CL215 Electrickery Groundschool Q?

[North Shore]

OK, I stumped Russell this afternoon in our groundschool, and no-one in our maintenance seems to know the answer either; so I thought I'd put it out here to see if anyone else might have the answer..

Pilot's Console, AC Circuitbreaker Panel, 115VAC bus, at the far left it says: 'PF CORR' above ENG INST and FLT INST 1. Also, on the row below, above FLT INST 2.

What does 'PF CORR' stand for?

[angry inch]

Power Factor Correction.

Maybe Colonel Sanders, or someone else can explain it.

I think Power Factor is basically a measure of the efficiency of your inverter system. How it is corrected is beyond me...

Then again, I might be TOTALLY WRONG....

[Beefitarian]

Initially I was drawing a blank. Google is not much help. So far I'm leaning toward guesses like "power factor corrected" or "primary fuse" I'm extra doubtful about the second one.

I see angry inch fast posted me. Power factor correction is done with capacitors but it's been so long since I learned about it I have very little memory of how. I think it changes the way current builds in a circuit with a coil as the counter emf develops to limit it. It might then limit the current to only the part that is needed to do the work. It can save a lot of energy if you have a lot of motors. Older equipment tended to have power factors that would benefit more from correction.

I'll come back later to make sure I said enough to be confusing and partially incorrect.

[High and Behind]

In North Shores case it stands for Pilot Flying Correcting, because he is always 2 dots left of center.

[Meatservo]

That can't be true. I have it on good authority that North Shore is an android.

Oh, by the way:

http://en.wikipedia.org/wiki/Power_factor

The wikipedia page sort of explains it in terms of large machines working off the power from the utility company.

In a plane I suppose the power factor correction circuit maximizes the efficiency of a relatively small AC power source? You could do without one but then your inverter and generator would have to be bigger than necessary to deal with transient loads?

Just a guess. You guys can read the wikipedia page as easily as I can. My eyes glaze over when they get to the wave-form diagrams. Electricity seems to be one of those things, like gardening, that you either have a knack for or you don't. I get zapped a lot when I try to tinker with it.

[Meatservo]

I clipped out what I found relevant from the Wikipedia page:
The power factor of an AC electric power system is defined as the ratio of the real power flowing to the load to the apparent power in the circuit,[1][2] and is a dimensionless number between 0 and 1. Real power is the capacity of the circuit for performing work in a particular time. Apparent power is the product of the current and voltage of the circuit. Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power will be greater than the real power.
...

A high power factor is generally desirable in a transmission system to reduce transmission losses and improve voltage regulation at the load. It is often desirable to adjust the power factor of a system to near 1.0. When reactive elements supply or absorb reactive power near the load, the apparent power is reduced. Power factor correction may be applied by an electrical power transmission utility to improve the stability and efficiency of the transmission network....

An automatic power factor correction unit consists of a number of capacitors that are switched by means of contactors. These contactors are controlled by a regulator that measures power factor in an electrical network. Depending on the load and power factor of the network, the power factor controller will switch the necessary blocks of capacitors in steps to make sure the power factor stays above a selected value.


So it seems like Dan summed it up nicely, but it's for AC not DC.

Indeed Power Factor Correction.
As I understand, using capacitors, etc to normalize the true power available through a distribution network.

[Beefitarian]

The electrons don't stop in direct current circuits until you are not using the power to do work. In alternating current they stop and change direction many times per seconed. How many is the frequency or cycles, measured in "Hertz".

When you have a coil of wire like in a motor if it's DC you need to limit the current with some sort of resistor. Most resistors use power and create heat, that wastes the power. Changing the resistance changes the speed a DC motor rotates because it reduces the amount of current that is being wasted by the resistor. The problem is if you take out the resistor the current will not be limited and the motor will burn out.

If it is AC the coil creates a current in the opposite direction every time it changes direction. That creates "reactive" resistance. This is when you get weird things happening to the waves and the appearent power can reduce the true power.
Adding "capacitive" resistance parralel to the load in that circuit makes it act more like true resistance and changes the power factor.

To change the speed in an AC motor you must change the frequency (hertz) of the power. That's kind of complicated and the units that do that, usually variable frequency drives were really bad until the mid 1990s.

In an AC circuit, capacitors work like a wave filter by smoothing out the flow of electrons. In DC they work like a battery by holding the electrons, once charged they wait to be discharged.

[DanWEC]

Whup, I accidentally deleted my post that Meatservo quoted. These night shifts are messing with me!
In the situation of instrumentation, it's likely that the power correction is desirable to eliminate indication errors caused by instruments seeing different potentials as along their bus- not good as some need a baseline in order to relay their information.

[Beefitarian]

Ah, so it's not for better efficiency in this case but to keep the power a bit more stable while you use other systems like the flap motor.

[High and Behind]

[quote="Meatservo"]That can't be true. I have it on good authority that North Shore is an android.quote]

Does he speak Bocce?

What I really need is a droid that understands the power factor corrections of the AC bus for a CL-215.

Damn Jawa's

[Just Duckie]

Get your hands on the Wiring Manual #2...24-20-00..sheet 1 and 2 of page 5. It goes to a mysterious place.....Hmmmm, damn Brit engineers!!

[Meatservo]

That can't be true. I have it on good authority that North Shore is an android.quote]

Does he speak Bocce?

What I really need is a droid that understands the power factor corrections of the AC bus for a CL-215.

Damn Jawa's

Don't blame him. He's not supposed to be able to tell a power socket from a computer terminal.

[High and Behind]

That was R2 not 3Po, wasn't it?

Shut down all the trash compactors on the detention level!!!!!

When can you not quote Star Wars...?

[Meatservo]

No, it was C3P0 that said that after R2D2 plugged into the wrong socket. I can't believe it but apparently when I was seven I memorized "Star Wars".

[iflyforpie]

Interesting.

On the Boeings I was involved in, they did it differently. If you wanted basic power, it was displayed in kilowatts. If you wanted to take in the capacitive and inductive reactance, you switched the gauge to KVAR which was Kilo Volt Amps Reactive.

[Meatservo]

^Officially over my head!

[Rowdy]

Uncle meatservo.. this North shore unit has a bad motivator!!

[Meatservo]

He always has, even when we bought him from the Jawas back in 1996.

[North Shore]

Meat, old chap, your memory fails - it was '97. And you didn't buy me from the Jawas, you sent me to live *with* the Jawas!

[Meatservo]

Oh, come on. Everybody could use a season flying a T16 on floats and eating raw womp-rats. Besides, I wasn't the one who sent you there.

[Colonel Sanders]

If you wanted basic power, it was displayed in kilowatts. If you wanted to take in the capacitive and inductive reactance, you switched the gauge to KVAR which was Kilo Volt Amps Reactive

This seems pretty straightforward.

If all you're dealing with is DC - ie the voltage never varies (at least, not much) - then you can model all loads as simply resistive. Anyone remember Thevenin-Norton equivalents? Anyways, think of a simple light bulb. You connect it to a battery, which puts voltage across the light bulb, which will have a certain DC resistance (measured in Ohms). As a result, the current starts to flow across the light bulb, and it converts the power into heat and light.

Life gets a lot more complicated with AC - ie the voltage is varying, generally as a sine curve. Up/down, up/down it goes, so many times a second. When you're using an AC power supply, you can't model loads as simply resistive any more, because they do funny things with power - they buffer them, and shoot them back out. There are these things called capacitors and inductors which don't do anything with DC - in fact with DC, a capacitor is an open circuit and an inductor is a closed circuit - but they become active with AC, which is pumping current in and out of the load as the voltage swings so many times per second.

Many decades ago when I was a kid in school we modelled RLC circuits with 2nd order ordinary differential equations, which had solutions of the form e to the i theta. Mostly what I remember is that poles in the right hand plane results in oscillatory systems which leads to horrible ethnic pilot jokes about right echelon which nobody comprehends, except maybe the science consultant to the Big Bang Theory, and that's really not a very large audience.

All this stuff is covered in 2nd year Electrical Engineering. At least it was, 'way back when it was uphill both ways to school and back, through pervert park

[Beefitarian]

Are the filaments coiled in light bulbs to create reverse EMF in order to limit current? I have been thinking of them as resistive loads. Motors are the most typical inductive loads discussed in the coursesI took. What else would be a significant enough to benefit from power factor correction in a plane?

[Colonel Sanders]

It's for heat:

http://www.lamptech.co.uk/Documents/IN%20Coiling.htm

[Beefitarian]

Ok, cool It's been so long since I was in school I wasn't sure. I think they taught us that lights were pretty much resistive loads. So far Dan's leading this thread with the best reason.

In the situation of instrumentation, it's likely that the power correction is desirable to eliminate indication errors caused by instruments seeing different potentials as along their bus- not good as some need a baseline in order to relay their information.

[North Shore]

I'm beginning to get a helmet fire trying to follow all of this!

I think that I'm just going to stick with: c/b in, all's good; c/b out, not so much!