Easiest explanation for PF

[Rockingit]

What's the easiest explanation for power factor that anyone's come across? To people who understand Volts, Amps and KW's. I often get asked and realise I confuse people by over-complicated answers!!

 

[Vortigern]

Pint of beer with the froth on top picture. Froth being the wasted part.

What's common for Beer Mug and Power Factor?

Power Factor (P.F.) is the ratio of Working Power to Apparent Power. kW is Working Power, kVAR is Reactive Power and kVA is Apparent Power.

electrical-engineering-portal.com

 

[James]

I usually describe it as efficiency
a device with pf of 0.8 is 80% efficient at converting amps into kw.

not technically correct but close enough to explain the concept to the layman.

 

[Rockingit]

Pint of beer with the froth on top picture. Froth being the wasted part.

What's common for Beer Mug and Power Factor?

Power Factor (P.F.) is the ratio of Working Power to Apparent Power. kW is Working Power, kVAR is Reactive Power and kVA is Apparent Power.

electrical-engineering-portal.com

That's a good one, thank you.

 

[Lucien Nunes]

I made up this explanation for a non-electrical audience to understand the commercial value of having a high power factor but the core of the explanation is equally useful in other contexts:

The current flowing through cables transfers energy from supply to equipment like trains carrying coal from a mine to a factory. Ideally you want to completely load each train at the mine, send it to the factory full, completely unload it there and return it to the mine empty. This is what happens when the waveform of the current drawn by equipment is in phase (i.e. in sync) with the waveform of the grid voltage.

Suppose the unloading at the factory gets out of sync with the train movements and the trains leave the factory before they have been completely unloaded. The coal left on board goes back to the mine, then back to the factory, and so on back and forth. Because each train only delivers a part load, extra trains have to run to meet the demand. As far as paying for the coal, the factory still only gets billed for the amount it uses, but the transport costs are increased because of the pointless carrying of coal back and forth.

This is what happens when the current drawn by equipment is out of phase with the grid voltage. The current is not fully utilised in delivering real power (kW) to the equipment, instead being partially wasted carrying reactive power (kVAr) which consists of energy travelling back and forth. As far as paying for the energy (kWh), the customer still only gets billed for the amount it uses, but large customers have to pay for, or are penalised for, the extra reactive power (kVAr) to cover the supplier's cost for larger cables and transformers to transport the extra amps pointlessly carrying kVArs.

The power factor is the fraction of each train's payload that is actually unloaded at the factory, or the fraction of the supply current that delivers real power to the equipment. The lower the power factor, the less efficiently the transport mechanism is being utilised. A power factor of one indicates that the entire payload of coal is delivered or that all the current is utilised in delivering real power. A power factor of zero indicates that none of the coal is delivered, the trains are just running back and forth fully laden without any loading or unloading going on, and likewise a current flowing that delivers no real power.

To resolve any confusion between low pf and low efficiency:
Low pf is like wasting train journeys by sending some of the coal back to the mine. The coal itself is not wasted.
Low efficiency is like wasting coal by burning it in a heap in the yard instead of putting it into the boiler.

 

[Lucien Nunes]

Apparent power (kVA) is what the signalman sees out of his window. He counts the trains passing just as an ammeter measures the current flowing in the circuit. He's only interested in the movement of trains, but if he multiplies the number arriving by their maximum payload he can get a maximum figure for how much coal the factory might be using. He has no knowledge of what fraction of that maximum is actually being unloaded at the factory and how much sent back to the mine. In the same way, multiplying the current passing a point and voltage at that point without regard to the phase angle gives the apparent power. It takes no account of how much of that power is delivered to the equipment as real power and how much is reactive.

A real power meter or energy meter works like the weighbridge operator, who finds out the difference between the inbound and outbound weights of each wagon and therefore knows the whole story of how much was really delivered.

Power factor correction is like a shunter who waits in the yard. When he sees a train about to leave the factory with some wagons still laden, he uncouples them and puts empty ones in their place. He then takes the laden wagons back to the drops and gets them emptied. Thus there are still excess wagon movements circulating within the factory premises but not along the main line, where all the transits are being fully utilised. In the same way the current associated with reactive power circulates between the load and pfc on the customers premises, but not along the supply cables from the grid. Those carry only the real power at a pf as close to unity as the correction can make it.

 

[Baddegg]

Every time @lucien! Every time you pip me to the good answers!……

 

[DPG]

That's quite a coincidence because whenever I get asked about the amount of coal in a wagon reaching its destination, I always liken it to electrical power factor