Maximum allowed single dv/dt of film capacitors

Thread Starter

Padderick

Joined Jan 7, 2012
13
Hallo together,

I am working on a AC input filter and the filter capacitor we use is made for repetetively 100V/µs.
When we connect the input filter with a relais to the grid, which happens daily in the field,
the AC input filter voltage rises around 280V/µs for 2.5µs up to arround 750V.
In our case we use a 1µF capacitor and get a single current flowing of I=C*du/dt=1µF*280V/µs=280A for the time of 2,8µs.

Questions:

1) Which effects occur when a voltage is switched on to a capacitor by a relais, when the high current due to the dv/dt and the capacitance is flowing through the capacitor?
2) Does anybody of you know how to get the maximum allowed value?
3) Are there any design notes concerning the maximum allowed single pulses on film capacitors/ capacitors in general?
4) Do you know any thermal models of any film capacitors?


Thanks in advance.

Best regards,

Friendly2Earth
 

Irving

Joined Jan 30, 2016
1,070
Duckduckgo could be your friend...

https://www.illinoiscapacitor.com/pdf/Papers/pulse_operation_film_capacitors.pdf

https://sh.kemet.com/Lists/ProductCatalog/Attachments/159/F9000_GenInfo_DCFilm.pdf (section 6 refers)

https://www.tdk-electronics.tdk.com...1513474ba/pdf-generaltechnicalinformation.pdf (section 3)

Also, it sounds like the capacitor you're using is under-spec'd:
see https://www.cde.com/resources/catalogs/946C.pdf , 1uF, 1200vDC part.


Is there an option to use electronic zero-voltage switching?
 

Thread Starter

Padderick

Joined Jan 7, 2012
13
Duckduckgo could be your friend...

https://www.illinoiscapacitor.com/pdf/Papers/pulse_operation_film_capacitors.pdf

https://sh.kemet.com/Lists/ProductCatalog/Attachments/159/F9000_GenInfo_DCFilm.pdf (section 6 refers)

https://www.tdk-electronics.tdk.com...1513474ba/pdf-generaltechnicalinformation.pdf (section 3)

Also, it sounds like the capacitor you're using is under-spec'd:
see https://www.cde.com/resources/catalogs/946C.pdf , 1uF, 1200vDC part.


Is there an option to use electronic zero-voltage switching?
Duckduckgo could be your friend...

https://www.illinoiscapacitor.com/pdf/Papers/pulse_operation_film_capacitors.pdf

https://sh.kemet.com/Lists/ProductCatalog/Attachments/159/F9000_GenInfo_DCFilm.pdf (section 6 refers)

https://www.tdk-electronics.tdk.com...1513474ba/pdf-generaltechnicalinformation.pdf (section 3)

Also, it sounds like the capacitor you're using is under-spec'd:
see https://www.cde.com/resources/catalogs/946C.pdf , 1uF, 1200vDC part.


Is there an option to use electronic zero-voltage switching?
Hallo,

yes DuckDuckgo could be a friend of mine, if DuckDuckgo could think like a human beeing and could answer questions in detail by a combination of knowledge and experience ;-)

Thank you for your interesting literature about film capacitors.

There is no option for zero voltage switching, due to the fact, that the customer has got to tell the relais, when it has to close.

We use X2-filter capacitors, these capacitors are able to withstand surge pulses up to 2.5 kV...

Do you know if

1) The specified value K0 is also valid for single pulses/surge pulses?
2) there exist any thermal model of film capacitors?

Thanks in advance.

Best regards,

Friendly2Earth
 

Irving

Joined Jan 30, 2016
1,070
Hallo,

yes DuckDuckgo could be a friend of mine, if DuckDuckgo could think like a human beeing and could answer questions in detail by a combination of knowledge and experience ;-)

Thank you for your interesting literature about film capacitors.

There is no option for zero voltage switching, due to the fact, that the customer has got to tell the relais, when it has to close.

We use X2-filter capacitors, these capacitors are able to withstand surge pulses up to 2.5 kV...

Do you know if

1) The specified value K0 is also valid for single pulses/surge pulses?
2) there exist any thermal model of film capacitors?

Thanks in advance.

Best regards,

Friendly2Earth
I think you are best advised to talk to a capacitor manufacturer, TDK seem to be quite responsive from my experience. Maybe also ask the question on the LTSpice forum to see if anyone has modelled this.

Regarding zero-switching, agreed the customer tells the relay when to close, but its still possible to implement a zero-switched soft start to reduce the inrush load. What is the load that causes this large peak current?
 
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