Page 249 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Transformer Insulating Oils
It serves twofunctions:
• Provide Cooling
• Provide insulation
Mineral oils generally used,but high flammabilitysynthetic esters are used as alternate.

Earlier used Polychlorinated biphenyls (PCBs) like askarels, now banned.
Flash point is the lowest temperature at which vapours of material will ignite, when given an ignition source.
The pour point of a liquid is the temperature at which it becomes semi solid and loses its flow characteristics.
transformer on load
Ideal Transformer

An ideal transformer is a lossless device with an input winding and an output winding. It has the following properties:
• No iron and copper losses
• No leakage fluxes
• A core of infinite magnetic permeability and of infinite electrical resistivity
• Flux is passing fully through the core

• winding having no resistance.
Ideal tx. two purely inductive coils wound on a loss-free core

Emf Equation Of Transformer
N1=No.of turns in primary
N2=No.of turns in secondary

f m=Maximum flux in core in webers = Bm A
f=Frequency of a.c.input inHZ
1
we know,Time period T=
f
Time for flux to increase from its zero value to
1
maximum value = One quarter of the cycle ( 4f second.)
fm
Average rate of change of flux = = 4f fm
1
4f

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