Film capacitor#Safety and EMI.2FRFI suppression film capacitors
Suppression capacitors and radio interference suppression or safety capacitors are electrical capacitors, eg, in line filters, to reduce interference with radio reception. They conduct high-frequency noise caused by the operation of electrical or electronic equipment against the ground or the neutral or close it short and thus bring about the reduction of electromagnetic interference. Electrically, they must be designed so that the remaining residual noise limits prescribed EMC standards EN 61000-6-3 (residential ) and EN 61000-6-4 not exceed ( industry). In addition, network - Interference Suppression both the device from incoming power surges (transients) must protect, and suppress line-bound reactions of the appliance to the mains supply.
Suppression capacitors are offered as a dielectric in wired version as ceramic capacitors, as metal - paper capacitors (MP- capacitors) and also as a plastic film capacitors with polypropylene ( MKP ) and polyester film ( MKT capacitors ). In the SMD version for surface mounting, there are currently only available as suppression capacitors ceramic capacitors.
Classification
To block and attenuate this noise radio interference suppression capacitors are used, which are defined depending on the requirements in the X and Y classes.
Class X capacitors are according to IEC 60384-1 electrical capacitors with " unlimited capacity ", which are connected between phase and neutral or between two phases. They are required for applications in which a failure due to a short circuit can not lead to a hazardous electrical shock.
Class Y capacitors are according to IEC 60384-1 electrical capacitors which are connected between phase respectively neutral conductors and earthed casing, and thus bridge the basic insulation. For Y- capacitors only those capacitors are permitted by this standard that have a verifiable increased electrical and mechanical safety with limited capacity, because their applications in the event of failure of a hazard to persons or animals may occur due to electric shock by shorting.
Designs
Since the high-frequency interference suppression also depends heavily on the design of the Entkoppelelementes, several embodiments are for radio interference suppression capacitors on the market:
- X - or Y - capacitors as individual components with two connections.
- XY three-terminal capacitors in combination with capacitors X and Y capacitors in a single housing. These capacitors are wound in a single operation. They are internally connected in star or delta-connected with each other.
- Through Capacitors with a central manager for the operating current. The structure can be coaxial or nichtkoaxial.
Use
Y capacitors are preferably used in devices for single-phase. Because here, for example, the Schuko plug can be plugged in two directions, is not pre- determined, on which of the two connecting wires of the outer conductor comes to rest. Therefore, both Y- capacitors for filtering are placed against the protective conductor, although this would not actually necessary for the neutral conductor. This is the only exception, where the protective conductor must be used for purposes other than for protective earthing and thus the protection of human lives against electric shock. If a short circuit in the condenser of the outer conductor to the ground wire and thus the metal casing of the device would be connected. Therefore, even higher safety standards than the X capacitors are. The latter are used in three-phase alternating current. Here is by the type of connector set, on which the connecting wires three phase conductors come to rest. The use of the protective conductor in line filters, which are used in three-phase alternating current equipment, can then be avoided.
Security
To the protective function of the protective conductor not to compromise as well as due to the operation directly on the low- power increased protection requirements are placed on the X-and Y- capacitors, which are examined by the respective national organizations in the government contract in Germany by the VDE and in the other European countries and certified. The shared capacitors could be so provided in the past with the respective logos such as VDE, SEMKO, DEMKO, NEMKO, etc.. As part of the harmonization of European standards, the countries of the European Union agreed in 2000 that it recognizes the country-specific safety regulations and their certificates to each other and to use a common logo ( ENEC ). Nevertheless, you can also find on newer suppression capacitors, provided space is available, continue to part many different logos, because in many countries of the American continent, the capacitors are certified by Underwriters Laboratories, short UL and Canada and other non - European countries, their have their own certification bodies with their logos.
The specific safety requirements for capacitors are increased dielectric strength and high pulse shock load capacity. X1 capacitors keep a pulse voltage of 4000 V was, X2 of 2500 V and Y capacitors twice the voltage pulse. Moreover, these capacitors must emit no spur to UL flame of destruction, and secrete no conductive material that could trigger elsewhere shorts. Non-conductive parts may flake off only with low acceleration ( no explosion ).
Until about 1990, only ceramic capacitors and special paper capacitors could meet the more stringent safety standard for X - and Y- capacitors. The MP - capacitors are due to the harzdurchtränkbaren paper until today as a safe solution, because the prescribed load tests inflate the capacitor at most. The destruction always takes place within the enclosure. The industrial pressure to reduce costs led in 1990 to the development of special plastic film capacitors ( MKP and MKT capacitors ). Their safety is nowadays also given and they have, if they are approved, the appropriate approvals. In contrast to the special paper capacitors, the housing of the capacitor is here almost always destroyed during sample loading, thus oxygen can reach the damaged area is under mains voltage. The experienced since the existence of such security capacitors strict interpretation of the rules was so watered down in favor of a reduction in costs, which is why plastic film capacitors for this application are not undisputed.
In the context of miniaturization in the industry, the surface mount SMD types are becoming increasingly important. This also applies to suppression capacitors. As far neither MP nor MKP or MKT - suppression capacitors are available in surface mount package, win SMD ceramic suppression capacitors in importance. Again, the original stricter safety aspect in favor of a cost reduction is softened, because currently there is no ceramic capacitors with a ENEC or UL approval.
Standardization
The conditions for the tests and measurements of electrical and mechanical parameters for the approval of the radio interference suppression capacitors in the European area ( ENEC ) are laid down in the DIN IEC 60384-14.