In the context of distribution systems, total power loss is the difference between the power leaving a distribution substation and the power delivered to the customer.  Technical loss is the portion of that power loss that occurs due to resistance in the distribution network.   Technical loss varies substantially depending on the type and age of equipment in a network, but also based on strategic choices about the day to day operation of the network.

Typical energy losses in urban distribution systems are 3-4% of the energy sold. Due to the need to span larger areas, technical loss in rural areas may be twice that.1 Energy losses result in loss of revenue for the utilities as well as unnecessary atmospheric emissions.  Decreasing system losses can lead to substantial savings for the utilities by reducing the amount of energy that goes unbilled.

The majority of distribution line losses occur within the primary and secondary distribution lines and transformers.  According to an EPRI study of 42 circuits in New York state, 54% of technical losses were accounted for by transformers, 38% by primary lines, and the rest by secondary lines.  There are two types of loss.  Core losses, incurred in charging magnetic cores of the transformers, are roughly independent of load on the transformer. Resistive losses, which scale with current squared times resistance (I2R) occur due to resistance along the powerlines or wiring within the transformer.

There are a number of common methods for calculating technical loss on a system.  They include using manufacturer testing results to find typical transformer loss, use of physical models to predict line losses, and sampling methods used to extend measured losses in portions of an electrical grid to an entire system.2

Some potential methods for dealing with loss include:

  • Replacing old equipmentOne way to reduce losses is to replace older equipment.  In very high usage regions of the network, installing replacement cables with a higher power rating can greatly reduce losses.  When replacing power cables, a careful load analysis predicting likely load on the cable is necessary to determine which cable is most efficient.  Similarly, updating distribution transformer equipment can lead to significant cost savings.  Distribution transformer upgrades needed to meet new DOE standards are expected to save 350 billion KWH over the next 30 years. 3  A predictive maintenance program can be used to decide when replacing a piece of equipment might be the most feasible.

  • Right-sizing transformersTransformers operate most efficiently when they are at 80-100% of maximum capacity. 2 Underloaded transformers are inefficient due to core losses.  If some transformers are frequently underloaded, it may be possible to strategically shut down certain transformers or install smaller transformers appropriate for the load.  If transformers are frequently overloaded, it might be safer and more efficient to install larger transformers, or rebalance the load such that the transformers are under capacity.  Again a careful analysis is needed to determine when it would make sense financially to upsize, downsize, or shut off a transformer.
  • Phase balancingBecause resistive losses, proportional to I2R, are a nonlinear function of current, balancing the current delivered through each phase line can reduce the total losses in the line, even if customer usage doesn’t change.   An analysis of customer loads and circuit geometry can be used to determine the best way to rebalance the loads on each phase.  When planning new infrastructure such as electric vehicle charging stations, taking system load and the phase balance into account can help ensure that the grid continues to operate at maximum efficiency.
  • Demand management

    Customer demand can be reduced by offering rewards for reducing power consumption during peak periods and for installing more efficient appliances.  Because loss is a nonlinear function of current flow, even modest reductions in power usage at peak periods can have a substantial effect on total loss.  
  • Using capacitor banks to increase reactive load.The two components of apparent load on a system are real load, which performs work, and reactive load, which is needed to magnetize an object such as a transformer core.  By installing or adjusting capacitor banks, the percentage of reactive load on the system can be decreased, reducing losses of real power. 2
  • Voltage optimizationBy carefully re-adjusting voltage levels in a network it may be possible to reduce the current flow in parts of the network, decreasing the total resistive loss in the system.

Identifying the causes of loss on a network and determining the best method for reducing loss can be challenging, but recent advances in smart meter infrastructure and machine learning can help substantially.  The increased temporal and spatial data resolution provided by smart grid technology can be used to better understand loss, sources of loss, and the evolution of loss over time.  Once a detailed map of system losses is determined, a cost effective method for reducing losses is much easier to develop.