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Author Topic: Large 3 phase CT meter. Is it right?  (Read 1088 times)
Scruff
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« Reply #30 on: June 13, 2018, 10:12:31 AM »

What are the odds the CT is flipped inside the casing?
We need to verify meter fidelity with another meter.
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jonesy
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« Reply #31 on: June 13, 2018, 11:32:11 AM »

Are we sure a leading power factor is incorrect?
'When the current waveform is leading the voltage waveform, the load is capacitive and is defined as a negative power factor.'
I've taken this quote from a datasheet from Analog Devices ADE7953 which is one of the (many) commercial chips that are inside meters.
My PF is currently -0.74 (or 0.74 leading), which is pretty normal for me, as most of my appliances are domestic, non-power factor corrected, switch mode supplies which are largely capacitive.

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Scruff
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« Reply #32 on: June 13, 2018, 11:37:10 AM »

Woulda 1ton+ hydro turnip have anything to do with it? Would that pf not be the inverse ova motor load?
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Westie
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« Reply #33 on: June 13, 2018, 11:56:26 AM »

Woulda 1ton+ hydro turnip have anything to do with it? Would that pf not be the inverse ova motor load?

Oooh! interesting point, he does have 18kw of generation on site....  but  the inverters are supposed to look at the local pf and follow it, they don't control it.....?
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Westie
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« Reply #34 on: June 13, 2018, 12:27:01 PM »

Are we sure a leading power factor is incorrect?
'When the current waveform is leading the voltage waveform, the load is capacitive and is defined as a negative power factor.'
I've taken this quote from a datasheet from Analog Devices ADE7953 which is one of the (many) commercial chips that are inside meters.
My PF is currently -0.74 (or 0.74 leading), which is pretty normal for me, as most of my appliances are domestic, non-power factor corrected, switch mode supplies which are largely capacitive.



Okay, trying hard to recall all that dormant college revision....   Resistive AC loads will have a unity pf (pf=1) ie voltage and current in phase. Inductive AC loads will cause the current waveform to lag (-pf) the voltage waveform because of Lenzes Law ie. a rising current in a coil will produce a back emf which opposes that rising current so the current lags the voltage increase. Capacitive AC loads will cause the current waveform to lead (+pf) because those capacitive  loads will dump current into the mains when the supply voltage is lower than the capacitive loads terminal voltage. 

It was always the case that industrial demand caused  lagging power factors, domestic too but to a lower extent....  But that was years ago, these days you'll be hard pressed to find a transformer in any power supply and many motor loads are inverter controlled so I'm not sure what a 'normal' Pf  would be these days!  When I was in industry we always tried to keep it from lagging below 0.8, we would do that by adding capacitive loads (capacitor Pf correction banks).   
 

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Scruff
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« Reply #35 on: June 13, 2018, 12:28:11 PM »

Inverters operate at unity exporting reactive powah to utility to deal with. Clicky
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Westie
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« Reply #36 on: June 13, 2018, 01:08:36 PM »

Inverters operate at unity exporting reactive powah to utility to deal with. Clicky

Hmmm...  I think we're getting side tracked by the Pf here... Guy says he's billed for kVAh not kVArh so the Pf isn't important wrt the bill.  I still wondering if the readings are getting transposed.

The Mark10 also logs export maybe that's been transposed and your being billed for what you export!  Shocked
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« Reply #37 on: June 13, 2018, 02:18:58 PM »

Billed or no we're investigating the whys of a leading pf.
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Westie
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« Reply #38 on: June 13, 2018, 04:40:13 PM »

Billed or no we're investigating the whys of a leading pf.

Well that's where we've ended up discussing but Guy is the OP and his concern is his 4.5k bill for last quarter.....  He says he is only billed for kVAh (kWhr) then the Pf shouldn't be the cause of a high bill.

Guy, may I suggest you make a video of the meter as you cycle it thro all the registers, post it on Youtube , and lets see if we can make sense of it.

 
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« Reply #39 on: June 13, 2018, 08:32:38 PM »

Indeed.

Check the zero reading is zero.
Check export is negative or non-cumulative.
Check loads are accurate to within meter tolerances.
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guydewdney
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« Reply #40 on: June 14, 2018, 12:39:11 AM »

Sorry boys, should have been clearer, this is my business, not my home. Same transformer but this leg has no RE at all (annoyingly).

Having chatted to 2 companies that sell pf correction equipment, both state that as I am on a kW bill not a kVAh bill that correction will make zero difference. Immhappy to accept this as they naturally would sell me a bit of kit if they could.

One suggested a voltage correction as my line voltage was about 248 on all phases.
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