Direction of flow of current in secondary circuit in AC transformer/rectifier

In this transformer/rectifier if the current in the primary circuit is clockwise what will be the direction of current in the secondary circuit?Why?

• I cannot comment on the correct answer because I just signed up. The generated current direction seems not correct based on the ampere right hand rule in the most voted answer and the link provided for "Read more about the dot notation". At the transformer input side, the magnetic flux is from down to top and hence at its output side, the magnetic flux is from top to down. If I applied ampere right hand rule at the transformer output, I get a 180 degree phase different current as the on May 8, 2018 at 17:34

Using Ampere's right hand rule:

Point your thumb in the direction of the current in the primary side and you can get the direction of the magnetic field from the direction of rotation of the other four fingers. The opposite is true, rotating the 4 fingers in the direction of the magnetic field will point your thumb to the direction of current. Try it on the secondary side.

Therefore*:

*Assuming the primary and secondary windings are wrapped in the same direction around the core of the transformer. Read more about the dot notation:

The direction of current in the primary circuit is clockwise & anti-clockwise as it is an AC source.

The direction of current in the secondary is clockwise only (ignoring reverse leakage)

• No that's not what I'm asking.Is the current in secondary circuit clockwise when the current in primary is clockwise or the other way?
– user96630
Jan 10, 2016 at 14:47
• Depends on the dot notation of the XFMR. That is why I didn't state the direction on the primary as there isn't enough information.
– user16222
Jan 10, 2016 at 15:08
• That will depend on the direction of the windings. Often transformer symbols have dots on each winding to indicate the polarity Jan 10, 2016 at 15:12
• The selected answer is incorrect. As myself and other posters have pointed out, the only sure way to know is if the drawing indicates the winding relative polarity. If we had dots on the top (or bottom) of both windings it would indicate that when the top of the primary is made positive, the voltage induced in the secondary will aldi be positive at the top, therefore clockwise current in both loops Jan 10, 2016 at 15:42
• @user1582568 , added an assumption to the answer. You are right. Jan 11, 2016 at 13:42

If there is no secondary load, when the top of the primary is positive, a small current flows clockwise in the primary circuit. As the current increases the rate of change of flux generates an emf which opposes the applied voltage. The transformed is designed so that only a small current builds up in each half cycle of the applied voltage. Now if we add a load current then the secondary current induces opposing flux in the transformer core. This requires the primary to supply increased flux in order to induce the sane emf. This extra flux requires primary current to generate it. As we increase load current then flux in the core is initially reduced (due to the opposing flux). This reduces the opposing emf in the primary. This causes more current to flow in the primary thereby restoring the flux level. As secondary current only flows in the half cycle where the top of the winding is positive, then the additional primary current only flows in this half cycle too. This is why the large current only flows clockwise in the primary. There will still be a small anticlockwise primary current on the other half cycle, just enough to generate the opposing emf.

• You mean when the current in primary circuit is clockwise then the current in secondary circuit will be clockwise?
– user96630
Jan 10, 2016 at 15:06
• Assuming windings are wound as shown then yes, clockwise in both Jan 10, 2016 at 15:14
• Can you tell me how to determine that?
– user96630
Jan 10, 2016 at 15:15