High Voltage Tesla Lab overview – part 1; the Generator

Before continuing the experiments let me walk you through our laboratory

It all starts with our generator which consists of

• an engine (Cummins 6BT5.9) – which is a 5.9 litre turbo diesel
• a generator (Stamford)
• a lot of electronics to regulate and control the whole thing

The generator is designed to give 3 phase output, but we can not use 3 phase power. Now you might think to use 1 or 2 phases and just leave the remaining one untouched. But that is not a good idea at all.
One turn of the engine can be divided into 6 parts, as every phase has a positive maximum and a negative maximum. By leaving 1 phase unconnected you create 2 parts during each turn where there is little resistance. So the engine and everything with it is unevenly loaded which will cause excessive wear on most of its components.

The solution is to rewire the generator to give 2 phase output. This is actually surprisingly easy.

For every phase the generator has 2 coils. If you connect these in series you will get 220-240 V, or if you connect them in parallel you will get 110-120 V at twice the amperage.
Normally -in a 3 phase configuration- the coils have 1 end connected together which then provides the “neutral”, and the other ends provide the 3 phases.
Like this:

(this configuration is called “series star” for obvious reasons)
By disconnecting one of the coils at the “Neutral” and reconnecting it at one of the remaining phases, you get this:

(this configuration is called “series zig-zag” for likewise obvious reasons)

L2 is now used to create an offset for L3, and as a result L3 becomes exactly opposite to L1.
Thus we have created a 2 phase output (L1 and L3).
Every coil can produce about 150 A, so the downside of this is that we go from 3 phase x 220V x 150 A = 99 KVA to 2 phase x 220V x 150 A = 66 KVA. So we can use less power while the engine consumes the same amount of fuel.
Then again, we can not use it in any other way, so we don’t have any other option.

After reconfiguring the coils we need to tell the electronics that the situation has changed, otherwise it will immediately shut down the engine.

The electronics consists of 3 major parts:

• one controls the output voltage (SX440)
• one controls the engine speed
• one controls the overall system (DSE 7320)

The SX440 senses the voltage across 2 coils around neutral. As we do not modify these coils we do not need to change anything here. The SX440 module then adjusts the strength of the magnetic field produced by the rotor in such a way that the stator coils pick up the desired voltage, independent of the engine speed.

The engine speed determines the output frequency, which has been set to 50 Hz. By running the engine slightly faster we could get 60 Hz. At this higher speed the engine produces more power so you could theoretically draw more current. But we are not interested in this. At a later stage we might want to change the frequency to a multiple of 11.7 Hz (46.8 Hz or 58.5 Hz) so we could (again) verify earth resonance. For now, we will leave this at 50 Hz.

The DSE7320 needs to be aware of our rewiring. It has a USB connector and with the appropriate software (unfortunately MS Windows only) we can change the settings.
Just to be sure, I also disconnected the ‘unused’ phase (L2) from the DSE7320.

So there we are. We now have a L-N of 220V and a L-L of 440V, 2 phase, 66 KVA generator.
We will be using the phase to phase 440 volts.