X Y capacitors

[Dan Teopoulos]

Hi,
We are trying to reduce interference in the power suppy of an
industrial installation and I was thinking of placing X / Y capacitors
at the installation's power supply input. However I have several
doubts about this type of components and how safe it is to carry this
out. I would appreciate it very much if anyone could help me with any
of this doubts:

- Do X and Y type capacitor assure that in case of component's failure
the will behave as an open circuit?
- In a data sheet of evox-rifa I have read that some capacitors are
"self healing" and others don't. Does this mean that some will behave
as open circuit in case of failure and the others will not?
- Is it a good idea to attach fuses to the capacitors to avoid short
circuit in case of failure?
- I have read that Y type capacitors are safer than X capacitors but
intended for use between phases and ground. Would there be any
problem in using Y capacitors between phases instead of X capacitors?

Thank you very much in advance:
Dan.

 

[Spehro Pefhany]

Hi,
We are trying to reduce interference in the power suppy of an
industrial installation and I was thinking of placing X / Y capacitors
at the installation's power supply input. However I have several
doubts about this type of components and how safe it is to carry this
out. I would appreciate it very much if anyone could help me with any
of this doubts:

- Do X and Y type capacitor assure that in case of component's failure
the will behave as an open circuit?

AFAIK, Y capacitors are designed so as to make failure extremely
unlikely. X type won't cause a fire if they fail. As a general rule,
everything insulating or semiconducting tends to fail short from
electrical stress, at least to begin with. If the leads break off or
the part snaps in half, that's different.

- In a data sheet of evox-rifa I have read that some capacitors are
"self healing" and others don't. Does this mean that some will behave
as open circuit in case of failure and the others will not?

Self healing means that they short, but energy from the circuit blows
the short away. The minimum current to blow the short away might be
enough to be fatal to a human. This would allow a less conservatively
rated capacitor to be used in an application where it might get a
very, very occasional damaging overvoltage.

- Is it a good idea to attach fuses to the capacitors to avoid short
circuit in case of failure?
- I have read that Y type capacitors are safer than X capacitors but
intended for use between phases and ground. Would there be any
problem in using Y capacitors between phases instead of X capacitors?

I don't think so, other than cost and size. John Woodgate would
probably know for sure.

Thank you very much in advance:
Dan.

Best regards,
Spehro Pefhany