Published On: Mar 06, 2015
Power Quality is one of the major issues in electricity distribution segment today. It is an issue, which is becoming increasingly important for electricity consumers at all levels of usage. PQ related issues are most discerning because of the extensive and increasing use of sensitive power electronic equipment. Power quality issues originate from utility as well as from end-customer; hence the solutions/mitigation should be adopted by both of them. Poor quality of power supply causes disruption to an end-customer’s process and equipment, leading to a loss of revenues. Conversely, a customer’s usage also affects the supply quality back into the electricity network. It is therefore important that to improve power quality; a systematic approach is adopted engaging all stakeholders.
Power Quality intervention techniques can be conventional, contemporary or hybrid (combination of first two) depending upon each stakeholders and their requirement. Some of the conventional intervention techniques include System design, Network Planning, Voltage Regulator, On-line Voltage stabilizer, K-rated transformer, Zig-Zag Transformer, Isolation transformer, PFC panel, Passive Filter etc. These techniques can be implemented at optimum cost, if properly planned during designing phase to ensure good PQ environment. While there are conventional techniques/methods in place for PQ mitigation, this blog attempts to focus on some of the key innovative technologies for PQ intervention and their benefits accrued to the concerned stakeholders.
Considering today’s scenario with usage of high power electronic devices, there is an urgent and immediate need of innovative/latest techniques to mitigate PQ.
Before we move ahead to understand the innovative PQ techniques, let us briefly see some of the key causes and effects due to poor PQ:
PQ Phenomenon | Typical Causes | Effects |
---|---|---|
Harmonics | Electromagnetic interference from appliances, machines, radio and TV Broadcasts | Continuous distortion of normal voltage, Random data errors |
Voltage Sag/Swells | Major equipment start up or shut down, Short circuits (faults), Undersized electrical wiring, Temporary voltage rise or drop | Memory loss, Data errors, Dim or bright lights, Shrinking display screens, Equipment shutdown |
Interruptions | Switching operator attempting to isolate electrical problem and maintain power to power distribution area | Equipment trips off, Lost Programming, Disk drive crashes |
Flicker | Arc furnace, Voltage fluctuations on utility transmission and distribution systems | Visual irritation, Introduction of many harmonic components in the supply power and their associated equipment |
Transients | Lightning, Turning major equipment on or off, Utility Switching. | Tripping, Processing Errors, Data loss, Burned circuit boards |
Table 1. PQ Phenomenon, its causes and effects
From the above table, it is quite evident that there is a need of addressing PQ issues using innovative techniques. Leading among innovative techniques is Flexible AC Transmission Systems (FACTS) based devices that are used to shield sensitive load against the most significant PQ problems. FACTS devices are also used by utilities to improve power transmission capability, voltage control, enhances voltage stability and improves power system stability.
Modern day solutions like Dynamic Voltage Restorer (DVR), Distributed Static Compensator (D-Statcom), Unified Power Quality Compensator (UPQC), Automatic Power Factor Controller Panel (APFC) panel, Active Filter and others are very effective in addressing PQ issues, those are vexed and dynamic. Although these solutions come with benefits, however there costs are also higher than contemporary solutions.
Key devices explained below are used by utilities and high-end industries both to mitigate power quality issues:
Above devices are mostly used by high-end industries and distribution utilities. While many end users may be unable to perceive or realize the impact of PQ on their systems and energy bills, however with deployment of innovative solutions through precise application engineering in PQ affected areas can help them realize these benefits.
For residential/small commercial premises, proper engineering and design at initial level will help reduce PQ issues significantly. Proper selection of equipment with right design and specification holds high relevance in PQ mitigation. Further, usage of Transient Voltage Surge Suppressors (TVSS) is the most basic, simplest and least expensive power protection device that protect against high transient level voltages. More details can be read from our previous blog: Common Mass perception around PQ. Affordable common PQ initiatives.
While we discussed above technological advancement for PQ intervention, it can also be managed by policies drafted by National Standard Bodies like Bureau of Indian Standards (BIS). It is the central body that establishes technical committee on Power Quality and develops standards on power quality and its related issues. Much of the PQ issues can be avoided/reduced, if planned properly at the design and construction stage based on the principle set of regulations under ‘National Electrical Code of India’. Electrical systems play an important role and it is of utmost priority to give attention to the Power Quality as well as electrical safety during any electrical installation. The onus lies upon utilities and industries to adopt the code in their business model for right implementation of PQ techniques.
Original Equipment Manufacturer (OEM) initiatives (like Computer Business Equipment Manufacturers Association (CBEMA) curve adopted by computer manufacturers themselves) are some of the forward ways of mitigating PQ issues. CBEMA Curve is one of the most frequently employed power acceptability curve. The CBEMA curve was originally derived to describe the tolerance of mainframe computer business equipment to the magnitude and duration of voltage variations on the power system. In addition, it is also designed to point out ways in which system reliability could be provided for electronic equipment. Eventually, it became a standard design target for sensitive equipment to be applied on the power system and a common format for reporting power quality variation data. The CBEMA curve was adapted from IEEE Standard 446 (Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications – Orange Book), which is typically used in the analysis of power quality monitoring results.
CASE STUDY: Mitigation of Harmonic and Reduction in Operating Cost for a Cement Plant
Problem Statement: The facility is one of the major cement plant of India with the state of the art technology. It has two manufacturing lines and each line has 8 cooler fans, 4 ESP transformers and raw mill classifiers. The facility receives power from state electricity board at 33kV level. In order to maintain quality of the product and optimize energy cost, all the cooler fans in the system were installed with variable frequency drive. But post installation of VFD’s the facility started experiencing problems like,
Solutions and benefits: A power quality study was carried out to investigate the cause of above problems and it was noticed that both the current and voltage harmonics level were up to 32.5% and 7.4% respectively. On the suggestion of power consultant, the facility management decided to install active harmonic filters at all places where VFD’s are installed. Post installation study was carried out to ascertain the benefits gained by installation of PQ mitigation equipment. The team noted that along with mitigation of harmonics, the energy losses have also been reduced which are associated with harmonics. This has resulted in a huge difference in utility’s electric bills. The table below shows top numbers:
Parameter |
Value |
---|---|
Investment |
2.2 Cr. (INR) |
Annual Monetary Saving |
0.6 Cr. (INR) |
Payback |
3.6 years |
Conclusion: The facility gained following additional benefits in addition to annual savings:
(For detailed case study, refer bullet #5 in References section below)
The deterioration of power quality levels; proliferation of more sensitive loads, and the increase in processes based on power electronics have in recent years been attracting growing concerns on power quality issues. These disturbances and outages have substantial economic losses.
The availability of different power electronic and mechanical based mitigation devices as well as customized solutions provide a range of equipment that satisfies user requirements both technically and economically. Hence, a holistic approach in selection of PQ devices with right design and specifications is a key to effective PQ mitigation.
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