[Amps] Electrical Distribution Methods

[peter chadwick]

At least here, 240 volt single phase is from the centre point of a Y connected transformer. The outside ends of the windings all have 415 volts between them i.e. if you wire them a to a delta load, the load is a three phase 415 volt load, and it seems the system in Chile is similar, but the voltages are different. Here distribution is at 400kV, 275kV, 132kV, 66kV, 33kV, 11kV and there may still be some places with 6.6kV or 3.3kV. It's now mainly 11 and 33kv distribution in rural areas. Our local expert is G4LDL, who is this week commissioning and in charge of the testing of a 90MVA 132kV primary transformer - rather bigger than what we are all accustomed to! I gather that in the US, the 'Pole Pig' is a single phase transformer with a primary connected between one phase and ground, which is also the star point of a Y connected transformer secondary. The secondary is then a 240 volt winding, with grounded centre tap, giving 120 - 0 - 120.

 I presume the Thai 4 wire system is three phases and a Y neutral. By transforming to 240 or 220 or whatever and not grounding one side, what prevents the line floating up? - for instance, you could have one wire at 300 volts above ground and the other at 540 volts above ground. I would expect that measuring the volts from each side to a good ground will show one pin somewhere  around a few volts above ground and the other 240 or so volts higher. Having typed  all this and checked what has come in, I see Manfred has exactly the same thought.

Ideally, Charly would use a HV tester to test the insulation between input wires and chassis (with the amp unplugged) and from the transformer primary terminals to chassis. It should be very high. As the amp doesn't use the chassis as a return for anything connected to the AC line, then the fusing of one side shouldn't make any difference although the main fuse should then feed other fuses so that fault tolerance is built in. What does need doing is to ensure a good external ground is connected to all the station equipment, and then it won't matter which way round the amp is plugged in.

73

Peter G3RZP