Transformer currents in primary and secondary question

In summary, when reviewing transformers, it is important to remember that the formulas for ideal transformers, Vs = Vp(Ns/Np) and Ip = Is(Ns/Np), may not accurately reflect the actual current in the primary coil. This is because the inductance value and resistance of the primary winding can also affect the current. Therefore, even if there is no load on the secondary terminal, there may still be a current flowing in the primary due to the inductance of the winding. Lower quality transformers may also have inadequate inductance, resulting in a larger than expected current flow.
  • #1
KrNx2Oh7
19
0
I'm reviewing transformers and I have some confusion over the current

s is for secondary and p is for primary

I know that
Vs = Vp(Ns/Np)
and
Ip = Is(Ns/Np)

So when you have a load across the secondary terminal you get your current through Vs/Rload.
But does this mean for current in the primary coil, it has nothing to do with the inductance value or resistance (if I added a resistor before the inductor in the primary section)? V/Z = I does not work here?

If this is true what would the current be if I left the secondary terminal open so no current will flow. What do i use to calculate current in the primary coil? Is it affected by the inductance value then?

thanks in advance
 
Engineering news on Phys.org
  • #2
KrNx2Oh7 said:
I'm reviewing transformers and I have some confusion over the current

s is for secondary and p is for primary

I know that
Vs = Vp(Ns/Np)
and
Ip = Is(Ns/Np)

So when you have a load across the secondary terminal you get your current through Vs/Rload.
But does this mean for current in the primary coil, it has nothing to do with the inductance value or resistance (if I added a resistor before the inductor in the primary section)? V/Z = I does not work here?

If this is true what would the current be if I left the secondary terminal open so no current will flow. What do i use to calculate current in the primary coil? Is it affected by the inductance value then?

thanks in advance

Those formulas are for ideal transformers. There will be a current in the primary due to the load in the secondary, but there will also be a current due to the inductance of the primary winding.
It is just a coil and it has to have some value of inductance and so it has a reactance which will allow a certain amount of current to flow from the supply.

Cheap transformers are sometimes wound on inadequate iron formers and so don't have enough inductance or reactance to stop a relatively large current flowing even if there is no load.
 

FAQ: Transformer currents in primary and secondary question

What is the difference between primary and secondary transformer currents?

The primary current is the current flowing through the primary winding of a transformer, while the secondary current is the current flowing through the secondary winding. The primary current is typically higher than the secondary current due to the transformer's step-up or step-down function.

How do you calculate the primary and secondary currents in a transformer?

The primary and secondary currents can be calculated using the formula Iprimary = Isecondary x Nsecondary/Nprimary, where Iprimary is the primary current, Isecondary is the secondary current, and N is the number of turns in each winding. This formula assumes an ideal transformer with no losses.

What factors affect the primary and secondary currents in a transformer?

The primary and secondary currents are affected by the transformer's turns ratio, the load on the secondary side, and the frequency of the input voltage. Other factors such as resistance, inductance, and core losses can also impact the currents in a real transformer.

Can the primary and secondary currents be different in a transformer?

Yes, the primary and secondary currents are typically different in a transformer due to the transformer's step-up or step-down function. However, in an ideal transformer with no losses, the primary and secondary currents would be equal.

How do transformer currents affect the efficiency of a transformer?

The primary and secondary currents are directly related to the losses in a transformer. Higher currents can lead to higher resistive losses and lower efficiency. Therefore, transformers are designed to have lower primary and secondary currents to improve efficiency.

Back
Top