HV Power Supply

[rockman7892]

I'm involved with a project where a HV power supply is being provide for transformer testing which include typical tests for new liquid filled manufacturing (loss testing, impedance testing, insulation testing, etc..)

The attached one-line gives a representation of the equipment that are part of this system. In looking at this I has some specific questions about this system I was hoping others may be able to help explain:

1) Why for a HV power supply application like this is the LV AC first converted to DC before being rectified back to AC and stepped up to the HV. I'm assuming it has to do with being able to control the voltage to the step-up transformer in order to vary the voltage across the output range? I'm curious why its more efficient to do this voltage control with DC as opposed to having a Variac or other device control on the LV AC side before being stepped up?

2) There is a waveform filter shown on the output of the inverter. Are such waveform filters common anytime an inverter is supplying an AC output? In other words are they also common in VFD, UPS, etc...

3) The step up transformer has a capacitor bank connected to the tertiary winding. I'm assuming the purpose of this Cap Bank is to supply reactive power to the output of the system as opposed to having it supplied by the source? If so why connect this to a tertiary winding as opposed to a direct connection on the transformer output. Perhaps having to do with the varying voltage?

4) The drawing shows HV PD filters and I've seen a lot of conversations around the need for varying levels of filtration related to different filter sizes to achieve a particular Pc rating. I'm curious how this filtration relates to PD testing/measurements and what these filters are trying to achieve on the system.

Thanks for the help

 

[rockman7892]

Just realized that I forgot attachment.

 

[thermionic1]

I'll take a stab..

1) Why for a HV power supply application like this is the LV AC first converted to DC before being rectified back to AC

I'm guessing that this allows for variable frequency AC, such as for the induced voltage test, which would be 120 Hz, on a 60 Hz unit. It may also allow for testing 50 hZ units. It may be that the generated frequency provides a highly regulated frequency not available by other means.​

2) Are such waveform filters common anytime an inverter is supplying an AC output?

Filters are quite common on these devices.​

3) The step up transformer has a capacitor bank connected to the tertiary winding.

I would think this is for PF correction of the mains. It provides the required reactive compensation and is likely a much lower voltage than the HV or Test winding, which reduces cost of said equipment.​

4) The drawing shows HV PD filters

PD is a very sensitive measurement (nano / pico coulombs). If the test transformer is a source of noise or PD, it can skew the results of the device under test.​