Electronic meters allow innovative electricity tariffs

Brihan Mumbai Electric Supply & Transport (BEST) Undertaking is one of the leading distribution utilities in India. It distributes power to a large portion of Mumbai City, the commercial capital of India, which has the highest per capita electricity consumption in the country. For some time now BEST has been known for its keen desire to provide better consumer services by using new technologies; the utility was among the first to introduce the use of electronic energy meters for tariff applications.

The problem

In 1990 it became apparent that BEST’s system efficiency was deteriorating. Customers were paying only for kWh consumption (and were therefore not bothered about the power factor of their loads) while the utility was paying its electricity supplier for both kWh and kVA demand. A year-long investigation was conducted into active/reactive consumption as well as power factor pattern. This data was recorded and observed with the help of electronic energy meters installed at the sample locations.

A careful study of the inherent power factor of the system indicated that predominantly industrial and air conditioning loads, supported by voluminous fluorescent and other discharge lighting loads, gave an inherent power factor between 0.6 and 0.7. With a peak demand of about 600 MW, the reactive load to be neutralised was almost equal to the active load.

Capacitors were installed at distribution substations, and this improved the power factor to over 0.93. However, it helped only to reduce the billing demand, thereby covering the cost of capacitors. This solution could not augment the system capacity throughout the LT network.

Conventional billing

In the case of conventional billing on a kWh basis, the concept of power factor was not applicable. The consumer used any type of load, operating at any power factor, but paid only for the active energy used. Here the control on power factor had to be organised by the electricity supplier – if residential and small industrial consumers had installed capacitors, a good many complications would have resulted.

Although it was considered to be ideal at the time, the two-part tariff (billing on kWh units and maximum demand in kVA) had one serious limitation. The consumers who installed power factor improving capacitors had to ensure that the capacitor was on whenever the load was in use. Since the maximum demand was recorded over a period of half an hour, any lapse or defect in the capacitors lasting over half an hour resulted in maximum demand crossover for the entire month. And once the maximum demand was already crossed, consumers would neglect restoration of the capacitor bank for the rest of the month.

Thus the purpose of implementing a two-part tariff was defeated, and the result was a poor power factor and a financial penalty for many consumers. On the other hand, those conscientious consumers who managed to set the capacitor system immediately did not benefit in any way.

The solution

BEST knew that the only solution was to call upon consumers to install the capacitors and maintain them throughout the month. And they knew that to succeed in this, they had to introduce incentives for improved power factor control.

Continuous load survey and power factor monitoring was made possible by installing electronic meters, and this allowed BEST to arrive at a tariff structure which benefited both consumers and electricity suppliers. The accurate SEMS electronic energy meters provided information on half-hourly load profiles for five parameters, including kW, kVAr (lag), kVAr (lead), kVA and power factor. With the help of these meters, BEST could easily establish the average consumption pattern (kWh as well as kVARh) for any sample size covering various types of consumer.

Power factor based tariff the ultimate solution

With this information to hand, BEST amended the tariff schedule in 1991. Tariffs were rescheduled into C1 category for kWh based units and C2 category for power factor based units. C2 category became a two-part tariff, with one part based on kWh units and an additional rkVAh charge and power factor surcharge. An rkVAh charge was levied for lagging rkVAh units.

The main barrier to introducing the new tariff structure was the electro-mechanical meters, which had up to then been used for registering active kWh units. BEST considered using separate meters for kWh and kVArh (an electro-mechanical meter can measure only one parameter).

Residuary Category However, a brainstorming session within the company led to the conclusion that this would require more space at consumer premises, additional maintenance and additional reading time. In addition, these meters had some inherent disadvantages such as inaccuracy, inconsistent field performance, the need for proper maintenance, the larger size – and above all they were unable to perform such functions as data storage and communication. The conventional meters were therefore gradually replaced by new electronic energy meters which measure all energy parameters, including power factor, and are capable of communication applications like remote meter reading and load management.

The findings

Power Factor Improvement Table A large number of consumers opted for the change in tariff to the module which consisted of kVArh billing. At the same time consumption under this tariff was growing compared to the earlier kWh billing, which continued unchanged. It was also seen that nearly 60% of consumers maintained the power factor above the 0.97 level, and of this figure 30% were able to keep it at 1.0 during the month. The system power factor also improved dramatically.

Many consumers were wary when the electronic energy meters were installed, as they knew them to be highly successful in detecting evidence of tampering. One of the unplanned-for benefits of moving to the new tariff system, however, was a noticeable reduction in theft of energy. Consumers realised that energy at an alternate and cheaper tariff was already legally available – all they had to do was invest a small amount of money in capacitors.

Visit the Secure Meters booth at Elecrama-99, Mumbai. You’ll find them in Hall 1, booth A2 F-16.