Navitron Renewable Energy and Sustainability Forum

Green Building and Design => Home Automation and Monitoring => Topic started by: guydewdney on June 09, 2018, 08:38:14 PM



Title: Large 3 phase CT meter. Is it right?
Post by: guydewdney on June 09, 2018, 08:38:14 PM
We have a large property with 3 phase. It is so big that the meter isn't direct, it uses CT clamps like the OWL meters etc.

When I had one of those type wireless energy monitors, it used to read all sorts of twaddle with low energy stuff.

So.... Is my meter reading massively high for the same reason? My last bill was 4500 quid a quarter.......... The electric company asked me how big my pool facepalm was....




Title: Re: Large 3 phase CT meter. Is it right?
Post by: rogeriko on June 09, 2018, 10:21:57 PM
Just buy another 3 phase meter with 3 current transformers and connect it yourself and see if the readings are the same over a one month period.. Shouldnt cost more than 200 pounds all in. Maybe half that if you search around.

Example

https://www.decmetrics.co.uk/product/elster-a1140-three-phase-meter-current-transformer-version/


Title: Re: Large 3 phase CT meter. Is it right?
Post by: knighty on June 09, 2018, 11:40:28 PM
how big are your main fuses?

at work I'm on 100amps/phase

but it's a normal old fashioned meter with feed in and out of it and spinning disks

bill averages £2000/month  (mostly big freezers)


Title: Re: Large 3 phase CT meter. Is it right?
Post by: guydewdney on June 10, 2018, 08:58:49 AM

(https://s15.postimg.cc/f9csio5wn/IMG_20180510_114704.jpg) (https://postimg.cc/image/f9csio5wn/)


Title: Re: Large 3 phase CT meter. Is it right?
Post by: guydewdney on June 10, 2018, 09:01:12 AM
I can’t see the fuse rating. There’s two standard 16mm type cables per phase coming out of the incomer if that gives some indication.

How would a second meter help? The issue might be that CTs assume voltage and power factor is about 1, whereas with a lot of led lighting (about 300 bulbs, 3 to 5w each) the pf is not 1.


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Iain on June 10, 2018, 09:06:37 AM
Hi
I would imagine they are monitoring the voltage at each phase as well so it should have the correct power factor by comparing the phase angle.
I think a second meter was suggested just to check if both read the same.
Could a CT be the wrong way around? Not sure how you can check and even if it would make a difference. It would  alter the Power factor reading I think.
Iain



Title: Re: Large 3 phase CT meter. Is it right?
Post by: A.L. on June 10, 2018, 09:44:16 AM
hello,

The issue might be that CTs assume voltage and power factor is about 1, whereas with a lot of led lighting (about 300 bulbs, 3 to 5w each) the pf is not 1.

- CTs can measure power factor if correctly constructed, not saying yours is though.................

https://www.navitron.org.uk/forum/index.php/topic,12168.msg133671.html#msg133671 (https://www.navitron.org.uk/forum/index.php/topic,12168.msg133671.html#msg133671)


Title: Re: Large 3 phase CT meter. Is it right?
Post by: azps on June 10, 2018, 10:49:37 AM
So.... Is my meter reading massively high for the same reason? My last bill was 4500 quid a quarter.......... The electric cc implant asked me how big my poo facepalm l was ....

Yeah, them saniflo's really can burn power, eh?


Title: Re: Large 3 phase CT meter. Is it right?
Post by: rogeriko on June 10, 2018, 10:53:45 AM
The meter is a relatively new digital type but the CT's look about 40 years old. I wonder when they changed the meter did they check the CT's were the right type?


Modern CT



Title: Re: Large 3 phase CT meter. Is it right?
Post by: guydewdney on June 11, 2018, 02:50:40 PM
CTS are 200/5 and meter is set to 200

PF is 0.78  :o leading


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Scruff on June 11, 2018, 02:58:31 PM
I've seen pf of 0.4 on LEDs through a load compensating charger.
I heart DC.  :lovefirefox

0.8 is normal for uncorrected installations.


Title: Re: Large 3 phase CT meter. Is it right?
Post by: jonesy on June 11, 2018, 11:05:17 PM
If you are a business, they may well be billing you in VA, so a poor pf will cost you more, vs domestic. I think a pf of 0.5 will cost you double a domestic client. What is a normal size bill?
Led lamps can have a pf of 1, but most are worse. I've a bunch of freebies with a pf of 0.5, given to me by the power companies, so they then have to manage the VAr on the network which I understand is tricky.
Turning on a large immersion should move the pf towards 1, so that will give a crude idea things are installed the right way. Commercial meters will read just fine with all sorts of crappy waveforms.


Title: Re: Large 3 phase CT meter. Is it right?
Post by: roys on June 12, 2018, 08:10:28 AM
How come your PF is leading, are you running large runs of fluorescent lighting?
Most installs tend to run with a lag PF.


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Iain on June 12, 2018, 08:40:15 AM
How come your PF is leading, are you running large runs of fluorescent lighting?
Most installs tend to run with a lag PF.


Unless the CT's are or a CT is connected the wrong way around?

Iain


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Westie on June 12, 2018, 08:45:23 AM
How come your PF is leading, are you running large runs of fluorescent lighting?
Most installs tend to run with a lag PF.


Unless the CT's are  or a CT is connected the wrong way around?

Iain

I agree, definitely something wrong, it's virtually impossible to get a leading Pf of that magnitude, check you CT polarities.


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Scruff on June 12, 2018, 09:33:07 AM
 ??? CTs don't have a polarity.

Hall effect sensors do.


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Iain on June 12, 2018, 09:43:09 AM
??? CTs don't have a polarity.

Hall effect sensors do.

If they are used in conjunction with voltage sensing to measure phase angle and current I am sure they are.

They will give the correct current reading either way around but if used with a voltage reference I am sure they are directional sensitive.

https://www.schneider-electric.co.uk/en/faqs/FA203850/

Quote
.CT's installed backwards provide inverted signals to the meters to which they are connected. Most meters note the polarity of the signal received from the current transformers, and use that polarity to help determine the direction of the flow of electricity, assigning a positive or negative value to calculated power and energy. It is imperative that current transformers are installed correctly with respect to their orientation on the load conductors that pass through them.

Iain


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Scruff on June 12, 2018, 09:48:13 AM
Most cheapy OWL type meters with only one CT are calculating export using pf, so I'm sure there's something to it.

Strictly speaking AC doesn't have a polarity either just an earth reference.

Seems easier for sparkies to think power enters the live and exits the neutral instead of oscillating at 50hz. ....I blame facebook... tumble:


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Stig on June 12, 2018, 10:47:54 AM
Seems easier for sparkies to think power enters the live and exits the neutral instead of oscillating at 50hz. ....I blame facebook... tumble:

Nah, with Facebook the power flows in the same direction as the data, from the user to the big company...


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Scruff on June 12, 2018, 11:09:24 AM
Data.  :hysteria
...I'd consider Monty Python a more reliable source..


Title: Re: Large 3 phase CT meter. Is it right?
Post by: roys on June 12, 2018, 06:11:53 PM
In days gone by I remember (only just 😀) flick testing ct's in 3 phase systems to ensure they were all connected with the same polarity.  Probably the last time I used an anolgue meter.


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Westie on June 12, 2018, 06:13:41 PM
??? CTs don't have a polarity.

Hall effect sensors do.

CT Polarity is applicable and is  important in a 3 phase power measurement system. In a single phase system it wouldn't make any difference to measured power but in a 3 phase measurement system you need to get each CT mounted the same way around physically and connected the same way around electrically, if you get one wrong the output current from that CT will be 180 degrees out of phase which will completely screw up the power measurement circuit.  If you look at Guys picture you can see the CT's connections are 'polarity' marked (sometimes marked with colours , other times X1,X2). Also CT's are marked to show their correct physical orientation,  physical sides are marked line and load, sometimes marked H1 on the line side and H2 on the the load side.

Also check the three phase connection to the meter they must also be in sequence with the CT inputs ie Red CT - Red phase , Blue CT - Blue phase...etc

As I said before if your meter is showing a Pf of .78 leading the meter is almost certainly connected incorrectly.



Title: Re: Large 3 phase CT meter. Is it right?
Post by: Westie on June 12, 2018, 06:21:20 PM
In days gone by I remember (only just 😀) flick testing ct's in 3 phase systems to ensure they were all connected with the same polarity.  Probably the last time I used an anolgue meter.

Yep,  used the same method to detect polarities (ie winding direction) on 3 phase motors that had 6 ends out and no cable markers.


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Scruff on June 12, 2018, 09:13:46 PM
Hrmmm tis a most vexing subject because the terminology has equal and opposing meanings I guess....and I'm a bit thick when it comes to triangles

Alternating current does not have a polarity or it can be argued it has but it inverts at 50hz.
To me polarity is the direction of a magnetic field or electron flow. I guess in this context it means front and back?

Like earth and ground. Earth = planet reference, ground = chassis reference. They can be the same (if you connect them) but they are not. 
I've only ever used CTs on single phase and they never read negative in either orientation.

It would help to be specific we are talking about apparent power measurement not real power. P = IVpf not P=IV....
Guy are you being billed for reactive power?

I'm not entirely getting how being 180° outtov phase will affect measurement but probably straight forwards if it was drawn.


Title: Re: Large 3 phase CT meter. Is it right?
Post by: guydewdney on June 12, 2018, 09:25:15 PM
I'm billed in kwh not kvah. There's no reactive power element to the bill. It's essentially a domestic bill but with an extra zero.....


Title: Re: Large 3 phase CT meter. Is it right?
Post by: roys on June 12, 2018, 10:25:16 PM
Why have you got a Japanese fighter plane on your bill😀
Anyways so if you are not getting billed for any reactive (kVAr) then surely your PF doesn't matter, however doesn't answer the question of why your PF is leading, which could be pointing to a connection error somewhere, what is your main loads? If you say you are running a big sychronous motor with lead PF, of happen to have connected up a large bank of capacitors you had lying about, then that would explain it. But if it is normal domestic or motor loads then it should be lag.
By the way your leccy bill is huge.


Title: Re: Large 3 phase CT meter. Is it right?
Post by: roys on June 12, 2018, 10:31:38 PM
Think I would also be borrowing 3 tong testers and putting them on the tails and monitoring for say the odd hour over different periods during the day and week as a spot check to see what:
the current draw was,
Identify what the loads were,
Work out roughly what your daily then quarterly consumption would be, multiply by tariff and see if it i roughly tallies with bill.
I you were near me you could borrow my testers but I think you are at the other side of the country.


Title: Re: Large 3 phase CT meter. Is it right?
Post by: roys on June 12, 2018, 10:34:50 PM
And another thought.
The meter reading hasn't been read wrong has it? Maybe a big digit entered wrongly.
Have you checked meter reading tally with bill.
Sorry if this is obvious I am just thinking out loud.


Title: Re: Large 3 phase CT meter. Is it right?
Post by: knighty on June 12, 2018, 10:36:20 PM
you could push for a smart meter?  (or 3 of them if they have no 3 phase ones? - my 3 phase at work is 3x single phase meters)

there's no point/need for the CT clamps unless you have massive loads?


does summer/winter make much difference to your bill?

with your water wheel and the pile of solare you have I thought you're bill would be much less than that


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Westie on June 13, 2018, 08:55:05 AM
I'm billed in kwh not kvah. There's no reactive power element to the bill. It's essentially a domestic bill but with an extra zero.....

Okay, so your bill is in kwhr.   Looking at the picture you posted the CTs all seem the right way around and the cabling to the JB bleow the meter all looks okay, obviously we can't vouch for the meter connections as we can't see behind the cover.  So, assuming the connections are correct we should think of other options.  #

Have you changed supplier recently?

Are you on single rate or E7?

The Mk10A meter is smart, is it read remotely or do always provide the reading?

If you provide the reading do you always give the them the T0 register figure for Total kWHr?

The MK10 meter is able to read MD, Export, kVAh and kVArh.  This is stored on Set B registers. They can be
read by holding down the Display Select button for 3 seconds this switches the meter
between Set A registers and Set B registers. If they are reading remotely the metering agent (not always the same as the supplier!)  could be transposing the T0 ans S6 registers so your billed for reactive power instead of real power.  I ask if you changer supplier recently because this sort of error seems to crop up when a new supplier takes on your smart meter.  

What is the kVArh reading on your meter, ie the S6 register, also what does S5 read - does the S5 or S6  value tally with the billed value?
 


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Scruff 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.


Title: Re: Large 3 phase CT meter. Is it right?
Post by: jonesy 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.



Title: Re: Large 3 phase CT meter. Is it right?
Post by: Scruff 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?


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Westie 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.....?


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Westie 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).   
 
(https://s22.postimg.cc/iyh71st6l/temp.jpg) (https://postimg.cc/image/iyh71st6l/)


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Scruff on June 13, 2018, 12:28:11 PM
Inverters operate at unity exporting reactive powah to utility to deal with. Clicky (https://www.renewableenergyworld.com/articles/print/pvw/volume-1/issue-4/solar-energy/how-pv-grid-tie-inverters-can-zap-utility-power-factor.html)


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Westie on June 13, 2018, 01:08:36 PM
Inverters operate at unity exporting reactive powah to utility to deal with. Clicky (https://www.renewableenergyworld.com/articles/print/pvw/volume-1/issue-4/solar-energy/how-pv-grid-tie-inverters-can-zap-utility-power-factor.html)

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!  :o


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Scruff on June 13, 2018, 02:18:58 PM
Billed or no we're investigating the whys of a leading pf.


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Westie 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.

 


Title: Re: Large 3 phase CT meter. Is it right?
Post by: Scruff 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.


Title: Re: Large 3 phase CT meter. Is it right?
Post by: guydewdney 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.