Interference suppression capacitor
Interference suppression capacitors , also radio interference suppression capacitors or safety capacitors , are electrical capacitors , for example in network filters , for radio interference suppression . They conduct high-frequency interference signals, caused by the operation of electrical or electronic equipment, to the ground or the neutral conductor or short-circuit them, thereby reducing electromagnetic interference (EMC).
Electrically, they must be designed in such a way that the remaining interference signals do not exceed the prescribed limits of the EMC standards EN 61000-6-3 (residential areas) and EN 61000-6-4 (industry). In addition, mains radio interference suppression capacitors must both protect the device from mains-side overvoltages ( transients ) and suppress line-related effects of the device on the supply network.
Interference suppression capacitors are available in wired design as ceramic capacitors , as metal- paper capacitors (MP capacitors) and also as plastic film capacitors with polypropylene films (MKP capacitors) and polyester films (MKT capacitors) as dielectric. The SMD version for surface mounting is currently only available as ceramic capacitors.
Classification
To block and dampen these interference signals, radio interference suppression capacitors are used, which are defined in classes X and Y depending on the requirement profile.
According to IEC 60384-1, class X capacitors are electrical capacitors with "unlimited capacity" that are connected between phase and neutral conductor or between two phases. They are prescribed for applications in which failure due to a short circuit cannot lead to dangerous electric shock.
| Classification of radio interference suppression capacitors of class X | |||
|---|---|---|---|
| Subclass | application | Pulse peak voltage in operation |
required pulse strength |
| X1 | Use at high peak voltages | 2.5 kV - 4 kV | 4 kV for C ≤ 1 µF |
| X2 | General requirements | ≤ 2.5 kV | 2.5 kV for C ≤ 1 µF |
| X3 | General requirements | ≤ 1.2 kV | - |
Class Y capacitors according to IEC 60384-1 are capacitors that are connected between the phase or neutral conductor and touchable, protective earthed device housing and thus bridge the basic insulation. According to this standard, only those capacitors are permitted for Y capacitors which have a verifiable increased electrical and mechanical safety with a limited capacity, since if they are used in the event of a failure due to a short circuit, people or animals can be endangered by electric shock.
| Classification of radio interference suppression capacitors of class Y | |||
|---|---|---|---|
| Subclass | Type of isolation bridged |
Rated voltage range (nominal voltage range) |
required pulse strength |
| Y1 | Double or reinforced insulation |
≤ 500 VAC | 8 kV |
| Y2 | Basic or additional insulation |
≥ 150 VAC - ≤ 300 VAC | 5 kV |
| Y3 | Basic or additional insulation |
≥ 150 VAC - ≤ 250 VAC | - |
| Y4 | Basic or additional insulation |
<150 VAC | 2.5 kV |
Designs
Since the high-frequency interference suppression also depends heavily on the design of the decoupling element, there are several versions of radio interference suppression capacitors on the market:
- X or Y capacitors as individual components with two connections.
- XY capacitors with three connections as combination capacitors with X and Y capacitors in one housing. These capacitors are wound in one operation. They are internally connected to one another in star or delta connection.
- Feed-through capacitors with a central conductor for the operating current. The structure can be coaxial or non-coaxial.
use
Y capacitors are used to suppress common mode interference . This is the only exception where the protective conductor may be used for purposes other than protective earthing and thus protecting human life against electric shock. In the event of a short circuit in the capacitor, the outer conductor is connected to the protective conductor and thus to the metal housing of the device. Therefore, higher safety standards apply than with X-capacitors, which only trigger a short circuit in the event of failure.
X capacitors are used to suppress differential mode interference.
X and Y capacitors are used in devices to improve immunity to interference and to reduce emissions. These include B. in particular:
- Commutator motors and devices containing them ( vacuum cleaners , drills , washing machines , etc.)
- Switching power supplies and devices that contain them (PC, TV, monitor)
- Phase angle controls ( dimmers , power controllers with thyristors or triac )
- electronic ballasts and mains voltage control gear for light emitting diodes
safety
In order not to jeopardize the protective function of the protective conductor and because of the operation directly on the low-resistance network, increased protection requirements are placed on X and Y capacitors, which are tested and certified by the VDE in Germany and in the other European countries by the respective national organizations. In the past, the released capacitors were allowed to bear the respective logos such as B. VDE, SEMKO, DEMKO, NEMKO etc. are provided. As part of the harmonization of European standards, the countries of the European Union agreed in 2000 to mutually recognize the country-specific safety regulations and their certificates and to use a common logo ( ENEC ). Nevertheless, even on newer interference suppression capacitors, if there is space, there are still many different logos, because in many states on the American continent the capacitors are certified by the Underwriters Laboratories , or UL for short, and Canada and other non-European countries have theirs have their own certification bodies with their logos.
The special protection requirements for the capacitors are increased dielectric strength and high impulse shock load capacity. X1 capacitors withstand a voltage pulse of 4000 V, X2- of 2500 V and Y capacitors double the voltage pulse. In addition, according to UL, these capacitors must not emit a flash of flame in the event of destruction and must not secrete conductive material that could trigger short circuits elsewhere. Non-conductive parts may only flake off with low acceleration (no explosion).
Up until around 1990, only ceramic capacitors and special paper capacitors could meet the increased safety standards for X and Y capacitors. Because of the resin-impregnated paper, the MP capacitors are still considered a safe solution today, because the prescribed load tests only inflate the capacitor at most. The destruction always takes place within the envelope. From 1990 industrial pressure to reduce costs led to the development of special plastic film capacitors (MKP and MKT capacitors). Their safety is also given nowadays and, provided they are certified, they have the appropriate approvals. In contrast to the special paper capacitors, the housing of the capacitor is almost always destroyed in the stress test, which means that oxygen can reach the damaged area under mains voltage. The strict interpretation of the regulations that has been practiced since the existence of such safety capacitors has therefore been weakened in favor of cost reduction, which is why plastic film capacitors are not undisputed for this application.
In the context of miniaturization in industry, surface-mountable SMD designs are becoming increasingly important. This also applies to interference suppression capacitors. Since up to now neither MP nor MKP nor MKT interference suppression capacitors in SMD design have been offered, SMD ceramic interference suppression capacitors are gaining in importance. Here, too, the originally stricter safety aspect is softened in favor of cost reduction, since there are currently no ceramic capacitors with ENEC or UL approval.
standardization
The conditions for the tests and measurements of the electrical and mechanical parameters for the approval of the radio interference suppression capacitors in the European area (ENEC) are specified in the standard DIN IEC 60384-14.
history
In the 1950s, interference suppression capacitors were tested according to VDE 0870. In the 1970s there was only one class X and one class Y as special categories for interference suppression capacitors. The regulations of VDE 0560-7 applied to class X, whereby class Y also had to meet the requirements of VDE 0560 part 7 / 11.67. The former class X corresponds to today's class X2.
literature
- Hans Loth [Roederstein]: Film capacitors . The library of technology, Verlag modern industry, ISBN 3-478-93046-4
- DIN EN 60940 (VDE 0565) guidelines for the use of capacitors, resistors, chokes and complete filter units to suppress electromagnetic interference . May 2013, dke.de
Web links
Individual evidence
- ↑ "Safety Recognized" ceramic capacitors from Murata (PDF; 1.7 MB)
- ↑ Study by the company WIMA on the flammability of radio interference suppression capacitors ( Memento from February 28, 2007 in the Internet Archive ), accessed on November 19, 2019.
- ^ VEB Keramische Werke Helmsdorf: "High frequency capacitors." Hermsdorf-Klosterlausnitz 1959.
- ^ Components, materials and assemblies. Capacitors Resistors (= Mullard [Hrsg.]: Mullard technical handbook . Volume 1 , no. 3 ). Burrup, Mathieson & Co, England 1981, p. B-330-1 and C-660-1 (English, online [accessed January 16, 2017]).