Permissible inrush current single phase

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

Parents
  • I've been pondering a similar-ish 'problem' with our domestic oven - 2kW on when it's calling for heat - 0kW when it's satisfied - doesn't work terribly well with the PV - often importing 1kW one moment (costly) and exporting 1kW the next (little cost benefit) - whereas the same effect could probably be produced by about 0.75kW constantly (depending on the exact temp required) and have it powered entirely by (free) solar. Even doing something like 2kW on full to get it warmed up and then switch 1kW in and out to maintain the temperature would be an improvement.

    1s on/0.2 second off does sound a little odd, but maybe the result of a slightly more sophisticated control system the alters the mark-space ratio ratio of a fixed frequency cycle depending on the temperature difference - rather than just a bimetallic thermostat which can have quite a large hysteresis.

       - Andy.

Reply
  • I've been pondering a similar-ish 'problem' with our domestic oven - 2kW on when it's calling for heat - 0kW when it's satisfied - doesn't work terribly well with the PV - often importing 1kW one moment (costly) and exporting 1kW the next (little cost benefit) - whereas the same effect could probably be produced by about 0.75kW constantly (depending on the exact temp required) and have it powered entirely by (free) solar. Even doing something like 2kW on full to get it warmed up and then switch 1kW in and out to maintain the temperature would be an improvement.

    1s on/0.2 second off does sound a little odd, but maybe the result of a slightly more sophisticated control system the alters the mark-space ratio ratio of a fixed frequency cycle depending on the temperature difference - rather than just a bimetallic thermostat which can have quite a large hysteresis.

       - Andy.

Children
  • Interesting point! But then your oven would have to get quite clever and have separately switched elements.

    I assume that you have no battery in your PV system. If there were one, it could soak up the spare electrons when the oven is off and give them back when it is on. If EVs can cope with periods of regenerative braking and periods on the throttle, a PV system should be able to do likewise.

  • I have been known to half the rating of an element by switching a diode in series with it, and have seen similar done inside a cheap hair dryer. I suspect the PV inverter will not appreciate a higher load on positive half cycles than negative however. Where there are two elements to switch from series to parallel or indeed just to knock one out for the maintain vs boost cases.

    Actually again as we move to non-rotating generation where the inertia spins you through short term variations and the load is averaged over several rotations, there are several kinds of load control like this that will need to be revisited.

    Mike.

  • Hi Andy,   to me that 1 sec cycle is just abuse of a system. I can see when it is on, the mains are vibrating. And the ammeters waving like fan blades. 

    It is a new appliance and electronically controlled. If It had a proper duty cycle then a soft start could be fitted.

    Regards  Tony