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WORLDTEK QUALITY POWER SOLUTIONS PRODUCT RANGE: CAPACITORS - PowerPoint PPT Presentation

Aug 19, 2023 •184 likes •478 views

WORLDTEK QUALITY POWER SOLUTIONS PRODUCT RANGE: CAPACITORS DETUNED REACTORS THYRISTOR SWITCH MODULES AUTOMATIC POWER FACTOR CONTROLLERS PRESENTATION ON HARMONICS HARMONICS GENERATION IN LT AC NETWORKS AND SOLUTION A pure sinusoidal

  1. WORLDTEK QUALITY POWER SOLUTIONS PRODUCT RANGE: CAPACITORS DETUNED REACTORS THYRISTOR SWITCH MODULES AUTOMATIC POWER FACTOR CONTROLLERS

  2. PRESENTATION ON HARMONICS

  3. HARMONICS GENERATION IN LT AC NETWORKS – AND SOLUTION A pure sinusoidal waveform is the most important theoretical assumption on which circuit analysis is carried out in conventional electrical engineering. Due to various reasons, such as increasing usage of non-linear loads, rapidly time-varying loads etc., this waveform has now become more or less extinct and in its place distorted waveforms are commonly found in most electrical networks. The distorted waveforms can be decomposed into various components using the Fourier Series. These individual components are referred to as harmonics. The order of harmonic “n” is defined as the ratio of the frequency of a harmonic to the fundamental network frequency or rated frequency. The type of loads used in the particular network influence the nature of harmonic distortion. In the modern context these loads could be static converters, variable speed drives, UPS systems, computer systems, new generation fluorescent lighting systems etc.

  4. Each of these loads have their own characteristics in terms of the type and magnitude of harmonic distortion that results from their use. Hence the nature and magnitude of harmonic distortion in low voltage networks has become quite varied and complex. 1) LOW VOLTAE SYSTEMS Industrial and commercial power systems which operate at low voltage levels i.e.415 Volts AC/230 Volts AC etc., have some unique differences in comparison to distribution systems. They can briefly be stated as follows. 1.1 The percentages of non-linear loads i.e. harmonic producing loads are generally higher. 1.2 The variety of non-linear loads are quite high due to the use of diverse power electronic equipment within the installation. 1.3 The content of resistive type load is generally small. As a result the ability of the load to provide damping close to resonant frequencies is limited Harmonic distortion can be very high if resonance is close to a generated harmonic within the installation.

  5. 1.4 The frequency response of the network is greatly influenced by the presence of significant quantity of capacitor banks, which are used for power factor improvement. As a result the probability of resonance occurring near lower order harmonics is quite high. 2) TYPES OF HARMONICS The most common sources of harmonics in low voltage net works are • AC/DC Converters (Rectifiers) • AC/DC (Frequency) Converters • Uninterrupted Power Supplies (UPS) • New generation fluorescent lighting systems. • Welding machines • Saturated transformers The AC/DC converters or rectifiers are mainly used for feeding DC motors, battery chargers, electrolysis plants etc and are normally 3 phase, 6 or 12 pulse type. The characteristic harmonic current generated by rectifiers can be calculated based on the Fourier theorem using the formula as follows.

  6. n= ((p) x (k) +/- 1 where p = number of the pulse and k= 1,2,3,4,5 …… which gives n= 5,7,11,13,17,19,23,25 for 6 pulse rectifier. Similarly, the 12 pulse rectifier generates n=11,13,23,25 …… . ”n” Where is the order of the harmonics. The AC/AC converters are mainly used for feeding high frequency induction furnaces, frequency modulated variable speed drives etc., the converter normally consists of 6 or 12 pulse AC/DC converter on the AC network side and DC/AC inverter on the load side. The order and magnitude of the characteristic harmonics can be calculated in a similar way as for AC/DC converters. It is however, quite common that in this application “ Inter- harmonics” are generated due to the modulation of the fundamental current by the drive frequency.

  7. Inter-harmonics are those harmonic frequencies which are non- integral multiples of the fundamental frequency, for e.g. n=5.5 i.e. 5.5 x 50 Hz=275 Hz. The power supplies for IT (Information Technology) and other sensitive equipment are usually single phase connected between phase and neutral. Such power suppliers are normally SMPS (Switch Mode Power Supply) type and typically give feed back of significant quantity of “ Triplen Harmonics. ” Triplen harmonics are defined as odd harmonics that are multiples of 3. e.g. 3,9,15,21 … . It is now self evident that when several different types of loads are used in a given installation, the resultant harmonic spectrum will consist of a wide range of harmonic and Inter-Harmonic frequencies. Some typical harmonic spectra measured in low voltage installations are shown in Fig. 1 & 2.

  10. 3) ILL-EFFECTS OF HARMONIC DISTORTION 3.1 Effects on rotating machines Motors and generators can be adversely affected by presence of harmonic voltages and currents due to increased heating caused by an increase in iron and copper losses at the harmonic frequencies. In addition to this harmonic currents can increase audible noise emission, reduce machine efficiency and torque developed. These effects combined together can increase energy consumption and reduce machine life considerably. 3.2 Effects on Transformers Harmonic currents cause increased copper losses and stray flux losses, whereas voltage harmonics cause an increase in iron losses. In addition the audible noise level shall increase. These effects generally result in high temperature rise within the transformer, thereby causing premature aging of the insulation and reduction in transformer life.

  11. 3.3 Effects on Switchgear and Power Cables Increased heating due to skin effect caused by the presence of harmonic currents is a common occurrence. Reduction in switchgear life and increase in cable faults are therefore quite common. 3.4 effects on Protective Relays High harmonic distortion levels are likely to cause mis-operation of relays due to change in the operating characteristics of the relay itself. Relays have a tendency to operate slower and / or with higher pick up values in such conditions. As a result, protection of the electrical installation can be compromised. 3.5 Effects on Capacitors Since capacitive reactance is inversely proportional to the applied frequency, harmonic currents are attracted into capacitor banks. This results in abnormal overload conditions on the capacitors thereby causing premature failure.

  12. 3.6 Effects on Power electronic Equipment Malfunction of power electronic equipment can occur due to conditions caused by increased Harmonic distortion. This is often caused due to shifting of voltage zero crossing, or a point at which one phase to phase voltage becomes greater than another phase to phase voltage. This leads to misfiring of thyristors followed by failure of expensive semiconductor devices used in power electronic equipment. 3.7 Effects on Control and Instrumentation Electronics Sensitive equipment such as computers, programmable controllers, electronic instruments etc., can operate erratically when subjected to higher level of harmonic content in the power supply. This erratic performance can result in malfunctions with serious consequences for process control and productivity etc. The combination of these effects results in • Frequent equipment failure • Increased down time of plant • Higher energy productivity • Increased operation cost.

  13. 4) CONVENTIONAL SOLUTION FOR REDUCING HARMONIC DISTORTION The solution, which is in use, is called a harmonic filter. A harmonic filter generally means equipment comprising of reactors, capacitors, and resistors if required. The filter is designed so as to give defined impedance over a specified frequency range. There are broadly three types of filters in use. Tuned filters : A tuned filter works on the principle of providing least impedance path for one or two harmonic frequencies and has a tuning frequency which is within +/- 10/% of the harmonic frequency to be filtered. Detuned Filters : A detuned filter works on the principle of avoiding resonance by achieving an inductive impedance at the relevant harmonic frequencies. The tuning frequency is generally lower than 90% of the lowest harmonic frequency whose amplitude is significant.

  14. Damped filters : A damped filter is one, which offers low and predominantly resistive impedance over a wide band of harmonic frequencies. Since these filters are impedance based, they are referred to as PASSIVE FILTERS . The design of such filters is mainly dependant on the impedance characteristics of the network in which they are to be installed. The analytical modeling of harmonic source can be determined from the single line diagram by creating a NORTON equivalent as seen by the harmonic source. Fig. 3.

  15. I fn I nn I gn z fn z RECTIFIER FILTER NORTON EQUIVALENT CKT. I gn GENERATED n-th HARMONIC CURRENT I fn n-th HARMONIC CURRENT ABSORBED BY THE FILTER I nn n-th HARMONIC CURRENT INJECTED TO THE NETWORK Z fn FILTER IMPEDANCE AT n-th HARMONIC Z nn NETWORK IMPEDANCE AT n-th HARMONIC

  16. A single line diagram showing the typical connection scheme of a passive filter is shown in fig. 6. Where more than one dominant harmonic frequency is present, a separate filter for each frequency is generally used. Filtering of Harmonics using Passive Filters Z HARMONIC FILTER OTHER GENERATING LOAD LOAD

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