Did you talk to the manufacturer?

Yes, I talked to the manufacturer. I didn't obtain all the data I needed to make the calculation, just his advice will work with capacitors. Because the manufacturer is not a name and the medium voltage contactors are still expensive, I wanted a second opinion, he said he exported in US, Australia and Taiwan.
Thank you for the answer.

Our company is currently testing them out for motor control use. We have set up an automated cycle tester and a load bank, testing them at low voltage, rated current, high duty cycle. So far so good, but it has not been long, maybe 2 weeks. Check back in this thread and I'll post our findings. I can't attest to their use in capacitor switching, but I will be curious to here as well.

Quando Omni Flunkus Moritati

Thank you jraef!
I understood you have checked the low voltage vacuum contactors (or the medium voltage?). I'm waiting the test results from you. If I decide to buy and use them, I shall share the information with you as well. To be onest, I'm affraid to take that chance, in capacitors switching the conditions are rough for contactors.

Pafi,
 The capacitor switching is a very harsh mode for any mechanical device. The pre-strike and the re-strike phenomena are well known in the industry and the device shall be capable to cope with it. My recommendation is to ask any vacuum contactor manufacturer to provide a certified test reports that their vacuum contactor or breaker is capable to switch capacitors without problems. You should also ask what the capacitor bank configuration was during the test (i.e. D or Y configuration etc.), and make sure your application is a similar.
The price is not only the point when one selects a contactor for capacitor switching.