NO-LOAD TRANSFORMER AND ITS PHASOR DIAGRAM
WHAT IS NO-LOAD ?
Before we start discussing about the no-load condition of a transformer, it is important to first understand that what is meant by no-load.
“A transformer is said to be on no-load when the secondary winding of the transformer is left open-circuited thereby reducing the secondary current to zero”.
WHAT HAPPENS WHEN TRANSFORMER IS AT NO-LOAD?
During no-load condition, secondary current in the transformer reduces to zero and when an alternating voltage is applied to the primary, a small current I₀ flows in the primary winding.
The current I₀ is called no-load current of the transformer and it is 3 to 5 percent of the rated primary current.
No-load current is made up of two components Iu and Im.
Iu is called magnetizing component.It magnetizes the core. We can also say that it sets up the flux in the core and therefore Im is in phase with ⲫ (flux). It is also called reactive or wattless component of no-load current.
The other component Iw supplies the hysteresis and eddy-current losses in the core. It is in the phase with the applied voltage V₁. It is also called active or wattful component of no-load current.
PHASOR DIAGRAM AT NO-LOAD
Phasor diagram for a transformer(real) under no-load condition is shown in the fig. below.
|NO-LOAD PHASOR DIAGRAM OF A PRACTICAL TRANSFORMER.|