EMI suppress examples
Filter usage examples and EMI of different appliances
All products not only consumer electronic, sold (prouced or
imported) in Cz Republic must comply with a law
No. 22/1997 Coll. - on technical
requirements
for products containing
electrical
components
from
EMC
- electromagnetic
compatibility
Government
Decree No. 169/97 Coll.
in EU countries. The same applies in the EU - CE. This tag must bear all products sold in the European
Union.
Essentially, it means that the product complies with all applicable standards that apply to this product. One of these standards are the standards for EMC. Simplz saying the product electromagnetically compatible is a product that does not disturb surroundings such as radiation and contrast is resistant against external interference.
It is possible to imagine an example that a microwave oven does not interfere with the effects of television receive and also that when we turn on the iron, the switching of the thermostat will not change the behavior of a microwave oven (randomly won't reprogram or switch off, and so on.). For industrial facilities in the often large-scale systems that must operate even under large external noise, but where a single failure (due to external interference) can be very expensive - such as destroying of an expensive piece cutting knife sudden shift caused by interference. Therefore, it is now increasingly striving to ensure that products would not interfered, and concurrently were resistive against outside interference.
The basis is the products don't interfere the surroundings. When they are susceptible to ambient noise and the not cause damage to health, not just a competitive product. But when the product disturbs surroundings, followed by the shutdown, the penalty for violation of law No 22. In any case, it is necessary to eliminate interference sources using the filter. Therefore it is necessary to purchase equipment from abroad (and older!) ensure interference and the require the supplier's certificate of compliance with IEC 61000-6-3 and EN 61000-6-4. The importer can not otherwise get to the issues listed above. It is also known to many cases where a foreign company confirmed suppression and in imported equipment there is no any filter.
Devices, that are usually sources of interference:
- Frequency converters
- pulse and thyristor suppliers and chargers
- thyristor DC speed motor controllers
- thyristor power regulators
- switchboards with contactors etc. with switching frequency higher than 5 times in 1 minute
EMI filters are used mostly for EMI suppression of these interference sources.
The reason for using it is to meet standards - EMC electromagnetic compatibility, in principle, ČSN EN 61000-6-3 and 61000-6-4. These standards define the effect of facilities on the surrounding area, whether the emission of higher harmonics, the emission of radio interference to power lines, radio emission of electromagnetic radiation, flicker and the other issues. These standards apply, unless there is standard number subject (lamps, traction equipment of information technology, etc.).
Filters are used to reduce interference in 150 kHz - 30 MHz band - it is interference monitoring and measurement of network terminals.
Terms of using EMI filters depends on:
circuit connection
voltage dimension
current dimensions
environment
permitted leakage current
Circuit connections.
EMI filters are connected (because of price and sizes) as a compesated inductance, vector sum of input currents must be zero. Practically, it means that through PE terminal can't flow operating current . For single-phase connections filter is connected to phase and neutral, for three-phase connection three coil EMI filter is used, if the device is connected so that a neutral
conductor N is used
as working one (if single-phase consumer, connected between phase an neutral) must be supplied by 5-wire ( 3 phase N and PE) and to use 4 coiled EMI filter (3 phase and N). Connection of N and PE should be completed
before EMC filter. EMI filters can't be used instead of phase reators - their inductance is compensated, thus the difference inuctance is minimum. EMI filters can be connected in parallel - because of uncompensated separate filters.
Filters dimensions
Filters dimensioned on voltage and current under the nominal input voltage and current of the used device. Filters are usually able to pass inrush current at startup without damaging , such as frequency converter at network (DC-link capacitor charging). The company ELFIS manufactures filters 2,3,4 3-coil 1600 A on the voltage to 750V AC.
Environment.
Environment can be divided into:
1. Industrial environment.
2. For residential, business spaces and light industry.
The division depends on the connection to the public distribution network where the industrial environment has its own HV
transformer
and on its LV side are directly connected to
residential
areas. It should be noted that the permitted noise limits for residential environments
are much more stringent
and
therefore more expensive than the interference suppression based on the industrial environment.
Leakage current
It should be payed attention when using the device with a flexible cords using earth leakage breaker.
This is a current that flows might flow through PE conductor - yellow and green. Ita can be seen as the current flew through the human body at protetive conductor PE interruption and one would keep skeleton with one hand and the seond hand would be grounded (for example touching the surronding heating, etc.). Permitted leakage current value is given by the standards, normal value is 0.75 mA nor 3.5 mA.
RCDs are designed to disconnect the protected device, if vector sum of all phase currents and N is not equal to zero (it is greater than current protector), when exceeding the rated current protector this protector diconnects the load.
When dimensioning RCDs there is a need to consider that at switching devices switching contacts don't have to switch all phases at the same time, itmay occur that only one phase switches and N won't switch, then the current that monitors the ciruit braker can be 6 x higher at three-phase connection an 2 x higher for one-phase connection than is then constant current PE conductor at steady state.
Then we can choose RCD, which supplies with delay, possibly using
a RCD with higher tripping current.
When using EMI filters the leakage capacitive
current arises using the suppress capaitors, connected between phase and
terminal PE.
It is also necessary to remember that the condensers from phase to ground may also include
other
devices
than suppression
filters,
such as
frequency
converters, switching power supplies
and etc.
EMI suppress examples
1. EMI supperss frequency converter with three-phase input, filter is monitored directly under the converter.
Required suppress: for industrial environment
Switchboard must orrespond the standards: ČSN EN 55011 for devices class A - net terminals interference voltare measurement in 150 kHz - 30 MHz range and therefore ČSN EN 61000-6-4 for industrial environments.
2. Switchboard EMI suppress, which contains frequency converter with one-phase input ( obvykle do 2,2 - 4 kW )
Required suppress: for residental builings, equipment is directly connectde on LV net in residental builing. Switchboard must correspond the standards: ČSN EN 55011 for equipment class B - interference voltage measuring on net terminals in 150 kHz - 30 MHz band and therefore ČSN EN 61000-6-3 for residental builings, comecial, office and light industry.
3. Switchboard EMI suppress, which contains frequency converter with three-phase input. Suppression devices used: fiv-wired power system, so suppression filter was used with four coils on the input. Required suppression: for industrial environments.
4. Odrušení rozváděče, který obsahuje třífázový tyristorový regulátor výkonu 1600A pro topení ve sklářské peci, zatěžovací odpory mohou být i elektrody ve vaně, zapojené přes oddělovací snižovací transformátor.
Požadované odrušení: pro průmyslová prostředí, sklárna má vlastní VN transformátor. Zařízení tedy musí odpovídat normě ČSN EN 61000-6-4 - pro prostředí průmyslová.
5. Odrušení frekvenčních měničů filtrem, který se montuje přímo pod měnič.
Pro úsporu místa v rozvaděčích se používají takto konstrukčně upravené filtry. Používají se jednoduché i dvojité filtry. Dvojité filtry jsou určeny pro prostředí obytná. V řadě proudů 3, 6, 10, 16 a 20A, je vyrábí firma ELFIS pro jednofázové (230V) i třífázové napájení ( 400V ). Rozměry upevňovacích matic pro připevnění měniče lze dodávat podle přání zákazníků.
Filtry pod frekvenční měniče OMRON, Siemens atd.
Zásady.
Při odrušování platí:
Nejvíce vyzařuje kabel mezi frekvenčním měničem a motorem.
Používáme stíněný kabel, pokud možno nepřerušený.
Řídící a ovládací signály k frekvenčnímu měniči vedeme co nejdále od výstupních vodičů k motoru, křížení nejlépe s úhlem 90 stupňů.
Zemnící spoj má být co nejkratší a zapojený do bodu s dokonalým uzemněním.
Používat pro zemnění vodič s větším průřezem, z důvodu nižší indukčnosti.
Většina problémů vzniká nedokonalým uzemněním, rušivá napětí na vstupu filtru jsou v normě, ale měření na vstupní svorkovnici je nad povolenou mezí.
Používání umělohmotných korýtek pro vedení vodičů často svádí k vedení odrušených vodičů (před filtrem ) k souběžnému vedení s neodrušenými vodiči a tím dojde ke snížení útlumu filtru (kapacitní a zejména induktivní vazby.