Servo Drive Transformer

[Neilf]

This is the circuit of an electronic servo drive transformer to change 380v 3 phase to 200v 3phase as advertised by several companies.
How does it work!

 

[rjenkinsgb]

It appears to put pulsed DC out, not AC.

It's using the phase to neutral voltage (so roughly 200V AC anyway) and combining two phases via the diodes.

The output may work for some things (like power supplies, that rectify the input) but I'd not use it for a motor or transformer etc. - the DC would magnetise it and drastically affect its operation, if it did not just overload the supply or the load due to the winding cores saturating.

 

[Neilf]

We have two Panasonic drives that have over volted running off these transformers, could a fault on the neutral cause the output voltage to go above 200v

 

[Nigel Goodwin]

We have two Panasonic drives that have over volted running off these transformers, could a fault on the neutral cause the output voltage to go above 200v

It's not a transformer, and looks a pretty nasty sort of thing. As it uses the neutral in it's (nasty) operation, then it's likely to cause damage if the neutral disappears.

 

[rjenkinsgb]

If neutral is lost, there is no current path through the other two phases as one will always have the diodes reverse biased.

What's more likely is the two-phase summing (via D2 & D3) is messing up the drive input circuit.

Also note that if the drives use any kind of synchronous rectification - or are regenerative - they have no chance of working properly with one of these gadgets long term, as the input waveforms will be totally messed up and there is no current path for regeneration, so excess energy in the drive DC link cannot be returned to the incoming supply.

You need a real (wound) power transformer..

 

[Neilf]

Thanks for the info,just a warning to anyone using these transformers some of the descriptions on the sellers sites is complete nonsense. Some of them say the transformers use the latest microwave devices etc. Had to get rid of the potting compound to find the real components

 

[Nigel Goodwin]

Thanks for the info,just a warning to anyone using these transformers some of the descriptions on the sellers sites is complete nonsense. Some of them say the transformers use the latest microwave devices etc. Had to get rid of the potting compound to find the real components

Must admit, that's one of the reasons we pot some of our products

The main reason though is water proofing.

 

[Neilf]

This is the description from one site.
Electronic Transformer uses the most advanced technology of three-phase full-bridge switching resonant, SPWM modulation, power module, so it less heat, basically without radiators, low energy consumption, completely eliminate EMI interference. Internal as well as electromagnetic filter regulator features and a variety of circuit protection, short circuit, over current, over voltage protection. When a transformer fails to prevent, protect against damage to the servo drive.