Module 202 revision

[Chrisuk]

I just want to know why you used brackets and then didn't use brackets, because if u use brackets for 8500/(230 x 0.65) = 56.86A

If college got it wrong ill tell them tomorrow

I just need to know brackets or no brackets? Because u used brackets for the 3 phase

 

[Simonslimline]

Sorry mate I realised I was wrong and edited the post. could you delete that please lol.

I used brackets for the calculation because if I type it in the calculator without them it wont work.

with the 230 V question you dont need the brackets

 

[Chrisuk]

I think I'm having a blonde moment, what's rt3? A root of 3?

I still can't get the answer on my calc

Square.r3(VxIxPf) but I don't have I

......

 

[Chrisuk]

Not a problem at all Si, you have showed me 100% how to work it out if 3 phase so I'm happy with that

But

For 230V if I don't need brackets then the answer is 24
But with brackets is 56 and college that it's 56 yet I'm not too convinced because the papers and docs from C&G have a ton of mistakes on them

Can someone please tell me if my answer to question 1 is correct, is it 227V

College said it is 226V but I can't sees where the 4V is coming from

 

[Chrisuk]

Sorry mate I realised I was wrong and edited the post. could you delete that please lol.

I used brackets for the calculation because if I type it in the calculator without them it wont work.

with the 230 V question you dont need the brackets

My only issue with that it's with brackets and without brackets gives 2 different answers

 

[dazza1981]

My only issue with that it's with brackets and without brackets gives 2 different answers

You need carol vorderman sitting next to you in college...... the maths side of it and formulas drove me nutty!!

 

[Silly Sausage]

Question 1

So A needs to be increased to 10A

10x0.2=2V
5x0.2=1v
Totally 3V
230-3v=227

Answer D

Yet my tutor said it's C

Can someone else see what answer they get please

Question 2 and I'm struggling with this because I don't know the correct formula

The line current of a 400V three phase load of 8kW at 0.8 power factor is

A. 11.54A
B. 14.43A «------ tutor said it's the correct answer
C. 20A
D. 25A

But it was time to leave and I want to know the formula

Isn't the answer the line current
The 400v surely is the line voltage?

The voltage across B.
So, 15A through the top and bottom left 0.1Ohm and 5A through the top and bottom right 0.1Ohm
So dropping 2 * (15 * 0.1 + 5 * 0.1) = 4

 

[Simonslimline]

Putting brackets in seperates each bit of the calculation in order for the calculator to give the correct answer. Its important to know what you doing with the calcs otherwise its easy to get missleading answers.

 

[dazza1981]

As simons pointed out, the brackets break the calculation up into segments.... without them you get a totally different answer as i used to get caught out with that all the time!

 

[Chrisuk]

You need carol vorderman sitting next to you in college...... the maths side of it and formulas drove me nutty!!

Haha, right I wonder if she's in the yellow pages

It does my head in too

 

[Chrisuk]

The voltage across B.
So, 15A through the top and bottom left 0.1Ohm and 5A through the top and bottom right 0.1Ohm
So dropping 2 * (15 * 0.1 + 5 * 0.1) = 4

Ok you added all A together giving you the 15A, easy

But I don't get why you times the total A by 0.1 then you also did the 5A I the right (isn't this in the total of 15A already?

If you take the total Ohms either top is 0.2, or left side of A, so 0.2, or left side of B, still 0.2

Why times it only 0.1

Seems you got the answer college got, Anglo not good that my tutor couldn't work it out, told us to leave it with him :/

 

[Chrisuk]

Right so Volts x Amps x power factor equals Watts.

So 230V x 56.86 Amps x 0.65 Power factor Equals 8500.57Watts

But this just blags my head more because doing this means the answer is 56.86A which is the answer college have and Its the answer I get if I use brackets

Using no brackets says it's 24.02.....:confused.com

 

[Simonslimline]

It is the answer mate, to get 24Amps I mistakenly did 8500/230 x 0.65 .(wrong answer)

It is actually 8500/230/0.65 equals 56.86A (correct answer)

Remember what the brackets are doing in the calculation in terms of seperating the numbers.

 

[Chrisuk]

It is the answer mate, to get 24Amps I mistakenly did 8500/230 x 0.65 .(wrong answer)

It is actually 8500/230/0.65 equals 56.86A (correct answer)

Remember what the brackets are doing in the calculation in terms of seperating the numbers.

I'll just remember 3 phase needs brackets
230V no brackets

I hope

Thanks for all your help

 

[Simonslimline]

That may not always be the case though mate. It will depend what you are trying to do. For instance the 230 calc you posted can be done without brackets. Other calcs using 230 may differ. If you break the calculations down you will see why.