Power Quality Analysis and Harmonic study

Power Quality Analysis and Harmonics Study

SERVICE PROVIDERS BY SACHU TECHNOLOGIES MIG 519,RK Nilayam,Phase III,KPHB,Kukatpally,Hyderabad-85 Cell:09493013535,Email:info@sachu.in, Web site: www.sachu.in

Sachu Technologies profile ď ľ

Sachu Technologies conducts power quality analysis, Harmonics monitoring & measurement services for complete facility power systems or for individual loads using state of the art circuit analysis and simulation software in PAN India basis in order to prevent electrical devices from any faults & damages.

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Sachu Technologies also offers Thermography Survey, Electrical Safety Audit, Energy Audit, Vibration Monitoring Analysis,Earth Audit,Lighting Survey and Thermovision Scanning for Transmission line Towers, Solar PV and Insulation resistance measurement all over India including Hyderabad, Bangalore,Noida, Chennai, Coimbatore, Kolkata, Visakhapatnam, Nagpur, Delhi, Pune, Mumbai, Ahmedabad, Guwahati, Indore, Surat, Baroda, Kanpur, Kochi, Bhubaneswar, Goa, Lucknow, Vijayawada, Nellore and other cities as a part of Preventive and predictive maintenance programs

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WHAT IS POWER QUALITY ANALYSIS

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Power quality analysis is exactly analyzing the quality of power supply.Power quality analysis is rewarding for electric utilities since it enables continuous monitoring, early excursion detection, root cause analysis, and timely corrective actions improving overall grid reliability.

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Power quality is also of interest for major energy consumers to minimize amount of power quality events and avoid expensive equipment failures.

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Power quality is a multi-dimensional and complex measure, especially as it applies to AC power circuits. PQ encompasses voltage, current, power factor and frequency spectrum magnitudes. It can involve electromagnetic field measures. Sudden or gradual changes in any of these measures have a big impact on power quality. PQ is really a comparison of the actual to the ideal or desired values of each of the characteristics of electrical power. Unlike current or power, which are measured in amperes and watts there is no scoring or measurement unit for PQ. Consequently, terms associated with power quality refer to the gaps or anomalies between the actual and desired values. Desired attributes of PQ are therefore negative terms; no dips, no spikes, no sags, no surges, no outages etc. www.sachu.in

Why Measure Power Quality?

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Power Quality (PQ) refers to the reliable delivery of electrical energy in a form that enables electrical equipment to operate properly. When dips and swells, spikes, surges, momentary outages, sags or other disturbances occur – computers and other electrically powered equipment may malfunction, fail prematurely or shut down unexpectedly. Many facilities simply cannot accept these consequences.

Consider hospitals, banks, data communications centers, manufacturing and other facilities that rely on smooth, reliable power for operations. The consequences of an unplanned outage can cost thousands of dollars each minute or result in unsafe conditions or other serious problems unsafe conditions or other serious problems.

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Reference standards used for Power Quality Study

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Power Quality Audit Services in India

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Harmonic Study Services in India power-quality-Analysis Instruments

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Power Quality related curves and shapes

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Power quality Analysers shall be used for work in the field

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Point of common coupling (PCC)

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The orthodox electric power distribution systems used to be generally radial and direction of flow of power was often from grid towards consumer. Sometimes, the transmission of power generated from newly set small power stations by using transmission network is not feasible due to the transmission losses, service cost on transmission lines and other related issues. That is why, in many cases, small power stations are connected directly to the local distribution network. These small power stations inject active and reactive power to the existing network, badly disturbing the flow of power hence injecting harmonics in the system at the point of common coupling (PCC).

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This harmonic injection at PCC due to a direct grid-connection of small power stations to the existing large electric power systems is identified. Also, the impact of harmonic incursion by these small generation units is analyzed using a straightforward and an effortless method. This simulation based method uses power system components simplified to basic inductive and capacitive elements and can be very helpful for a fast assessment of harmonic incursion at PCC if extended to the practical large inter-connected electric power systems. www.sachu.in

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Total Harmonic Distortion (THD)

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Total harmonic distortion (THD) is the cumulative degree of distortion within an electrical current compared to the ideal.

Most household electrical systems draw linear loads. On a linear current sine curve, the peaks and troughs are smooth, even, and sinusoidal. Some distortion can take effect in residential circuits but not enough to cause significant efficiency issues.

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Total harmonic distortion is inversely proportional to power factor. If a given load has a higher power factor, its THD factor will be lower and the system will be more efficient. Fortunately, most power utilities adhere to standards that require supply voltage to have a relatively low THD factor; the power entering your facility is relatively linear

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What is Total Harmonic Distortion ď ľ

Total harmonic distortion is a complex and often confusing concept to grasp.

However, when broken down into the basic definitions of harmonics and distortion, it becomes much easier to understand.

Now imagine that this load is going to take on one of two basic types: linear or nonlinear. The type of load is going to affect the power quality of the system. This is due to the current draw of each type of load. Linear loads draw current that is sinusoidal in nature so they generally do not distort the waveform (Figure 2). Most household appliances are categorized as linear loads. Non-linear loads, however, can draw current that is not perfectly sinusoidal . Since the current waveform deviates from a sine wave, voltage waveform distortions are created. www.sachu.in

Importance of Mitigating THD

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While there is no national standard dictating THD limits on systems, there are recommended values for acceptable harmonic distortion. IEEE Std 519,RECOMMENDED PRACTICES AND REQUIREMENTS FOR HARMONIC CONTROL IN ELECTRICAL POWER SYSTEMS provides suggested harmonic values for power systems.

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The limits on voltage harmonics are thus set at 5% for THD and 3% for any single harmonic. It is important to note that the suggestions and values given in this standard are purely voluntary. However, keeping low THD values on a system will further ensure proper operation of equipment and a longer equipment life span.

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Reactive Power 

Reactive loads such as inductors and capacitors dissipate zero power, yet the fact that they drop voltage and draw current gives the deceptive impression that they actually do dissipate power. This “phantom power” is called reactive power, and it is measured in a unit called Volt-Amps-Reactive (VAR), rather than watts. The mathematical symbol for reactive power is (unfortunately) the capital letter Q.

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The actual amount of power being used, or dissipated, in a circuit is called true power, and it is measured in watts (symbolized by the capital letter P, as always).

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The combination of reactive power and true power is called apparent power, and it is the product of a circuit’s voltage and current, without reference to phase angle. Apparent power is measured in the unit of Volt-Amps (VA) and is symbolized by the capital letter S. www.sachu.in

Need of Reactive Power Compensation

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Electrical utility may have to take the power factors of these industrial customers into account paying a penalty if their power factor drops below a prescribed value because it costs the utility companies more to supply industrial customers since larger conductors, larger transformers, larger switchgear, etc, is required to handle the larger currents.

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Generally, for a load with a power factor of less than 0.95 more reactive power is required. For a load with a power factor value higher than 0.95 is considered good as the power is being consumed more effectively, and a load with a power factor of 1.0 or unity is considered perfect and does not use any reactive power.

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Active or real power is a result of a circuit containing resistive components only, while reactive power results from a circuit containing either capacitive and inductive components. Almost all AC circuits will contain a combination of these R, L and C components.

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To avoid reactive power charges, is to install power factor correction capacitors

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Reactive Power factor compensation solutions

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Reactive Power need and no harmonics-----Capacitor Banks

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Reactive Power need and no distortion even if Harmonics are present ------Detuned Filters

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Reactive Power need and distortion problems---Tuned Filters

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Reactive Power need and strong distortion problems such as fast

voltage fluctuations ----- SVC’s A static VAR compensator (SVC) is a set of electrical devices for providing fastacting reactive power used in Transmission line Networks Reducing reactive power to help improve the power factor and system efficiency is a good thing, one of the disadvantages of reactive power is that a sufficient quantity of it is required to control the voltage and overcome the losses. This is because if the electrical network voltage is not high enough, active power cannot be supplied. But having too much reactive power flowing around in the network can cause excess heating (I2*R losses) and undesirable voltage drops and loss of power www.sachu.in

LV Capacitors, HV Capacitors, Capacitor Banks,Detuned Filters

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Power Factor 

Active power (P) It is the useful power that is doing the actual work. It is measured in W, kW, MW & calculated as, P = S x cos φ

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Reactive power (Q) It is a consequence of an AC system. Reactive power are used to build up magnetic fields. It is measured in var, kvar, Mvar & calculated as, Q = S x sin φ or P x tan φ

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Apparent power (S) Or total power (S) is the combination of active and reactive power. Apparent power is measured in VA, kVA, MVA

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Power factor is a measurement of the efficiency in a system. PF describes the relationship between active (P) and apparent Power (S) Power Factor is ratio of the actual electrical power dissipated by an AC circuit to the product of the r.m.s. values of current and voltage. The difference between the two is caused by reactance in the circuit and represents power that does no useful work. Displacement Power Factor

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The displacement power factor is the power factor due to the phase shift between voltage and current at the fundamental line frequency. For sinusoidal (non-distorted) currents, the displacement power factor is the same as the apparent power factor.Inductive loads cause current to lag behind voltage, while capacitive loads cause current to lead voltage www.sachu.in

Power Factor (Cosθ) 

In Electrical Engineering, Power Factor is only related to AC Circuits i.e. There is no Power Factor (P.f) in DC Circuits due to zero frequency.

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Power Factor may be defined by three definitions and formals as follow

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The Cosine of angle between Current and Voltage is called Power Factor.

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P = VI Cosθ OR

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Cosθ = P / V I OR

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Cosθ = kW / kVA OR

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Cosθ = True Power/ Apparent Power

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The ratio between resistance and Impedance is Called Power Factor

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The ratio between Actual Power and Apparent Power is called power factor

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Cosθ = kW / kVA

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The ratio between resistance and Impedance is Called Power Factor

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Cosθ = R/Z

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The ratio between Actual Power and Apparent Power is called power factor

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Cosθ = kW / kVA www.sachu.in

Power factor means

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Automatic Power Factor Control Panel

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Automatic Power factor correction panel (APFC)

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Automatic Power factor correction panel is fully automatic in operation and can achieve desired power factor under fluctuating load conditions. Electrical loads such as motors can cause electrical systems to be very inductive, which results in very ‘lagging power factor’ i.e. wastage of energy.

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The simple solution to maintain the power factor in required range is to connect or disconnect the power factor correction capacitors. Manual switching is just impossible for rapidly fluctuating loads and hence an automatic control system is required which continuously monitors the power factor and make appropriate corrections to maintain it within the required range.

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Voltage sags

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A voltage sag is a short duration decrease in voltage values. Voltage sags longer than two minutes are classified as undervoltages. Common causes of voltage sags and undervoltages are short circuits (faults) on the electric power system, motor starting, customer load additions, and large load additions in the utility service area.

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Sags can cause computers and other sensitive equipment to malfunction or simply shut off. Undervoltage conditions can damage certain types of electrical equipment.

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Distortion (Harmonics)

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Distortion occurs when harmonic frequencies are added to the 60 Hertz (60Hz) voltage or current waveform, making the usually smooth wave appear jagged or distorted. Distortion can be caused by solid state devices such as rectifiers, adjustable speed controls, fluorescent lights, and even computers themselves.

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At high levels, distortion can cause computers to malfunctions and cause motors, transformers, and wires to heat up excessively. Distortion is probably the most complicated and least understood of all power disturbances.

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Interruptions

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Interruptions occur when voltage levels drop to zero.

Interruptions are classified as momentary, temporary, or long-term. Momentary interruptions occur when service is interrupted, but then is automatically restored in less than two seconds.

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Temporary interruptions occur when service is interrupted for more than two seconds, but is automatically restored in less than 2 minutes. Long-term interruptions last longer than two minutes and may require field work to restore service.

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In some cases, momentary outages may go unnoticed or cause no apparent problems. However, even momentary outages can last long enough to shut down computers and disrupt the operation of sensitive electrical equipment.

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Transients

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Transients are sudden but significant deviations from normal voltage or current levels. Transients typically last from 200 millionths of a second to half a second.

Transients are typically caused by lightning, electrostatic discharges, load switching or faulty wiring.

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Transients can erase or alter computer data, resulting in difficult-to-detect computational errors. In extreme cases, transients can destroy electronic circuitry and damage electrical equipment.

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Voltage swells

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A voltage swell is a short duration increase in voltage values. Voltage swells lasting longer than two minutes are classified as over voltages. Voltage swells and over voltages are commonly caused by large load changes and power line switching.

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If swells reach too high a peak, they can damage electrical equipment. The utility's voltage regulating equipment may not react quickly enough to prevent all swells or sags.

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Flicker

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Flicker can be defined as small amplitude changes in voltage levels occurring at frequencies less then 25 Hertz (25Hz). Flicker is caused by large, rapidly fluctuating loads such as arc furnaces and electric welders.

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Flicker is rarely harmful to electronic equipment, but is more of a nuisance because it causes annoying, noticeable changes in lighting levels.

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Harmonics Study

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What are Harmonic Studies ď ľ

Harmonic studies are performed to determine harmonic distortion levels and filtering requirements within a facility and to determine if harmonic voltages and currents are at acceptable levels. Field measurements and computer simulations are used to characterize adjustable-speed drives (ASDs) and other nonlinear loads and simulations are then performed to determine the filter specifications and effectiveness.

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The application of harmonic filters will significantly alter the frequency response of the power system. An evaluation of the harmonic voltage and current limits, (e.g., IEEE Std. 519) is completed to determine the effectiveness of the proposed filter installation. www.sachu.in

Why are Harmonic Studies important

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Avoids damage due to excessive harmonic currents in transformers and capacitor banks.

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Ensures sensitive electronic equipment will not malfunction due to excessive harmonic voltage distortion.

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Satisfies the utility's voltage distortion requirements.

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Harmonic studies should be considered whenever there are solid state drivers or electric furnaces and capacitor banks in the power system. www.sachu.in

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current

harmonic

Harmonics Analyser

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Harmonics Curves

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Combined waveform represents fundamental, resulting and harmonic wave

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Current harmonic distortion standards IEEE-519

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Harmonic Mitigation Techniques Part I

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Reliability issues and costs can be avoided if the proper harmonic mitigation solution is implemented. Choosing the best one will depend on the nature of the load and the power demand of connected equipment.

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Smoothing the flow: reactors and chokes. AC line reactors and DC link chokes help reduce the level of harmonics on the electrical system by effectively expanding out and reducing the peaks caused by a VFD’s inverter. Typically used for applications up to 500 kW of unit power or 1000 kW of total drives power, these devices have the added benefit of increasing the lifetime of each VFD. They are also the most reasonably priced and compact solution, but less effective at mitigating the harmonic distortions in total.

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Harmonic Mitigation Techniques Part II

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Cancel out the problem: 12-pulse drives. For larger drives above 400 kW, the 12-pulse arrangement is a good option to consider.

This solution uses a 30-degree phase shift transformer, with the standard output supplying one set of VFDs while the 30degree output feeds a second set of VFDs. A 6-pulse converter bridge connected to each of the outputs enables cancellation of harmonics. If even greater mitigation is required, 18- and 24pulse configurations are possible. Multi-pulse solutions are most efficient in terms of least power losses, but they are not simple and require the additional expense of a transformer.

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The low-cost option: passive filters. Combining reactors (inductors) and capacitors, a passive filter creates a resonant circuit, tuned to the frequency of the harmonic order you need to eliminate. Multiple filters can be combined to tackle multiple harmonics. They are a good, low cost option. However, they have a low power factor at partial loads and therefore risk causing resonances within the grid. www.sachu.in

Harmonic Mitigation Techniques Part III

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Measure and counteract: active filters. By measuring the harmonics produced by VFDs in real time, active filters then generate an equivalent harmonic spectrum, but in reverse phase. When added to the VFD current, the two harmonic series cancel out. Active filters are installed in parallel to VFDs, and can be a good moderately priced solution because a single filter can be used to provide mitigation for several drives that have one point of coupling. But keep in mind that these filters must also be oversized to compensate for decreased power factor.

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Swap out the source: low harmonic drive. VFDs designed with an ‘IGBT’ converter on the mains side instead of the typical diode rectifier consuming sinusoidal current without harmonic currents from the mains.

These are called low harmonic drives, and the result is completely avoiding the impact of harmonics and idle power on the electrical system.

They are in the midrange in terms of cost and are simpler than an active filter, but they require more overall space in case of lower power rating compared with active filter compensating a group of drives. www.sachu.in

Active Harmonic Filters (AHF) Types

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AHF Types

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There are three basic types of active harmonic filters based on how they are connected on the electrical system:

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1.

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It is in parallel with the AC line and is used to remove harmonic distortions caused by nonlinear loads. Therefore, this type of filter is independent on the load or electrical AC system characteristics. Subsequently, it needs only to be sized for the harmonic current drawn by the nonlinear loads.

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2.

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It is connected in series with the AC distribution network and functions to offset harmonic distortions that are present in the electrical system. This solution is technically similar to power line conditioners and should be sized for the total load rating.

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3.

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This is a combination of an active and a passive filter, and could either of the shunt or series type. In special cases, it may be a cost-effective solution. Here, the passive filter performs the basic filtering and the active filter, through its dynamic and precise method, removes the other harmonics.

Shunt filter

Series filter

Hybrid filter

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AHF (Active Harmonic Filter)

Active Harmonic Filters (AHF) are power quality devices that monitor the nonlinear load and dynamically provide controlled current injection, which cancels out the harmonic currents in the electrical system. They also correct poor displacement power factor (DPF) by compensating the system’s reactive current

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Major Covered Power Quality measurement Parameters 

TRMS AC+DC voltage up to 1,000 V

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TRMS AC+DC current: 5 mA to 10 kA depending on the sensors

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Frequency

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Power values: W, VA, var, VAD, PF, DPF, cos φ, tan φ

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Energy values: Wh, varh, VAh, VADh, BTU, toe, Joule

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Harmonics from 0 to the 50th order, phase

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Transients: up to 50

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Inrush over 4 periods

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Recording of a selection of parameters at the maximum sampling rate for several days to several weeks

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Alarms: 4,000 of 10 different types

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Peak detection

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Vectorial representation

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Benefits Of Power Quality Analysis 

Assist in preventative and predictive maintenance

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Identify source and frequency of events

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Establish precise location and timing of events

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Develop maintenance schedules

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Monitor and trend conditions

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Analyze harmonics, Flicker , Transients frequency

variation ,voltage variations (sag & swell .) 

Ensure equipment performance

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Assess sensitivity of process equipment to disturbances

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Evaluate performance against specifications www.sachu.in

Advantages of the PQA ď ľ

The PQA final report provides a complete picture of the electrical system’s correct state of operation.

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The report is a tool of primary importance for preventive maintenance, in that it lists all the measures to be taken promptly when disturbances are detected, before the negative impact on production and the running of the equipment is felt.

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Customers 

Plants &Industries

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Power &Generation

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Paper &Pulp

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Oil&Gas

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Petro chemical

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Steel &Mining

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Cement

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Cement and Fertiliser

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Software companies ( Buildings and Towers)

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Please feel free to contact Sachu Technologies

Hyderabad Cell:09493013535,Email:info@sachu.in, Web site: www.sachu.in www.sachu.in