# Is current measured in Watts or kW?

1. Apr 13, 2009

### JosephF

1. The problem statement, all variables and given/known data

I'm using the following equation:

Is Vs = Ip Vp

Is the current measured in Watts or kW?

2. Relevant equations

n/a

3. The attempt at a solution

n/a

2. Apr 13, 2009

### RoryP

Re: Transformers

well power is measured in Watts, not current.

3. Apr 13, 2009

### JosephF

Re: Transformers

Ok. I'll show you the question and hopefully I've gone in the right direction.

1. The problem statement, all variables and given/known data

A power line supplies electrical energy to a transformer in a manufacturing plant.
The input voltage to the transformer is 11,000V. The transformer changes this to 415V for use in the manufacturing plant. The power input to the transformer is 800kW.

i. Calculate the current in the secondary coil of the transformer, stating any assumptions you have made about the transformer.

2. Relevant equations

$$I_p V_p = I_s V_s$$

3. The attempt at a solution

Assuming 100% efficency in the transformer.

x / 415 = 800,000 / 11,000

x = 30.181 (3dp) kW

I think I'm using the right equation but have I got my units mixed up?

Thanks,

4. Apr 13, 2009

### RoryP

Re: Transformers

you are using the right equation except that you have substituted the power as the current!
you need to get the primary current using P=IV
then you can use that equation =]

5. Apr 13, 2009

### RoryP

Re: Transformers

i get 1927.7 Amps, is this correct?

6. Apr 13, 2009

### JosephF

Re: Transformers

I also got 1927.7108....

Thanks for your help Rory :)

7. Apr 13, 2009

### RoryP

Re: Transformers

Excellent!
No worries JospephF =]