Which current flows when a bank is first energized, not during steady-state operation?

Which current flows when a bank is first energized, not during steady-state operation?

• A. Armature current
• B. Magnetizing current
• C. Load current
• D. Friction current

Answer: (B)

When a transformer bank is energized, the first current that flows is the magnetizing current, sometimes called the exciting current. This current is needed to establish the magnetic flux in the core and it flows even with no load on the secondary. It is largely reactive, and you can see a brief inrush spike at switch-on as the core flux builds, after which it settles to the normal magnetizing current value. Armature current would be the current in rotating machine windings and isn’t what appears just from energizing a transformer. Load current would only flow if there is a connected load on the secondary, and friction current isn’t a standard term for this context. So the initial current when the bank is energized is the magnetizing current.

When a transformer bank is energized, the first current that flows is the magnetizing current, sometimes called the exciting current. This current is needed to establish the magnetic flux in the core and it flows even with no load on the secondary. It is largely reactive, and you can see a brief inrush spike at switch-on as the core flux builds, after which it settles to the normal magnetizing current value. Armature current would be the current in rotating machine windings and isn’t what appears just from energizing a transformer. Load current would only flow if there is a connected load on the secondary, and friction current isn’t a standard term for this context. So the initial current when the bank is energized is the magnetizing current.