RPS 7-8 HVDS

8/8/2019 RPS 7-8 HVDS

1/6

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

Space forInstitution Logo

Rural Power Supply and Participatory ModelsDistribution Reform, Upgrades and Management (DRUM) Training Program

HIGH VOLTAGE DISTRIBUTION SYSTEM (HVDS)

CSV ChariEmpanelled Faculty, CIRE

The existing rural distribution system in India consists of largely 3 phase 11 KV maindistribution feeders with 3 phase spur lines and 11/0.4 KV three phase distributiontransformers. The distribution system on low voltage side is done by 3 phase 4 wire, 3phase 5 wire, single phase 3 wire, and single phase 2 wire LT lines. This systeminvolves nearly 2:1 ratio of LV and HV line lengths. Large LT network results in highoccurrence of LT faults leading to frequent interruptions in supply and high incidence ofdistribution transformer failures due to LT fault currents.

This system is unsuitable to cater certain areas like desert, tribal and forests, where theload density is very low and the development of load in these areas is slow. Heavy

capital investment on 3 phase 11 KV lines with higher rating 3 phase transformers is noteconomically justified.

To improve the quality of supply, one of the recommendations is the implementation of"Single phase HT distribution system with small capacity single phase transformers.Under this system HT line is extended up to or as near the load as possible and to erectsmall capacity distribution transformers i.e. 10 KVA, 16 KVA and to extend supply to theconsumer through a short length of LT lines, preferably insulated overhead cable (AerialBunched Cables) system.

Due to use of smaller rating transformers, either 3 phase or single phase length of LT

lines is considerably reduced and power is distributed mainly through HV (11 KV) lines.Distribution system employs a suitable mix of 11 KV 3 phase and single phase or 3phase configuration for giving supply either to small rating lines. With the main linebeing 3 phase, the spur line comprises of either single phase or three phaseconfiguration for giving supply to small rating single phase or three phase distributiontransformers.

Types of HV Distribution System

I) Single phase and 1 Neutral (continuous neutral from Sub-station)II) 2 Phase 2 wire (Rigidly earthed natural system)

III) 3 Phase small rating transformers with 3 phase HV system

In case of (1), Single Phase + Neutral, the Primary Voltage of distribution transformer

shall be 6.35 KV (11/ 3 KV) between the phase and neutral on HV side. For thissystem, there is a need to run the earth wire from 33/11 KV sub-station through out.

1

8/8/2019 RPS 7-8 HVDS

2/6




In case of (II), 2 phase 2 wire is adoptable where additional earth wire is not being runfrom the sub-station. Two phases of main 11 KV 3 phase line can be tapped and 1phase distribution transformer of primary voltage rating of 11 KV be connected.

In case of single phase transformer with phase to neutral system, a continuous earth

wire is required to be drawn from 33/11 sub-station and earth wire is to be earthed at allthe poles. The neutral of the distribution transformer is also earthed on HV and LVsides. The voltage on the secondary side of the transformer is 0-250 V. The singlephase transformer can be oil filled or dry type (Resin encapsulated). The failure ofsingle phase distribution transformers is reported to be less as compared toconventional distribution transformers. Only small group of connections with AerialBunch Cables (ABC) are given and no overloading of distribution transformers occurs.

Advantages of HVDS compared to LVDS

For distribution of same quantum of power, the comparison of losses and voltages drop

are given below (per 100 as LT base).

S. No Parameters 1 Phase 6.35KV HVDS

3 Phase 4 Wire,415V LVDS

1. Current (Amps) 11.0 100

2. Losses (KW) 8.5 100

3. Voltage drop (KV) 12.7 100

The LT lines have to be laid using aerial bunched cables (ABC) of size 16 Sq. mm witha bearer wire. The length of LT lines has to be kept minimum level to reduce LT losses.It is seen that the cost of line is cheaper compared to conventional LT 3 phase line used

in LT distribution system.

The major advantage of ABC is that the fault on the LT lines are totally eliminatedthereby improving the quality of supply, besides elimination of theft of energy/conductors reduced height of supports and elimination of isolators/ associatedhardware, etc.

Advantages of High Voltage Distribution System

The HVDS offers the following direct advantages.

1) In single phase system only few numbers of consumers are connected totransformers and as a result chances of unauthorized connections and theftof energy are reduced.

2) Reduction of system faults because of low length of LV lines.3) Distribution losses are reduced by 75% or more depending on the load factor

2

8/8/2019 RPS 7-8 HVDS

3/6




4) The HVDS is cost effective to electrify remote villages and hamlets wherebringing of long 3 phase lines is costly due to low demand.

5) The single phase line can be upgraded to 2 phase or 3 phase circuits infuture, if the load growth warrants it. The power utilities can keep theinvestment low and cut down the expenses during the initial period of low

demand and electrifying remote rural areas.6) In the event of failure of transformers, it will affect only a small number ofconsumers, whereas failure of large sized distribution transformers will affectlarge number of consumers.

7) In view of less LT system and usage of ABC, which has tough insulatingcover, direct tapping by unscrupulous consumers is avoided.

8) Since losses are reduced considerably, power can be supplied to additionalloads without any further investment on infrastructure.

9) No additional generation capacity is needed for giving new loads due toreduction in power drawl.

10) Single phase motor up to 5 HP can operate efficiently on single phase lines.

The power factor of these motors is nearly unity. And thus the systemefficiency also gets improved.

Merits and Demerits in comparison to 3 phase LV systems

1. Line Losses: The losses in HVDS for distribution of same power are less than thatof LV line. Thus, the losses in LV network are negligible bringing down the totalenergy losses considerably.

2. Voltage Drop: The voltage drop for distribution of same power is less than that ofLVDS and thus ensures proper voltage profile at consumer points.

3. System Power Factor: The single phase motors have built in capacitors and PF ismore than 0.95. This high PF causes low energy losses and better voltage profile.

4. Failure of Distribution Transformers: The failure of distribution transformers due toLV line faults is eliminated as the length of LT lines is minimized and usage of AerialBunched Cables (ABC) system. The over loading is prevented as each singlephase transformer caters 2 to 3 consumers.

5. Theft of Energy: The LT lines are virtually eliminated and even short LT linesrequired will be with AB Cables. This makes direct tapping very difficult.

6. End Use Equipment: Due to better voltage profile, the efficiency of end useequipment is high, bringing in considerable benefit by way of energy conservation.

7. Reliability of Supply: The failure of transformer will affect only a small number ofconsumers served by it, thus the reliability of supply is high.

3

8/8/2019 RPS 7-8 HVDS

4/6




8. Voltage Fluctuations: The voltage drop on LV lines is negligible and voltage profileis very stable. Any voltage fluctuations occurring can be remedied by installationsof Automatic Voltage Regulators on HV line.

HVDS A CASE STUDY

Details of 4 cases where LVDS is changed to 11 KV HVDS and the results obtained aretabulated below:

Studies are conducted by erecting 11 KV CTPT set and HT Tri-vector at DTR location(100 KVA) existing prior to conversion. The results obtained and a comparison betweenthe parameters before and after conversion to HVDS is given below:

A) Existing System

S. No Particulars S/S-I S/S-II S/S-III S/S-IV1. Cropping pattern Sugarcane, Paddy

Coconut,Mango,Paddy,Sugarcane

Sugarcane(90%),Paddy,Groundnut

Sugarcane, Paddy,Coconut,Mango

2. LT Lines 3.6 KM 3.0 KM 1.59 KM 3.3 KM

3 No. of Pump 39 24 9 38

4 Connected load (CL) 179.5 HP 130 HP 72.5 HP +2.25 KW

130 HP

5. No. of days 13 14 40 19

6. Input (Units) 4290 3059 17672 6152

7. Output(Units) 3490.4 2638 14700 51498. Loss of units 799.60 421 2972 1003

9. % Line Loss 18.63% 13.76% 16.82% 16.30%

A) After conversion to HVDS (with small rating 3 pahse transformers)

Sl No Particulars S/S-I S/S-II S/S-III S/S-IV

1. 15 KV DTs 11 10 8 9

2. No. of days 15 13 - -

3. Inputs (units) 5310 3926 1299 334

4. Output (Units) 5019.2 3712.2 1229 321.4

5. Loss (Units) 290.8 213.8 69.7 12.66. %age of losses on HVDS 5.47% 5.44% 5.30 3.77

7. % of losses on earlier LTDistribution System

18.63% 13.76% 16.82% 16.30%

4

8/8/2019 RPS 7-8 HVDS

5/6




8. Net reduction of losses (in%)

13.16% 8.32% 11.52% 12.53%

C) Comparison between LV Systems with HVDS

The voltage improvement and loss reduction obtained in all 4 cases are as follows:

) S/S-I

Sl No Particulars LT System HVDS

1. HT Lines (KM) - 2.6

2. LT Lines (KM) 3.6 1.0

3. No. of DTs-3 1 x 100 KVA 11 x 15 KVA

4. Voltage at Tail End 350 V 420 V

5. % Line losses 18.63% 5.47%

2) S/S-II

Sl No. Particulars LT System HVDS

1. HT Lines (KM) - 2.04

2. LT Lines (KM) 3.6 0.96

3. No. of DTs-3 1 x 100 KVA 10 x 15 KVA


5. % Line losses 13.76% 5.44%

3) S/S-III

SlNo.

Particulars LT System HVDS

1. HT Lines (KM) - 1.59

2. LT Lines (KM) 1.59 -

3. No. of DTs- 3 1 x 63 KVA 8 x 15 KVA


5. % Line losses 16.82% 5.30%

5

8/8/2019 RPS 7-8 HVDS

6/6




4) S/S-IV

Sl No. Particulars LT System HVDS

1. HT Lines (KM) - 2.5

2. LT 3.3 0.8

3. No. of DTs- 3 1 x 100 KVA 9 x 15 KVA4. Voltage at Tail End 320 V 430 V

5. % Line losses 16.30% 3.77%

Conclusion

The HVDS is technically superior to conventional LV Distribution system with regard toquality of supply, i.e., better voltage profile, reduced losses and better reliability.However, the capital cost will be marginally higher at initial stage due to increase innumber of transformers and total capacity. If overall cost and benefit of the system is

taken into account, the HVDS may be economical/beneficial compared to LVDS.

*****

6

RPS 7-8 HVDS

Documents

Transcript of RPS 7-8 HVDS