Harmonic filtering
Our references:
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Today
several electrical
equipments generate current distortions in networks. Those distortions,
named harmonics, can be modelized as a collection of sinus current at
different frequencies and amplitudes added to the basic network
current. They cause many different sorts of problems, such as :
- Increased losses,- Malfunctioning of control system, - High currents in phase and neutral. |
 Filtering resistor 130 kW pt - 347 ohms |
Power harmonic filters are built up from passive LC components (i.e. reactors and capacitors tuned in order to shunt off most of harmonics. The addition of a resistor allows :
- more precision in the original adjustment of the filters,
- Stretching of the effective bandwidth,
- Dituning due to fluctuations in components (owing to temperature).
DESIGNING OF POWER
RESISTORS FOR HARMONIC
FILTER
1. Power dissipation :
This power is partially stored in the metal or the material of the heating element. The non stored power has to be transferred to the surroundings either by radiation or by convection which depends on :
- the design of the resistors,
- the surface of the heating elements,
- the temperature difference between ambient air and the heating elements.
2. Résistance value :
Customer requirements must imperatively indicate the nominal value of the resistor.
3. Voltage resistance :
The resistor must be designed in accordance with various limits (grid-banks - enclosures, arcing distances, creepage distances, BIL withstandings).
4. Current resistance :
Connections have to be carefully designed and examined because the interventions of high current transients can create undesirable electromagnetic forces.
5. Miscellaneous :
Environmental and site conditions (pollution degree, sismic level, corrosive ambient, wind, altitude).
To check the caracteristics necessary for the calculation of your resistor, please consult our technical data available in the section "PRODUCTS DOCUMENTATION" or ask us for an estimate.