frequency...how important

**Dave A** · 28-Jan-11, 01:00 PM

Originally posted by murdock

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.

**Justloadit** · 28-Jan-11, 01:09 PM

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.

**Martinco** · 28-Jan-11, 01:41 PM

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.

**Justloadit** · 28-Jan-11, 06:58 PM

Originally posted by Martinco

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.

**AndyD** · 28-Jan-11, 11:39 PM

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.

**Dave A** · 29-Jan-11, 09:54 AM

Originally posted by AndyD

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.

**Martinco** · 29-Jan-11, 11:17 AM

Originally posted by AndyD

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.

**AndyD** · 29-Jan-11, 05:02 PM

Originally posted by Dave A

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.

Originally posted by Martinco

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;

Originally posted by murdock

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

**Dave A** · 29-Jan-11, 05:37 PM

Originally posted by AndyD

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).

**Justloadit** · 29-Jan-11, 07:23 PM

Originally posted by Dave A

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).

A very good point, anyone touching earth and the neutral of the generator would get a brutal wallop. Earthing prevents this from happening.

**murdock** · 30-Jan-11, 03:19 PM

well it been a week now and i am become very efficient without a connection to the electricity department...cost for the week R250 for 7 days...and improving as i am putting measures into place...by doing what i have done i am forced to make positive progress.

i am busy taking step to become completely isolated from the durban electricity department...i have discoonected and removed their supply from my meter...

i have already setup gas for all cooking...

i will be looking into gas units to heat the water...

a pure sine wave invertor to charge my equipment batteries and cellphones and to run my computer equipment.

a gas fridge which i hav already connected a camping one but will be looking into a bigger gas fridge which can run on electrcity and gas.

i hoofed my old deep freeze out the house...moved all the into the bottom of the fridge freezer and will replace what is needed on a weekly basis.

putting solar lighting thru out the house which will run completely independant from any electricty supply...the solar panels will charge a 7 amp hour batteries which can run 4 LEM lights for 10 hours...

When i am ready to reconnect to the council...my meter will be changed to a pre paid meter and i cant see my bill will be more than R200 a month...by the time i am finished...i havent worked out what the cost of the gas is yet but have noticed...having the quick heat from the gas stoves etc there is no waiting for plate to warm up etc

i did consider a solar geyser but it doesnt help me for morning baths and showers and washing dishers ...by the time the solar panels heat the water it will already be afternoon so the element still has to switch on....so the huge outlay for a solar geyser just sounds like a money making racket to me...whereas with the gas it is instant as and when required.

as for geyser blankets...no comment...before you buy a geyser blanket think a little and look into the construction of a geyser and you will know why the no comment...and i wont even go into expensive geyser management systems...rather keep quiet...come on people stop being so gulible and just think a little before you go out and waste huge amounts of money.

i want to see a real reduction in my electricity account not an estimate...

i have already started with the water...collecting big drums...and will start rerouting gutters etc...i might even loo into a small water purification works...i built them for 10 years i sure i can come up with a small system to service my house and who knows maybe all my neighbours climb on the band wagon...the reason for this is because of the levy for sewage which they now nailing us with...then i need to stop the refuse removal...also becoming a money making racket.

and last my rates i need to find out what makes up my rates so i can look into how i can reduse it back to R300 like it was 3 years ago before the ridiculous increase to R980 which they still cant justify.

**murdock** · 30-Jan-11, 03:32 PM

and you ask why i am wasting my time...because i have had enough...i tired of holding my ankles...

**Justloadit** · 30-Jan-11, 03:39 PM

The solar geyser does help, one adjusts your hygienic cycle to suite, but gas is the new energy resource for the next 50 years. So you are definitely on the right path.

Also look at investing in a gas driven generator, just for the times you need a boost in power, it comes handy, and the beauty of the gas fuel, is that you can store gas indefinitely, and do not have to worry about muck blocking your carburetor from prolonged standby.

**AndyD** · 30-Jan-11, 04:23 PM

Originally posted by murdock

...........so i can look into how i can reduse it back to R300 like it was 3 years ago before the ridiculous increase to R980 which they still cant justify.

The only way you're going to do that is to get your property revalued at a much lower price.

frequency...how important

frequency...how important

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