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FAQ Harmonics

Please find below the frequently asked questions with answers. For more information and to download our entire product Datasheets, visit our Collateral Library.


Power Quality Audit
Questions
1. Audit features
1.1 How to know about the Harmonic Audit?
2. Clarifications
2.1 How to get clarifications on Harmonic Analysis and Services?
2.2 What is harmonics and what are its effects in the electrical system and network?
2.3 What are the sources of harmonics?
2.4 What are the effects of Harmonics?
2.5 What are the disadvantageous of Harmonic?
2.6 What is the difference between Surges/Spikes and Harmonic?
2.7 What is the solution to Harmonics?
2.8 Why harmonic audit is required to suggest harmonic filter system?
2.9 What is a Harmonic Filter System?
2.10 What are the benefits of harmonic analysis and use of filters?
2.11 What are the indications of harmonic presence in the electrical network?
2.12 How a tuned filter system works? Will it improve the Power Factor also or whether the user has to install separate capacitor banks for Power Factor improvement?
2.13 What is the scope of Conzerv for Harmonic study and harmonic solutions?
2.14 What are Tuned Filters (Absorption Filters)?
2.15 What is an active filter and passive filter?
2.16 What is the difference between tuned and detuned filters?
3. Limits for Harmonics

 

Answers
1. Audit features
1.1 How to know about the Harmonic Audit?
  1.Visit our Website www.conzerv.com for details.
  2.Call nearest contact point of Conzerv for assistance
  3..Call our dealers across the country, UAE, Thailand, Malaysia, Australia and Singapore. Visit web site for details.
  4.Call 1800 425 0555 (Toll Free Phone No. – all over India) for clarifications.
  5.Write to contact@conzerv.com for details
2. Clarifications
2.1 How to get clarifications on Harmonic Analysis and Services?
 
  1. Call nearest contact point of Conzerv for assistance
  2. Call our dealers across India, UAE, Thailand, Malaysia, Indonesia, Australia and Singapore. Visit web site for details.
  3. Call 1800 425 0555 (Toll Free Phone No. – all over India) for clarifications.
  4. Write to contact@conzerv.com for details.
2.2 What is harmonic and what are its effects in the electrical system and network?
 
  1. The semiconductor devices that alters the 50Hz sine wave, distorts both the current and voltage waveforms. The distorted wave form frequency will be higher than the fundamental frequency and is integer multipliable
  2. Harmonic is defined as a component of periodic wave or signal whose frequency is integral multiple of the fundamental frequency. This can be either current harmonics or voltage harmonics whose combined action distorts mains wave from. If the harmonics are not limited to the permissible limit, it can lead to numerous problems to the electrical network.
A typical 5th Harmonic Distortion Waveform
2.3. What are the Sources of Harmonics?
  The use of non-linear loads like Thyristor / IGBT based drives / VFDs, induction heating furnaces, arc furnaces, battery charging rectifiers, UPS, SMPS, PCs, electronic chokes in lights etc. are the main sources of harmonics in the electrical network. . For example, devices like SMPS, Single Phase UPS systems, lighting loads generates 3rd harmonics, whereas devices like a six pulse Thyristor Drive, VFD or a Rectifier generates 5th and 7th harmonics predominantly. Same way a 12-pulse device will generate predominantly 11th and 13th harmonics.
2.4 What are the effects of Harmonics?
  The major ill-effects of harmonics are as follows:-
  • Sudden increase in demand, reduced capacity utilisation and increased energy losses
  • Increase in neutral current and overheating of motor winding, overloading of D G sets, fire hazards due to burning of overheated neutral cables.
  • Saturation of transformers, frequent damages to switchgears, controls
  • Amplification of harmonic currents in capacitor bank and frequent failure of capacitors
  • Inaccurate and excess recording by meters
  • Interference with communication equipment
  • Nuisance tripping of circuits and interruption in production flow
2.5. What are the disadvantageous of Harmonics?
 
  1. It draws more kVAr from the electrical network leading to poor Power Factor and sudden increase in KVA demand. This leads to penalisation by Utility (E.B)
  2. Degradation of system efficiency.
  3. Increase in stray losses in Transformers.
  4. Overheating of motor windings and cables.
  5. Increase in neutral current (for 3rd harmonics)
  6. Energy losses
  7. Increased maintenance problem (Failure of capacitors & contactors).
  8. Malfunctioning of measuring instruments.
  9. Security Risks (Fire hazards).
2.6. What is the difference between Surges/Spikes and Harmonics?
  Surges and Spikes occur due to switching ON/OFF of loads, equipment or disturbance in the electrical network and are momentary. The harmonics are generated due to the usage of certain semiconductor-based devices and equipment and the harmonics persists in the network, which leads to generation of heat and energy losses and always persists.
2.7. What is the solution to Harmonics?
 
  1. Installation of harmonics filter.
  2. The Power System Group of Conzerv has long years of expertise in harmonic analysis, filter design, supply and installation. Conzerv provides comprehensive solutions to harmonics in Power System network.
2.8. Why harmonic audit is required to suggest harmonic filter system?
 
  1. In industries and commercial establishments, if non-linear loads such as D.C. Drives, Variable Frequency Drives (VFDs), Rectifiers, Battery Charges, UPS and energy saving lamps, etc. are more than 20 to 30%, generation of harmonics in the network is quite certain. A harmonic audit will help to ascertain the level of distortion and the Power Factor at the main feeder lines.
  2. This will also help us to know the PF, KW, KVA, kVAr, etc., at various points apart from the individual and harmonic distortion at these points. The measurements with a true RMS meter will be carried out at various load conditions, cycle of operation and with / without Power Factor improvement Capacitors in the network. This will also help us to find out parallel resonance if any and help the Designer to design an appropriate filter system.
2.9. What is a Harmonic Filter System?
  A harmonic filter system basically consists of capacitor banks connected in delta along with a series reactor. These will be housed in a panel with interconnecting bus bars and switchgears.
2.10 What are the benefits of harmonic analysis and use of filters?
  Installation of harmonic filter system provides the following benefits:
  • Improved system efficiency
  • Reduction in energy losses and savings in energy bill
  • Reduction in unexpected KVA demand due to harmonic currents
  • Less equipment failure and maintenance
  • Increase in available capacity
  • Increase in life of electrical equipment, measuring instruments and cables
  • Lower work interruption and downtime
  • Lower maintenance costs
  • Accurate measurement by installed meters
  • Better capacity utilization of network
  • Improved safety
  • Improved system power factor
2.11. What are the indications of harmonic presence in the electrical network?
  If you are facing any of the following problems in your electrical network, then it could be an indicator of harmonics in the network.
  • Blinking of incandescent bulbs
  • Capacitor failure
  • Circuit breaker tripping
  • Computer malfunction or lockup
  • Conductor failure
  • Failure of electronic equipments
  • Flickering of fluorescent tubes
  • Fuses blowing for no apparent reason
  • Motor failures due to overheating
  • Excessive neutral current
  • Neutral conductor and terminal failures
  • Failure of electromagnetic loads
  • Overheating of metal enclosures
  • Power interference on voice communication
  • Transformer failures etc.
2.12. How a tuned filter system works? Will it improve the Power Factor also or whether the user has to install separate capacitor banks for Power Factor improvement?
 
  1. Harmonic Filter system is a combination of capacitor banks with a series reactor
  2. It is tuned for the predominant harmonic frequency.
  3. Below the harmonics frequency, it injects kVAr to the network and improves the Power Factor. Beyond the tuned frequency, it is inductive.
  4. It provides a low impedance path for the predominant harmonic frequency thus attracting the harmonic currents to the filter and protecting other devices from the evil affects of harmonics.
  5. The series reactor takes care of the harmonic currents and thereby protecting the capacitors.
  6. Preventing resonance in the network.
  7. The Harmonic Filter System takes care of both Reactive Power Compensation and harmonics distortion and there is no need of installation of separate capacitor banks.
2.13. What is the scope of Conzerv for Harmonic study and harmonic solutions?
  Conzerv adopts the following approach for harmonic solutions:-
  • Establishing the presence of harmonics is the first step towards its cure. We conduct comprehensive harmonic audits to establish presence of harmonics in the network.
  • Identification of type, individual harmonics, amplitude of distortion and percentage of ITHD and VTHD.
  • Design of tuned filters to nullify effects of identified harmonics with respect to individual harmonics, amplitude of distortion and percentage of THD.
  • Supply, installation and commissioning of filters
  • Performance evaluation of filters and benefits after installation
2.14. What are Tuned Filters (Absorption Filters)?
 
  • A filter essentially consists of power factor correction capacitors, connected in delta, combined with a suitable series reactor, tuned for the predominant frequency.
  • The filter circuit is capacitive and injects reactive power below the harmonic frequency and provides an inductive impedance path to the harmonic currents at the tuned frequency. Thus a filter is not capacitive at harmonic frequencies.
  • There is no scope for resonance at harmonic frequencies and cannot magnify the harmonic voltage and currents. The filter will absorb the tuned harmonic frequency current and thus the same is not circulated through the network.
  • Tuned filters are recommended where the harmonic distortion is severe and a particular harmonics is predominant. In most of the cases, industries like Cement, Steel, Paper, Sugar etc. as well as other process industries where 6 pulse based DC drives, VFDs, Hydrogenation Rectifiers, Electroplating rectifiers and battery charging rectifiers are used, the total harmonic distortion as well as 5th and 7th harmonics is generally high and it is advisable to go in for tuned filters to remove the additional burden in the network.
2.15 What is an active filter and passive filter?
 
  1. An active filter system basically consist of Thyristor pack with switching and monitoring devices to monitor the level of harmonics and injects a counter frequency to nullify the affects of the harmonics generated by the network systems. However, the cost is prohibitive and is not widely used in India.
  2. Tuned filter is passive filter and it consists of combination of capacitors and reactors.
2.16 What is the difference between Tuned and De-Tuned filter?
  Difference between Tuned and De-tuned Filters
  Tuned Filter De-tuned Filter
Advantages Maximum filtering of harmonics Reduced heat losses Increased system Efficiency Faster pay back Lesser Rating of capacitor and reactor. Less expensive Power factor improvement
Disadvantages More Expensive Lower filtering of harmonics Chances of harmonic resonance Possibility of failure in harmonic intensive network Higher pay back period
3. Limits for Harmonics
 
  1. Harmonic Distortion limit as per IEEE 519: 1992
  2. "IEEE recommended practices and requirements for harmonic control in electrical power system: represents a standard level of acceptable harmonic distortion in a power system.
a) Current Distortion Limits (12 V to 69KV) – User's Responsibility
Isc/I1 < I1 I1<= h<17 I7<=h<23 23<=h<35 35<=h THD
<20* * 4.0 2.0 1.5 0.6 0.3 5.0
20<50 7.0 3.5 2.5 1.0 0.5 8.0
50<100 10.0 4.5 4.0 1.5 0.7 12.0
100<1000 12.0 5.5 5.0 2.0 1.0 15.0
>1000 15.0 7.0 6.0 2.5 1.4 20.0
Note: *All power generation equipment are limited those values regardless their Isc11.
1) Represents odd harmonics as % of 11 (fundamental at PCC) 2) Even harmonics are limited to 25% of odd harmonic's limits.
Isc - Short Circuit current at the point of common coupling (PCC) corresponding to System MVA level 11 - Fundamental full load current in Amps. h - Harmonic number In - nth harmonic current (like 15 is 5th harmonic current etc., 11<=h <17 - Represents all harmonic currents between 11th to 16th.
THD - Total harmonic distortions
b). Voltage distortion Limit – Utility's Responsibility
Bus voltage at PCC Individual voltage distortion THD Remark
<=69 KV 69>=161 KV >161 KV
3.0 1.5 1.0 5 2.5 1.5 HV System may have up to 2% THD as in HVDC terminal that attenuates while tapped for a user
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