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Thread: frequency...how important

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    frequency...how important

    when running any other source of electricity...generator...ups...invertor...etc

    how important is the frequency?

    i have been running tests on a standby generator...and found that certain items like my invertor...cellphone charger and fast chargers for my hilti battery machines do not function correctly when connected to a generator...

    i found that the generator is running at 54.3 hz and 106 volts neutral to earth...i can only asume that this is the issue for the chargers and invertors...in fact if you connect the invertor the lights start flickering and the earth leakage trips....you have to switch off the invertor when the generator is running is unplug it.

    the wave form is really bad but most items work fine...or so it seems.

    i found some ups units will also not function if connected to a generator...we found that the ups had to be replaced with newer models which could operate between 45 anf 55 hz...the older units only operate between 49.5 and 50.5 hz...if the frequency was higher or lower the unit would just buzz constantly.

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    Site Caretaker Dave A's Avatar
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    Quote Originally Posted by murdock View Post
    i found that the generator is running at 54.3 hz and 106 volts neutral to earth...
    This comment has nothing to do with the frequency question, but what you've got is a floating neutral. Bridge the earth and neutral at the generator. This might also resolve your tripping earth leakage issue with the inverter plugged in.
    Last edited by Dave A; 28-Jan-11 at 08:44 PM.
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    Diamond Member Justloadit's Avatar
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    I think the problem is not the frequency, but rather the high spike inrush current when the inverters are working due to the switch mode designs, which the generator can not handle. The latest requirements are to have equipment with a power factor of as close to One as possible. So special electronics has been designed to attempt to maintain the voltage and current in phase to reduce the impact of the high short impulse currents.
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    Gold Member Martinco's Avatar
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    My UPS also runs poorly on my 50KVA Genset and seems to be the cycles because with no load on the genset, the UPS is fine but as soon as I put maybe 20 KVA load then the UPS switches over to batteries. So cycles does play a part in all of this.
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    Diamond Member Justloadit's Avatar
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    Quote Originally Posted by Martinco View Post
    My UPS also runs poorly on my 50KVA Genset and seems to be the cycles because with no load on the genset, the UPS is fine but as soon as I put maybe 20 KVA load then the UPS switches over to batteries. So cycles does play a part in all of this.
    It could be the nature of the design of the UPS. Many UPS's watch the mains, and pick up a missing half cycle, which immediately triggers the UPS on batteries. It could be that they are specifically looking for a 50Hz cycle, which of course would be unhappy with varying generator frequency.

    A well designed UPS would have no problem with this, and hence the high cost. This type of UPS is know as an online UPS.
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    Diamond Member AndyD's Avatar
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    Many electronic devices don't like the shape of the waveform made by a genset. Is your generator 'pure sine' output or 'modified sine'? Modified sine wave, which is actually a square wave with the corners clipped off, is problematic because the RMS value of the waveform is not the same as a pure sine output. The 45-55 hz output will cause any half decent UPS to kick into battery mode as it quite rightly should do.

    I'm not too sure about bonding the neutral of the generator supply to earth. I would look at the circuit diagram for the genset and its associated regulator first or take it on advisement from the generator suppliers.

    If the regulator is poor quality then you're probably fighting a losing battle. I use Honda pure sine generators for UPS system backup power, they're double the price the price of the Chinese no name units but bitter experience has shown it's worth the extra.
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    Site Caretaker Dave A's Avatar
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    Quote Originally Posted by AndyD View Post
    I'm not too sure about bonding the neutral of the generator supply to earth.
    Andy, if you don't peg the neutral to the same potential as the earth at some point in a single phase AC installation, you end up with the live and neutral having very similar voltages when tested to earth. In a 220v situation, both live and neutral will test out at about 110v to earth while live to neutral will test out at 220v. The only difference between the live and neutral in this situation is they're 180 degrees off phase from each other. If you don't solve the floating neutral problem, I suggest you no longer have a single phase 220v system, but a [-]dual[/] two phase 110v system.

    I agree in 3 phase and complex single phase backup genset installations you'd have to take care just where you bridge the earth and neutral. But just as with mains power, the closer to the power source the better. On mains supply we're typically relying on a bridge at the transformer.
    Last edited by Dave A; 29-Jan-11 at 11:58 AM.
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    Gold Member Martinco's Avatar
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    Quote Originally Posted by AndyD View Post
    Many electronic devices don't like the shape of the waveform made by a genset. Is your generator 'pure sine' output or 'modified sine'?
    Andy, to the best of my knowledge a genset with a rotating "armature" can only give a pure sine wave so I guess it is a pure sine wave but the cycles not being constant at 50 causes the problem.
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    Diamond Member AndyD's Avatar
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    Quote Originally Posted by Dave A View Post
    Andy, if you don't peg the neutral to the same potential as the earth at some point in a single phase AC installation, you end up with the live and neutral having very similar voltages when tested to earth. In a 220v situation, both live and neutral will test out at about 110v to earth while live to neutral will test out at 220v. The only difference between the live and neutral in this situation is they're 180 degrees off phase from each other. If you don't solve the floating neutral problem, I suggest you no longer have a single phase 220v system, but a [-]dual[/] two phase 110v system.
    I'll firstly state I'm not a generator expert so I'll dig out some concrete info when I'm in my office. I agree with what you're saying about it then becoming a two phase supply in effect but to the best of my knowledge some generators and their associated AVR's are designed specifically to work this way, especially European 'site generators' where the live and the neutral are both in effect phases at 180 degrees apart. This is because building sites are considered particularly high risk areas for trailing cable damage and in this event the touch voltage encountered by the victim is far lower than the live voltage in a standard system. That said I think most site supplies and equipment in Europe is actually 110volt so the live and neutral voltages would be around half of that.
    My other line of thinking was that a generator is an autonomous supply entity which doesn't have its own earth spike in many cases, if the neutral is at a voltage and you bond it to the chassis then the chassis will then become the same potential as the neutral rather than the other way around.


    Quote Originally Posted by Martinco View Post
    Andy, to the best of my knowledge a genset with a rotating "armature" can only give a pure sine wave so I guess it is a pure sine wave but the cycles not being constant at 50 causes the problem.
    Sorry I my brain works faster than my one typing finger, I was talking about the inverter not the generator. In the op he said;
    Quote Originally Posted by murdock View Post
    the wave form is really bad but most items work fine...or so it seems.
    Last edited by AndyD; 29-Jan-11 at 07:30 PM.
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    Site Caretaker Dave A's Avatar
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    Quote Originally Posted by AndyD View Post
    My other line of thinking was that a generator is an autonomous supply entity which doesn't have its own earth spike in many cases, if the neutral is at a voltage and you bond it to the chassis then the chassis will then become the same potential as the neutral rather than the other way around.
    Not much sense in calling a terminal an earth if it isn't "earthed" properly

    Here's an idle thought - If your live and neutral are completely "untethered" to the local potential throughout the entire installation, what are the chances of you developing a fairly substantial voltage difference between earth and the phases? (I'm thinking if there was some sort of Van De Graaf generator effect in that genset or elsewhere in the installation for some bizarre reason).
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