Losses in Distribution & Transmission Lines

 Transmission and distribution (T&D) loss are amounts that are not paid for by users.

T&D Losses= (Energy Input to feeder (Kwh)-Billed Energy to Consumer (Kwh)) / Energy Input kwh x100.

  Distribution Sector considered as the weakest link in the entire power sector. Transmission losses are approximately 17% while distribution losses are approximately 50%. There are two types of transmission and distribution losses:

1. Technical Losses
2. Non-Technical Losses (Commercial Losses)

Technical Losses

  The technical losses are due to energy dissipated in the conductors, equipment used for transmission line, transformer, sub- transmission line and distribution line and magnetic losses in transformers. Technical losses are normally 22.5%, and directly depend on the network characteristics and the mode of operation. The major amount of losses in a power system is in primary and secondary distribution lines. While transmission and sub-transmission lines account for only about 30% of the total losses. Therefore, the primary and secondary distribution systems must be properly planned to ensure within limits. The unexpected load increase was reflected in the increase of technical losses above the normal level Losses are inherent to the distribution of electricity and cannot be eliminated.

There are two types of technical losses.

a. Permanent / Fixed Technical Losses

  Fixed losses do not vary according to current. These losses take the form of heat and noise and occur as long as a transformer is energized. Between 1/4 and 1/3 of technical losses on distribution networks are fixed losses. Fixed losses on a network can be influenced in the ways set out below:

• Corona Losses
• Leakage Current Losses
• Dielectric Losses
• Open-circuit Losses
• Losses caused by continuous load of measuring elements
• Losses caused by continuous load of control elements

(b) Variable Technical losses

  Variable losses vary with the amount of electricity distributed and are, more precisely, proportional to the square of the current. Consequently, a 1% increase in current leads to an increase in losses of more than 1%. Between 2/3 and 3/4 of technical (or physical) losses on distribution networks are variable losses. By increasing the cross sectional area of lines and cables for a given load, losses will fall. This leads to a direct trade-off between cost of losses and cost of capital expenditure. It has been suggested that optimal average utilization rate on a distribution network that considers the cost of losses in its design could be as low as 30 per cent.

• joule losses in lines in each voltage level
• impedance losses
• Losses caused by contact resistance.

Main Reasons for Technical Losses

Lengthy Distribution lines

• In practical, 11 KV and 415 volt lines in rural areas are extended over long distances to feed loads scattered over large areas. Thus, the primary and secondary distributions lines in rural areas are largely radial laid usually extend over long distances. This results in high line resistance and therefore, high I2R losses in the line.
• Haphazard growths of sub-transmission and distribution system into new areas.
• Large scale rural electrification through long 11kV and LT lines.

Inadequate Size of Conductors of Distribution lines

  The size of the conductors should be selected on the basis of KVA x KM capacity of standard conductor for a required voltage regulation but rural loads are usually scattered and generally fed by radial feeders. The conductor size of these feeders should be adequate.

Installation of Distribution Transformers away from Load Centers

  Distribution transformers are not located at load center on the secondary distribution system. In most of case, distribution transformers are not located centrally with respect to consumers. Consequently, the farthest consumers obtain an extremity low voltage even though a good voltage levels maintained at the transformers secondary. This again leads to higher line losses. The reason for the line losses increasing as a result of decreased voltage at the consumers end. Therefore, in order to reduce the voltage drop in the line to the farthest consumers, the distribution transformer should be located at the load centre to keep voltage drop within permissible limits.

Low Power Factor of Primary and Secondary Distribution System

  In most LT distribution circuits normally the power factor ranges from 0.65 to 0.75. A low power factor contributes towards high distribution losses. For a given load, if the power factor is low, the current drawn in high and losses proportional to square of the current will be more. Thus, line losses owing to the poor PF can be reduced by improving the power factor. This can be done by application of shunt capacitors. Shunt capacitors can be connected either in secondary side (11 KV side) of the 33/11 KV power transformers or at various point of distribution line. The optimum rating of capacitor banks for a distribution system is 2/3rd of the average KVAR requirement of that distribution system. The vantage point is at 2/3rd the length of the main distributor from the transformer. A more appropriate manner of improving this PF of the distribution system and thereby, reduce the line losses is to connect capacitors across the terminals of the consumers having inductive loads. By connecting the capacitors across individual loads, the line loss is reduced from 4 to 9% depending upon the extent of PF improvement.

Bad Workmanship

  Bad Workmanship contributes significant role towards increasing distribution losses. Joints are a source of power loss. Therefore, the number of joints should be kept to a minimum. Proper joining techniques should be used to ensure firm connections. Connections to the transformer bushing-stem, drop out fuse, isolator, and LT switch etc should be periodically inspected and proper pressure maintained to avoid sparking and heating of contacts. Replacement of deteriorated wires and services should also be made timely to avoid any cause of leaking and loss of power.

Feeder Phase Current and Load Balancing

  One of the easiest loss savings of the distribution system is balancing current along three-phase circuits. Feeder phase balancing also tends to balance voltage drop among phases giving three-phase customers less voltage unbalance. Amperage magnitude at the substation doesn’t guarantee load is balanced throughout the feeder length. Feeder phase unbalance may vary during the day and with different seasons. Feeders are usually considered “balanced” when phase current magnitudes are within 10. Similarly, balancing load among distribution feeders will also lower losses assuming similar conductor resistance. This may require installing additional switches between feeders to allow for appropriate load transfer.

Load Factor Effect on Losses

  Power consumption of customer varies throughout the day and over seasons. Residential customers generally draw their highest power demand in the evening hours. Same commercial customer load generally peaks in the early afternoon. Because current level (hence, load) is the primary driver in distribution power losses, keeping power consumption more level throughout the day will lower peak power loss and overall energy losses. Load variation is called load factor and it varies from 0 to 1.

  Load Factor=Average load in a specified time period / peak load during that time period.

  For example, for 30days month (720 hours) peak load of the feeder is 10 MW. If the feeder supplied a total energy of 5,000 MWH, the load factor for that month is (5,000 MWh)/ (10MW x 720) =0.69.

  Lower power and energy losses are reduced by raising the load factor, which, evens out feeder demand variation throughout the feeder. The load factor has been increased by offering customers “time-of-use” rates. Companies use pricing power to influence consumers to shift electric-intensive activities during off-peak times (such as, electric water and space heating, air conditioning, irrigating, and pool filter pumping).

  With financial incentives, some electric customers are also allowing utilities to interrupt large electric loads remotely through radio frequency or power line carrier during periods of peak use. Utilities can try to design in higher load factors by running the same feeders through residential and commercial areas

Transformer Sizing and Selection

  Distribution transformers use copper conductor windings to induce a magnetic field into a grain-oriented silicon steel core. Therefore, transformers have both load losses and no-load core losses. Transformer copper losses vary with load based on the resistive power loss equation (Ploss = I2R). For some utilities, economic transformer loading means loading distribution transformers to capacity or slightly above capacity for a short time in an effort to minimize capital costs and still maintain long transformer life. However, since peak generation is usually the most expensive, total cost of ownership (TCO) studies should take into account the cost of peak transformer losses. Increasing distribution transformer capacity during peak by one size will often result in lower total peak power dissipation-more so if it is over loaded. Transformer no-load excitation loss (iron loss) occurs from a changing magnetic field in the transformer core whenever it is energized. Core loss varies slightly with voltage but is essentially considered constant. Fixed iron loss depends on transformer core design and steel lamination molecular structure. Improved manufacturing of steel cores and introducing amorphous metals (such as metallic glass) have reduced core losses.

Balancing Three Phase Loads

  Balancing 3-phase loads periodically throughout a network can reduce losses significantly. It can be done relatively easily on overhead networks and consequently offers considerable scope for cost effective loss reduction, given suitable incentives.

Switching off Transformers

  One method of reducing fixed losses is to switch off transformers in periods of low demand. If two transformers of a certain size are required at a substation during peak periods, only one might be required during times of low demand so that the other transformer might be switched off in order to reduce fixed losses.

  This will produce some offsetting increase in variable losses and might affect security and quality of supply as well as the operational condition of the transformer itself. However, these trade-offs will not be explored and optimized unless the cost of losses are taken into account.

Other Reasons for Technical Losses

• Unequal load distribution among three phases in L.T system causing high neutral currents.
• Leaking and loss of power
• Over loading of lines.
• Abnormal operating conditions at which power and distribution transformers are operated
• Low voltages at consumer terminals causing higher drawl of currents by inductive loads.
• Poor quality of equipment used in agricultural pumping in rural areas, cooler air-conditioners and industrial loads in urban areas.

Non-Technical / Commercial Losses

  Non-technical losses are at 16.6%, and related to meter reading, defective meter and error in meter reading, billing of customer energy consumption, lack of administration, financial constraints, and estimating unmetered supply of energy as well as energy thefts.

Main Reasons for Non-Technical Losses

Power Theft

  Theft of power is energy delivered to customers that is not measured by the energy meter for the customer. Customer tempers the meter by mechanical jerks, placement of powerful magnets or disturbing the disc rotation with foreign matters, stopping the meters by remote control.

Metering Inaccuracies

  Losses due to metering inaccuracies are defined as the difference between the amount of energy actually delivered through the meters and the amount registered by the meters. All energy meters have some level of error which requires that standards be established. Measurement Canada, formerly Industry Canada, is responsible for regulating energy meter accuracy. Statutory requirements5 are for meters to be within an accuracy range of +2.5% and – 3.5%. Old technology meters normally started life with negligible errors, but as their mechanisms aged they slowed down resulting in under-recording. Modern electronic meters do not under-record with age in this way. Consequently, with the introduction of electronic meters, there should have been a progressive reduction in meter errors. Increasing the rate of replacement of mechanical meters should accelerate this process.

Unmetered Losses for very small Load

  Unmetered losses are situations where the energy usage is estimated instead of measured with an energy meter. This happens when the loads are very small and energy meter installation is economically impractical. Examples of this are streetlights and cable television amplifiers.

Unmetered Supply

  Unmetered supply to agricultural pumps is one of the major reasons for commercial losses. In most states, the agricultural tariff is based on the unit horsepower (HP) of the motors. Such power loads get sanctioned at the low load declarations. Once the connections are released, the consumers increase their connected loads without obtaining necessary sanction for increased loading from the utility. Further, estimation of the energy consumed in unmetered supply has a great bearing on the estimation of T&D losses on account of inherent errors in estimation. Most of the utilities deliberately overestimate the unmetered agricultural consumption to get higher subsidy from the State Government and also project reduction in losses. In other words, higher the estimates of the unmetered consumption, lesser the T&D loss figure and vice versa. Moreover, the correct estimation of unmetered consumption by the agricultural sector greatly depends upon the cropping pattern, ground water level, seasonal variation, hours of operation etc.

Error in Meter Reading

  Proper Calibrated Meter should be used to measure electrical energy. Defective Energy Meter should be replaced immediately. The reason for defective meter are burning of meters, burn out terminal box of meter due to heavy load, improper C.T ratio and reducing the recording, Improper testing and calibration of meters.

Billing Problems

• Faulty and untimely serving bill should be main part of non-technical losses.
• Normal complaint regarding billing are not receipt of bill, late receipt of bill, receiving wrong bill , wrong meter reading, wrong tariff, wrong calculations.

Reducing Technical Losses

Converting LV Line to HV Line

  Many distribution pockets of low voltage (430V) in town are surrounded by higher voltage feeders. At this lower voltage, more conductor current flows for the same power delivered, resulting in higher I2R losses. Converting old LV (430V) feeders to higher voltage the investment cost is high and often not economically justifiable but if parts of the LV (430V) primary feeders are in relatively good condition, installing multiple step-down power transformers at the periphery of the 430 volt area will reduce copper losses by injecting load current at more points (i.e., reducing overall conductor current and the distance travelled by the current to serve the load).

Large Commercial / Industrial Consumer get direct Line from Feeder

  Design the distribution network system in such a way that if it is possible than large consumer gets direct power line from feeder.

Adopting High Voltage Distribution Service (HVDS) for Agricultural Customer

  In High Voltage Direct Service (HVDS), 11KV line direct given to cluster of 2 to 3 Agricultural Customer for Agricultural Pump set and employed small distribution Transformer (15KVA) for given these 2 to 3 customer through smallest ( almost negligible) LT distribution lines. In HVDS, there is less distribution losses due to minimum length of distribution line, high quality of power supply with no voltage drop, less burn out of motor due to less voltage fluctuation and Good quality of Power, to avoid overloading of transformer.

Adopting Arial Bundle Conductor (ABC)

  Where LT Lines are not totally avoidable use Arial Bundle Conductor to minimize faults in lines to avoid direct theft from line (tampering of line).

Reduce Number of Transformer

• Reduce the number of transformation steps.
• Transformers are responsible for almost half of network losses.
• High efficiency distribution transformers can make a large impact on reduction of distribution losses.

Utilize Feeder on its Average Capacity

  By overloading of distribution feeder, distribution losses will be increased. The higher the load on a power line, the higher its variable losses. It has been suggested that the optimal average utilizations rate of distribution network cables should be as low as 30% if the cost of losses is taken into account.

Replacements of Old Conductor or Cables

  By using the higher the cross-section area of conductor / cables, the losses will be lower but the same time cost will be high. So, by forecasting the future load, an optimum balance between investment cost and network losses should be maintained.

Feeder Renovation / Improvement Program

• Reconductoring of Transmission and Distribution Line according to Load.
• Identification of the weakest areas in the distribution system and strengthening or improving them.
• Reducing the length of LT lines by relocation of distribution sub stations or installations of additional new distribution transformers.
• Installation of lower capacity distribution transformers at each consumer premises instead of cluster formation and substitution of distribution transformers with those having lower no load losses such as amorphous core transformers.
• Installation of shunt capacitors for improvement of power factor.
• Installation of single-phase transformers to feed domestic and nondomestic load in rural areas.
• Providing of small 25kVA distribution transformers with a distribution box attached to its body, having provision for installation of meters, MCCB and capacitor.
• Lying of direct insulated service line to each agriculture consumer from distribution transformers.
• Due to Feeder Renovation Program T&D loss may be reduced from 60-70% to 15-20%.
Industrial / Urban Focus Program
• Separations of rural feeders from industrial feeders
• Instantly release of New Industrial or HT connections
• Identify and replacement of slow and sluggish meters by electronics type meters.
• In industrial and agricultural consumer adopt one consumer, one transformer scheme with meter should be Introduced.
• Change of old service line by armoured cable.
• Due to Feeder Renovation Program, T&D loss may be reduced from 60-70% to 15-20%.
Strictly Follow Preventive Maintenance Program
• Required to adopt Preventive Maintenance Program of Line to reduce Losses due to Faulty / Leakage Line Parts.
• Required to tights of Joints, Wire to reduce leakage current.

Reducing Non-Technical Losses

Making mapping / Data of Distribution Line

• Mapping of complete primary and secondary distribution system with all parameters such as conductor size, line lengths etc.
• Compilation of data regarding existing loads, operating conditions, forecast of expected loads etc.
• Preparation of long-term plans for phased strengthening and improvement of the distribution systems along with transmission system.

Implementation of Energy Audits Schemes

  It should be obligatory for all big industries and utilities to carry out energy audits of their system. Further, time bound action for initiating studies for realistic assessment of the total T&D losses into technical and non-technical losses has also to be drawn by utilities for identifying high loss areas to initiate remedial measures to reduce the same.

  The realistic assessment of T&D loss of a utility greatly depends on the chosen sample size which in turn has a bearing on the level of confidence desired and the tolerance limit of variation in results. In view of this, it is very essential to fix a limit of the sample size for realistic quick estimates of losses.

Mitigating power theft by Power theft checking Drives

• Theft of electric power is a major problem faced by all electric utilities. It is necessary to make strict rule by state government regarding power theft. Indian Electricity Act has been amended to make theft of energy and its abetment as a cognizable offence with deterrent punishment of up to 3 years imprisonment. The impact of theft is not limited to loss of revenue, it also affects power quality resulting in low voltage and voltage dips.
• Required to install proper seal management at meter terminal box, at CT/PT terminal to prevent power theft. Identify power theft area and required to expedite power theft checking drives.
• Installation of medium voltage distribution (MVD) networks in theft-prone areas, with direct connection of each consumer to the low voltage terminal of the supply transformer.
• All existing unmetered services should be immediately stopped.
Replacement of Faulty/Sluggish Energy Meter
• It is necessary to replace faulty or sluggish meter by distribution agency to reduce unmetered electrical energy.
• Required to test meter periodically for testing of accuracy of meter. Replacement of old erroneous electromechanical meters with accurate electro static meter (Micro presser base) for accurate measurement of energy consumption.
• Use of meter boxes and seals them properly to ensure that the meters are properly sealed and cannot be tampered.
Bill Collection Facility
• Increase bill’s payment cells, increasing drop box facility in all area for payment collection.
• E-payment facility gives more relief to customer for bill payment and supply agency will get payment regularly and speedily from customer.
• Effectively disconnect the connection of defaulter customer who does not pay the bill rather than give them chance to pay the bill.

Reduce Debit areas of Sub-Division

• Recovery of old debts in selected cases through legal, communication and judicial actions.
• Ensuring police action when required to disconnect connection of defaulter Consumer.
Watchdog Effect on Users 
• Users must aware that the distribution Agency can monitor consumption at its convenience. This allows the company fast detection of any abnormal consumption due to tampering or by-passing of a meter and enables the company to take corrective action. 
• The result is consumer discipline. This has been shown to be extremely effective with all categories of large and medium consumers having a history of stealing electricity. They stop stealing once they become aware that the utility has the means to detect and record it.
• These measures can significantly increase the revenues of utilities with high non-technical losses.

Loss Reduction Programmed

• The increased hours of supply to agriculture and rural domestic consumers have resulted in higher loss levels.

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