Mains transformer core is earthed?

[Faringdon]

Hi,
Is the core of this isolation transformer earthed?

https://www.screwfix.com/p/carroll-meynell-3000va-intermittent-isolation-transformer-230v-230v-blue/320HV?kpid=320HV&cm_mmc=Google-_-Datafeed-_-Electrical%20and%20Lighting?kpid=KINASEKPID&cm_mmc=Google-_-TOKEN1-_-TOKEN2&gad_source=1&gclid=EAIaIQobChMIurKz6pO_hwMVZo9QBh2u4gyPEAQYASABEgJZOvD_BwE&gclsrc=aw.ds


https://www.carroll-meynell.com/product/isolation-transformer-230-230v-3kva-cm3000-230-euro/

Earth goes into it...do you know what that earth connects to?
& Why is it so noisy when its switched ON, even with its secondary open?
(ie noisy electrically to other equipment plugged in on the same phase, making it malfunction)

[techneut]

My guess is that there is a shield between primary and secundary windings that is earthed. I have a 2A isolation transformer and you can realy hear the dumph when it is powered on. The magnatising current with it's mgnetic field is my guess.

[Faringdon]

Thanks, i was thinking the same, but the magnetising current isnt that much since the inductance is so high?
I am thinking its capacitively putting a big   common mode transient into earth, since the earthed shield is highly "strayly" capacitively coupled to the primary.
But not sure the exact reason.

[garrettm]

Why is it so noisy when its switched ON, even with its secondary open?
(ie noisy electrically to other equipment plugged in on the same phase, making it malfunction)

I doubt this is a capacitive effect here. At 50 to 60 Hz a few nanofarads of stray capacitance to earth ground would act as a very high impedance. I suspect you have a shorted turn or high leakage to earth ground from a damaged primary coil. You could disconnect the earth ground and see what that changes. You could also try measuring the current passed to earth ground with a current clamp, or use a power meter to see how much real power is being consumed by the unloaded transformer (should be mostly reactive).

I suspect the transformer has a bad primary winding. It's rare, but it happens.

[AVGresponding]

If it's used rather than new it's probably more common than you think, as the gorillas on sites usually take the intermittent rating as the continuous one and cook the things

[nali]

Earth goes into it...do you know what that earth connects to?
& Why is it so noisy when its switched ON, even with its secondary open?
(ie noisy electrically to other equipment plugged in on the same phase, making it malfunction)

Just undo the 4 screws holding the top on - all will be revealed!
(And, no I'm not going to tell you - get your lazy arse in gear and look for youself!)

[adam4521]

At the moment of switch on,  this system is not responding to ‘steady state’ ac equations. There’s no magnetic flux, no back emf, and you connect a step voltage. The dv/dt and the di/dt is very high. There will be considerable interaction between the supply impedance and the transformer, so transient effects fully expected- expect an instantaneous current in excess of 100A followed by oscillations to reach the steady state. I expect the transformer is behaving normally.

[Faringdon]

Just undo the 4 screws holding the top on - all will be revealed!
(And, no I'm not going to tell you - get your lazy arse in gear and look for youself!)

Thanks,  thats a great idea....but the project has been completed now...with all targets met as by the organisation's requirement, so i wouldnt be at liberty to go taking apart their equipment for some post project research.