Inductive Reactance?

[FORTUNATA]

How come so many online tutorials about inductive reactance use extensive calculus formulae (and often don't provide the key to some of the symbols)?

John C Payne touches on it in his book Marine Electrical/Electronics Bible but the whole subject he condenses into 2 paragraphs. So, I had a look on the net for more details and the calculus is pretty fundamental.

Most electricians here will know what inductive reactance and lagging power factors mean.

Do I need to learn the calculus or doesn't it matter?

 

Found this:

http://www.electricalway.blogspot.co.uk/2011/08/inductive-and-capacitive-reactance.html

[RLWP]

What do you want to do?

 

Richard

[matty40s]

What do you want to do?

 

Richard

 

wire a plug ???

[RLWP]

wire a plug ???

 

Install a powerstation?

 

Richard

[Grace and Favour]

wire a plug ???

 

Turn the radio on?

[jonathanA]

How come so many online tutorials about inductive reactance use extensive calculus formulae (and often don't provide the key to some of the symbols)?

John C Payne touches on it in his book Marine Electrical/Electronics Bible but the whole subject he condenses into 2 paragraphs. So, I had a look on the net for more details and the calculus is pretty fundamental.

Most electricians here will know what inductive reactance and lagging power factors mean.

Do I need to learn the calculus or doesn't it matter?

 

unless your building some complex AC machine or messing about with Radio frequencies I can't imangine why you would want to get into that sort of maths. square root of minus one and all that stuff is pretty scary...

 

The basics of Reactance and inductance are very similar to Resistance for DC except they apply to alternating currents and the frequency of the signal is important. (so completely different then )

 

Not sure there's that much relevance to boating, but if its for your own interest then I'd find either a good electronics text book or good physics text book, preferably something aimed at A level or first year degree students. you don't need calculus if you just want to calculate/understand inductance/reactance and how that relates to capacitors or inductors.

 

Turn the radio on?

 

design the power distribution network for a small country....

Edited June 8, 2012 by jonathanA

[FORTUNATA]

Want to get to the meat and bones. Here's where I'm at:

We all really need to have at least some idea about watts on our boats and we all understand most appliances are rated in K.W. So, I have a 1.5 KW kettle.

Then we hear of KVA or KiloVoltAmps and we very often come across this term even in boating magazines.

However, soon as you get into KVA and power factors, then the whole subject of in phase, out of phase circuits and reactance come into play.

And then the calculus rolls out.

I now know that with inductive reactance the voltage leads the current and that a given circuit is out of phase. As opposed to a purely resistive circuit that is in phase.

To answer your question I first need to know the very very basic calculus symbols (if I really need it).

I'd also like to calculate lagging power factors.

I think if Payne hadn't gone into it, I'd not have bothered trying to figure it out.

 

What do you want to do?

 

Richard

[Serenity Malc]

Yello,

 

NO !

 

That sort of maths is not required for electrical qualification at a tradesman level. Power factor on 3 phase is a requirement though here in the UK.

 

As said before ....... what are you trying to do ?

 

Cheers Malc.

[FORTUNATA]

Where do you stop? Anyone ever noticed how easy it is to use terms such as KVA but not really understand what it all means? In order to do so, it always seems as if you go deeper and deeper to try and sum it up. You end up in a maze. Same goes when you look up a technical word in a dictionary and the definition uses another word you don't understand either. On it goes.

I know KVA is really just Kilowatts but with slight differences.

I found some semi basic tutorials and some that went way way into formulae.

We all know inverters use quasi sine waves so reactance ties up with that as well.

 

 

unless your building some complex AC machine or messing about with Radio frequencies I can't imangine why you would want to get into that sort of maths. square root of minus one and all that stuff is pretty scary...

 

The basics of Reactance and inductance are very similar to Resistance for DC except they apply to alternating currents and the frequency of the signal is important. (so completely different then )

 

Not sure there's that much relevance to boating, but if its for your own interest then I'd find either a good electronics text book or good physics text book, preferably something aimed at A level or first year degree students. you don't need calculus if you just want to calculate/understand inductance/reactance and how that relates to capacitors or inductors.

 

 

 

design the power distribution network for a small country....

[RLWP]

<snip>

 

NO !

 

<snip>

 

Cheers Malc.

 

This is an excellent answer.

 

I can remember doing some calculations on power factor as a part of my mechanical engineering degree.

 

I've done lots of electrics since and never needed that knowledge since

 

You won't need to know this to put your sockets and water heater on your boat

 

Richard

Edited June 8, 2012 by RLWP

[richardf]

I think this is a very subtle attempt at flushing Gibbo out again!

[FORTUNATA]

O.K. precisely...:

All I need to do is understand the basics of:

(1) Purely resistive circuits such as heaters.

(2) Circuits where inductive reactance creates a lagging power factor. It will be sufficient to make a very basic calculation of the lag but nothing OTT.

(3) Capacitors used in principle to correct lagging power factors.

That's it!

The basics may well be doable without complicated formulae.

And, yes, I agree it's probably of questionable practicality.

 

Yello,

 

NO !

 

That sort of maths is not required for electrical qualification at a tradesman level. Power factor on 3 phase is a requirement though here in the UK.

 

As said before ....... what are you trying to do ?

 

Cheers Malc.

 

I'm told he's pretty good and could probably make it very simple for me.

 

I think this is a very subtle attempt at flushing Gibbo out again!

[Giggetty]

O.K. precisely...:

All I need to do is understand the basics of:

(1) Purely resistive circuits such as heaters.

(2) Circuits where inductive reactance creates a lagging power factor. It will be sufficient to make a very basic calculation of the lag but nothing OTT.

(3) Capacitors used in principle to correct lagging power factors.

That's it!

The basics may well be doable without complicated formulae.

And, yes, I agree it's probably of questionable practicality.

 

 

 

I'm told he's pretty good and could probably make it very simple for me.

Isn't there the power equivalent of a Smith Chart, as used in radio engineering?

[RLWP]

Isn't there the power equivalent of a Smith Chart, as used in radio engineering?

 

Oh look, a whole new can of worms

 

Richard

[Serenity Malc]

Yello,

 

When I was younger, wasn't inductive reactance known as capacitance ?

 

 

Probably the basic thing you need to know is that 4A current ( Amperes ) @ 240V ....roughly = 1000 watts = 1 kilowatt

 

Simples ... Malc.

[PhilR]

Want to get to the meat and bones. Here's where I'm at:

We all really need to have at least some idea about watts on our boats and we all understand most appliances are rated in K.W. So, I have a 1.5 KW kettle.

Then we hear of KVA or KiloVoltAmps and we very often come across this term even in boating magazines.

However, soon as you get into KVA and power factors, then the whole subject of in phase, out of phase circuits and reactance come into play.

And then the calculus rolls out.

I now know that with inductive reactance the voltage leads the current and that a given circuit is out of phase. As opposed to a purely resistive circuit that is in phase.

To answer your question I first need to know the very very basic calculus symbols (if I really need it).

I'd also like to calculate lagging power factors.

I think if Payne hadn't gone into it, I'd not have bothered trying to figure it out.

 

 

 

I'm probably being very naive here, but why don't you put a kettle (not the 1.5 Kw kettle) on a gas hob or solid fuel stove?

 

Payne is a pain .................

[Guest]

Yello,

 

When I was younger, wasn't inductive reactance known as capacitance ?

 

 

Probably the basic thing you need to know is that 4A current ( Amperes ) @ 240V ....roughly = 1000 watts = 1 kilowatt

 

Simples ... Malc.

Yep 4amps to't Kw has got me by for 41 years. I remember doing all the inductive reactance and cos phi stuff at college, but truth is you likely never use it again. The engineers at the leccy board where I worked used to do such calculations for PF capacitors but it was all either on a computer screen or in tables. They didn't work it out with a pencil (unlike the constipated mathematician.)

[RLWP]

<snip>

 

They didn't work it out with a pencil (unlike the constipated mathematician.)

 

Better than using logs

 

Richard

[Batavia]

Provided that you are only interested in steady state sinusoidal voltages and currents, then you don't need to bother with calculus, as all the d /dt bits turn into convenient 90 degree phase shifts for pure inductors and capacitors.

 

A modicum of knowledge about vector representation and complex numbers is useful, though.

 

Chris G

 

 

[jonathanA]

O.K. precisely...:

All I need to do is understand the basics of:

(1) Purely resistive circuits such as heaters.

(2) Circuits where inductive reactance creates a lagging power factor. It will be sufficient to make a very basic calculation of the lag but nothing OTT.

(3) Capacitors used in principle to correct lagging power factors.

That's it!

The basics may well be doable without complicated formulae.

And, yes, I agree it's probably of questionable practicality.

 

I think you have a tendenacy to over complicate things and its good to have an inquiring outlook (i find this forum a fantastic source of info for all sorts of boat related matters) but actually calculating power factors is quite complex for a start you have to know the capacitance or inductance, plus the resistance of whatever circuit/system your looking at. how are you going to find those out ? on proper AC motors/machines you might see a power factor (usually denoted by the greek symbol for 'theta') but you won't find 0.5Farads or something stamped on the side and I've never seen the inductance (measured in Henry's) stamped on anything (other than electonic components). you'll need to also know the resistance in ohms and so it goes on.

 

Again unless your running something that is very inductive (motors or coils) or very capacitive (flourescent lighting with no ballast) then to all intents and purposes KVA=KW. As many on here will attest running an electric drill or other motor from a generator is usually fine providing the generator VA rating is greater than the power tools 'watt' rating.

 

you cleary understand some of the basic concepts and the only reason PF is important is to avoid having to provide cables that can carry massive currents but delivering very little actual power which is the practical effect of a power factor of much less than one.

 

hope that helps. if you still want to tie you self up in knots to work out whether you need a capacitor or a bit of wire wound round a bit of ferrite to get a power factor of 1 then good luck and let us know how you get on.

[FORTUNATA]

You're on the right "wave" length (pardon the pun).

It's not really as difficult as it sounds if you leave out the heavy calculus formulae (the whole point of my thread).

Capacitive reactance corrects inductive reactance by use of capacitors.

Here are the basics as I understand thus far:

Induction has something to do with magnetic fields and coils that produce electric as the coil rotates.

We all now that speed is a factor when a coil rotates (say with an alternator). The voltage and current produced is called induction.

Reactance is merely the same as resistance in D.C. There is reactance or resistance of the coil and reactance of EMF waves. With inductive reactance the voltage leads the current so the circuit is out of phase.

I still haven't quite grasped it but it would help if I could bypass all the calculus or at least find all the keys to the symbols such as XL (that means inductive reactance)but not all are keyed to make life simpler.

 

Yello,

 

When I was younger, wasn't inductive reactance known as capacitance ?

 

 

Probably the basic thing you need to know is that 4A current ( Amperes ) @ 240V ....roughly = 1000 watts = 1 kilowatt

 

Simples ... Malc.

 

Well, it bothered me Payne just flew into lagging power factors as if the whole issue could be grasped in just one page. It got me curious so I tried to find more information online. Some of it helped. I now understand a lot more but I suppose the truth is the more I glean, the more I conclude I don't quite fully understand the mechanics of electricity.

I do I suppose understand the absolute basics of Hertz, alternating cycles, induction, KVA and KW but hope to find something a bit more specific on inductive reactance.

 

I'm probably being very naive here, but why don't you put a kettle (not the 1.5 Kw kettle) on a gas hob or solid fuel stove?

 

Payne is a pain .................

[madcat]

Fortunata you are obviously of an enquiring mind and currently unemployed could you get sent for re training as a Lecky? This is a serious suggestion

[RLWP]

Fortunata you are obviously of an enquiring mind and currently unemployed could you get sent for re training as a Lecky? This is a serious suggestion

 

For fun, go and check out his engine rebuild thread:

 

http://www.canalworld.net/forums/index.php?showtopic=31621&st=0&p=557149&hl=diesel&fromsearch=1entry557149

 

Richard

Edited June 8, 2012 by RLWP

[dmr]

I understand your frustration: most textbooks are written by academics and are a bit heavy on the maths but fail to give an "untuitive" understanding of the subject. Most "real world" engineers get by on intuition and a bit of relatively easy maths.

Batavia is correct, you don't need calculus, you can probably even get by without complex (imaginary) numbers (square root of -1), but you will need some basic trig (sines and cosines).

Have a good search of the www and you might find something that suits the way you want to learn.

Its probably too much to ask the forum to produce a tutorial, but if you have specific questions I reckon there are quite a few electrical/electronic engineers here who can give answers.

..........Dave

[nicknorman]

O.K. precisely...:

All I need to do is understand the basics of:

(1) Purely resistive circuits such as heaters.

(2) Circuits where inductive reactance creates a lagging power factor. It will be sufficient to make a very basic calculation of the lag but nothing OTT.

(3) Capacitors used in principle to correct lagging power factors.

That's it!

The basics may well be doable without complicated formulae.

And, yes, I agree it's probably of questionable practicality.

 

 

 

I'm told he's pretty good and could probably make it very simple for me.

(1) -ohms law such current = voltage/resistance, and power = voltage x current

(2) in order to calculate this, you need to know the inductance and resistance, something which is not normally on equipment labels. You would have to measure it, something that cannot be done staticly with most motors ( motors being typically the inductive element of a circuit). Alternatively use a power factor meter or even oscilloscope measuring voltage and current to measure the power factor directly. If you know the inductance and resistance, you just have to work out the reactance of the inductance at the appropriate frequency which is 2 x pie x frequency x inductance. So then you know the reactive impedance and the resistive impedance. An easy way to work out the power factor is to draw a graph with a line representing reactance on x axis, and resistance on y axis, and make up a rectangle. Draw a line from origin to the opposite corner, and the angle of this line is the phase shift between voltage and current from which the power factor can easily be worked out.

 

(3) To correct the power factor to unity, you need a capacitor whose reactance at the appropriate frequency is the same as the inductors reactance (opposite imaginary sign of course). A capacitor's reactance is 1 / (2 x pie x frequency x capacitance)

 

You do not need calculus for steady state sine wave stuff, the above formulas are all you need!

 

ETA power factor easier worked out by using PF = resistance / (resistance + total reactance)

Edited June 9, 2012 by nicknorman