In Previous Unit of the course BEE-002, you have learnt that there are inherent losses in transmission and distribution of electrical energy from the generating stations to the ultimate consumer. The energy losses occurring in the Transmission and Distribution system are known as T&D losses. Let us define the term T&D loss.
Defination of T&D Loss
T&D loss is the difference between units injected into the system and the units billed to the ultimate consumer and is generally
expressed as percentage of units injected:
T&D loss ( %) =((Energy in put − Energy bil led)/Energy input) × 100
T&D loss is generally calculated for a period of one year, which is usually the financial year. It accounts for the loss of energy in this period from the point of generation to the point of billing.
The transmission and distribution (T&D) losses in our country, which were around 15% up to 1966-67, increased gradually to 23.28% by 1989-90. Aftera brief spell of reduction in T&D losses to 21.13% (1994-95), there has been an upswing and the losses reached a level of 33.98% during 2001-02. Since then, a reducing trend has been observed as T&D losses have come down to 32.54% during 2002-03, 32.53% during 2003-04 and 31.25% during 2004-05.
You may like to study the T&D losses for the various States/UTs since 2002-03 given at Annexure I . The T&D losses of many states are much higher than the all India figure, which is itself considered as high.The Transmission and Distribution losses in the advanced countries of the world have been ranging between 6 to 11%. Even in many developing countries, T&D losses are less than the level obtaining in our country. However, the T&D losses in India are not comparable with advanced countries as the system operating conditions there are different from those obtainable in our country. As per the ‘Guidelines for Reduction of T&D Losses’ issued by CEA, taking into consideration the Indian conditions, it would be reasonable to aim for containing T&D losses within 10 to 15% in different States.
Transmission and distribution losses occur on account of technical and commercial reasons. The losses occurring on account of technical factors are known as technical losses. The losses occurring on account of non-technical factors or commercial factors are known as commercial losses.We now discuss these losses.
Technical Loss
Technical loss is inherent in electrical systems, as all electrical devices have some resistance and the flow of currents causes a power loss (I 2 R loss).Integration of this power loss over time, i.e. ∫ I 2 R.dt is the energy loss. Every element in a power system (a line or a transformer) offers resistance to power flow and, thus, consumes some energy while performing the duty expected of it. The cumulative energy consumed by all these elements is classified as “Technical Loss.” Technical losses are due to energy dissipated in the conductors and equipment used for Transmission, Transformation, Sub-transmission and Distribution of Power. These occur at many places in a distribution system in lines, mid-span joints and terminations transformers,service cables and connections, etc. (Table).
Defination of T&D Loss
T&D loss is the difference between units injected into the system and the units billed to the ultimate consumer and is generally
expressed as percentage of units injected:
T&D loss ( %) =((Energy in put − Energy bil led)/Energy input) × 100
T&D loss is generally calculated for a period of one year, which is usually the financial year. It accounts for the loss of energy in this period from the point of generation to the point of billing.
The transmission and distribution (T&D) losses in our country, which were around 15% up to 1966-67, increased gradually to 23.28% by 1989-90. Aftera brief spell of reduction in T&D losses to 21.13% (1994-95), there has been an upswing and the losses reached a level of 33.98% during 2001-02. Since then, a reducing trend has been observed as T&D losses have come down to 32.54% during 2002-03, 32.53% during 2003-04 and 31.25% during 2004-05.
You may like to study the T&D losses for the various States/UTs since 2002-03 given at Annexure I . The T&D losses of many states are much higher than the all India figure, which is itself considered as high.The Transmission and Distribution losses in the advanced countries of the world have been ranging between 6 to 11%. Even in many developing countries, T&D losses are less than the level obtaining in our country. However, the T&D losses in India are not comparable with advanced countries as the system operating conditions there are different from those obtainable in our country. As per the ‘Guidelines for Reduction of T&D Losses’ issued by CEA, taking into consideration the Indian conditions, it would be reasonable to aim for containing T&D losses within 10 to 15% in different States.
Transmission and distribution losses occur on account of technical and commercial reasons. The losses occurring on account of technical factors are known as technical losses. The losses occurring on account of non-technical factors or commercial factors are known as commercial losses.We now discuss these losses.
Technical Loss
Technical loss is inherent in electrical systems, as all electrical devices have some resistance and the flow of currents causes a power loss (I 2 R loss).Integration of this power loss over time, i.e. ∫ I 2 R.dt is the energy loss. Every element in a power system (a line or a transformer) offers resistance to power flow and, thus, consumes some energy while performing the duty expected of it. The cumulative energy consumed by all these elements is classified as “Technical Loss.” Technical losses are due to energy dissipated in the conductors and equipment used for Transmission, Transformation, Sub-transmission and Distribution of Power. These occur at many places in a distribution system in lines, mid-span joints and terminations transformers,service cables and connections, etc. (Table).
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| Losses Due to Technical Reasons |
The magnitude of energy dissipation depends largely on the pattern of loading of transmission and distribution lines, types of loads, design of lines, etc.(Fig.). It is not possible to eliminate such losses inherent in a systemaltogether. They could, however, be reduced to some extent. The technical losses can be further sub-grouped depending upon the stage of power transformation and transmission system as Transmission losses (400 kV/220 kV/132 kV/66 kV), Sub-transmission losses (33 kV/11kV) and Distribution
losses (11 kV/0.4 kV).
losses (11 kV/0.4 kV).
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| Some Factors Affecting Technical Losses |
Commercial Losses
Commercial losses are caused by pilferage, theft, defective meters, and errors in meter reading and in estimating un-metered supply of energy(Box).
Box : Reasons for commercial losses
• Non-performing and under-performing meters.
• Wrong application of multiplying factors.
• Defects in CT and PT circuitry.
• Non-reading of meters.
• Pilferage by manipulating or bypassing of meters.
• Theft by direct tapping, etc.
All these losses are due to non-metering or under-metering of actual consumption. Non-technical losses occur at many places in a distribution system (Table).
Revenue Loss Due to Loss of Opportunity to Serve
The revenue loss due to “loss of opportunity to serve” is a very relevant but
less visible aspect of revenue loss. Guarding against technical and non technical loss is one aspect, but there is an equal need to guard against loss of revenue due to lost opportunity (Box 10.2).
Box : Reasons for Loss of Opportunity to Serve
• System outage (any part or total system) leading to loss of revenue−
•due to breakdown;
•due to preventive maintenance;
•due to load shedding.
•Overloading and unbalancing
− high voltage drop in lines leading to low voltage at consumer premises and lesser consumption;
− high voltage drop at tail end of affected phases in case of unbalance,leading to lesser consumption;
− high voltage drop due to large reactive currents causing I 2 R drop in lines and resulting in lesser voltage and low consumption.
Tree touching
voltage sag at consumer premises, leading to lower consumption.
It is observed that after restoration of power the load on the system shoots up.Healthy installation and maintenance practices together with proper equipment design can help in reducing breakdowns and maintenance and assuring a better reliability of supply at proper voltages.
Commercial losses are caused by pilferage, theft, defective meters, and errors in meter reading and in estimating un-metered supply of energy(Box).
Box : Reasons for commercial losses
• Non-performing and under-performing meters.
• Wrong application of multiplying factors.
• Defects in CT and PT circuitry.
• Non-reading of meters.
• Pilferage by manipulating or bypassing of meters.
• Theft by direct tapping, etc.
All these losses are due to non-metering or under-metering of actual consumption. Non-technical losses occur at many places in a distribution system (Table).
Revenue Loss Due to Loss of Opportunity to Serve
The revenue loss due to “loss of opportunity to serve” is a very relevant but
less visible aspect of revenue loss. Guarding against technical and non technical loss is one aspect, but there is an equal need to guard against loss of revenue due to lost opportunity (Box 10.2).
Box : Reasons for Loss of Opportunity to Serve
• System outage (any part or total system) leading to loss of revenue−
•due to breakdown;
•due to preventive maintenance;
•due to load shedding.
•Overloading and unbalancing
− high voltage drop in lines leading to low voltage at consumer premises and lesser consumption;
− high voltage drop at tail end of affected phases in case of unbalance,leading to lesser consumption;
− high voltage drop due to large reactive currents causing I 2 R drop in lines and resulting in lesser voltage and low consumption.
Tree touching
voltage sag at consumer premises, leading to lower consumption.
It is observed that after restoration of power the load on the system shoots up.Healthy installation and maintenance practices together with proper equipment design can help in reducing breakdowns and maintenance and assuring a better reliability of supply at proper voltages.
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