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Harmonic Filter

Power Transmission and distribution networks are designed to operate with sinusoidal voltage and current having constant frequency. However there are number of non -linear loads, such as thyristor drives and converters, that generate harmonics on the network, causing distortion in the voltage and current waveforms. These harmonic filters are used when the main objective is not the reactive power compensation at the fundamental frequency, but to reduce the harmonic distortion in the supply system.

Active Harmonic Filter

Active Harmonic Filter
The IGBT based Active Harmonic filter Banks are designed to solve the faults and the unbalanced current itself at 50 Hz achieving practically neutral currents which may occur in a four wire, three phase installation.
It includes the following functions:
  • The Harmonic filtering.
  • Phase current balance.
  • Power factor correction.

Technical Specification of Active Harmonic Filter :

Power Supply Voltage 360…400 V ac
Frequency 47…63 Hz
Connection 3 phase + neutral (4 wire)
Function Correction Of:
Up to 21st harmonics
Current unbalance
Reactive power
Switching frequency 10 Hz
Losses 15 W/A
EMI tests EN- 50081-1, EN-50081-2, Class A

Operating temperature 35 0C
Relative humidity 80% sin condensation

Application of Active Harmonic Filter :
  • This is the ideal solution for installations with a large amount of the single-phase and three-phase loads generating harmonics such as computers, the UPC, lights lifting equipment.

Advantage of Active Harmonic Filter :
  • Bolts and outlet to ensure the reliability and stability of the wiring, to meet the requirements of large-capacity, high current.
  • Safe and reliable American pressure explosion-proof structure, built-in discharge resistor, making the product safer and more reliable.
  • Long-life, multi-component designs to increase the cooling area, the lower the temperature rise of the capacitor, to extend the life of the capacitor.
  • Capacitor components with special metalized film side blocking both high self-healing properties, but also meets the requirements of high reliability contacts and high-pressure.
  • Safe and effective protective measures to remove the injury to the human body.
  • Convenient and reliable installation, improve work efficiency.

Typical Customer :
  • Small industries of all kind
  • Power utilities
  • Contractors
  • Small commercial premises

Tuned Harmonic Filter

Tuned Harmonic Filter
Power Transmission and Distribution networks are designed to operate with sinusoidal voltage and current having constant frequency. However there are number of non-linear loads, such as thyristor drives and converters, which generate harmonics on the network, causing distortion in the voltage and current waveforms. Harmonic filters are usually formed by series filter reactor capacitive below its running frequency, whereby they also contribute, even if in a small scale, to the reactive power compensation at the fundamental frequency. Apply the correct amount of capacitance (kVAR) to the network to avoid resonance with the source. This may be difficult, especially in automatic systems as the capacitance is always changing. This solution usually means connecting less capacitance to the system than is actually needed for optimum power factor correction.

Install reactors in series with capacitors to lower the resonance be low critical order harmonics; i.e., 5th, 7th, 11th & 13th. This design tunes the resonant frequency of the system well below the 5th harmonic and is called a detuned filter bank. This solution allows the capacitors to operate in a Harmonic environment.

Filters are recommended if a problem exists with harmonic distortion before the application of power factor correction.

Application of Tuned Harmonic Filter :

  • 3rd Harmonic Filter
  • Isolation Filter
  • Absorption Filter HAF
  • High Pass Filter HPF
  • Active Filter SINAF


Technical specification of Tuned Harmonic Filter :


Phase-neutral tension Up to 750 V
Frequency 50/60 Hz
Nominal Current (IR) 6…100 A
Current max. transitory 1,5 In (1 min.of each 10 min.)
Construction Metal Cabinet
Degree Of Protection IP 00/IP 21
Colour Grey RAL 7035
Installation Indoor
Temperature Range -100 to +500 C
Relative Humidity 95.00%

Detuned Harmonic Filter

Detuned Harmonic Filter
Detuned Harmonic Filter: Detuned filter are used, in supply networks having a high level of harmonic distortion, when the final objective is reactive power compensation at the fundamental frequency. Their purpose is to avoid the harmonic currents overload to the capacitors by diverting them to the mains. Protection filters are made by connecting reactors in series with capacitors, in such a way that the tuning frequency of the whole unit is set at a value between the fundamental frequency and the frequency of the lowest present harmonics, which is usually the 5th order harmonic. In this the filter has a high inductive impedance for all the harmonic frequencies.

Technical Specification of Detuned Harmonic Filter :

Rated voltage of the main 230 / 400 V
Frequency 50 Hz
Rated Voltage of the Capacitor 260 / 460 V
Filter type Low tuning
Resonance frequency 189 Hz (7%)
Inductance tolerance ± 3 %
Maximum Harmonics Overload 0.35 In
Construction INA: Aluminium
INR: Copper
Thermal protection By thermostat
Connection Aluminium Bus Bar
Degree Of Protection INR: IP 20
Category of temperature Class F(155 0C)
Installation Indoor
Standards IEC 60289, EN 60289

INA/INR reactors are designed to work in supply systems with a high level of harmonic distortion in such a way that they allow a safe and reliable service of the power factor detuned, so that, the whole unit has an inductive are specially designed to work in series with FMF capacitors correction equipments. Reactors are connected in series with power capacitors, forming a resonant circuit conveniently.

Connection of a reactor in series with a power capacitor, makes the capacitor to work at a voltage higher than the supply voltage. Because of this, capacitors need to be connected to protection reactors and need to be designed to work at higher voltages than standard capacitors. The choice of the tuning point of the filters is to balance between the quantity of harmonics rejected by the filter and the voltage increase produced in the capacitor at the fundamental frequency.

It is to be also kept in mind that reactive power supplied by the filter at rated frequency (50 or 60 Hz), is different to the one that the capacitor would supply without the reactor. Taking all the above into account, the reactor is normally chosen in such a way that its impedance is about 7% of the impedance of the capacitor that protects. This will give a tuning frequency, for example at 50 Hz, of 189 Hz. Other tuning frequencies are also available.

Third Harmonic Filter

Third Harmonic Filter
Third harmonic filter is basically passive filters with a parallel combination of inductance and condenser. The advantages of third harmonic filter are:
  • Reduction of the third overtone until a 90%.
  • Significant Reduction of other overtones.
  • Reduction current of neutral absorbed.
  • Reduction of losses in the installation.
  • Reduction of the interferences.
  • Improvement of the power factor.
Filter HBF-T has to be selected in agreement with the current of the breaker that protects the circuit. They are connected in the neutral conductor of the three-phase installation, and it is possible to be seen in scheme 1. Technical Characteristics
Phase-neutral tension Up to 750 V
Frequency 50 / 60Hz
(IR)Nominal current (IR) 6-100A
Current max. transitory (1 min.of each 10 min.)
Construction Metal Cabinet
Degree of protection IP 00/IP21
Color/Colour Gris/Grey RAL 7035
Installation Interior/Indoor
Temperature range -10º C + 50ºC
Relative humidity 95%

High Pass Filter

High Pass Filter
Desciption: In installations with 3rd harmonic generation loads, the current through the neutral cable can be higher than the one in the phases, even in case of balanced loads. The most proper solution for these problems is to use a specific equipment for the 3rd harmonic filtering, consisting basically in a three-phase isolating transformer, delta-star connected, that filters the 3rd harmonic current, plus a passive filter which reduces the 5th harmonic.

Passive Harmonic Filter

Passive Harmonic Filter
Passive Filters or can say Protection Filters are used on distribution networks which have a high THD (Total harmonic distortion), when the final target is to compensate the power factor at the fundamental frequency.

Its purpose is to avoid overloads due to harmonic currents in the capacitor, deflecting them to the network.

Protection filters are made with serial reactors and capacitors. The tuned frequency of each unit is adjusted between the fundamental and the lower harmonic present in the net, which usually is the 5 th order.

In this way, the filters present high inductive impedance for all the harmonic frequencies.

Harmonic Passive Filter

Harmonic Passive Filter


Ab Power System Solution
Alok Kumar (Director)
Gat No. 258/1, Plot No. 8/2, Village Khalumbre, Chakan - Talegaon Road, Tal. Khed, Near Lohr TSI Compound
Pune - 410501, Maharashtra, India

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