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

  • It's not really an inrush problem, more of a pulsed load, and it does sound like the sort of thing designed to cause trouble- especially to gesnet derived  supplies
    There is not a lot  in BS 7671 relating to pulsed loads, but there are certainly recommendations on ENA side of things that are types of load the DNO will not accept withoug consultation.
    See this doc

    The key line in there is probably.y Equipment with a rated current < 75 A can be connected to LV public electricity supply systems under this stage without reference to the network operator providing it conforms to the technical requirements in BS EN 61000 3 3 and the service current capacity is confirmed as being adequate for connection of the equipment.

    so what does  EN 61000 3 3 permit.? Well  assuming you do not have the rather pricey standard this leaflet may be of help, but basically it all depends on the number of events per minute, but if it really is 60 events per minute, then they need to be aiming for something rather less than 1% dip on load.- so in big handfuls the supply needs a PSSC at the point the oven final circuit connects in parallel to any other load of at least 3,9kA.
    Now this is a rare enough requirement that really the makers ought to mention it in the instructions.

    It might be fun to ask for the results of the testing to EN61000 that they should have done as part of their CE marking data pack. I bet they have not.

    mike

  • The description seems very odd - why is it taking full current for prolonged periods? I would expect that once the thermostat is satisfied that the device will draw current only intermittently.

    Was there ever an installation manual - I cannot find one online?

  • 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.

  • 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.

  • Have you had a look in the oven terminal box?

    Often these things are actually the same physical oven with just links to configure it for three phase or single phase supply.

    You might be able to convert it back to 3 x 13A which would make its use on your 3 phase 65kVA set more palatable?

    As an aside... when you say "40kVA single phase supply" do you mean 40kVA from the grid or a 40kVA Genset?

  • Many thanks for that Mike.

    It was made in Denmark by Houno but Badged as a Lincat to me. There is a CE certificate in the pack. But no mention of EN 61000.

    I will look at that. It is under warrentee and I can't put a spanner on it. Also it has not functioned correctly, since installation. So I have taken out a case against Lincat Ltd.

    They insist that the one second continual abuse, on my system is correct to design. But any Engineer can see with modern control gear, this is not correct. Soft starting and on / off cycling has been achievable for many years.

    Tony 

  • Hi Chris

    I bought it new from LIncat UK-- but it turned out to be a Houno KPE 1.06- 10 kw single phase-- Combi Oven . made in Denmark. The Houno guy claims that banging in 40 amps at one second intervals for hours is correct.!!

    You have also observed why I am taking out a case against LIncat. The Combi sits there for hours with the Temp and Humidity readouts over shooting and under shooting continually. They sent "TECHS" here five times and changed half the sensors, but it remains unfixed.

    It would appear to me, that the controller is up the Swanee, but they have not changed that. It is under warrentee and they have given up on it.

    Has anyone else had problems with Lincat Ltd or Houno equipment?

    Regards  Tony

  • 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

  • Hi Adrian. Thanks for that.

    My first question was about inrush current allowed in the UK. It just doesn't look right for electronically controlled gear. The One second pulsing is a problem. 

    I can't put a spanner on it -as it is under warrentee.

    They have sent  "TECHS" out five times and changed half the sensors for cooking operation issues --without success. 

    The mains are single phase -I have 50kva MD allowed.  I built a hybrid changeover to bring in my ---65 kva 3 phase standby genset on line. 

    Regards  Tony