ELECTRICAL ENGINEERING

A contactor is an electromechanical device used to switch an electrical circuit on or off. It's commonly used in control circuits for motors, lighting, heating, and other electrical loads. Contactors use an electromagnetic coil to control the opening and closing of electrical contacts to manage the flow of electricity in a circuit. A contactor typically consists of several key components: 1. Coil: The coil is an electromagnet that, when energized, generates a magnetic field to pull in the contacts, closing the circuit. Contact of coil in the contactor named A1 and A2 2. Contacts : These are the points where the electrical circuit is either connected or disconnected. Contacts can be made of various materials, like silver, and are designed to handle specific voltage and current ratings. Normlly close (NC) and Normally Open (NO) 3. Enclosure: This is the housing that protects the internal components of the contactor, shielding them from environmental factors and ensuring safety. 4.

Gravity Power Plants As the world becomes increasingly aware of the need for sustainable energy solutions, researchers and engineers are constantly exploring new technologies to harness renewable sources of power. One promising area of research is the development of gravity power plants, which use the force of gravity to generate electricity.   A gravity power plant is a type of energy storage system that works by lifting heavy weights to a higher elevation, storing potential energy in the process. When electricity is needed, the weights are released, and the potential energy is converted into kinetic energy as the weights fall to a lower elevation. This motion is then used to generate electricity, which can be fed into the power grid.   One advantage of gravity power plants is that they can be located in areas where other forms of renewable energy are less practical. For example, solar and wind power require specific weather conditions to generate electricity, whereas gravity powe

Resistances in Series When some conductors having resistances R 1 , R 2 , and R 3 etc. are joined end on end as in figure below they are said to be connected in series. It can be proved that the equivalent resistance or total resistance between points A and D is equal to the sum of the three individual resistances. Being a series circuit, it should be kept in mind that figure 1 figure 2 (i) current is the same through all three conductors   (I = I 1 = I 2 = I 3 ) (ii) voltage drop across each is different due to Its resistance and is given by Ohm's Law (iii) sum of the three voltage drops is equal to the voltage applied across the three conductors.  There is a progressive fall in potential as we go from point A to D as shown in Figure 3 figure 3   V = V 1 + V 2 + V 3 = IR 1 + IR 2 + IR 3 But V = IR where R is the equivalent resistance of the series combination. IR=IR 1 + IR 2 + IR 3 R eq =R 1 +R 2 +R 3 Resistances in Parallel Three resistances, as joined in Figure 4

 Ohm's Law This law, which is applicable to electrical conduction through reliable conductors, can be formulated as follows. If the conductor's temperature is constant, the ratio of the potential difference (V) between any two places on it to the current (I) flowing between them will remain constant. What I mean is, V/I = constant, or V/I   = R where R is the resistance of the conductor between the two points considered. Put in another way, It simply means that provided R is kept constant, current is directly proportional to the potential difference across the ends of a conductor. However, this linear relationship between V and I does not apply to all non-metallic conductors. For example, for silicon carbide, the relationship is given by V = KI m   where K and m are constants and m is less   Example 1 : A coil of copper has a resistance of 20 ohm at 10 o C   and is connected to a 220 V supply. By how much must the voltage be Increased in order to maintain current c

Not only resistance but specific resistance or resistivity of metallic conductors also increases With rise in temperature and vice versa. According to the picture below the resistivities of metals vary linearly with temperature over a range of temperature, the variation becoming non-linear both at very high and at very low temperatures. Let, for any metallic conductor, ρ 1  =    resistivity at t 1   o C ρ 2  =    resistivity at t 2   o C m  = slope of the linier part of the curve Next, it is evident that m  = (ρ 2  - ρ 1  ) / (t 2  – t 1  )     or      ρ 2  = ρ 1  +  m  (t 2  – t 1  )   or ρ 2  = ρ 1  [1 + ( m/  ρ 1 ) (t 2  – t 1 )   ] The ratio of m / ρ 1 is called the temperature coefficient of resistivity at temperature t 1 0 C. It may be defined as numerically equal to the fractional change in ρ 1 per 0 C change in temperature from t 1 0 C. It is almost equal to temperature-coefficient of resistance α 1 . therefore, substituting  α 1  =  m / ρ 1,  we get  ρ 2  = ρ 1  [1 + α 1  (t

So far we did not make any distinction between values of α ( alpha)   at different temperatures. But it is found that value of  α ( alpha)  itself is not cönstant, but depends on the initial temperature on which the increment in resistance is based. When the increment is based on the resistance measured at 0 0 C, then α has the value of  α 0   ( alpha nol)  any other initial temperature t 0 C, value of α is α t , and so on. It should be remembered that, for any conductor, α 0 has the maximum value.  Suppose a conductor of resistance R 0   at 0 0 C (point A in Fig. above)  is heated to t o C (point B).  Its resistance R t  after heating is given by  R t   = R 0  (1 +  α 0   t)                                                     … eq (1) where   α 0  is the temperature-coeffcient at 0 0 C. Now, suppose that we have a conductor of resistance  R t  at temperature t 0 C. Let this conductor be cooled from t o C to 0 0 . Obviously, now the initial point is B and the final point is A. The fi