What happen if primary of transformer connected to dc?

Answer 1

Nothing noticeable. DC power is not transmitted between the coils of a transformer. There would be no current on the other side of the transformer, unless the power of the source was constantly modulated. bescause flux does not change its state.

after some time excessive heat is produced and winding may burn

Answer

A transformer's primary winding presents two forms of opposition to current flow. The first is resistance, which is dependent upon the length, cross-sectional area, and resistivity of the wound conductor. The second is reactance, which depends upon the inductance of the winding and the frequency of the supply. Resistance opposes both AC and DC currents, while reactance opposes only AC current. In the case of a transformer's windings, the resistance is relatively low while the reactance is very high. When an AC voltage is applied, the reactance is sufficiently high to limit the value of AC current flowing through the winding. However, the resistance is so low that a large current would flow if an equivalent DC voltage was applied instead. This current would likely overheat the winding's insulation, resulting in its breakdown, causing a short circuit(s) which could severely damage the transformer.

Answer 2

When a transformer is connected to a DC voltage source, the primary winding behaves like a RL circuit: for much less than one second, the current increases (transient behaviour) and reaches and stays at a maximum that depends on resistance, since the latter in transformer is often low, that would amount to make a near short-circuit.

On the secondary winding(s), you would measure (with a voltmeter) a pulse during the transient behaviour, then nothing.

The core will saturate; just as if it became saturated in AC, you will get inrush level currents (much beyond the transformer's capability to handle). In short, the transformer will cook, and/or you'll blow a fuse/breaker.

Answer 3

When you apply an AC voltage across the transformer primary, a voltage is induced into the primary which is very nearly equal to, but which opposes, the supply voltage, and the resulting current is very low (magnetising current).

However, if you were to apply the DC equivalent of the transformer's rated voltage across the primary winding then, because the winding's resistancc is relatively low, the resulting current would likely be high enough to burn out the winding.

Answer 4

transformer works only in ac

Answer

The primary winding of a transformer has a very low resistance so, if the d.c. voltage were equivalent to the rated a.c. voltage, then the resulting current would likely be high enough to burn out that winding.

Answer 5

A transformer will not work with d.c. This is because a transformer works on the principle of mutual induction, by which a changing current in the primary winding is required to induce a voltage into the secondary winding. D.C. current does not vary, so no mutual induction can take place (other than the instant it is switched on, or switched off).

Additionally, if the d.c. voltage applied to the transformer's primary is of the same or similar value as the transformer-primary's rated a.c. voltage then, because of the winding's very low resistance, a very high current will flow. This current will be very much bigger than the rated a.c. current, and it is likely to overheat and damage the primary winding and its insulation, and severely damage the transformer.

So applying d.c. to a transformer can actually damage it.

You can, however, apply d.c. to a type of transformer called an induction coil. This is the type of coil used in a car ignition circuit, used to raise the 12-V d.c. voltage to the thousands of volts necessary to operate its spark plugs. This works by continuously interrupting the d.c. current (using a switch driven by the engine) passing through its primary winding. This continous on/off current will act in a similar way to a.c., enabling the induction coil to step up the applied d.c. voltage.

Answer 6

You get useless heat -- the transformer acts like a space heater, but not intentionally. The transformer will burn up if the input power is high enough.

Answer 7

you need to call bag to debug it