big denford triac problems

[mark35gun]

no neutral on the m/c, the voltages across the 3 phases are 440,440,380, i am sure that the problem exists when the rotary phase converter is turned off without isolating the m/c first as it has done this twice now as soon as the motor shuts down the ammeter shows a current draw of +40 amps which lunches the control, normal running the ammeter shows 2-3 amps with the m/c on, i don't understand why there should be a large current draw when the phase converter is turned off and the m/c isolator is closed, i have no experience of rotary phase converters so i do not know if this behaviour is normal or not

[m_c]

no neutral on the m/c, the voltages across the 3 phases are 440,440,380, i am sure that the problem exists when the rotary phase converter is turned off without isolating the m/c first as it has done this twice now as soon as the motor shuts down the ammeter shows a current draw of +40 amps which lunches the control, normal running the ammeter shows 2-3 amps with the m/c on, i don't understand why there should be a large current draw when the phase converter is turned off and the m/c isolator is closed, i have no experience of rotary phase converters so i do not know if this behaviour is normal or not

Any chance you could take a photo of the inside of the phase converter?
When you say you switch of the phase converter, how do you switch it off?

My suspicion is switching off the phase converter doesn't actually isolates it's output, so it's still outputting 2 phases at full voltage, along with leaving the balancing capacitors active (aka acting like a static phase converter), which when combined with a switch mode load (aka the FANUC power module), could be resulting in some very high voltages on the false phase.

[mark35gun]

yes i will take some shortly, i think you are right, just stopping the phase converter with the stop start control Ie stop button, which is fine as long as you know to isolate before stopping.
i have always used vfd inverters where required but never rotary types, i was on the understanding that the rotary types were ok for non electronic machines, but too "coarse" for sensitive equipment, in saying that this m/c has run with this setup for many years so should it be considered ok?

[m_c]

Rotary converters are fine, however you just have to be aware of their limitations.
Some equipment won't tolerate a big mis-match on voltages, but even your mains 3 phase is rarely perfectly matched. You're only likely to get problems if the false leg is majorly out of tolerance, or you are pushing equipment to it's limit.

However some rotary converters leave a lot to be desired in terms of controlling the false leg, and safety protection.

[mark35gun]

pics of the phase converter, well part of it the other bit is the previous pic with the ammeter which is not so easy to get the lid off
you can see the stop button i use for off