end Voltage in LT System
Tail end Voltage in HVD System

56. MURAKAMBATTU SS-II 100 KVA
Particulars LT
HVDS
Length of HT lines -
2.04Km
Length of LT lines
3.6 Km
0.96 Km
No of Distribution transformers
100 KVA –1 no/..
15KVA- 10 no/..
Voltage at tail end
385 volts
430 volts
% line losses
13.76%
5.44%

57. Tail end Voltage in LT System
Tail end Voltage in HVD System

59. PATNAM SS-II 63 KVA
Particulars LT
HVDS
Length of HT lines -
1.59 Km
Length of LT lines
No of Distribution transformers
63 KVA –1 no/..
15KVA- 8 no/..
Voltage at tail end
340 volts
420 volts
% line losses
16.82 %
5.30%

60. Tail end Voltage in LT System

62. NEW VERSION OF HVDS SYSTEM Bangaru Palem SS-IV 100 KVA
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.

63. Bangaru Palem SS-IV 100 KVA with reinforcement of conductor and installing rated capacitors.
Particulars LT
HVDS
Length of HT lines -
2.5 Km
Length of LT lines
3.3 Km
0.8 Km
No of Distribution transformers
100 KVA –1 no/..
15KVA- 9 no/..
Voltage at tail end
320 volts
430 volts
% line losses
16.30 %
3.77%

64. Bangaru Palem SS-IV 100 KVA.
Comparison between HVDS with existing conductor and HVDS with reinforcement of conductor and installing rated capacitors
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%

65. Tail end Voltage in LT System
Tail end Voltage in HVD System
Tail end Voltage in LT System

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

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