PASSIVE HARMONICS FILTER

It is the most common method for the cancellation of harmonic current in the distribution system. Passive harmonic filter are basically designed on principle of either single tuned or band pass filter technology. As the name suggests shunt type filter are connected in system parallel with load. Passive filter offer a very low impedance in the network at the tuned frequency to divert all the related current & at given tuned frequency. Because of passive filter always have tendency of offering some reactive power in the circuit so the design of passive shunt filter take place for the two purpose one is the filtering purpose & another one is to provide reactive compensation purpose of correcting power factor in the circuit at desired level. The advantage with the passive shunt type filter is that it only carry fraction of current so the whole system AC power losses are reduced compare to series type filter. The given figure shows the schematic diagram of 6 pulse converter system connected with shunt passive type filter which are simply employed ever connection in distribution system have R-L load in system.

CHARACTERISTICS OF PASSIVE FILTER WITH FIXED ELEMENTS

Passive filters were preferred in the earlier days for harmonic compensation because they are simple in structure and easy to install Different topologies of passive filters were emerged during stages of research. They are generally classified into series and shunt passive filters. Series passive filters use high series impedance to block harmonics, and shunt filters divert harmonics by means of a low impedance shunt path. The series filters must be designed to carry full load current, whereas shunt filters carry only a fraction of the current that a series filter carries. Also shunt filters, if properly designed, supply reactive power to the load at the fundamental frequency. Hence the most practical approach is to use shunt passive filters. The shunt passive filter is made up of passive elements resistance, inductance and capacitance. When the inductive and capacitive reactance of the passive filter become equal at a particular harmonic frequency, shunt passive filter acts as low impedance path for that harmonic component.

SPECIFICATION

ADVANTAGES OF PASSIVE FILTERS

1. Higher power factor, improved voltage stability and lower network losses.
2. Filtering of harmonics in the system to acceptable levels.
3. Lowering of resonance problems and amplification of electrical disturbances
4. Less Cost.
5. Gain and Frequency adjustment flexibility
6. No Loading Problem
7. Non-floating Input and output
   

 APPLICATIONS

Nonlinear loads such as saturated coils and transformers are the main cause of producing harmonics in power system. Power electronic creates most of the due to its non liner characteristics pollution issues. Most of the pollution issues are created due to the nonlinear characteristics and fast switching of Power electronics.

Classically, shunt passive harmonic filters, mainly consist of tuned LC filters and or high passive filters are used to reduce the harmonics and power capacitors are used to improve the power factor. But they have the limitations of fixed compensation, large size and can also exile resonance conditions. In this work both shunt passive filter is used for power quality improvement. Transformers, motors, cables, interrupters and capacitors are the some equipment which is affected by harmonics converters mainly produces notches and they basically affect the electronic control devices.

There are two routes to the reduction of power quality problems. The first way is known as load conditioning, which assures that the equipment is made less sensitive and effective to power disturbances. The second technique is, to install line-conditioning systems that counteract or suppress the power system disturbances .In distribution systems passive filters have been used to limit of harmonic currents.