Green Belt Lean Six Sigma

A discussion about passive filters implementation

Fernando N. Belchior, IEEE Member, Bruno P.Campos, Paulo F. Ribeiro, IEEE Fellow Member, Evandro Vaciloto,

Federal University of Itajubá

Itajubá – MG, Brazil

Abstract – The growing use of non linear loads in commercial, residential and industrial sector has been distorting the currents and voltage waves of the power network. These distortions are known as harmonic distortions, and its presence can cause serious problems to equipments linked to this polluted source. One well known solution to mitigate this issue is the use of passive filter. This paper presents many aspects of passive filter, explaining about its types and the steps for a project.  

Index Terms: Passive Filter; harmonic distortions; non linear loads

I – Introduction

It is common understanding, nowadays, the electric energy works with a very important, if not indispensable role in the life of the human being. The quality of supply in Brazil in recent decades has suffered an accentuated decline. This has occurred in part by the increasing population demand, the insufficient investments in infrastructure, and, sometimes, unfavorable climatic factor. This climatic factor has vital importance for the hydroelectric power generation in the whole length of the country.

The development of industry and national trade brought the installation of non-linear loads, representing distortions in the electric power system. The survey of information through statistical data on these types of loads has become an important parameter for the development of new standards of control, limits and procedures established by the agencies responsible for auditing the generation and distribution companies in the country.

To understand the loads which are not linear it is firstly necessary to understand the loads which are linear, these ones have a linear relationship between voltage and current.

Most of the loads installed in electrical systems have non-linear properties, like semiconductors, transformers, motors, etc. They are not linear, since they have a non-linear relationship between the voltage and current

The non-linear loads are basically classified into three categories:

• Ferromagnetic Devices: include transformers, motors, generators, reactors, etc;

Luiz Rico Souza,

University

• Static power converters: common in electronic devices frequency inverters, etc;
• Devices that work with electric arc. Welding machines, industrial arc furnaces, etc.

So, the harmonic distortion is a sinusoidal component of the voltage or current at a multiple frequency of the fundamental frequency.

The figure below shows a signal at the fundamental frequency at 60 Hz with an harmonic signal of 300 Hz.

[pic 1]

Fig.1 Signal with fundamental frequency and 5th harmonic order

Filter Operation

The classic solution to reduce harmonic currents in electrical systems is the use of filters connected in derivation feeder. A typical structure of a passive filter current harmonics is shown in Figure 3. The various LC series cells are tuned to values closed of frequencies that are wanted to eliminate, which, as a rule, are the lower order components. In general, for the highest frequency, is used a simple capacitor functioning as high-pass filter.[pic 2]

Fig.2 Typical structure of a passive filter

Passive Filters

Passive filters are typically composed for inductors, capacitors and resistors, tuned to a characteristic resonance frequency. They also may be constructed in many combinations, so they can be tuned to various frequencies simultaneously. The function of passive filters is to absorb the load harmonic currents, preventing them from circulating through the electrical system.

Active Filters

Active filters, although they have the same function as passive filters, they are developed with electronic equipment and they are made to inject harmonic currents adequately lagged to those generated by the loads, so when the currents are added together they will cancel each other. While passive filters are usually dependent and specified by the values of inductors, capacitors and switching elements that compose them, active filters are specified by the current they will filter.