I have always thought that cement works were prone to explosions due to the dust.
Thatās just awful Visitor! Safety is a big factor when youāre working with dangerously high voltages
Yes, I agree. It is dangerous. But you mitigate the risks. Thatās what we do. My point though was that fifty years or so that I have doing this was just the two incidents. None would be better but I think we have achieved a pretty good safety safety record.
Absolutely Visitor!
Thatās an outstanding safety record for your long career. Iām certain though that both incidents were one too many for you.
A transmitter engineer working on the Voice of Peace killed themselves when the ship moved on a wave & they touched something high voltage.
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Oh my word, thatās so tragic Gee.
Dangerous occupation - working with electrical stuff
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Itās why you are told to work with one hand in your pocket if itās live. Although capacitors hold voltage, so switching it off is not always that much safer. And a capacitor can acquire a good charge, just sitting on a shelf, all by itās self.
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That is really hectic. It must be really stressful
My personal favourites are mercury arc rectifiers, one of the power stations I worked at in the heart of Sydney (Pyrmont) used them to power the precipitators to remove dust from the smoke.
They are large, sealed glass vessels containing a pool of mercury with a long electric arc between the anode and the mercury. Very spectacular.
This is just a random Youtube video of them working
How was the motor wound? i.e. was it a schrage slip ring job or summat else? At 3.3kv it must have been a fair size and powerful. I can remember HV motors driving York compressors at one of the installations I supervised.
It was squirrel cage induction motor. That is a stator and rotor. Itās a simple and robust machine, the most common type of machine for industry. In this case it 700kW. The cement mill has several larger motors, 2,200kW at 11,000V and these are wound rotor machines with slip rings so a bit more complex.
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And just to think Besoeker, these massive motors controlled initially by mere milliamperesā¦
Just curious why would it need a speed controller? Squirrel cage motors are synchronous motors. Or was that stuff just to reduce starting current? All the motors I worked with were direct on line so they drew 5 times the running current at start up. but as we generated it it didnāt matter.
At Pyrmont Power Station when we started the first feed pump we dimmed the lights in the whole suburb
Yes it does. Impressive gain! The electronic supplies are 12-0-12 DC.
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[quote=āBruce, post:33, topic:85479ā]
Just curious why would it need a speed controller? Squirrel cage motors are synchronous motors. Or was that stuff just to reduce starting current? All the motors I worked with were direct on line so they drew 5 times the running current at start up. but as we generated it it didnāt matter.[/quote]
Actually squirrel cage motors are asynchronous machines. For example a 50Hz motor at full load speed would run at 1485 rpm. Anyway, our application required speed control. It was for a variable speed fan controller.
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Unless motor construction has changed in the last say 20yrs, I would expect rotor speed to be dictated by the number of poles in an induction motor at a given frequency. My brain is too age addled to do the maths, so Iād better leave this subject now, and as for rotor currents and stator flux ā¦pfft, Iām outta here 
A variable frequency drive can operate the motor at any speed from zero to maximum.
Thatās what I did for a kiving.
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Yep, many motors(for example feed pumps) used hydraulic speed controllers between them and the pump however they themselves were controlled either pneumatically (Bailey) in older equipment or electronically in later versions. Fans generally were centrifugal and used dampers to control output.
As Longdriver pointed out the motor speed is dictated by the number of poles but is proportional to the supply frequency less āslippageā so it does vary slightly with load, the motors you worked with were obviously four pole motors.
Accrtally, the particular motor I was referring to was a six-pole unit. And the chips I| mentioned in the opening post were for the variable speed drive. So no, the slip didnāt just vary very slightly - it operates from zero to full speed.
Variable speed drives was what I did. Mostly cage induction motors and DC drives with a few others like slip-ring machines. These latter units were usually 11kV and several MW but still variable speed drives.
At 1485rpm surely it couldnāt be a 6 pole motor ? A six pole squirrel cage motor at 50hz would rotate at 1000rpm less slippage - say 970rpm? Am I missing something? Are you sure it was a squirrel cage motor? they are not variable speed motors.