To achieve a smart electrical grid, both HT and LT sectors need to be fitted with smart meters. Since LT represents the bottom of a pyramid with a wide base (large number of small consumers), such an implementation poses a big challenge, particularly due to the higher cost of smart technologies. On the other hand, the high amount of Aggregate Technical and Commercial (ATC) losses in the LT power sector offers an elegant scope for exploitation of the smart technologies in the LT.
High technical losses are primarily due to overloaded systems with high currents flowing to feed poor power factor loads. In this article, we highlight the importance of defining Power Factor (PF) and apparent energy correctly for effective reduction in the technical losses. Next, we demonstrate the use of smart LT apparent energy (kVAh) meters supported by a fair apparent energy based tariff.
This elegant single parameter based tariff incorporates an embedded power factor based discount mechanism to offer a Win-Win solution, where consumers can avail discounts in their electricity bills while the utilities minimise their line losses through reduction in harmonic and reactive currents. Its successful pilot implementation at Anand, Gujarat is covered in this article.
Introduction
The century old electrical network share is under challenge. While the energy generation landscape is changing with a drive for small and non-carbon based generation technologies, the demand side, too, is witnessing a change due to a push for a greatly improved efficiency, with the networks enabling the consumers to interact with them. These ‘smart’ networks are becoming more and more consumer centric with fundamental changes in the design and control of networks. And when billions of dollars are being spent on building the elements of our ‘smart’ electric power grids, framing and adhering to standards and protocols to achieve inter-operability of the smart grid devices and systems, gain significance.
India has been facing numerous problems due to insufficient generation and transmission capacities and overloaded distribution systems. One of the topmost issues is that of high Aggregate Technical and Commercial (ATC) losses and the resulting high tariffs. To counter this problem, the Ministry of Power (MOP), Govt. of India, in 2001, had initiated large scale deployment of static (electronic) meters under its ‘Accelerated Power Development Program’. Even as the execution of the 100% metering program is in progress, these meters are facing a threat of obsolescence. Unless, the MOP and its technical wing – Central Electricity Authority formulates a framework in India for its own smart grid, a lot of investment that it is envisaging for strengthening the power sector would face a threat of becoming prematurely obsolete.
Implementation of the Smart grid in the LT sector is challenging due to its large number of small consumers. The additional cost of smart Advanced Metering Infrastructure (AMI) is a big burden for the Indian electric utilities.
In the developed countries, smart metering aims to shave off the peaks and flatten the load curve through Demand Side Management (DSM) techniques. But, in a developing country like India, the only manner in which AMI can be effectively adopted is by justifying the Return on additional Investment (ROI). Only if the smart project is made to addressthe ATC loss problem (in addition to DSM), can the cost of the smart technologies be offset against the savings in losses, making the project viable. We propose the use of smart LT apparent energy meters for effective reduction in ATC losses. In this article, we focus on the reduction of technical component of the ATC losses through the implementation of a fair apparent energy based tariff.
Smart solution for technical losses
While the utilities have been able to handle the poor Power Factor (PF) problem in the HT sector by incorporating suitable penalty mechanism in the tariff, the problem has been essentially unaddressed in the LT sector. As a consequence, the line loss in the LT feeders is observed to be considerably higher than that in the HT feeders. Due to the exponential relationship between the line current and losses, it is wise to take appropriate measures to reduce the current flowing in the overloaded LT lines.
War of currents – II
We have indicated how at the Centre for Apparent Energy Research, CAER, we are fighting the War of Currents – II (WC-II), more than a century after the WC- I was fought between Edison, a brute-force experimenter who promoted DC, and Tesla, a mathematician who advocated AC distribution. The AC generation at Niagara Falls in 1893, jointly by Tesla and Westinghouse, marked the defeat of DC. The key to the success of the AC system, then, was the ease with which AC voltage levels could be changed with simple and efficient transformers having no moving parts.
Today, while we are fighting the WC-II, the load scenario has changed considerably. In the LV distribution system, most of the home or office appliances incorporate electronic devices that operate on DC.
Hence, the need for AC to DC converters – internal (desktops, LCD monitors, LED Lamps) or external (mobile phones, cameras) that not only make the appliances complex and expensive but also inefficient (these black boxes are observed to invariably operate at poor PF and inject high levels of harmonic currents). By resorting to DC power distribution such as the ‘380 V DC wiring for Building wide Power Distribution’, a single more efficient AC to DC converter at the building entry point can result in atleast 15% savings in energy.
However, DC distribution is a major change – and for a developing country like India it is advisable not to opt for this change keeping in view the high level of investments already put in for AC distribution. But, unless the utilities adopt stronger measures to become more efficient, we predict that the change-over to DC distribution is inevitable.
We, at CAER, support Tesla’s AC system and believe that Apparent Energy tariffs can help the utilities resist the pressure to change over to a DC system.
The WC-II that we have initiated through the launch of Apparent Energy Tariffs and Metering in opposition to the well established Active Energy Tariffs is significant. While ‘simplicity’ was the theme Tesla chose to win WC-I, we have chosen ‘power quality’ to be the theme for winning the WC–II, and our focus is on harmonic currents and reactive currents.
Street lighting pilot
Empowered with recommendations from the Ministry of Power, and two separate directives from the Gujarat Electricity Regulatory Commission (GERC), CAER has been successful in demonstrating technical loss reduction to the tune of an amazing 92.7% in a pilot street lighting project involving three such feeders of Anand Municipality. The total power consumption per lamp (street lamp + line loss) was lowered down from the initial values of 58W and 108VA to the final values of 27W and 27.7VA respectively. This corresponds to current reduction of 73% and line loss reduction by 92.7% (see TABLE I).
In other words, on project completion, the current and line loss levels were down to 27% and an amazingly low – 7.3%, respectively, from their original levels. A saving of 8 Watts (in line loss) amounts to a saving of Rs 11 per street lamp per month. If we consider a typical street light feeder with 80 lamps, this represents a savings of Rs 880 per month. Considering the cost of a smart energy meter to be Rs 1,600, the return on investment is less than two months.
More importantly, this pilot has given a basis for CAER’s estimate of national level savings potential of Rs 15 million per hour. Through the implementation of an apparent energy tariff with 25% discount, CAER was able to demonstrate its effectiveness in reducing, both the harmonic current and reactive current levels. TABLE II. shows the street lighting (SL) tariff rates as offered by the GERC.
Correct definition of apparent energy
There is a lot of clutter associated with the measurement of ‘apparent energy’ that means different things to different people. For some, it simply replaces measurement of active energy and power factor, while for others, it may be a replacement for active and reactive energy measurements.
Even the official documents published by the Ministry of Power, Govt. of India, and the Regulators had erroneous or misleading interpretations of the terms ‘Power Factor’ and ‘apparent power’. To get rid of the misconceptions, we have shown in, why apparent energy is a scalar and cannot be computed as a vector sum.
To eliminate scope for wrong usage, we have focused on the correct definitions of Apparent Power and Energy and justify why they cannot be defined in any other way. We chose to refer to the definitions of the IEEE Standard 1459 – 2010 released by the IEEE Power and Energy Society (PES) as a basis, and have thereby verified that our implementation of apparent power S, in Volt-Ampere (VA), as the product of RMS voltage, V, and RMS current, I, in our energy meters is correct. That is,
S = VI (1)
For a constant line power loss, and a constant load rms voltage V, the apparent power is the maximum active power that can be transmitted through the line. In other words, minimizing S means maximising the amount of useful energy transmitted while keeping the thermal stress of the line constant. It is surprising therefore, that such a key parameter remained dormant and unexploited for over a hundred years!
What is even more astonishing is that the parameter, which the electric utilities are currently measuring as apparent power is actually nothing more than the ‘Fundamental Apparent Power’, S1, and considerably different from the original correct definition of apparent power, S. Probably the reason for the confusion is because both, S and S1, share the same units – namely Volt-Amperes (VA). However, the basic difference crops up from the fact that, consistent with the IEEE 1459-2010 definitions, the fundamental apparent power, S1, is measured using fundamental active and reactive components, according to
It is interesting to note is that, though the old Ferraris meters have been replaced by sophisticated static ones, all the current meters still measure S1, wherein the harmonic currents go undetected.
Correct definition of power factor
The confusion in the definition of apparent energy does not end there. It has also been responsible for the confusion in the definition of another important parameter, namely power factor. Let us begin with the correct definition. The power factor PF is the ratio of active power over apparent power. It is dimensionless.
PF can be interpreted as the ratio between the energy actually transmitted to the load over the maximum energy that could have been transmitted keeping the line losses the same. It is clear, therefore, that maximum utilization of the line occurs when P = S, and hence PF can also be considered to be a utilization factor indicator.
On the other hand, the fundamental power factor, denoted as PF1, also dimensionless, is the ratio between fundamental active power P1 and fundamental apparent power S1.
Since S1 can differ considerably from S in the presence of harmonics, it is clear that PF1 can differ considerably from PF. Hence, it is clear that the measurements of kVAh and PF as taken by the electric utilities are incorrect in the scenario of non-sinusoidal currents.
Solving the neighbour’s problem
To curb harmonics, we have shown the need for utilities to choose PF over PF1 and measurement of S instead of S1 or P. In spite of this deterrent, if harmonics continue to get injected, then there is still a major hurdle that needs to be overcome.
Assume that your neighbour is injecting large amounts of harmonics into the electrical grid. There is no doubt that he will be paying a much higher bill when billed on the basis of S instead of P. But what happens to the harmonic currents so injected. Ideally we expect that the utility would have active devices installed on the lines that quench these harmonics. This would prevent the harmonic currents from flowing through the grid, sneaking through and damaging sensitive electrical appliances at your home. In reality, utilities are observed not to take this responsibility.
In such a situation, the harmonic currents would enter your home and get registered by your S meter. Would this problem negate the use of S meters? No. The purpose of using S meters to encourage consumers to use resistive loads is still being met. In our case, if we use Smart Switched Mode Power Supplies (SSMPS), we can continue to operate at unity power factor by lowering down the S consumption to match the P consumption, thereby restoring your own bills back to normal levels.
In other words, the SSMPS has the capability of offering a resistive load to the distorted voltage waveform offered by the utility and distortedon account of such neighbours.
Moreover, we also expect the above example to be a rare occurrence. When an electrical revolution gets triggered with S as an enabler, the market forces would stabilize to a scenario where loads injecting high harmonic currents get systematically eliminated from the system.
Smart apparent energy meters
By taking commonly used electrical appliances, we have shown inTABLE III, that S is generally significantly greater than S1.
To be successful in effectively demonstrating the role of apparent energy tariffs in curbing loads that inject harmonics in addition to reactive loads, it is therefore essential that the energy meters record and display S instead of S1. Keeping this in mind, CAER developed low cost meters that record true apparent power, S, (and not S1) way back in the year 1996. However, it was not before fourteen years had passed that CAER could succeed in putting in place a pilot project with meters that record S instead of S1.
In 2011, CAER redesigned the apparent energy meters and based on them a new energy metering chip – the EM773 from NXP Semiconductors that has an inbuilt metrology engine to compute S, as per the new IEEE 1459.Further, to offer a smart solution, the EM773 chip was connected to a two way RF transceiver – OL2381 (also from NXP), that gave it a wireless M-Bus communication capability.
Figure 2 shows the user interface offered by such a smart apparent energy meter. The differences between S and S1 or PF and PF1 for a typical household appliance can be observed from the readings displayed.
Looking at the project’s success, GERC has changed the status of Street Lighting (SL) tariff from Pilot / experimental in 2010, to one that can be applied to any SL feeder under any of the four electric utilities throughout Gujarat state in 2011. Thus, CAER has succeeded in achieving billing on true kVAh, or S, on a non-experimental basis for the first time worldwide!
At the time of publication of this article, we have noticed a number of street light feeders in Anand and Vadodara districts that are billed on the basis of true kVAh (S). Big industrial estates, municipalities and even small village panchayats have opted to get billed on the basis of Safter replacing their old inefficient street lamps with smart dimmable LED lamps that operate at unity PF.
Conclusions
We have proposed a smart apparent energy metering solution that has ROI in less than a year. The benefits of using the unit (kVAh) of the correct apparent energy parameter, S, as a tariff unit include better power quality for a range of needs, while optimizing asset utilization and operating efficiency.
