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Permissible inrush current single phase

Anthony Dicker

Hi

I have had the misfortune to buy a Lincat Combination Oven for my Hotel.

These normally come in 10kw three phase.  3 x  13amps That's not too bad.

I have the single phase version 1 x 39 amps. Not so good.

It is operating at 1 second on 39 amps

                          0.2 second off  0 amps

                          Cycling continually. for hours.

I have a 40kva single phase supply and can hear the current hammering away incessantly. Lights flickering etc. I asked the manufacture for details of soft starting and duty cycle. They say this is the way they were designed to work. Bang on and Bang off --1 second cycle continually.

I don't have a current (Hee Hee)  Reg book. So I ask is there a reg in place that covers the single phase load criteria.

To add insult to injury-- I have a three phase 65kva standby set.-- I would not put that destructive abuse on one of my 20kva phases, it would shake it apart. So I cannot run it.

Regards -- Tony

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  • 0

    No Andy, you have that wrong, a PID controller CANNOT work in that way. I suggest a textbook on control systems design would be a good start. You will find that the system requires a time constant to enable it to be stable, If you work on a 50Hz sample period the control loop requires damping sufficiently that "overshoot" cannot occur, which is one of the symptoms in this case. The integral cannot work if the control is not fine enough, and the proportional part needs to be exactly that, the error must be able to be set without any overshoot. So if 1 cycle of power leads to a small increase in temperature (which it will), the control system must then provide a longer gap to reverse the error, a rough description of the proportional part. The time constant stops the control system oscillating around the set point. This product is simply defective. Working it on 3 phases reduces the current but does nothing else useful. The control needs to be fully linear too, but that is only provided with a suitably high PWM frequenbc, considerably higher than the temperature sample rate (which makes the control quasi-linear).

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    No Andy, you have that wrong, a PID controller CANNOT work in that way. I suggest a textbook on control systems design would be a good start. You will find that the system requires a time constant to enable it to be stable, If you work on a 50Hz sample period the control loop requires damping sufficiently that "overshoot" cannot occur, which is one of the symptoms in this case. The integral cannot work if the control is not fine enough, and the proportional part needs to be exactly that, the error must be able to be set without any overshoot. So if 1 cycle of power leads to a small increase in temperature (which it will), the control system must then provide a longer gap to reverse the error, a rough description of the proportional part. The time constant stops the control system oscillating around the set point. This product is simply defective. Working it on 3 phases reduces the current but does nothing else useful. The control needs to be fully linear too, but that is only provided with a suitably high PWM frequenbc, considerably higher than the temperature sample rate (which makes the control quasi-linear).

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