Harmonics are current and voltage waveform distortions in power supply. Harmonics occur in integer multiples of the fundamental (supply) frequency - 50 Hz in India/Europe, 60 Hz in North America.
A distorted waveform creates heat in the power delivery equipment that can cause severe damage to both domestic and industrial equipment that use the utility power supply. Harmonics are created due to the presence of non-linear loads which draw non-sinusoidal currents from an essentially sinusoidal voltage source. As a consequence, this leads to corruption of the supply voltage in the main power lines. Some of the non-linear equipment that trigger harmonics include:
Harmonics are an integral aspect of today's Power Systems and every effort has to be made through proper design and architecture to mitigate the problem of Harmonics.
One of the most effective ways to reduce harmonics in power systems is using Harmonic Filters. Harmonic Filters are capable of eliminating excess currents in 2 ways:
Harmonic Filters contain a combination of inductors, capacitors and resistors (LCR) circuits that are capable of removing unwanted harmonic currents. The LCR circuitry is connected either in series or parallel, depending on the specific application and configuration.
Passive Harmonic Filters
Passive Harmonic Filters are designed to provide an alternate path for the harmonic currents and thus keep the main supply lines close to the fundamental frequency. For every harmonic current, separate Harmonic Filter stage has to be added.
In high impedance applications, filter is connected in series with the load and blocks the harmonic currents. In low impedance applications, filter is connected in parallel with the load. All the harmonic current specific to a specific Harmonic will flow through this shunt Filter that can then be grounded.
Advantages of Passive Harmonic Filters:
Disadvantages of Passive Harmonic Filters
Active Harmonic Filters:
These filters consist of combinations of LCR circuits along with power electronic circuitry. They operate by injecting in the opposite direction, the harmonics generated by the load. This reduces the harmonics in the line. These filters are capable of reducing a broad range of harmonic frequencies. Typically used in commercial installations with load less than 200 kVA. Capable of eliminating current distortion that could lead to equipment heating and current overloads. Ideal for systems that have multiple loads like UPS, VFD and DC drives.
Characteristics of Active Harmonic Filters include:
Advantages of Active Harmonic Filters include:
Active Harmonic Filters are ideal in the following applications:
Hybrid Filters: Combines the features of both passive and active filters. Typically used Industrial applications with load in excess of 500 kVA. Capable of catering to different power and performance levels.
EMIS Passive harmonic filters are designed and manufactured to provide an economical solution in harmonic mitigation in Power Systems by maintaining THID 5% in compliance with current and voltage requirements of IEEE 519.
Applications of EMIS filters