EMI, EMC FILTERS
In order that an item of electronics equipment can pass its EMC testing and gain its EMC compliance, it is necessary to incorporate various elements into the design. By designing the circuit to meet the electromagnetic compatibility, EMC requirements it is possible to significantly reduce the levels of unwanted signals entering and leaving the unit. One of the major ways in which this can be done is to use an EMC filter or a series of filters.
A 3-phase Line Reactor is a set of three (3) coils (also known as windings, chokes or inductors) in one assembly. It is a series device, which means it is connected in the supply line such that all line current flows through the reactor, as shown below. Line Reactors are current-limiting devices and oppose rapid changes in current because of their impedance. They hold down any spikes of current and limit any peak currents. This resistance to change is measured in ohms as the Line Reactor's AC impedance (XL) and is calculated.
ACTIVE HARMONICS FILTERS
In recent decades, commercial, institutional, and industrial facilities have experienced tremendous growth in the use of equipment that generates "harmonic" distortion in power systems. Examples of this equipment include DC drives, AC variable frequency drives, rectifiers, induction furnaces, and uninterruptible power supply (UPS) systems. Harmonic distortion creates a wave form resulting in higher than normal current values (and heat).
PASSIVE HARMONICS FILTERS
Is a capacitor and reactor combination .The detuned reactor is designed to mitigate harmonics, improve power factor and avoid electrical resonance in low voltage electrical network. An LC circuit, tuned to each harmonic order to be filtered, is installed in parallel with the non-linear load . This bypass circuit absorbs the harmonics, thus avoiding their flow in the distribution network.
POWER FACTOR CORRECTION
Loads are predominantly inductive or resistive in most modern electrical distribution systems. Resistive loads include incandescent lighting and resistance heating. Inductive loads include motors, induction furnaces, transformers and ballast-type lighting. Inductive loads, such as motors.
MEASUREMENTS AND SOLUTIONS
Harmonic analysis was conducted using Fluke make harmonic analyzer type 435 Consisting of three phase voltage probe max 800 volts, Three phase tongue tester Max 1 to 3000A. Analyzer is communicated to computer through RS232 port for Printouts of captured data.
TA harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency, i.e. if the fundamental frequency is f, the harmonics have frequencies 2f, 3f, 4f, . . .etc.
The harmonics have the property that they are all periodic at the fundamental frequency, therefore the sum of harmonics is also periodic at that frequency. Harmonic frequencies are equally spaced by the width of the fundamental frequency and can be found by repeatedly adding that frequency. For example, if the fundamental frequency (first harmonic) is 25 Hz, the frequencies of the next harmonics are: 50 Hz (2nd harmonic), 75 Hz (3rd harmonic), 100 Hz (4th harmonic) etc.
Harmonics voltages and currents in an electric power system are a result of non-linear electric loads. Harmonic frequencies in the power grid are a frequent cause of power quality problems. Harmonics in power systems result in increased heating in the equipment and conductors, misfiring in variable speed drives, and torque pulsations in motors. Reduction of harmonics is considered desirable.
DETECT AND ELIMINATE HARMONICS WHY?
From Electrical Installation Guide
Disturbances caused by harmonics
- Harmonics flowing in distribution networks downgrade the quality of electrical power. This can have a number of negative effects
- Overloads on distribution networks due to the increase in rms current.
- Overloads in neutral conductors due to the cumulative increase in third-order harmonics created by single-phase loads.
- Overloads, vibration and premature ageing of generators, transformers and motors as well as increased transformer hum.
- Overloads and premature ageing of power-factor correction capacitors .
- Distortion of the supply voltage that can disturb sensitive loads.
- Disturbances in communication networks and on telephone lines .
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