1. Switchgear
We all familiar with low voltage switches and re-wirable fuses in our home. The switch is
used to manually open and close the electrical circuit in our home and electrical fuse is used
to protect our household electrical circuit from over current and short circuit faults. In same
way every electrical circuit including high voltage electrical power system needs switching
and protective devices. But in high voltage and extra high voltage system, this switching and
protective scheme becomes complicated one for high fault current interruption in safe and
secure way. In addition to that from commercial point of view every electrical power system
needs measuring, control and regulating arrangement. Collectively the whole system is called
Switchgear and Protection of power system.
Switchgear protection plays a vital role in modern power system network, right from
generation through transmission to distribution end. The current interruption device or
switching device is called circuit breaker in Switchgear protection system. The circuit breaker
can be operated manually as when required and it is also operated during over current and
short circuit or any other faults in the system by sensing the abnormality of system. The
circuit breaker senses the faulty condition of system through protection relay and this relay is
again actuated by faulty signal normally comes from current transformer or voltage
transformer.
A switchgear has to perform the function of carrying, making and breaking the normal load
current like a switch and it has to perform the function of clearing the fault in addition to that
it also has provision of metering and regulating the various parameters of electrical power
system.
Electric switchgear is necessary at every switching point in the electrical power system.
There are various voltage levels and hence various fault levels between the generating
stations and load centres. Therefore various types of switchgear assembly are required
depending upon different voltage levels of the system.
Besides the power system network, electrical switchgear is also required in industrial works,
industrial projects, domestic and commercial buildings.
Transformer
A transformer is a static electrical device that transfers energy from one circuit to other by
inductive coupling between its winding circuits. A varying current in the primary winding
creates a varying magnetic flux in the transformer's core and thus a varying magnetic flux
through the secondary winding. This varying magnetic flux induces a varying electromotive
force (emf) or voltage in the secondary winding based on faraday’s law of electromagnetic
induction. Transformers are frequently used to create higher or lower voltages, but they also
used to isolate circuits from each other.
Power transformer is used for the transmission purpose at heavy load, high voltage greater
than 33 KV & 100% efficiency. It also having a big in size as compare to distribution
transformer, it used in generating station and Transmission substation .high insulation level.

2. The distribution transformer is used for the distribution of electrical energy at low voltage as
less than 33KV in industrial purpose and 440v-220v in domestic purpose. It work at low
efficiency at 50-70%, small size, easy in installation, having low magnetic losses & it is not
always fully loaded.
Although commercial electric companies use a large number of transformers throughout their
power distribution system, that industry pretty much reserves the name "distribution
transformer" for the final transformer in the system before the electricity enters a residence or
a business. Various types of distribution transformers serve different needs according to
amount of power needed as well as physical and environmental considerations.
ILLUMINATION
Visible light (commonly referred to simply as light) is electromagnetic radiation that is
visible to the human eye, and is responsible for the sense of sight. Visible light has a
wavelength in the range of about 380 nanometres (nm), or 380×10−9
m, to about 740
nanometres.
Primary properties of visible light are intensity, propagation direction, frequency or
wavelength spectrum, and polarisation, while its speed in a vacuum, 299,792,458 meters per
second, is one of the fundamental constants of nature. Visible light, as with all types of
electromagnetic radiation (EMR), is experimentally found to always move at this speed in
vacuum. In common with all types of EMR, visible light is emitted and absorbed in tiny
"packets" called photons, and exhibits properties of both waves and particles. This property is
referred to as the wave–particle duality.
Newton bought a prism and noticed how when the sun shone on it, he got different colours
out. This made him very curious. Does this change the light, or does the sunlight have lots of
colours that the prism puts into different places? How does the prism do it?

3. He discovered that the separation of light was even clearer. There was red, then orange, then
yellow, then green, and then blue. Newton was pretty sure that what was happening was that
the light from the sun had all these colours in it, and that what the prism was doing was
bending them all to go into slightly different directions. To test this he got two prisms and a
card with a hole in it. He used the first prism to get the sunlight to make different colours.
Then he would choose a colour and put the hole so than only that colour went through into
the next prism. He then had a very thin line of red, yellow or some other colour of light going
to the second prism.
He discovered that when the light came out of the other side of the next prism, it was still the
same colour as when it went in. So the prism doesn't change the light's colour. What the
prism did do was to bend the path the light went on, so that it hit a different place than when
the prism wasn't there. When he tried different colours of light he found that the prism bent
them all a little bit differently. That was why light that looked white, which had all the
colours in it, made different colours when it went through the prism - the different colours all
came out of it in slightly different directions.
LAWS OF LIGHT
Reflection:
When a ray of light strikes a plane mirror, the light ray reflects off the mirror. Reflection
involves a change in direction of the light ray. The convention used to express the direction
of a light ray is to indicate the angle which the light ray makes with a normal line drawn to
the surface of the mirror. The angle of incidence is the angle between this normal line and the
incident ray; the angle of reflection is the angle between this normal line and the reflected
ray. According to the law of reflection, the angle of incidence equals the angle of reflection.
object but inverted.

4. Refraction:
Refraction is the change in direction of a wave due to a change in its transmission medium.
Refraction is essentially a surface phenomenon. The phenomenon is mainly in governance to
the law of conservation of energy and momentum. Due to change of medium, the phase
velocity of the wave is changed but its frequency remains constant. This is most commonly
observed when a wave passes from one medium to another at any angle other than 90° or 0°.
Inverse Square Law
The inverse square law defines the relationship between the irradiance from a point source and distance. It states that the intensity per
unit area varies in inverse proportion to the square of the distance. Distance is measured to the first luminating surface - the filament of
a clear blulb, or the glass envelope of a frosted bub.
Example: You measure 10.0 lm/m² from a light bulb at 1.0 meter. What will the flux density be at half the distance?
Solution:
E1=(d1/d2)²*E2
E0.5 m=(1.0/0.5)²*10.0 = 40 lm/m²
In optics, Lambert's cosine law says that the radiant intensity or luminous intensity observed
from an ideal diffusely reflecting surface or ideal diffuse radiator is directly proportional to

5. the cosine of the angle θ between the observer's line of sight and the surface normal. The law
is also known as the cosine emission law or Lambert's emission law.

6. the cosine of the angle θ between the observer's line of sight and the surface normal. The law
is also known as the cosine emission law or Lambert's emission law.