Page 252 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

• I2 has own m.m.f. (=N2I2)

• known as demagnetizing amp-turns.
• flux 2 is in opposition to the main primary flux due to I0.
• The opposing secondary flux 2 weakens the primary flux momentarily,
• primary back e.m.f. E1 reduce for a moment

• V 1 gains the upper hand over E1 and causes more current to flow in primary.
• additional primary current is I2’ .
• I2’ is known as load component of primary current.
• I2’ is antiphase with additional primary m.m.f. N1 I2’ sets up its own flux 2’
• which is in opposition to 2

• and equal to it in magnitude.
• Hence, the two cancel each other out.
• So, magnetic effects of secondary current I2 are immediately neutralized by
• the additional primary current I2’
• Hence, whatever the load conditions, the net flux passing through the core is approximately the same as at
no-load.
due to the constant core flux at all loads, the core loss is also practically the same under all load conditions
Transformer on NO Load

• On no-load, the primary input current is not wholly reactive.
• The primary input current under no-load conditions has to supply
i Iron losses in the core i.e. hysteresis loss and eddy current loss and
ii A very small amount of copper loss in primary
• Hence, the no-load primary input current I0 is not at 90° behind V1 but lags it by an angle 0 <90°.

• The no-load primary current I0 is very small as compared to the full-load primary current.
• It is about 1 per cent of the full-load current.
• The no-load primary Cu loss is negligibly small
• No-load primary input is practically equal to the iron loss f

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CITS : Power - Electrician & Wireman - Lesson 41-49 CITS : Power - Electrician & Wireman - Lesson 41-49