Frequency - Volts - Amps. A little help please.

[Simonslimline]

Ok i just spotted this in the main section of the forum and it got me thinking about the answers. I dont remember doing this at college.


A reactor allows a current of 15a to flow from a 230v 50 Hz supply.

Determine the current which will flow at the same voltage if the frequency changes to-(A) 45Hz, (B) 55Hz.


I have had a go and i think the answers are as follows @45Hz a Current flow of 16.57A @55Hz a current flow of 13.57A


Can anyone please show the formula to work this out. ​

 

[SirKit Breaker]

Ok i just spotted this in the main section of the forum and it got me thinking about the answers. I dont remember doing this at college.


A reactor allows a current of 15a to flow from a 230v 50 Hz supply.

Determine the current which will flow at the same voltage if the frequency changes to-(A) 45Hz, (B) 55Hz.


I have had a go and i think the answers are as follows @45Hz a Current flow of 16.57A @55Hz a current flow of 13.57A


Can anyone please show the formula to work this out. ​

Put your workings out up first, and await comments.

Cheers............Howard

 

[Simonslimline]

Ok my thinking was, 230V / 15A = 15.3ohms. So 2 x 3.142 x 50 x 0.049 = 15.4 ohms

2 x 3.142 x 45 x 0.049 = 13.85 ohms. 230v / 13.85 = 16.60A

2 x 3.142 x 55 x 0.049 = 16.93 ohms 230v / 16.93 = 13.58A

I have probably done this wrong, my answers were slightly different this time. must of miss typed before.

 

[Silly Sausage]

Off the top of my head, work out the Inductance (Henrys) from the original statement.
Then re-calc with the new freq.

 

[Simonslimline]

yeah that was my thinking and where i got the 0.049 from. I just put figures in until i got as close to 15.3 as possible.

I am not sure the correct way to work out the reactance from the original question? IE - 230V 15A 50Hz

 

[Silly Sausage]

X = 2.pi.f.L

 

[Simonslimline]

Yeah i am happy with this Archy, sorry my problem is how to find L to put in the formula?

 

[Silly Sausage]

I get 16.67A @ 45Hz and 13.64A @ 55Hz

Looks like you were right, the difference is probably from rounding down/up errors.

 

[Silly Sausage]

Yeah i am happy with this Archy, sorry my problem is how to find L to put in the formula?

I'm assuming the inductance is the only thing in circuit, so, X is V/I, then L is X/(2pif)

 

[Simonslimline]

I'm assuming the inductance is the only thing in circuit, so, X is V/I, then L is X/(2pif)

Nice one thanks for that

 

[Silly Sausage]

By the way, my original post on the main forum was unadulterated BS!

 

[Simonslimline]

By the way, my original post on the main forum was unadulterated BS!

mg_smile: