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‣  Protection of Transformer‣  Equivalent Circuit diagram of single phase Transformer ‣  Core type Transformer and Shell type Transformer‣  Transformer with winding Resistance and Magnetic Leakage‣  Transformer with winding Resistance but No Magnetic Leakage‣  Equivalent Resistance of single phase Transformer‣  Magnetic leakage of Single Phase Transformer‣  Oil Flow Indicator of the pump of Power Transformer‣  Silica Gel Breather of Transformer‣  Oil Pump of Transformer ‣  Radiator of Transformer and working of Radiator‣  PRD of Transformer‣  MOG ( magnetic oil gauge ) of Transformer‣  Bushing of Transformer ( for H.V side and L.V side )‣  WTI and OTI of Transformer‣  Buchholz Relay of Transformer and Working of Buchholz Relay‣  Conservator tank of Transformer‣  What is a Power Transformer ?‣  Short Circuit Test or Full load Cu loss of Transformer ‣  Open circuit test or No load Test of Transformer ‣  Parallel operation of 3-phase Transformer‣  Earthing or Neutral Grounding Transformer ‣  Transformer on On load Condition ‣  What is a Transformer ?‣  E.m.f Equation of Transformer ‣  Transformer on No load Condition

Index

Transformer on On load Condition

When load is connected to the secondary winding of a transformer , I₂ (secondary current) is set up in the secondary winding. The magnitude and phase of I₂ with respect to V₂ (secondary voltage) depends upon the characteristics of the load. Secondary current I₂ is in phase with V₂,if load is no inductive , lags if load is inductive and it leads if load is capacitive.

This secondary current sets up m.m.f( =N₂I₂ ) and hence it produce magnetic flux Φ ₂ which is in opposition to the main primary flux Φ . The secondary ampere-turns N₂I₂ are known as demagnetizing amp-turns. The opposing secondary flux Φ ₂ weakens the primary flux Φ momentarily, hence the primary winding back e.m.f E₁ tends to be reduced. For a moment V₁ > E₁ and hence more current to flow in the primary winding . Let the additional primary current be I₂’ which is known as load component of primary current. This current (I₂) is anti-phase with I₂.This load component of primary current(I₂’) sets up its own flux Φ ₂’ which is in opposition to secondary flux Φ ₂ , but is in the same direction as primary flux Φ. And flux Φ ₂’ is equal to Φ ₂. Hence, the two flux cancel each other out.

So, we can say that whatever the load conditions, the net flux passing through the core is approximately the same as at no-load. Due to the constancy of core flux at all loads, the core loss is also practically the same under all load conditions. As Φ ₂= Φ ₂’

Hence, when transformer is no load, the primary winding has two currents in it; one is I₀ and the other is I₂’ which is anti-phase with I₂ and K times in magnitude. The total primary current is the vector sum of I₀ and I₂’.

In Fig. shown the vector diagram of a transformer when the load is non-inductive and when the load is inductive. If we assume voltage transformation ratio is unity , ( i.e K= 1 )

In the fig.-1, shown the vector diagram of a transformer when load is non-inductive

I₂= secondary current in phase with E₂= V₂

I₂’= load component of primary current which is anti-phase with I₂ and also equal to it in magnitude( as K=1 )

I₁= Primary current which is vector sum of I₀ and I₂’ and lags behind V₁ by angle φ₁.

In the fig.-2, shown the vector diagram of a transformer when load is inductive,

I₂= secondary current lags E₂ by φ₂.

I₂’= load component of primary current which is anti-phase with I₂ and also equal to it in magnitude( as K=1 )

I₁= Primary current which is vector sum of I₀ and I₂’ and lags behind V₁ by angle φ₁.

It is seen from the fig.-2 that the angle φ₁is slightly greater than φ₂.

In figure , It is seen that I₀ is neglect as compared to I₂’, then φ₁= φ₂. Besides, under this assumption , N₁I₂’= N₂I₁= N₁I₂

It is shown that under the full-load condition, the ratio of primary and secondary current is constant. The relationship is made the basis of current transformer, such a transformer which is used with a low-range ammeter for measuring currents in circuits.

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