SESSION:12

FOR DOWNLOADING pdf FILE PLEASE CLICK HERE.

(The pdf File is Password Protected, write your Email in Comment Box to get Password)

1)       What is lead resistance and contact resistance?

Lead resistance and Contact resistance are two different things. Contact resistance is the resistance offered by the joints in equipment like Disconnect Switch / Isolator, Circuit Breaker etc while lead resistance generally means the resistance of the connecting lead of the Tests Kit. 

2)       What is wave trap and use of wave trap?

Wave trap is a device used in the substation at the incoming lines. Wave trap is also called as line trap.As the name indicates a wave trap, is used to trap/catch the wave. The substations use the power line for communication purpose also. They use high frequency waves to communicate between the substations. Communication between the substations was done using the power lines in the days where communication through the telephone/communication lines was difficult. But still PLCC is adopted in the substations as it is faster, easier, cost effective and also very safe to transmit the messages without any interference. f the communication frequencies are not filtered, then it would act as harmonics to the electrical equipments like transformers, circuit breakers and damage the equipments.

So in order to protect the electrical equipments and for communication purpose the wave trap is used in the substation. I have attended industrial training at a substation and I have seen these wave traps directly and how the maintenance works are done at substation.

3)       What is the voltage used in USA for domestic purpose?

120V with 60 Hz frequency. So the appliances manufactured should be supporting these specifications.

4)       Why efficiency in thermal power plant is low?

As thermal power plant works on Rankine Cycle and most of the heat energy is lost to have a heat sink. Therefore the efficiency becomes low around 35%.

5)       What is a System?

When a number of elements or components are connected in a sequence to perform a specific function, the group of elements that all constitute a System.

6)       What is Control System?

In a System the output and inputs are interrelated in such a manner that the output quantity or variable is controlled by input quantity, then such a system is called Control System.
The output quantity is called controlled variable or response and the input quantity is called command signal or excitation.

7)       What are different types of Control Systems?

Two major types of Control Systems are

1) Open loop Control System

2) Closed Loop Control Systems

Open loop Control Systems: The Open loop Control System is one in which the Output Quantity has no effect on the Input Quantity. No feedback is present from the output quantity to the input quantity for correction.

Closed Loop Control System: The Closed loop Control System is one in which the feedback is provided from the Output quantity to the input quantity for the correction so as to maintain the desired output of the system.

8)       What is a feedback in Control System?

The Feedback in Control System in one in which the output is sampled and proportional signal is fed back to the input for automatic correction of the error (any change in desired output) for further processing to get back the desired output.

9)       Why Negative Feedback is preferred in the Control System?

The role of Feedback in control system is to take the sampled output back to the input and compare output signal with input signal for error (deviation from the desired result). Negative Feedback results in the better stability of the system and rejects any disturbance signals and is less sensitive to the parameter variations. Hence in control systems negative feedback is considered.

10)    What is the effect of positive feedback on stability of the system?

Positive feedback is not used generally in the control system because it increases the error signal and drives the system to instability. But positive feedbacks are used in minor loop control systems to amplify certain internal signals and parameters.