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EMI / RFI Line Filter Parameters

1. Rated Voltage – The maximum permissible is referred to as the rated voltage. Single phase filters from Elcom International are rated at 250 VAC at the nominal frequency of 50 Hz. The three phase filters are rated at 440 VAC at nominal frequency of 50 Hz.

2. Rated Current – The filter can be continuously operated at the rated current within reasonable ambient temperature. Elcom International filter range includes filters with various current ratings from 1 Amps for single phase and three phase operations.

3. High Voltage Testing – The process includes testing the insulation and capacitors of a filter assembly by applying voltage much higher than is usually experienced in normal operations between phase and neutral shortened together and earth. The purpose is to assure safety and reliability of the products.

4. Leakage Current – The leakage current is the sum of total of the leakage current of the capacitors between the line and neutral to the earth, and the leakage of the stray capacitance to the earth. International standards define different classes of the equipment and the maximum permissible leakage current for the class.

5. Insulation Resistance – The attenuation of the filter is measured as an insertion loss. Ii is a measure of the effectiveness of the filter. The insertion loss is determined as:

Insertion loss = 20 log 10(V0/2 V2) dB
V0 = Input Voltage
V2 = Output Voltage
Asymmetrical attenuation is measured between line and neutral connected together and ground. Symmetrical attenuation is measured between line and neutral with earth kept open.

6. Surge Suppression – Transient over-voltage or surges of the order of 6 KV induced on power lines are harmful to electronic components like diodes, transistors ICs etc. A surge suppressor is the solution for this problem. Metal Oxide Varistors (MOV) are generally used.

Normally MOV draw a very small operating current (100 micro amp). When exposed to a high energy transient, the impedance of MOV decreases to a very low value thus opening a low impedance path for the transient. In process, the transient high voltage is clamped to a safe level, protecting rest of the electronic circuitry.
Advantages of MOVs are :
- Very low operating current and low clamping voltage. Fast response time.
- High surge energy absorption capability and hence suitability for bith line surges abd lightening induced surges.
- Wide operating temperature range

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Resources

EMI / RFI Line Filter Parameters

EMI / RFI Line Filter Parameters