Electricity getting very expensive in the Workshop

[awemawson]

As part of my 'Electricity Reduction Exercise' I wanted to fit an 'Owl' real time monitor to my incoming three phase supply. I'd bought the monitor on eBay some time ago and knew that it worked however it's sensing current transformers that clip round the cable were too small for this massive cable. These are 70 mm csa / 225 amp rated and about 16.5 mm o/d . The sensors that I had would only accept up to 11 mm o/d.

Well it turns out Owl do make a suitable sensor but they are far from common. As luck would have it, trawling eBay produced two used ones and one brand new one that arrived today.

I've fitted them after a bit of a struggle wrangling the cables to get sufficient separation to clip the devices on.

As part of the testing I wanted a decent three phase load, so I thought that I'd run the spindle motor on the Beaver CNC lathe. A nice steady 1000 rpm, no load on it and it was drawing 30 kW  Now the motor is rated at 26.5 kW so the remaining 3.5 kW must be the servo system, hydraulic pump etc.

Now OK it's a big beefy motor but with electricity at the price it now is that's practically £1 an hour just to spin the blooming motor 

. . . . . not going to be leaving that idling to warm up in the future  !

[Pete49]

And we keep getting told that renewables make power cheaper. We need to get rid of subsidies on wind and solar to show the real cost to the people.

[philf]

At the moment wind power is the biggest contributor at 12.95 GW, solar is 2.55 GW. Nuclear is 5.25 GW.

http://www.gridwatch.templar.co.uk/index.php

[awemawson]

Well you wouldn't think I got the Maths prize at school all those years ago - that lathe motor calculation is out by a factor of ten!

30 kW at 29.48 pence per kwH is 30 x 29.49 / 100 = £8.847 per hour 

Dare I ever turn it on again !

(oddly this morning it's drawing 26.97 kw not 30    )

[WeldingRod]

That sounds really -wrong-.  A spindle motor drawing full power with no load???  It should be maybe 3kW!  If it is a three phase motor rather than a vfd you might be seeing reactive power rather than real power.  Or your spindle brake is on   A simple rectifier input VFD will have horrid harmonics that will totally flummox cheap power measurement chips...
If you've got an IR gun or camera you might look at the motor or cables.  30 kW going into any of that will make stuff hot PDQ!

Um, now that i think more, I bet your current transformer ratio is off by ten!

Do you have any dumb three phase heaters you could turn on?

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[awemawson]

The motor is a DC Mawdsley one . It has a 1.5 HP cooling fan blowing into it all the time.

Current consumption of other devices seems sensible - certainly not out by a factor of ten

[vtsteam]

26.97 KW = 36 Hp. 

It can't really take that much to spin a ground shaft in precision bearings.

[awemawson]

OK it's spinning the gear train as well but I agree to being surprised.

Does a DC motor actually vary it's consumption much? With AC drive you have the motor reactance which goes down on load hence drawing more amps - what is the case in a DC drive?

[vtsteam]

Maybe Ebay purchases didn't pan out this time? Not that I don't make them myself......

[awemawson]

26.97 KW = 36 Hp. 

It can't really take that much to spin a ground shaft in precision bearings.

It's rated at 26.5 HP 400 volts and  34 to 75 amps DC depending on speed with 170 volts on the field coils whose current is separately controlled  - plate below

[awemawson]

Maybe Ebay purchases didn't pan out this time? Not that I don't make them myself......

Not sure what you're referring to Steve - the Owl monitor (had it for years) and the new genuine Owl sensors and the used ones  check out 100% - after all they are only a few turns of copper wire and a split ferrite core in a plastic housing.

. . . may be you were referring to something else 

[vtsteam]

Andrew are they the appropriate senders for that monitor? Does the monitor have internal settings for different model senders/transducers? Do the two used transducers check out?

I have depth sounders that take same brand transducers. BUT, you have to go into settings to change to the model number transducer. I don't own an OWL, so I have no way of knowing, simply asking questions that occur.

[awemawson]

The transmitter unit takes in the coil connections from the three phases and Owl seem to only sell two varieties, examples of both of which I have. There is no setting up on the transmitter but as I  say the readings seem sensible with other loads.

I'll try it with the Kiln when I go over and feed the pigs in a minute

[vtsteam]

Well, as was said earlier, all that power is eventually going into heat. You have a 27 killowatt heater running if somehow this power reading isn't wrong. So are you seeing 92,000 BTU/hr in the vicinity?

[awemawson]

Pigs fed and kiln power measured. It's rated or at least plated, at 13.5 kW three phase. From a base load of about 2kW the power used jumped up to 14.4 kW.

So I reckon the Owl monitor, though not calibrated to NPL standards, is giving a pretty fair indication of power used.

Now the machine drives the Mawdsley DC motor using a KDK DC drive with its associated blower cooling. Attached the to KDK drive is a Field Driver that I have actually added a fan to as it's output Thyristor used to run unacceptably hot. The main motor has as I previously mentioned it's own external cooling fan (750 watts NOT 1.5 kW as I had thought).

So energy as heat is being extracted all over the place and yes it does warm the workshop in a nice but expensive way!

I am as puzzled as others regarding the fact that the consumption is so high unloaded - the motor does not over heat by the way.

. . . I think the readings on the Owl monitor are roughly correct

I'll try and get some readings with the Beaver powered up and ready to rock but without the motor spinning - I suspect the various other elements gobble up quite a few electrons.

[PekkaNF]

Power factor on measurement? Resistive loads are fairly easy to use for calibration. I am sure you have factored this in.

[hermetic]

Can you get a tong tester round the input phases and get a current reading for each phase?

[awemawson]

Probably Phil. I certainly used to have at least three Ferranti clamp amp metres - certainly still have one but may have given the others away over the years.

[awemawson]

Now this is getting REALLY curious - I don't quite understand what is happening.

Running the machine up to the point that the motor can be started under program control, but NOT running, the OWL is telling me it's drawing about 3kw which is not unexpected.

Starting the motor and running it at a steady 1000 rpm at the spindle (through a belt / gear train so not motor rpm) my Fluke clamp ammeter is showing approx 16, 17, and 18 amps on the three phase inputs to the machine.

Now the OWL is showing about 11 kw attributable to the Beaver lathe (other things drawing a few 100 watts)

Now under these circumstances the other day it was drawing 26 kw, and I'm not imagining it as I have the photographs !

So I don't  really understand what is going on 

[vtsteam]

What kind of functions does the Owl have -- Hold, or Peak?

[vtsteam]

Looked at a manual... doesn't look like it shows peak.

But a change in the voltage setting could account for the difference betw 27 and 11 readings. What is/was the voltage set at?

Or......could be the Beaver.....

[awemawson]

Looked at a manual... doesn't look like it shows peak.

But a change in the voltage setting could account for the difference betw 27 and 11 readings. What is/was the voltage set at?

Or......could be the Beaver.....

Absolutely nothing was changed on the OWL settings, and anyway it shows sensible consumption when the 13.5 kW kiln is turned on so I don't think it's that Steve.

It make absolutely no logical sense to me at the moment. Even the 11 kW seems awfully high just spinning an unloaded motor.

One thing that DOES tally  up is the 16 /17 / 18 amps draw on the 415 volt three phase input to the Beaver equates to about 11 kW power again confirming that the OWL is telling the truth.

Incidentally, in the past I have checked the Fluke clamp meter against my trusty Avo 8 multimeter and they correspond exactly.

[vtsteam]

Well as Pekka said, power factor?

No telling how the Owl factors that in. It isn't something it allows you to set. And just making one assumption for everything could yield wildly differing results. If it uses a dynamic estimation internally, maybe it senses whether an inductive load is connected vs rectifier (as also mentioned earlier by Welding Rod). Maybe it estimated a different power factor for the two measurement samples?

It's basically just a clip on ammeter with internal calculations to yield power/energy usage. How it handles power factor is unknown.

One other possibility, Andrew I came across -- someone on a forum said rotating the connectors solved one of his reading problems -- worth a try?

Actually, Andrew, your Fluke ammeter will allow you to estimate power factor -- and energy consumption without the convenience of the owl, of course. But where they disagree, I'd trust the old meter and your personal calculations.

[awemawson]

But Steve the odd thing is that I set up EXACTLY the same measuring conditions on the two occasions.


. . . no change to the Owl or it's sensors and transmitter - they weren't even moved

. . . no change to the Beaver Lathe whatsoever - in each case it was turned on, passed over it's references in X & Z, then the motor started with an S1000 M03 command to spin clockwise at 1000 rpm

Yesterday 26 kW . . . today 11kW . . . . it makes no sense whatsoever

(But today I WAS able to corroborate the 11kW using the clamp meter)

[vtsteam]

Well, I wasn't thinking you changed anything --- that leaves something changed internally in the meter, or the Beaver drew more one day than the next.