Power Quality is a neglected subject, despite its potential to boost industry and economy.
A lot of initiatives are being taken in the power sector for improving generation, transmission and distribution segments. In the generation segment, the focus is being shifted to renewable energy sources, with particular spotlight on solar, besides nuclear. Initiatives like ´Power for All´ and Smart Cities programme are expected to change the way power is transmitted, distributed and used in the years to come. However, there is one critical aspect of power supply that is failing to catch the attention - ´Power Quality´ (PQ).
As one mentions about the need for focus on power quality, the general refrain from the power sector officials is, ´When we are yet to achieve ´Power for All´, where is the need for thinking about PQ now.´ That speaks volumes on the apathy on PQ initiatives.
A study undertaken by Wartsila India in 2009 estimated that India suffers a staggering loss of Rs 1000 billion (A billion rupees equals Rs 100 crore), because of power disturbances, primarily because of outages. It also estimated that the industries are spending close to Rs 300 billion annually to operate inefficient power back-ups, gensets and inverters (See Asia Power Quality Initiative (APQI) article following this article).
´Definition of PQ, depends on one´s frame of reference,´ says Prakash Nayak, Senior Member of the Institution of Engineering and Technology (IET). For example, a utility may define PQ as reliability and show statistics that its system is 98% or 99% reliable. This is the usual criteria established by regulatory agencies. A manufacturer of electrical equipment may define PQ as those characteristics of the power supply that enable the equipment to work properly. Power quality is ultimately a consumer driven issue, and the end-user´s point of reference takes precedence. ´Therefore, the definition of a PQ problem is any power problem manifested in voltage, current, or frequency deviations those results in failure or mal-operation of customer equipment.´ Nayak added. Power quality, like quality in other goods and services, is difficult to quantify.
There are many causes of such poor quality of power, including transients, interruption, harmonics, sag and swell and power factor. A recent survey of PQ experts indicates that 50% of all power quality problems are related to grounding, ground bonds, and neutral to ground voltages, ground loops, ground current or other ground associated issues and electrically operated or connected equipment. Determining the exact problem requires sophisticated electronic test equipment.
There are surges in the voltages in current levels of electrical power created because of transients, which happen mainly because of faults. Transient is one of the main reasons for deterioration of power quality. Interruption is another major reason. There is a lot of load tripping happening in this country. Just they switch off the 11kV transformer and all the customers connected below are subjected to load shedding or there is a fault in a line and there is a tripping of a breaker. Till that fault is detected and rectified, the consumer has to wait for power supply.
Under voltage is called sag and overvoltage is called swell, that is variation of voltage. In India, commercial and residential customer is to be connected to 230 volts, plus or minus 10%. But sometimes, we can see sag where the voltage drops to 120 volts, or could even reach 280-270 volts both ways the customer has 30-40% of voltage fluctuation. ´So such variations are very dangerous for the equipment. You might lose a complete range of consumer electronics or the appliances connected to the variation in PQ,´ says Anil Kadam, Senior Manager - Solution Architect (Utility Segment), Schneider Electric India. Continuous voltage fluctuation, another issue, is caused by continuous sag-swell fluctuations.
Harmonics means there are a lot of super imposed high frequency power AC side waves or different waves which are super imposed on the fundamental frequency (50 hertz) and 230 volts of power supply. There could be 13 harmonics in all. These are created by the lower loads which are connected to the power. Mostly power electronic devices or power electronic loads create this harmonic and because of harmonic created by one load another load suffers. For example, electronics might get spoilt because of the harmonics created by power electronics.
The power factor is the power distributing capacity of the network and a lot of other things.
Continuous Process Plants
For a continuous process plant like an integrated steel plant or a cement plant, reliability and quality of power is very important. For a steel plant, voltage dip (momentary sag of supply voltage, of millisecond duration) due to fault in the power system network is an important quality parameter of the power supply. ´This is normally not well appreciated by the utility because it generally does not lead to power failure anywhere. However, severe voltage dip may lead to complete stoppage of the continuous process and normalisation may take a few hours,´ says Amrendra Ranjan, Chief of Electrical Maintenance, Shared Services Division, Tata Steel Limited. Since the power system networks are interconnected and vast, and it passes through rough terrains and forests, it is not possible to eliminate fault in the network.
However, the numbers can be controlled by proper inspection and action. The duration of the fault can be controlled by proper designing of protection and relaying system. ´In FY16 (2015-16) there were 18 cases of voltage dip due to fault in 132 kV grid and 10 cases of voltage dip due to fault in 400 kV grid to which Tata Steel is connected. Out of these, on 13 occasions some of the plants of Tata Steel got affected,´ Ranjan said responding to a Power Today query.
The frequency which used to vary from 47 Hz to 53 Hz about 15 years ago, has improved significantly over the years and now varies between 49.5 Hz to 50.3 Hz, and is not a concern anymore for steel plant operation.
Interruption of power supply from utility is very critical and has large impact on the steel plant process. ´To ensure continuous supply of power to important loads, Tata Steel has generating units installed within its premises, which are connected with the utility. So, even during outage of the supply from utility, these generating units keep on supplying power to all important plants,´ Tata Power said. The power system is designed such that outage of single equipment/ line does not have any impact on the power supply. ´In 2015-16, there were two cases of outage of utility supply at 132 kV grid to which Tata Steel Jamshedpur is connected. Both the times, power supply to Tata Steel plants continued from the generating units within its area,´ Ranjan said.
Stating that there were some improvements in the past 5 years, but looking at present and future industrial growth, India is far behind in power quality and reliability, MM Rathi, Vice President (Power Plant), Shree Cement Ltd said that in comparison to advanced countries India was lagging due to:
a) Lack of common code of conduct for all discoms.
b) High local interference in transmission and distribution system (Theft of Power, Damage to Power lines, Theft of equipment)
c) No concrete philosophy for providing Quality of Power to consumer, every measure is taken at consumer-end only.
d) Implementation of ring main system to replace radial system for better system reliability.
Shree Cement highlighted two types of PQ issues it faces in their day-to-day operations. From the service provider´s point of view, the plant faces load level bus voltage unbalance followed by grid input voltage unbalance, resulting in heavy current disturbance and motor/equipment overheating, which increase the chances of failure. Though alternative processes of using controllers are available, they are a costly affair.
The cement company is also facing high harmonic levels in 6 pulse LT VFD used in the system, leading to overheating of equipment.
Responding to a query on what these continuous process plants expect from discoms in an ideal situation, Shree Cement has sought balance supply voltage (< 1 per cent unbalance) at every level with smooth sine wave supply (THDV < 3 per cent and THDC < 5 per cent as per IEEE 519). ´We are facing unbalance voltage supply problems with frequent sag and swells in voltage amplitude,´ Rathi said.
Tata Steel has sought elimination of restrictions of power consumption imposed by the distribution companies, due to shortage of power at their end. It cited opening up of the power market and establishment of power exchange for trading of power on a short term basis as the facilitators.
There are a lot of products and solutions available for power quality improvement. Generally a systems approach is undertaken by experts for addressing PQ issues. First, a thorough audit is undertaken to analyse network in the premises, types of loads and types of sources from where the power is coming.
An audit report of the likes of Schneider Electric highlights power quality issues in the insulation and because of which what kind of the potential problems that a customer is facing. Based on the findings rectification process follows.´We provide them solutions like change of configuration of network which is passive, by bringing in a lot of active equipments. For example, the simplest offer what Schneider can provide a customer is a power quality meter, which measures sag-swell, voltage fluctuation, power factor, harmonics, what other harmonics are available, that is a power quality meter,´ said Kadam of Schneider.
Schneider provides centralised monitoring systems using SCADA, control systems using power factor capacitors and APFC panels, and interruption mitigation systems using smart grid technologies for distribution companies (discoms) and Advanced Distribution Management Systems (ADMS), which create a command and control centre for discoms.
It is understood that ´Network Improvement´ bolsters power quality, reliability of supply which in turn will reduce technical losses and improve energy efficiency.
´Since power quality problems often involve interactions between the supply system and the customer facility and equipment, regulators should make sure that there are established guidelines and codes for distribution companies, attach some incentives to work with customers and help customers solve these problems,´says Nayak.
Central Electricity Authority (CEA) and Central Electricity Regulatory Commission (CERC), have laid down some regulations for discoms for improving PQ levels.
Besides many State Electricity Regulatory Commissions (SERC) also have come up with guidelines. Most of these guidelines cover issues like reliability, voltage, current and harmonics. However, there are no penalties prescribed.
´Although there are certain standards of performance for power distribution companies mentioned by the Central and state electricity regulatory commissions, they are not properly monitored,´ said Kadam.
There are measuring indices called SAIDI and SAIFI, which stand for Standard Average Interruption Duration Index and Standard Average Interruption Frequency Index, which measure how many times did a 11kV or 33kV transformer saw interruption in a year. This has to be published by the discom on their website and should be in public domain. But very few distribution companies are doing it.
´As such we have to improve the standards of performance. Otherwise, some discoms think they have done their job when even the power is restored in about six hours after an interruption, whereas, even one or two minutes of interruption is not acceptable in countries like Singapore. Utilities are being penalised in Singapore and US for providing non-quality power to the consumers,´ Kadam added. So, implementation of the regulations is the key for success of PQ initiatives.
While PQ initiatives involve additional costs which should be reflected in power pricing, the electricity regulatory commissions are inclined to reducing the tariff. Even the discoms also need to understand the fact that this will ultimately improve their ROR (Rate of Return).
The issue of electric power quality is gaining importance, of late, because of several reasons -society´s increasing dependence on electrical supply; huge economical impact on the industrial consumers; and harm long interruptions can cause to all operations in the modern society as was witnessed at the time of black out in North India in 2012. One has to factor in the growing consciousness of customers on PQ and rising voice of demand for high quality power.
Despite PQ providing an opportunity for boosting their profits, discoms are yet to embrace it. Ultimately competition could be a great leveller. The system of multiple discoms catering to a location has already been introduced in Mumbai, where Tata and Reliance slug it out for attracting more and more customers, including based on quality of supply.
Sometimes it is not economical to eliminate power quality variations on the supply side. In such cases, the optimal solution to a problem may involve making a particular piece of customer´s sensitive equipment less sensitive to PQ variations. However, many latest gadgets manufactured are more sensitive to the variations. In response to this growing concern for power quality, discoms have floated programmes that address customers´ concerns. But they are still in a reactive mode than being proactive. That attitude must change, then only we can expect some PQ improvement in the coming years.
Even all the stakeholders have to be educated about the need for improving PQ. This will create a healthy and reliable power grid, enhancing productivity and GDP growth.
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