EE 61--70

61: Could you explain about reverse power relay?

You have to talk about function of reverse power relay in which it prevents the reverse power flow from bus bar to generator. A reverse power relay is a directional power relay that is used to monitor the power from a generator running in parallel with another generator or the utility. The function of the reverse power relay is to prevent a reverse power condition in which power flows from the bus bar into the generator. Also include the point that the condition occurs when the prime mover fails that is required to drive the turbine or engine.

62: You may have noticed there are fuse and circuit breakers. What is the difference between the both?

You need to say first that the function of fuse is to detect and interrupt while circuit breaker functions as interrupter. Also you could say that breaking capacity and the operating time of fuse is smaller when compared to circuit breaker. The circuit breaker does not require a replacement like the fuse which needs to be replaced. or
A fuse is made up of a piece of metal that melts when overheated; a circuit breaker has an internal switch mechanism that is tripped by an unsafe surge of electricity. Fuses tend to be quicker to interrupt the flow of power, but must be replaced after they melt, while circuit breakers can usually simply be reset.

63: What does tripping means in transmission lines?

Tripping means interruption in electricity supply. An electric line is tripped of, if it starts carrying fault current. It is basically a protective measure to isolate the faulty part from the rest of the healthy section.
In easy words, it refers to circuit breaker tripping. 

64: What is Trash Racks?

Trash Racks are long, flat vertical bars spaced accordingly such that it provides the minimum passage width to the water through the turbine. They are employed to prevent the ingress of floating and other material to the turbine.

65: What is water hammering phenomenon?

When the load on the generator reduces suddenly, governor mechanism will close the turbine gates and thus create an increased pressure in the penstock. This results in water hammering phenomenon' and may need pipe (penstock) of extra ordinary strength to withstand the pressure otherwise the penstock will burst. To avoid this positive water hammering pressure some means are provided to take the rejected flow. This job will be carried out by small storage tank or reservoir for receiving the rejected flow. This storage reservoir or tank is called as 'surge tank'. 

66: What is Penstock?

It is the closed conduit or pipe which connects the forebay or surge tank to the scroll case of the turbine. Penstocks are built of steel or reinforced concrete. The thickness of the penstock must be adequate to withstand both the normal hydrostatic pressure and also sudden surges both above and below normal caused by fluctuations in the load and in emergency conditions

67: Tell me in detail about c.t. and p.t.?

The term C.T means current transformer,and the term P.T means potential transformer.In circuit where measurements of high voltage and high current is involved they are used there.Particularly when a measuring device like voltmeter or ammeter is not able to measure such high value of quantity because of large value of torque due to such high value it can damage the measuring device.so, CT and PT are introduced in the circuits. They work on the same principle of transformer, which is based on linkage of electromagneticflux produced by primary with secondary. They work on the ratio to they are designed. E.g if CTis of ratio 50005A and it has to measure secondary current of 8000A.then ANS-8000*55000=8Aand this result will be given to ammeter .and after measuring 8A we can calculate the primary current.same is the operation of PT but measuring voltage.

68: why syn. generators r used for the production of electricity?

synchronous machines have capability to work on different power factor(or say different imaginary pow varying the field emf. Hence syn. generators r used for the production of electricity.

69: What are the advantages of speed control using thyristor?

1. Fast Switching Characterstics than
Mosfet, BJT, IGBT
2. Low cost
3. Higher Accurate.

70: Whats is MARX CIRCUIT?

It is used with generators for charging a number of capacitor in parallel and discharging them in series. It is used when voltage required for testing is higher than the available.