Published On: Oct 18, 2014

Industrial end-customers in India use nearly 44% of the electricity produced in the country (according to total electricity sales in 2011-12). While the sector already faces the crisis of bridging the gap between demand and supply, the insufficient power supply so produced has led to loss in industrial process / equipments / output, etc. In addition due to supply and demand gap, almost all the industries not only suffer due to various power quality problems but also forced into non-core areas of business (e.g steel plant going for captive power plant (CPP) too. During the last decade, power quality has become an important aspect in the electricity network and is steadily gaining importance. The increasingly high concentrations of power electronic equipment usage such as: Variable Speed Drives (VSD), Programmable Logic Controllers (PLC), Power Electronics Converters and other appliances have changed the basic nature of electric load. This sensitive equipment not only demand undistorted power supply but also are the major producers of PQ disturbances because of their non-linear current characteristics. Some of the PQ problems (such as voltage dips, transients etc.) can cause large techno-economical inconveniences to the customers while some other PQ problems (such as harmonics) can have adverse impacts on the operation and life of the network components.

In today’s competitive market, any loss of production hour for an industry due to poor PQ might cause large financial losses. In India, there has been no elaborate and systematic study that establishes the economic loss suffered by the Industries due to poor PQ. However, a study undertaken by Wartsila India, in 2009 estimated that India suffers a staggering loss of INR 1,000 Billion because of power disturbances and outages. It also estimated that industries are spending nearly INR 300 Billion annually to operate inefficient power back-ups, Gensets and Inverters. A rough estimate indicates that the country may be losing 2% of it’s GDP due to poor PQ environment.

This blog attempts to capture, (1) the impact of poor power quality on industrial equipment/customers and (2) mitigation techniques & solutions that can be applied to minimize shutdowns, avoid safety breach and equipment damage. The term industries include Pharmaceuticals, Pulp and Paper, Oil/Petroleum Refining, Textiles, Plastics & Rubber, Metallurgy, Iron & Steel and others.

MOST FREQUENT PQ DISTURBANCES AND ITS IMPACT ON INDUSTRIES

Due to widespread use of electronic equipment (for e.g. VSD, PLC, automation & data processors, inverters, computerized numerical control, etc.) in today’s industrial environment, various PQ problems like voltage dips, short / long interruptions, harmonics, transients & surges and other PQ related problems are frequently encountered. Such interruptions cause huge financial losses both – to the utility and to the end-consumer.

Some of the key physical manifestations of the PQ issues are mentioned below:

Figure 2. Industries reported problem due to poor PQ environment

It can be observed from Figure 2 that PQ variations affect different electrical equipment of industries. Industrial production is frequently affected due to power-cuts in their units; however, they don’t realize that the impact due to momentary interruptions and voltage sags is far greater. These shorter duration events are most important for industrial customers. Power disturbances ranging from milliseconds (voltage sags) to several seconds (momentary interruptions) impact industrial processes. For a continuous manufacturing process or assembly line, an unreliable power supply not only slows down production; it also leads to equipment damage and additional maintenance efforts and costs. Moreover, the staff involved can be left idle until the line is running again. Revenues are postponed (if not entirely lost), cash flow is affected and the reputation of organisation for product quality and supply reliability suffers.
Consider this as an example: A 0.1-second event (which literally is the blink of an eye) can cause a refinery to shut down or a semiconductor processing plant to stop production. Once down, it usually takes hours to come back to normal production. If such is the scenario in the developed countries like USA, imagine the significance for quality and the reliability of power supply and the financial losses that one may suffer in absence of quality and reliability. (See detailed report – Power Quality Loss Survey Report )
From worldwide customer surveys on the electric supply, it is found that voltage dip and long interruptions are PQ problems that cause large inconveniences and have significant financial impacts to various industrial process equipment. The actual financial losses are customer specific and depend mainly on customer category, type and nature of activities interrupted and the customer size. Also, financial losses are event specific and different severity could incur different losses to various customers.
Hence, it is very critical and important to take into consideration as many precautions as necessary to minimize possible PQ issues in an industrial unit. This requires advanced planning and additional solutions investment. PQ related issues can be effectively mitigated if industries make right propositions with the following suggested solutions:

• Solutions to voltage sags: Most voltage-sags can be reduced by Ferro-resonant transformers. These power conditioners are also known as constant-voltage transformers (CVTs), which are ideally suited for constant, low-power loads. On load voltage controllers or UPS are other option to tackle sag based on sensitivity and response time need
• Solutions to Harmonic Problems: A possible method is to use harmonic filters to divert harmonic current from facility equipment. Also, adding reactors or isolation transformers on the feeders connected to harmonic producing loads can be right option
• Solution to Motor Issues: This can be done through two methods – voltage unbalance and Incompatibilities between Adjustable-Speed Drives and Motors
• Solutions to Surges: Voltage surges caused by lightning or switching can be mitigated by surge-suppression devices. Surge-suppression devices protect equipment by diverting the energy to ground when the voltage exceeds the breakdown voltage of the device
• Solutions to Electromagnetic Interference Problems: This can be done through four methods – proper grounding, attenuating emissions at the source, shielding sensitive equipment, and capturing and returning emissions to the source
• Using: reactors at the input of an Adjustable Speed Drives (ASD) or connected to its DC link is the most cost effective way to minimize the effect of capacitor-switching transients on ASDs

NEED OF ADOPTION OF HIGH PQ APPROACH IN TODAY’S INDUSTRIES

While we understand typical PQ cost in an industry, still it is quite difficult to make a general conclusion on financial losses in different industries as PQ cost depends largely on the customer’s installation characteristic and the equipment / devices used. Among the industries also, there can be a wide range of variety in device usages and their sensitivity to PQ problems. A semiconductor industry may consider even a slightest PQ issue as extreme but the same issue may be perceived tolerable by some engineering industry.

Across various PQ disturbances, it is observed that end-customers are responsible for roughly 70% of the PQ problems, while the remaining 30% come from the network. For every PQ disturbance, the cost impacts per event are much higher in an industry than a services firm. Hence, it is critical that industries today consider investment in PQ solutions rather than incurring continuous losses due to poor PQ. Implementing PQ solutions at the early stage often cost less than the cost required to mitigate/resolve those when they occur. 

Decision makers (like CEOs / CFOs) in an industry should not treat PQ solutions as a routine operation (O&M) expense, but rather make an investment to safeguard against loss of productivity, competitiveness and missing opportunity. Investing in PQ leads to Total Cost Reduction (TCR) and addresses Quality in output, thus enhancing Energy Efficiency and Safety. TCR should not be misconstrued only as a money saving activity but rather considered as an approach to optimize the three elements – (T)ariff, (C)arbon emissions and (R)eliability – thereby leading us towards safe and sustainable power.

CASE STUDY 1 – REDUCTION IN BREAK DOWN AND SPECIFIC ENERGY CONSUMPTION BY REDUCING HARMONICS

Problem Statement: India’s largest steel wire rope manufacturers’ plant with more than 2000 motors was having high electrical breakdowns. After many Root Cause Analysis (RCAs), brainstorming, debates, various discussions with many experts, it was concluded that the quality of power may be the major reason for these high Electrical failures. It was reported that there was a high level of Harmonic in the Power supply which may be a major cause of these electrical breakdown.
Solution: The company installed Passive Filter to mitigate harmonics. The passive harmonic filters were designed as per load current and order of harmonics. It was installed In the section where high level of harmonics was observed. The investment was of Rs. 95 lacs for 2 nos of Passive Harmonic Filters.

Conclusion: Benefits for the company

• Reduction in specific energy consumption from 173 kWh/Ton to 153 kWh/Ton (11.6%)
• Breakdown time reduction by 98 hours / month
• Average cost saved (~Rs. 30 lacs per annum) in repair / maintenance / replacement for breakdown in motor, drives and PLC
• There were no operation issue in running & operating the Filters
• Simple Payback was 5.5 months

(See reference #6 for more details about the case study)

CASE STUDY 2 – PQ IMPROVEMENT AND ENERGY SAVING USING SOLID STATE HARMONIC FILTER

Problem Statement: This case is of a 1.5 MVA transformer used for powering the spinning action of a textile mill, which normally gets over heated. Harmonic current generated by nonlinear loads like motors driven by Variable Frequency Drives (VFD) caused power system heating and added to user’s power bills. The harmonics related losses are present in the power cables, bus bars linking the loads with source, the power transformer itself. A more serious effect of harmonic loads served by transformer is due to an increase in winding eddy current losses.

Problems faced by the mill: The transformer loaded at 70% of its rated capacity was working at unity power factor and no harmonics was present. Due to non-linear loads, harmonic current generated in the system resulted into additional losses.

Solution: To mitigate the additional loss due to harmonic current, the mill installed Active Harmonic Filter in power distribution system (i.e. feeder of spinning unit supplied by transformer). This transformer supports other linear loads in addition to the variable frequency drives (VFD) loads connected to the system. This has resulted in decreasing the losses in the power transformer. The readings were recorded and compared to see the improvement achieved by eliminating the harmonics in the feeder line.

Conclusion: The maximum savings due to cancellation of harmonics from the transformer comes from eddy current loss component of the total loss of the transformer. In this case, the current total harmonic distortion (THD) came down and the transformer was able to drive higher loads due to other feeders supporting linear loads powered by the same transformer.
(See reference #7 for more details about the case study).

CONCLUSION

PQ is an issue where we have to live with it in today’s digital society. The availability of electric power with high quality is a must for the efficient running of modern industry. To avoid huge losses related to PQ, consumers need to take action so as to prevent the problems. Among the various mitigation steps, green field oversizing of power distribution equipment, selection of less PQ sensitive equipment can play an important role. When the most robust equipment is affected, then other measures must be taken, viz installation of resorting technologies, distributed generation or an interface device in order to prevent PQ problems.

There isn’t one solution to ensure reliable power as there are numerous sources and types of power disturbances. A PQ audit or design analysis at the initial stage identifies possible threats that may impact PQ. Maintaining PQ requires a multi-tiered approach, for instance, grouping power-offending devices such as drives, motors, welders, large compressors and feeding them from separate feeder of plant power distribution system so that local mitigation techniques prevents outreach of harmonic and PQ issues to other areas of the network. Essential and sensitive equipment, such as PLCs, monitors, drives, vision systems and industrial computers must be safeguarded as well as appropriate Filters (active, passive, hybrid, etc.) and Surge Protective Devices could be used to mitigate PQ problems in an industry.

Improving facility performance to prevent PQ events can result in significant cost savings in energy, equipment, maintenance, raw materials, production output, etc. Facility managers and utility engineers must know the economic impacts of PQ events against the cost of preventing such events in their particular industries. Remember it is an investment approach and not an operational approach so be prepared to answer the questions how it reduces loss, enhances safety, and avoid opportunity loss to win your CEO or CFO’s approval.

REFERENCES

1. Mr. Manas Kundu –Poor Power Quality (PQ) Are Developing Economies at Risk?
2. Sharmistha Bhattacharyya and Sjef Cobben, Technical University of Eindhoven, Consequences of Poor Power Quality – An Overview
3. M. S. Shashikala, M. S. Balasundaram, Dr. K. L. Puttabuddhi & Dr. Bhrargav S. V. Ramachandra, Power Quality & Reliability Costs Using Demand Side Management
4. Electrical Load Consumption in Industries
5. Power Quality Solutions for Industrial Consumers
6. Reduction in Break Down and Specific Energy Consumption by Reducing Harmonics – Case Study 1
7. M.K.Pradhan, Kamlesh Keharia, Rajesh Darapu, B. Mariappan – EMCO Limited, Thane –Case Study 2
8. APQI – IIT Delhi Joint Study on Economic Impact of Poor PQ in various Industrial Sectors in India