Just a follow up here.

Today 01 Mar 2006, I was back at the tunnel to collect two dataloggers from one of the transformers, to check for voltage sags.
the worst readings were 220 Volts ( about 4% under Unom. is 235 Volts ) at low speed at the 500 kVA spare transformer.
The feeder trip was recorded also and lasted for 10 minutes, Auchh!! [Linked Image]

At the moment they are not allowed to drill at full speed, 1500 RPM because of the D.O.L. start will take out the feeder.
An engineer will try to sort ou the trip settings on the local switch to the 1000 kVA transformer, while off loading branch lines from this feeder is looked at by the lines company at the moment.

I had a look in the tunnel which is about 20 metres inwards in hard rock.
Arc is about 12 metres wide.
The drill is manned with 2 operators.
The swivel part with the drill extends about 6 to 8 metres from the machine and does the breaking of the rocks, very noisy and clouds of dust.
The water cooling jets are not being used at the moment because of low speed operation at 750 RPM, although the drill bit ran a lot slower, more like 2 to 3 revolutions per second. still a lot of heat is generated though.

The tunnel is supported in 5 metre sections, The drill operator is not allowed to work in the unsupported area of the tunnel, hence the swivel option and extendable drill shaft, works in the unsupported area of the tunnel.
The machine can be remotely controlled, in case of dangerous unstable rock area's and camera's provide the information.

As soon a 5 metre segment is cleared of rocks, steel guirders are inserted, to support the tunnel roof.

I forgot my camera, but the dusty conditions were far from ideal anyway to take a good photo. An other site visit will happen in the near future and hopefully conditions are better then.

The product of rotation, excitation and flux produces electricty.