EMC / RFI Power Line Filters
  3Phase RFI Power Line Filters offer exceptional EMI and RFI protection:

GR Power line filters have been designed as engineered solutions for equipment malfunctions due to unwanted high frequency electrical noise. These frequencies can be either noise conducted through power lines or radiated through the on to the power lines. Designed to be installed at input terminals of VFD, filters provide simple installation and enhanced drive performance and durability.

  Harmful High frequency noise EMI (Electro magnetic Interference) and RFI (Radio Frequency Interference):

The terms EMI and RFI are often used inter changeably. EMI is actually any frequency of electrical noise, where as RFI is a specific subset of electrical noise on the EMI spectrum. There are two types of EMI. Conducted EMT is unwanted high frequencies that ride on the AC wave form. Radiated EMI is similar to an unwanted radio broadcast being emitted from the power lines. There are many pieces of equipment that can generate EMI, variable frequency drives included. In the case of VFDs, the electrical noise produced is primarily contained in the switching edges of PWM controller. As the technology of the drives evolves, switching frequencies increase. These increases also increase the effective edge frequencies, there by increasing the amount electrical noise.

  Common Mode (CM) and Differential Mode (DM):

Common mode is the electrical noise on all power lines to ground. Differential mode is noise on the line with respect to another line. When considering the filter for use in a VFD application, it is important to note that common mode noise reduction is the most important factor. VFDs produce very little differential mode, or line to line, electrical noise due to presence of DC bus capacitors.

  Noise Standards:

International agencies agree that a certain threshold of electrical noise, typically in the 150 KHz to 30 MHz band, is likely to cause interference problems. Generally, these standards allow 1 to 10mv of noise on AC line with respect to ground. It is important to note these standards are all based on noise on a power line with respect to ground; or common mode noise.

The most important specifications for EMI filters and RFI filters include rated voltage, rated current, and insertion loss. The rated voltage is the voltage for which the EMI / RFI filter was designed. The rated current is the current for which the EMI / RFI filter was designed. Insertion loss is a statement of the filter's attenuation characteristics, exercising in decibels (dB) the ratio of noise that would get through without the filter, to that which gets through with the filter installed. Another important specification to consider when searching for EMI filters and RFI filters is the operating temperature; the temperature range the filter was designed to operate correctly.

GR RFI filters use a combination of high frequency inductors and capacitors to reduce noise in the critical 150 KHz to 30 MHz frequency range. The inductors act as open circuits and the capacitors act as short circuits at high frequencies while allowing power line frequencies to pass untouched. The filters assist with cost effective compliance to EMC directives, in a compact, efficient, light weight design. The high common mode and differential mode reduction in the critical 150 KHz to 30 MHz frequency assures that potential interference from AC drives is reduced or eliminated.

  Noise Attenuation:

Noise attenuation is expressed as a ratio of the output transient energy (Vto) to the input transient (Vti) or by decibels (dB). The table shows the relationship of this ratio to decibels. Most electrical systems are provided with 40dB attenuation, which is adequate.

  Hi-Pot Testing:

The term ?hi-pot’ is an acronym for ??high potential”. Hi-pot testing stress the insulation and capacitors much higher than is usually experienced in normal operation.

  Leakage Current:

Leakage current is an important specification of power line filters. Leakage current is not a function of the quality of components, but is a direct function of the line- to- ground capacitance value. The larger the capacitance, the lower the impedance to common mode currents, and the greater the common mode interference rejection. Hence, a leakage current is a measure of filter performance – the higher, the better.

  Consideration When Applying Power Line Filters:

Proper installation of filters can have a dramatic effect on over all performance. Although the filter reduces electrical noise on the power lines (conducted emissions), it should be located as close as possible to the VFD to reduce broad casting of noise (radiated emissions) from the power line themselves. The capacitors within filters short the noise to ground, so it is imperative that the filter maintains a good ground. A short, heavy stranded conductor from the filter chassis to the main ground bus is recommended for top performance. The flexible cable with many fine strands is recommended for best grounding performance.Radiation of noise is also a concern for power line routing, as it can effectively bypass the filter. Input and output filter leads should be separated by a maximum practical distance within enclosures and should be routed separately in interconnecting conduits when used.

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