A transprevious is an equipment which step-up or step-down the level of AC existing or voltage without altering the primary (i.e. input source) frequency. 

Transprevious only works on AC and can’t be operated on DC i.e. it has actually been designed to be operated only and also just on alternating existing and also voltage. To know that what will take place if we connected a DC resource to the major of a transprevious, watch the adhering to examples where we affix a transprevious to the AC initially and DC then.

You are watching: Why does a transformer require ac?

Related Posts:


Transprevious Connected to the AC Supply

Suppose we connect a transformer to the AC supply via the following information.

Key Voltage = V1 = 230VResistance = R1 = 10 ΩInductance = L = 0.4 HSource Frequency = 50Hz

Lets see just how much current will flow through the main of a transprevious in situation of AC.

We understand that resistance in AC = Impedance

Impedance = Z = V / I in Ω

Wright here Z = √ (R2 + XL)2 in situation of inductive circuit.

XL = 2πfL

XL = 2 x 3.1415 x 50Hz x 0.4H

XL = 125.67Ω

Now for impedance

Z = √ (R2 + XL)2

Putting the values

Z = √ (102 Ω + 125.672 Ω)

Z = 126.1 Ω

Now present in the primary

I = V / Z

I = 230V / 126.1Ω = 1.82A

The Primary current in case of AC = 1.82A

Related Posts:

Transformer Connected to the DC Supply

Now affix the very same transprevious to the DC voltage and also allows check out what happens.

We recognize that tbelow is no frequency in DC i.e. f = 0. Thus, the inductive reactance XL would certainly be zero if we put f = 0 in the XL = 2πfL.

Thus, existing in the primary of a transformer in case of DC source.

I = V / R

I = 230V / 10Ω

I = 23A. 

The Primary present in case of DC = 23A

Related Posts: 

The above calculation mirrors that too much present will certainly circulation in the main of a transprevious in situation of DC supply which will certainly burn the primary coils of the transformer. This is not the just reason as the current will be DC, currently allows check out what happens in situation of stady state present in the transprevious.

If the primary of a transformer is linked to the DC supply, the major will certainly draw a secure current and also for this reason create a continuous flux. Consequently, no ago EMF will be produced. They major winding will certainly attract too much existing due to low resistance of the main bereason we recognize that inductive reactance (XL) is zero because of the inductive reactance formula (XL = 2πfL) wbelow frequency of the DC source is zero. Thus result is that the main winding will overheat and burn out or the fuse and also circuit breaker will certainly blow. Care have to be taken not to the connect the main of a transprevious throughout the DC Supply.

Related Posts:

Why a Transformer Can’t be Operated on DC instead of AC?

If we use the DC voltage or current to the main of a transformer, The complying with are the results

We recognize that 

v = L (di/dt)


v = Instantaneous voltage across the major coilsL = Inductance of the inductordi/dt = Instantaneous rate of present adjust in A/s

Now in this instance, the voltage are consistent i.e. DC, Now the current (i) will swiftly rise until the the iron core of the transprevious saturated.

At this stage, current (i) will certainly increase to the dangerous level and also sheight transforming. When tbelow is no readjust in present (i), the induced voltage in the primary will certainly be zero as di/dt = 0 which leads to brief circuit the transprevious winding through the appalled DC resource.

When current gone beyond the safe level, high power loss will certainly take place as P = I2R. which will increase the temperature to the dangerous level and also there may a possibility of explosion of the transformer and also transprevious oil may capture fire as well.

Or let’s watch by Faraday’s Second Law

e = N dΦ / dt


e = Induced EMFN = the number of turnsdΦ = Change in fluxdt = Change in time

In situation of DC voltage to the transformer, there would certainly be continuous flux (Φ) induced in the main due to consistent present. 

Now the induced EMF in the main will be zero as (dΦ/dt = 0) i.e. e = N dϕ/dt = 0 because of continuous flux induced by continuous current.

We additionally understand that tright here is no frequency in DC supply and flux is inversely propositional to the frequency (Φ = V / f) which satuprices the transprevious core.

Its mean, the major of the transformer will certainly act a short circuit route to the additional DC current which may blow the overall transformer. That’s the specific factor we must not connect a transformer to the DC supply rather of AC.

Related Posts:

Under What Condition is DC Supply Applied Safely to the Key of a Transformer?

In the majority of instances, this is an electric and also electronics engineering interwatch kind question, so lets watch how to attach a transformer to the DC supply.

Tright here are two Conditions wright here we have the right to attach a transprevious to the DC.

Pulsating DC as InputHigh Resistance in Series via primary winding

Pulsating DC in Transformer

In this strategy, a pulsating DC (which contains ripples and also not a pure form of stable state current) to the major side of a transformer. In this instance, the negative cycle reset the flux and also time integral of voltage is zero in one finish cycle which aacquire helps to reset the flux in the winding. This principle is supplied in SMPS (Switched-Setting Power Supply.

High Resistor in Series through Transformer

As we know that a transformer works only on AC. in instance of DC supply, the primary of a transformer might begin to smoke and burn. But tbelow is a method wright here we have the right to operate a Transformer on D.C (although the circuit is useless with no output) by adding a high worth resistor in series through the major of the transformer.

When the major winding of a transformer is to be linked to a DC supply. a high resistance is connected in series with the major. This series resistance limits the main present to a safe DC value and therefore prevent the major from burning out.

See more: Why Do New Yorkers Hate New Jersey ? Why Is New York One Of The Most Hated States

Please be advised that don’t attach a transformer to the DC supply without a high resistance in series through major. Due to the fact that tright here is no frequency in DC and the impedance (Z) of inductor is zero. If you put Z = 0 in the I = V/Z, Current will certainly be too much high i.e. inductor acts as a brief circuit to the DC voltage and also curleas.