A transformer's 'no load' current is not 'high'. On the contrary, it is zero!
'No load' means that there is nothing connected to the secondary (output) of the transformer -i.e. it is an open circuit. So a transformer's secondary 'no load' current is zero! The primary current still has to provide a magnetising current, but that current will be very small.
Don't forget, a 'light load' means little current is drawn, so the load must have a high resistance; a 'heavy load' means lots of current is drawn, so the load must have a low resistance.
It is a transformer with No load attach to it.
2 to 5% of full load current
To calculate the no load current from transformer & core loss is also calculated.
If the load current is too high, the power lost in the transformer windings will be too high and it will overheat. If the voltage is excessive, the power lost in eddy currents in the magnetic core will be too high and it will overheat.
The secondary load current will change. This, in turn, will cause the primary current to change (the primary current being the phasor sum of the [IS (Np/Ns)] and the primary current (Io).
load
It is a transformer with No load attach to it.
2 to 5% of full load current
is it primary current ?
No load current is energizing current. This is effectively "lost" power, power used in the transformer to energize the core. It, therefore, should be small!
To calculate the no load current from transformer & core loss is also calculated.
No load current, in a transformer for example, is the current necessary for exciting the transformer. If you wish to keep it energized, and you need to keep it energized at full voltage, there is nothing you can do to reduce this other than replace the transformer with one that has lower no load current. If you are referring to a different piece of equipment, you may need to specify what you are meaning by "no load current".
When the secondary of a transformer is opened, there is no longer any load on the transformer. There will be some current flowing in the primary winding, which is needed to induce the voltage in the secondary. This primary current is referred to as the "no load" current, and is indicative of the core losses in the transformer.
If the load current is too high, the power lost in the transformer windings will be too high and it will overheat. If the voltage is excessive, the power lost in eddy currents in the magnetic core will be too high and it will overheat.
The secondary load current will change. This, in turn, will cause the primary current to change (the primary current being the phasor sum of the [IS (Np/Ns)] and the primary current (Io).
No load current depends on the design of the transformer, and what voltage it is energized at. It will typically be below 1% of full load, and can be significantly below 1% for utility sized transformers.
The secondary current is determined by the load, not by the transformer. For example, if the secondary voltage is 50 V and the load is 100 ohms, then the secondary current will be 0.5 A. If the load is 25 ohms, then the secondary current will be 2 A. It is important that a continuous secondary current doesn't exceed the rated secondary current of the transformer.