Hi folks.
Lets talk something about transformers. (if you don't think of Optimus prime or Auto-bots after listening to this word and instead imagine a pole mounted dump metal box with oil stains on it, You are a true electrical engineer).
Q 1) Magnetization current in the transformer is desirable or not?
Q 2) Why transformer makes noise while working?
Answer 1- If we think logically, transformer draws magnetizing current to magnetize the core or to produce flux in the core. We must have flux in the core to have transformer action. So the magnetizing current is desirable. But it is absolutely FALSE #logical thinking is not always right!
Lets us see why. The answer to the above question lies in the ideal transformer concept. Ideal transformer has infinite core permeability. It implies that it needs zero external efforts to set up flux in the core. In case of practical transformer, as permeability is finite, we need to put in some energy to align the dipoles and to produce flux. That extra energy we give in the form of magnetizing current. So ideally magnetizing current should be zero. Magnetizing current under saturation condition leads to high no load current and worst power factor. So even though flux in the core is desirable, Magnetizing current is not.
Answer 2- Magnetostriction. We all know that there is dipole alignment process going on inside core when we magnetize it or demagnetize it. When the core is magnetized, to accommodate for the aligned dipoles, it expands. Similarly, for demagnetization, due to reverse process, it contracts. So the core undergoes contraction and expansion twice in one cycle of supply frequency (draw a sine wave and you will get it). So we get 2 compression and rarefaction (of resultant sound wave) in the 1 cycle of supply voltage. For 50 Hz supply, we get 100 Hz as the frequency of noise and that falls in our audio range (20-20,000 Hz). So we hear noise, that is often called magnetic hum. To avoid this, the laminations in the core are tightly stacked.
For the electronic transformers the same noise is produced but as they work on very high frequency, We are unable to hear that.
Lets talk something about transformers. (if you don't think of Optimus prime or Auto-bots after listening to this word and instead imagine a pole mounted dump metal box with oil stains on it, You are a true electrical engineer).
Q 1) Magnetization current in the transformer is desirable or not?
Q 2) Why transformer makes noise while working?
Answer 1- If we think logically, transformer draws magnetizing current to magnetize the core or to produce flux in the core. We must have flux in the core to have transformer action. So the magnetizing current is desirable. But it is absolutely FALSE #logical thinking is not always right!
Lets us see why. The answer to the above question lies in the ideal transformer concept. Ideal transformer has infinite core permeability. It implies that it needs zero external efforts to set up flux in the core. In case of practical transformer, as permeability is finite, we need to put in some energy to align the dipoles and to produce flux. That extra energy we give in the form of magnetizing current. So ideally magnetizing current should be zero. Magnetizing current under saturation condition leads to high no load current and worst power factor. So even though flux in the core is desirable, Magnetizing current is not.
Answer 2- Magnetostriction. We all know that there is dipole alignment process going on inside core when we magnetize it or demagnetize it. When the core is magnetized, to accommodate for the aligned dipoles, it expands. Similarly, for demagnetization, due to reverse process, it contracts. So the core undergoes contraction and expansion twice in one cycle of supply frequency (draw a sine wave and you will get it). So we get 2 compression and rarefaction (of resultant sound wave) in the 1 cycle of supply voltage. For 50 Hz supply, we get 100 Hz as the frequency of noise and that falls in our audio range (20-20,000 Hz). So we hear noise, that is often called magnetic hum. To avoid this, the laminations in the core are tightly stacked.
For the electronic transformers the same noise is produced but as they work on very high frequency, We are unable to hear that.
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