IEC 60940 pdf download

IEC 60940 pdf download.Guidance information on the application of capacitors, resistors, inductors and complete filter units for electromagnetic interference suppression
3 Electromagnetic and Radio frequency interference suppression (EMI/RFI)
3.1 General Electromagnetic interference, EMI, is any electromagnetic emission or any electric or electronic disturbance which causes an undesirable response, malfunctioning or degradation in the performance of electrical equipment. Radio frequency interference, RFI, is any electrical energy with content within the frequency range dedicated to radio frequency transmission. Conducted RFI is most often found in the low frequency range from 1 50 kHz to 30 MHz. Radiated RFI is most often found in the frequency range from 30 MHz to 1 0 GHz. EMI or RFI propagate through conduction over signal and power lines and through radiation in free space. Electrical machines and apparatus may generate electromagnetic interferences (EMI) which are fed back into power supply mains. These electromagnetic interferences may be picked up by apparatus connected to or placed close to the same power system up to a certain distance from the machine or apparatus. The radio-frequency voltages may be generated both between conductors (phases) of the power system (symmetrical interference) and also between conductors (phases) and earth (asymmetrical interference). These voltages can cause electromagnetic radiation from the power lines.Radio interference can be suppressed by providing a low impedance path for radio frequency currents close to the place where the radio frequency voltages are generated. This may be combined with a high impedance element which prevents the radio frequency currents from penetrating into the power supply system, but has no appreciable effect on the flow of power current. 3.2 Limits of interference In various countries, mandatory limits are set to the radio-frequency in a given frequency range emanating from electrical machines and apparatus. A survey of these limits is given in relevant EMC-standards such as CISPR 1 1 . Some electrical apparatus require for their operation a power-supply voltage free from radio- interference to a greater extent than that guaranteed by the requirements mentioned above. In these cases, similar measures should be taken at a place in the power supply system close to the place where the apparatus is connected. When the apparatus is shielded (or placed in a shielded room), interference suppression will generally be applied at each point where the power supply system enters the shielded enclosure.
4 Classification of suppression components
4.1 Suppression components An example of use of suppression components in EMI filter is shown in Figure 1 .4.2 Capacitors Radio interference suppression capacitors may be divided into the following groups: a) Two-terminal capacitors, which can be connected to the machine, apparatus or supply system to provide for either symmetrical or asymmetrical interference suppression. b) Combinations of capacitors (either combinations of separate capacitors or multi-section capacitor the sections of which may be connected in a certain manner), which can be connected to the machine, apparatus or supply system to provide for both symmetrical and asymmetrical interference suppression. c) Lead-through capacitors (asymmetrical or symmetrical) or combinations thereof, in which one or more sets of terminations are interconnected by means of a conductor intended to carry the power supply current. These capacitors are especially suited to provide interference suppression at the place where the supply system phases through a shielded housing. d) Resistor-capacitor combinations consisting of a capacitor with the capacitor utilizing the resistance of the capacitor electrodes. RC combinations are often used for the suppression of switching surges. 4.3 Inductors Radio interference suppression inductors may be divided into the following groups: a) Simple coils either with an air core or wound on a magnetic core. The UHF choke is an example of this type of inductor. b) Coils wound on a closed magnetic core. These inductors may have two or more coils wound on the same core, which is often of ferrite material. The windings are often arranged so that there is no resultant magnetization induced in the core due to the power current, when the inductor is known as current-compensated. c) Inductance, at high frequencies, may be obtained for suppression purposes by threading ferrite beads on to lead wires. d) Some core materials, especially ferrite materials, can be designed to introduce fairly high resistive losses at VHF and UHF, adding to the suppression obtained by the inductance of the coil.