Urgent need to Increase Efficiency for Transformer

Transformers convert electrical power from one circuit to another in the same frequency. In this process, they can raise or lower the voltage in one of the circuits with corresponding decrease or increase in current. Transformers achieve the above thorough mutual induction between the two circuits that are linked by a common magnetic flux in its core.

The invention of transformer

  Transformers range in size from radio frequency transformers less than a few grams in weight to industrial transformers interconnecting the power grid, weighing hundreds of tons. A wide range of transformer designs is encountered in electronic and electric power applications. Since their invention in 1886, transformers have become the back bone of AC transmission, distribution, and utilization of electrical energy.

Importance of transformers

  Transformers play an indispensable role in the power distribution network. After transmission lines, transformers are the second large loss making equipment in electricity networks. Failure of a transformer causes sudden outage in the power supply, leading to loss in industrial production. High efficiency transformers create economic benefits in terms of lower operating costs besides reduced greenhouse gas emissions, improved reliability and potentially longer service life. In view of these important benefits, many countries including India have taken policy initiatives – to establish mandatory and voluntary programmers to conserve energy and help domestic markets be competitive by adopting high efficiency transformers. Moreover, it is relatively easy to replace the inefficient transformers with the efficient ones – when compared with laborious / time consuming efforts needed for change in lines or cables.

High efficiency vs life cycle cost

  Life cycle cost of a transformer is calculated by adding the purchase cost (investment cost including bank interest), the cost of energy losses, cost of failure / repairs, cost of maintenance and de-commissioning cost after providing for resale price (residual value) of the transformer at the time of its replacement. The cost of energy losses (iron, copper and stray) can be reduced by improving the efficiency of the transformer. This in turn reduces the life cycle cost.

  Also, due to use of better grade materials and optimum design, sudden failures are reduced along with lower cost of maintenance, leading to increased life expectancy. These benefits add up and balance against the inevitable increase in purchase cost as additional copper in the windings and better materials in the core will be used in the manufacture of high efficiency transformers.

Urgent need to increase efficiency

The demand for distribution transformers has been increasing at a rapid pace due to rising population and migration of people from rural areas to urban cities. This has further led to increased demand for reliable power supply systems within the country.

Reduction in transmission and distribution losses and providing reliable uninterrupted power supply have gained top most attention in our government’s thinking. The emission of greenhouse gas is reduced with decrease in energy loss. Also, every unit of energy saved is equivalent to about two units of energy generated. It is well known that the electrical energy tariffs are subsidized in certain segments in our country. The distribution transformers are special and critical as they are the final equipment – through which each unit of electricity consumed by the end user has to be delivered. Hence, it is essential that every unit of electricity reaches the consumer in a reliable and efficient way for ensuring a viable distribution.

Bureau of Energy Efficiency (BEE), Government of India, has brought out ‘star rating plan,’ through which the distribution transformers (for the first time) are classified into ‘1star’ to ‘5star’ classifications. The transformers under ‘5Star’ grade are the most efficient. Total loss figures are stipulated both at 50% loading and at 100% loading for each star classification.

Electricity networks

Power is generated at generating stations at voltage level ranging from 10 to 30kV. This power is converted to typically 230kV* to 400kV* by step-up transformers for transmission to the consumers’ distribution networks, which are located at urban areas far away. At the distribution substations, the transformers step down the power to more usable levels of 110kV* for industries. For shorter distances, power flows at 110kV* level and at urban substations, voltage is again reduced to 11kV. Further along the streets/roads distribution is carried out at 11kV and distribution transformers are used to step down from 11kV to user voltage levels of 415/240V at the street level, very close to the consumers. Thus on an average, electrical power is transformed approximately 4 times from the generating station down to the consumer. The voltage levels indicated in this paragraph are typical values. The exact levels are determined by the quantum of power to be transmitted and the distance between the two sub-stations (based on economics)

 Technical losses are present in all electrical equipment’s as all equipment’s offer some resistance to the flow of current causing, I2R losses. Integrated over a period of time, ‘t’, this constitutes energy loss, namely, I2Rt. Technical losses are categorized and discussed in paragraphs below.
Line loss comprises energy loss in conductors and cables (due to selection of lower size), unbalanced loading (more than designed value of current flowing in one of the phase conductors), neutral conductor loading due to pre-dominant single phase loads, loosening of strands in ACSR conductors etc.

Losses at joints and terminations including mid-span joints caused due to improper choice of materials and fasteners.
Losses in transformers (apply more to distribution transformers) such as:

  • Loose connection at the bushings
  • Bend in jumpers at the connectors where the strands are not tightly held
  • High no-load losses due to the type of core used and/or improperly tightened cores in the case of repaired units
  • High copper losses due to sub-optimal loading.

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