Electric network anywhere in the world wide availability of good quality power supplied by electricity board energizing electric grid to power System operation & control providing reliability and safety, efficiently improves life span of plant and system by reducing energy crisis. Energy crisis results Green House Gas(GHG) emission in the environment and increases Global Warming Potential(GWP).
Power quality auditors adopting benchmarking methods and technology resources according to IEEE – 519, 1992 and IEC-61000, and EN-50160 standards for power grid system protection purpose. To improve the electric gird reliability and safety aspects with the help of Instant power quality auditing summary full report data representation facilities for risk identification and mitigation.
Poor power quality behavior causes energy losses and breakdowns of plant and system in any of the industry. Power quality audit techniques are integrated with new models and tools for research activity management and data analysis instruments like electronics hardware and Software’s tools interface with computer system by adopting latest technologies to improving power system efficiency. Power quality systems monitoring and research activity throughout the development of advanced applications like new data visualization and waveform, FFT Spectrum analysis results incipient fault identification.
Major concern in power system is harmonics mitigation for representation of integral and fundamental currents or voltages multiple frequencies. Electric grid system concern about reliability and safety aspects throughout Harmonic mitigation in Transmission and Distribution to avoid energy losses by adding Harmonic Filters. High harmonic distortions lead to overloading of switchgears, overheating of transformers, nuisance tripping of circuit breakers, stress on electromechanically equipment’s, electronic card failure, voltage distortions and DG Hunting and ATS (Automatic Transfer Switch) malfunctioning etc.,
“Power Quality” is the study of the steady state of 50 Hz frequency, sinusoidal voltage and current waveforms. Power quality is of major concern to all types of industries. Harmonics: A cause of high speed switching used for automation is that in addition to the voltage and current waveforms appearing as sinusoidal waveforms in their fundamental frequency of 50Hz, they also appear in multiples of their fundamental frequency.
Power quality audit measures the various features of power are Active Power, Apparent Power, Average Demand, Transient’s events, Kilo watt hour, Phase angle, Telephonic interference factor, Crest factor, voltage, currents, K-factor, Neutral Current, Inrush currents, Power Factor, Under voltage, Over voltage, Short-Term Voltage Fluctuations, Voltage Sags, Voltage Swells, Imbalance, Flickers, Imbalanced Voltage, Unbalanced load, RMS Value, Harmonics, Frequency, interruptions etc.
In modern electronic equipment Inrush Currents at switching loads, such as personal computers, monitors, television sets and office equipment use a type of power supply that converts mains electricity to the low voltage direct current without a low frequency transformer. This type of supply is known as a switched mode power supply (SMPS) and works by rectifying mains current directly and storing the direct voltage on a large capacitor which charges to the peak of the supply voltage. Conversion circuits draw current from the capacitor and generate the required low voltage, usually via a high frequency transformer to provide galvanic isolation. SMPS is very cheap, but it causes problems in installations because it produces large harmonic currents and draws very large inrush currents to initially charge the storage capacitor.
Nuisance Tripping in many commercial and industrial installations suffer from persistent so-called ‘nuisance tripping’ of circuit breakers. The term refers to the apparently random and inexplicable nature of these events which, although there is no apparent fault, can cause significant disruption and financial loss. Of course, there is always a reason for the nuisance tripping of a breaker and there are two common causes. The first possible cause is the inrush currents that occur when some switching loads, particularly personal computers and other electronic devices, are switched on. The second possible cause is that the true RMS current flowing in the circuit has been under-measured – in other words, the true current really is too high and the trips are valid.
Circuit breakers nuisance tripping is a common problem in many Power system installations. This Application Note explains the need to use true RMS measurement instruments when troubleshooting and analyzing the performance of a power quality. True RMS meters, which take the complete distorted waveform into account, should be used to identify the causes.
Harmonic currents distort the current waveform and increase the load current required to deliver energy to the load. Many measurement instruments, even quite modern ones, use an averaging measurement technique that does not measure harmonic currents correctly. The readings may be as much as 40% too low, and circuit breakers and cable sizes may be underrated as a result causes nuisance tripping of circuit breakers is often caused by the load current being distorted by the presence of harmonic currents drawn by non-linear loads.
Non-linear loads in industries and extensive proliferation of energy-efficient power electronic based equipment’s lead power quality problems in electrical power system and becoming a great concern for utilities and customers draws harmonics current and reactive power components from the utility. In three-phase systems, they could also induce imbalance and draw excessive neutral current.
Apart from power electronic controllers, any electromagnetic circuit operating in non-linear region generates harmonic currents. Sources of Harmonics are Converters containing the non-linear loads generate harmonics in supply line currents. Choppers, Phase back AC voltage regulators, Thyristor converters, Diode bridge rectifiers with capacitor filter, are some examples of such power electronic controllers.
In today’s world, such power electronic controllers are extensively used in the areas of industrial AC & DC drive systems. Electromagnetic circuits can operate in non-linear region due to over loading or due to bad design/ manufacturing. Motors, power transformers are examples of such sources of harmonic currents. A transformer supplying asymmetrical load, with DC component, which result in saturation of its magnetic core, greatly increases the level of all harmonic components. Thus, Solid-state power controllers used in Modern industries require automation of their operation enabling them to produce quality products and for mass production.
The conventional systems are being replaced by modern Power Electronic systems, bringing a variety of advantages to the users. Classic examples are DC & AC Drives, VFD (Variable Frequency Drive), VSD (Variable Speed Drives) UPS, soft starters, etc. The Thyristor Converter technology is most rampantly used technology for this automation. The use of this technology is however contaminating the power supply as the ideal sinusoidal current and voltage waveforms are getting distorted. This in turn is affecting the performance of the equipment in the electrical network.
Harmonic currents are generated with the use of above devices results since the device either has impedance which varies during each half cycle of applied emf or it generates a back emf of non-sinusoidal shape. It is necessary to determine the distortion of the voltage wave shape due to flow of harmonic current throughout the network and the effect of such distortion causes triplen harmonics.
Triplen Harmonics are defined as the odd multiples of fundamental frequency, such as 3rd, 9th, 15th etc. are called Triplen Harmonics. When triplen harmonics are present in a 3-Phase system, they add together in the neutral conductor. 3rd Harmonics result in high 180Hz current flowing through the Motor neutral terminal. The core steel of the Motor has stray losses that will increase dramatically with Harmonic Distortion. These effects cause the Motors to operate at significantly higher temperatures.
5th and 11th Harmonics – The 5th and 11th harmonics are also of particular concern to industry today. Although the 5th harmonic is much more prevalent, both have a negative sequence. This means that when distorted voltage containing the 5th or 11th harmonic is applied to a 3-phase motor, it will attempt to drive the motor in reverse, creating a negative torque. In order to compensate for this negative torque, the motor must draw additional fundamental current. This, in turn, can cause overheating and/or the tripping of over-current protection devices. 6-Pulse adjustable speed drives are a major source of the 5th, 7th and 11th harmonics. 12-Pulse drives are significantly more expensive and are a source of the 11th and 13th harmonics, but through their design are able to eliminate the 5th and 7th.
Today, in this highly competitive world, operating costs have become a major concern for all industries. Power is a huge component of the Operating cost for any industry. Poor power quality and inefficient usage of power can increase leakages and lead to significantly inflated energy Bills and affects the reliable operation of machines, systems, automation, equipment’s, processes reduced productivity.
With the good aim to introduce power quality audit new techniques, to achieve better performance and to be able to control and to transfer more power over the power system and to reduce the power consumption of the loads, also a new topic was introduced for new techniques consist of non-linear components that are used to control the load current. The current became distorted, i.e. deviates from the ideal sinusoidal waveform, and can be described by harmonic and interharmonics currents.
Many of these new devices are more sensitive to the voltage quality than conventional linear loads for providing reliable power with a steady voltage and frequency has been recognized since the inception of the electric utility industry. The increased sensitivity in various processes (industrial, services and even residential) to PQ problems turns the availability of electric power with quality a crucial factor for competitiveness in every activity sector.
The most critical areas are the continuous process industry and the information technology services. When a disturbance occurs, huge financial losses may happen, with the consequent loss of productivity and competitiveness. Moreover, poor power quality, high harmonic distortions and high Neutral current conditions lead to increased failure resulting in unintended and expensive downtimes of Electro Mechanical Equipment’s results Predictive Maintenance activities like MTBF and MTBR in the Plant and System.
The active filter is the newest technology of all types of filters, and due to the highly electronic nature is considered the least reliable and most difficult to trouble shoot. Product improvements are still being implemented due to the infancy of this product. To minimize the impact of facility harmonic distortion on the utility power system and on neighboring facilities, IEEE-std-519 was developed.
This attracted power electronics and power system engineers to develop dynamic and adjustable solutions to the power quality problems by various custom power devices like active power filter (APF), hybrid filter, unified power quality compensator (UPQC) etc and many passive and active harmonic filters have been investigated to satisfy the power quality problems.
Passive filtering has been preferred for harmonic compensation in the electrical system due to low cost, simplicity, reliability, and control less operation. Active power filters (APF) have many advantages over the passive filters. Depending on the APF type, controllable reactive power compensation for power factor correction, voltage regulation, load balancing, voltage-flicker reduction, harmonic damping, harmonic isolation and / or their combinations could be provided.
They can suppress not only the supply current harmonics, but also the reactive currents and without causing harmful resonances with the power distribution systems like passive filters. In the beginning, the APFs were used for suppression of harmonics generated by thyristor-based converters and inverters used in HVDC transmission system.
However, the design could not become technologically and economically practicable until the last two decades when fast and cost-effective semiconductor devices such as Insulated Gate Bipolar Transistors (IGBTs) and Metal Oxide Semiconductor Field Effect Transistors (MOSFETs), and high performance and cost effective digital Signal Processors (DSPs) became available.
Modern active filters Control Strategies are superior in filtering performance since they inject voltage / current harmonics produced by nonlinear loads of same magnitude but of opposite sign, so they cancel each other, and sinusoidal waveforms are obtained at the power line.
Surge and Transient Voltage Surge are temporary rise in voltage and current on an electrical circuit. Their voltage ranges are greater than 2000 volt and current ranges are greater than 100 ampere. Typical rise time is in the 1 to 10 microsecond range. Transient or surge is the most common power problems and its compacts are caused significant damages such as electrical or electronic equipments failure, frequent downtime, lost data, lost time and business downtime, etc.
All these issues create serious problems for power quality. The effective compensation of harmonics, reactive power, neutral current and supply current balancing with other power quality improvement are essential for the utilities as well as the end users by implementing reliable products.
Power Quality Audit deploys in-depth analysis and reporting the conditions of the power thought out identification of deficiencies and risk present in the power system overcome the major power quality issues. Furthermore, power quality problems useful for analysis of signals affecting the magnitude, waveform, frequency and symmetry of the voltage and currents signals, bandwidth etc. Several of these characteristics may be modified simultaneously by any one type of disturbances classified according to their IEEE-519, IEC-61000, and EN-50160 Standards.
Power quality audit reports recommended reliable product specification for several applications to get benefits of Harmonics Mitigations and many other products recommended depends upon the type of risk identification in Power System for achieving the maximum energy savings due to the production of wasteful harmonics and energy losses in plant system reliability of equipment’s and for Machinery Safety Purpose.
In general, harmonics present on a distribution system can have the following deleterious effects:
Decreased kVA capacity
Neutral overloading Unacceptable neutral-to-ground voltages distorted voltage and current waveforms
Failed capacitor banks and De-aeration of Capacitor Bank
Increase in Hysteresis losses and I2R Losses.
Interference on phone and communications systems
Unreliable operation of electronic equipment
Erroneous register of electric meters
Wasted energy / higher electric bills – kW & kWh Wasted capacity
Inefficient distribution of power will increase maintenance Practices.
Wasted generation capacity (kVA)
Increased maximum demand (kVA) charges
Wasted Power system capacity (kVA)
Reduced Power system efficiency (kW)
Possible poor power factor
Wasted investment and operating capital
Circuit breakers and Relays NUISANCE tripping.
Overheating of transformers & rotating equipment.
Increased Hysteresis losses
The systematic study of the incoming raw power, the measurement of the extent of distortion in the incoming raw power, the identification of the causes of this distortion and the various recommendations for seeking to solve these power quality problems, a facility will realize the following cost-saving benefits.
Savings in energy bills due to Overheating reduced losses.
Reduced Interference with Telecommunication circuits
No maloperation of Protection and Metering Systems
Improved efficiency and life span of electrical equipment.
Reduction in nuisance tripping & breakdowns
Accurate measurement by installed meters
Improved Plant and System reliability and safety.
Increased Life Span of Electro-Mechanical Equipment’s.
Reduced kVA demand.
Accurate measurement by installed meters
Improved system efficiency and Better capacity utilization of network
Better production rate and quality due to reduced interruptions
Enhanced life of electrical network and components
Improved system power factor for No overloading of power factor correction capacitors.
As per IEEE 519-1992 standards Harmonics in L&MV system allowable voltage THD is 5%. The profile shows that the average voltage distortion is below 5% (<5%). Therefore, the voltage distortion is in limit.
As per ANSI/IEEE C57.110-1986 standards Harmonics in L&MV system allowable current distortion is 15%. Therefore, the current distortion is in limit.
Power quality audits logging various necessary parameters for recommendations the severity fault identifications throughout the power system to clients and demonstrating onsite by implementation of Harmonic filter to achieve energy savings.
Power quality audit can also be monitor in the plant system for the benefit of client’s work place engineers by observing power quality data’s recording instrument’s availability at the time of data logging.
Report preparation and recommendations depending upon the client requirement as per mentioned below standards.
Institute of Electrical and Electronic Engineers(IEEE).
International Electro Technical Commission(IEC)
Bureau of Indian Standards. (BIS)
American National Standards Institute(ANSI)
Canadian Standards Association(CSA)
Japanese Industrial Standards(JIS).
Detailed plant Layout.
Single line Diagram.
Power and Energy.
Sag and Swell.
Unbalance and imbalance.
Total RMS distortion Factor
Phase angle Measurement
Crest Factor and Surge Factor
Impedance of the load Circuit.
Series resistance of the load circuit.
Series reactance of the load circuit.
Parallel resistance of the load circuit.
Parallel reactance of the load circuit.
Harmonic Filter Design.
Estimation and Coasting.
Funding and Implementation.