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Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
Schematics, all pictures etc:
Features: start/stop, emergency stop, lockable mains switch, mains relay and circuit breaker. A PMA data monitor KS3010 to measure voltage and current on all 3 phases. The data monitor has 6 analogue input channels for signals in the range of +/- 12 VDC and samples these values as a average over 125 ms, which corresponds to 8 samples per second. Step down transformers are used for voltage measurements and CR Magnetics CR4210S-30 RMS AC current transfucers are used for the current.
SKM200 IGBT brick on top of it for size comparison :)
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
Patrick wrote ...
looks like it powers the electric chair.
I would hope for those ending up in one that it was only a switch for full power, slowing ramping up the voltage is properly something used by various agencies in various countries. I can only hope to engage in a multi-million dollar military contract to deliver a "interrogation tool" from a time where a certain country was great, no more water boarding ;)
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
Very nice video.
Some things to consider, may be part of the circuit already. When the start button is pressed and the unit is running, should the mains fail, when the mains restore power, will the unit start up again without the need of again pressing the start button?
Another thing to consider, is a 'phase failure' relay or system. This will shut the unit down, or prevent starting, until all three phases are present.
Another item, is an interlock, which could be switched in, that would require the main voltage control to be set to zero, before the start control would work.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
radiotech wrote ...
Very nice video.
Some things to consider, may be part of the circuit already. When the start button is pressed and the unit is running, should the mains fail, when the mains restore power, will the unit start up again without the need of again pressing the start button?
Another thing to consider, is a 'phase failure' relay or system. This will shut the unit down, or prevent starting, until all three phases are present.
Another item, is an interlock, which could be switched in, that would require the main voltage control to be set to zero, before the start control would work.
If you look at the schematic, you can see that start/stop buttons are pulsed, start condition is held by selfhold with the control relay, so any emergency stop, stop or mains failure will make the selfhold fall and it will have to be actively started again.
Good idea with the phase-failure detection, it could be made real simple with just 3 relays, each coil powered from a phase and their contacts put in series with the start/stop circuit. Add in 3 lamps to show which relays are energized.
I like to be able to set the variac to a voltage and then start/stop it, so I do not have to adjust for a certain voltage each time during some experiment.
I will in the future add connector for remote emergency stop and some kind of dead man switch if I find a good actuator that will release upon muscle cramp. I did not search for such yet.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
The low voltage release looks good. Sometimes our three phase systems had a phase failure/ sequence relay shut things down, or prevented starting if the incoming lines got reversed, ABC to ACB ,or a phase was lost.
You can make yourself a sequence indicator, easily, by Y connecting two incandescent lamps and a capacitor. Xc = R of one of the lamps. The Y point floats. When hooked up system, only 1 lamp will light. If you swap any two of the line wires, the other lamp will light. If you choose an inductor instead of a capacitor, it will work the same, except for a given sequence, the opposite lamp will light.
If you can find a three phase power transducer, then your total wattage can be measured. The one shown is a Scientific Columbus 2 element 3 phase 50 Hz unit that outputs 1.0 mA, into 0 to 10 k Ohms to indicate 875 watts.
Such old transducers lurk in industrial electrical junk heaps.
Other thing I've seen is a pot ganged along with a motor, to turn the Variac. The pot will remember where a setting was, and the motor will turn the Variac back to the setting, when the controller calls for a certain set point.
Depending on the experiment, you may want a PID control loop to adjust to a certain power level. That was exactly what my watt transducer did, until our crew revamped the whole system, using a 60 Hz type,
With a watt transducer, like the one shown below, your controller, could show kilowatts of load on the entire system. You will need only two current transformers. If you add a var transducer you can read kilovars.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
I could take a chance with one of these cheap Chinese phase sequence relays:
I just today put up article and video about my Merlin Gerin PM700 power condition meter:
I can just plug that in front of the variac stack to have some modern commodities like harmonic distortion, power factor and power consumed measurements :)
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
The phase sequence relay is interesting for that amount of money. It would need some good stickers, if was to used on a passenger elevator here .
It would be interesting to see how the power condition meter reported unbalanced loads, with different reactive loading on each phase. Around here I have some large power factor correction capacitors to play with. Can the condition meter connect to a computer for remote operation, or custom programming over R 232 link ?
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3 phase 13 A Lübcke variac with safety and monitoring
