max demand at petrol pump

[Mad Spark]

Hi was called out earlier as a client has been asked by supplier to confirm KvA in order for him to downgrade meter as he feels he is paying a rate which is too high. (Dont ask me why, but if one of you guys know then please let me know too)

I had a look at supply and its a three phase supply with each phase on a 100A BS88 fuse.
the feed then runs in to a DB ( lets call it submain) which supplys DB's all around the fore court.

Submain Has:
a B32 feeding a single phase board marked Plant room,
a B40 feeding a single phase board marked 'Save LEC',
a B63 feeding a single phase board marked Pump Board,
a B63 feeding a three phase board marked DB2,
a B63 feeding a three phase board marked car wash,
a B40 feeding a three phase board marked DB3


Plant room board circuits
B6 Lights
B16 sockets
B16 lights (outside)
B20 sockets (outside)

Save LEC board circuits

B10 lights
B10 lights
B10 lights
B10 lights
B10 lights
B6 lights,

Pump board circuits,

C6 'DOMS'
B10 Contactor
B16 pumps 1,2
B16 Pumps 3,4
B16 Pumps 5,6
B16 Pumps 7,8

DB2 Circuits

B10 Alarm
B16 Cigarette machine
B16 leak detector
B16 data box
B10 Shop toilet Lights
B16 Water Heater
B32 counter Ring
C16 Vacume+air
B10 car wwash lights
B10 flood lights
B16 camera spur
B16 shop heater
B16 console heater
B16 office heater
B32 shop ring
D40 jet wash

Car wash board circuits

C40(3phase) car wash
C40(3phase) car wash

DB3 circuits

B32 (3phase) refrigerator
B16 ATM
B6 jet wash lights
B10 unknown.

As this petrol pump is operating 24 hours a day is it possible to apply diversity on these circuits,
there are places which are only used during daylight hours, there are circuits which dont get used any more, ie the car wash board is not supplying anything anymore, what I am asking really is how to go about working this out. any help or advice would be gratly appreciated.

 

[UKMeterman]

You can hire from several places energy analyzers, these come with three clip together CTs and either 3 voltage connections or one voltage connection and use it to measure the power consumption over a couple of weeks and download the data to a PC.

 

[Mad Spark]

how would that help in thin situation?
sorry not to sound rude, just want to figure out what you mean

 

[UKMeterman]

Hi,
You could actually measure the true maximum demand for the property useing the kit I suggested put a safety factor on it and then from that go to the supply company and say you only need a supply of X KVA
elcomponent SPC pro power & energy analyser | hire | inlec

 

[Engineer54]

how would that help in thin situation?
sorry not to sound rude, just want to figure out what you mean

The analyser will tell you exactly what KVA you will be using over a given period!! You don't need 2 weeks worth to give you the ball park figure you need, 3 or 4 days over the busiest days will give you that information...

 

[Mad Spark]

thats an expensive bit ov kit aintit, the way things are these days i dont know if i'm gonna even invoice as much as that for a max demand calculation.

any way thanks for that i appreciate it, any ideas on working this out, woould i be able to apply diversity, and if so, would that be at 'sub main' or at each board.

 

[robsparky1975]

I think that the client should be prepared to pay £200 or so in order to get an accurate anaylisis of the power consumption on his site,because after you have provided the realtime readings from such a unit they could save themselves £1000s possibly,id go for hiring the unit,it will give them all the info they need.

 

[Mad Spark]

i'm just worried aboout quoting that much, as times are tough right now for everyone. i was chatting to a letting agent earlier on today, and he was complaining about the tough times too, saying how landlords don't want to spend a penny unless they absolutly have to.
I feel as we ought to look out for one and other and helping out where we can, charge a fair amount and both parties be happy. Other wise we've got the rest of the cheap unqualified guys that will do it for pennies and leave us out to dry. so i thought a calculation might be a better idea as it will save him that extra 100 pounds and make me 100 pounds and we will both be happy

 

[Engineer54]

thats an expensive bit ov kit aintit, the way things are these days i dont know if i'm gonna even invoice as much as that for a max demand calculation.

any way thanks for that i appreciate it, any ideas on working this out, woould i be able to apply diversity, and if so, would that be at 'sub main' or at each board.

The analyzer will be giving you the ''accurate'' total max KVA the installation is using ....so you can't and don't require any diversity to be applied. You connect the unit to the supply of the main DB, so it will record ''Total'' KVA of the installation.

You don't need 2 weeks of hire to give you this information, as they are hired out on weekly basis then you only need to hire for a week, so 100 quid, not 200. Well worth the cost to your client, on the savings he can potentially make immediately and in the future....

 

[Mad Spark]

You connect the unit to the supply of the main DB, so it will record ''Total'' KVA of the installation.

Do you mean to the incoming tails?
and I will go with this idea. I think its the correct way and if he doesnt want it the thats up to him.
Thanks guys.

Ps I love this forum

 

[Engineer54]

How experienced are you at undertaking maximum demand calculations?? If you need to ask for advice on the subject then i would think not very!! Even Engineers can get things wrong, if they don't understand the system/installation use they are applying their calculations too. I wouldn't mind betting the figure you calculate will be a lot different to what the analyzer will record as the installations max KVA requirement!!

I'm not saying that your incompetent, just that it takes a fair bit of experience to make accurate MD assessments to installations... And if you get it wrong it could cost your client a whole heap of money in this case!!!

 

[UKMeterman]

Hi, The idea of that bit of kit is so that it can go round the incoming tails, live and in service with reasonable safety, you may need to connect the voltage via suitable means. One of them can take the voltage from a single 13A plug top and then takes an educated guess about the other two phases.

 

[Mad Spark]

plugging it into the one phase would only give an accurate reading for that phase and as you say gives an educated guess for the other two, would that not still mean that its only a guess rather than a figure which can be more accurate using diversity.

 

[Engineer54]

Hi, The idea of that bit of kit is so that it can go round the incoming tails, live and in service with reasonable safety, you may need to connect the voltage via suitable means. One of them can take the voltage from a single 13A plug top and then takes an educated guess about the other two phases.

No need for any educated guesses here, the analysers of today do the calculations for you on 3 phase supplies where only one phase voltage is being monitored.

 

[Mad Spark]

Thats the thing engineer54, when its not monitoring the other two phases surely its taking a guess at whaat they are doing, therefore an educated guess. How else is it possible for it to give me information which it hasn't even been plugged into.

 

[Engineer54]

Mad Spark, that's why they cost so much to hire, they DON'T guess, they calculate!! The same way your MFT test kit calculates various readings... These units are very sophisticated bits of kit. If your that worried, then hire a unit that has 3 voltage inputs one for each phase, believe me you don't need too, for the information your requiring!!

 

[Mad Spark]

I really admire your knowledge engineer54 and your determination in letting us have a little portion of it too, however on this occasion I just cant see how its possible to calculate something that its not being fed. But as I said earlier you are the man with the know how and experience and I totally respect ya. Thanks for all your input on this matter

 

[Engineer54]

Mad Spark, ....I use these units on a fairly regular basis, they do exactly what it says on the box!! I've never had any reason to doubt the information/values i've been given by any of them...


Just think about this for a second or two, just how much do you think the supply voltage is going to differ between each of the phases?? Go look at the specifications of one of these units, you will probably find accuracy % figures for each parameter the unit records. Your worrying about nothing!! lol!!

 

[MarkieSparkie]

Mad Spark, ....I use these units on a fairly regular basis, they do exactly what it says on the box!! I've never had any reason to doubt the information/values i've been given by any of them...


Just think about this for a second or two, just how much do you think the supply voltage is going to differ between each of the phases?? Go look at the specifications of one of these units, you will probably find accuracy % figures for each parameter the unit records. Your worrying about nothing!! lol!!

Hi madspark, I can echo E54 excellent advice. Your client is a commercial business, his/her largest fixed overheads are staff wages and energy cost. If you put a sound case of accurately assessing their typical energy usage and the possibility resulting from it of trimming their energy budget they are likely to grab the opportunity because of the economic climate and the spiralling cost of energy.

 

[Knobhead]

The last time I used one of these units I was working on a 3.3KV supply. The unit was quite happily doing it’s job using 230V as it’s reference.
It highlighted we were wasting a lot of power, that caused me headaches later but that’s another story.

at £80+ VAT to hire for a week it seems good deal to me considering what could be saved.

 

[UKMeterman]

Hi,
There are a number of further questions;
1. Are there any TRUE three phase loads on site, loads that do need 400V? If so could you even get a smaller 3 phase supply?
2. Are there any particular safety requirments regarding petrol stations if the mains intake is altered.
3. Have you considered fitting a sub meter with GSM loging facilites ?

 

[Mad Spark]

Hi lads,
I took your advice on board and have aquired the energy analyser, I have had it running at site for three days before i went to fetch the results. its seems great really easy to set up and to remove, as described earlier its fool proof, ahh....
Now ive downloaded all data on to my laptopo and looking at the graphs I'm getting confused can you guys help please.
The problem I'm having is I'm not sure weather to calculate KVA for each phase seperatly and then add together, or just for the one phase which has the highest reading. I am assuming that I should calculate for each one. But do I simply add them all together for a final figure or is there another way.

 

[Mad Spark]

i have to say engineer54 i now understand 'how it can get the value for the 3 phases now being only plugged into one', me eating my words here.

 

[Engineer54]

Why are you needing to calculate KVA, ...the energy analyser should be giving you actual measured KVA results. In fact you should have results for, ....A, KW, KVA, KVAr, THD, V, etc.

Not much of an analyser if it doesn't give you all of those and a few more parameters too.

What make and model of analyser did you hire eventually then???

 

[Mad Spark]

just to clarify ukmeterman, the incoming are not going to be alterd at all he is on a 06 meter which is used for heavy industries, whereas for petrol stations normally 03/04 are suffice, so he was asked from his supplieer to find out kva at site for them to asertain if he is on the right tarrif or not, and sorry for not answering your questions sooner just been runing around and havent had the chance. you know how it is trying to earn an honest buck.