Power Factor and New Power Company Digi Meters

One significant source of loss which most people don't think about is the vent pipe, convection currents can be set up within the pipe to allow the contents of the tank to be gradually cooled.

Tim

Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service

High risk maybe... estimate your kW use.. offer the board payment of that amount and tell them they have no proof that you used more despite the metre reading. They have no right to charge for energy they have not supplied. In court they would not have a leg to stand on. Downside is they might say they no longer wanted you as a customer.

Regards Jonathan.

My bill clearly states I am paying for kWh... nothing about power factor on it... If there metre has a design fault it's their problem, as they can't prove how much electricity they have supplied.

Regards Jonathan.

High risk definitely, energy suppliers will sell your debt to a debt collector at the drop of a hat. I had this when British Gas made a mistake on the billing address of one of my buy-to-lets, they sent the usual red reminder, one further warning and they sold the debt without making any further attempts to contact me. I of course saw none of these, and thought the bill had been paid as I was on dual fuel and had paid a bill thinking it was for both, for some reason known only to themselves they had decided to split the bill and sent the electricity one to me and the gas one to another address!.

The most annoying part about it was that the debt collector just phoned me using the number BG had for me and asked why I hadn't paid, something BG couldn't be arsed to do, in fact I have 3 other accounts with BG with the right addresses and all cross referenced but could they be arsed to look ? oh no.

Of course then I had to contend with a string of abusive phone calls and threats that these parasites deal in, though I got my own back by paying British Gas directly thus cutting them out of their profit. So beware, unpaid bills will only cause you grief.

Greg

I think someone asked me how to correct power factor so here it is:

Correct each machine individually and fit the corection caps across the motor, that way you don't have caps connected to the supply without the matching machine which would make a leading pf all the time.

Before you can correct pf you need to be able to measure it, I believe you can buy cheap meters but have no experience of them, what you need is the pf, the current drawn and the voltage. Measure these with the machine operating in a representative manner as you can only correct accurately at one load.

Draw a right angled triangle and mark the hypotenuse with the current, the longer side with the current multiplied by the pf, and work out the third side using pythagoras. For example if you measure 10A and 0.8pf the triangle sides are 10, 8, 6 where 6A is the lagging component of the current.

Now you need a capacitor which passed this same current to 'cancel out' the inductive current, or more correctly cause it to circulate around the motor and capacitor rather than the grid. So just apply Ohms law i.e. the impedance of the capacitor Xc = U/I so assuming you measured 240V Xc =

240/6 = 40 Ohms.

Now the last step, the impedance of a capacitor Xc = 1/(2 PI f C) so rearranging C = 1/(2 PI f Xc) In the example C = 1/(2 x 3.14 x 50 x 40) = 80uF

That can be a single capacitor or a parallel combination where the total is

80uF, you must use motor RUN capacitor not motor start capacitors and they must be rated for the supply voltage. Of course if you are not completely confident in your abilities with wiring then get someone who is to do it.

There may be some rule of thumb for all this that I'm not aware of, but being an engineer I just get my pocket calculator out!.

Greg

Power factor meters are not commonly available as consumer items so in most cases you're stuck with the nameplate rating of the motors. Although the PF of a motor varies with mechanical load this is mainly because of the increase in the "in phase" current with load - there is little change in the lagging reactive current which stays roughly constant.

Because of this a single value of PF correction capacitor is OK for all loads. It can be found experimentally by simply finding the capacitance value which results in minimum input current.

PF should always be under corrected - 80% correction is the usual aim. This partly economic - diminishing returns as you approach 100% but also because with an overcorrected motor (i.e. capacitative load) there is danger of resonant self excitation when power is removed. This results in overvoltage and large braking forces.

Jim

In article , snipped-for-privacy@yahoo.com writes

I say, steady on old chap!

Yes they are, Maplin do one for £27 part number L61AQ so long as your machine can be run from a 13A socket. This was explained earlier in the thread.

Greg