The type of protection that does not respond to faults occurring beyond its zone even though the fault current may pass through the zone is
Unit type schemes protect a specific area of the system i.e. a transformer, transmission line, generator or bus bar. The unit protection schemes are based on Kirchhoff’s Current Law (the sum of the currents entering an area of the system must be zero). Any deviation from this must indicate an abnormal current path. In these schemes, the effects of any disturbance or operating condition outside the area of interest are totally ignored and the protection must be designed to be stable above the maximum possible fault current that could flow through the protected area.
Which components of the symmetrical system have three phasors with equal magnitude but are displaced from each other by 120 degree having reverse phase sequence as compared to that of original?
Positive sequence component: It represents three equal phasors, phase displaced by 120° and has phase sequence same as the original phasors.
Negative sequence component: It represents three equal phasors, phase displaced by 120° with each other and has phase sequence opposite to that of the original phasors.
Zero sequence component: It represents three equal and parallel phasors with zero degree phase displacement.
Isolators are used for disconnecting a circuit when
Isolators are used to open a circuit under no load. Its main purpose is to isolate one portion of the circuit from the other and is not intended to be opened while current is flowing in the line. Isolators are generally used on both ends of the breaker in order that repair or replacement of circuit breaker can be done without and danger.
How should a fuse be installed in a circuit to ensure proper operation?
A fuse is a short length of wire designed to melt and separate in the event of excessive current. Fuses are always connected in series with the components to be protected from over current. When the fuse blows, it will open the entire circuit and stop current through the components.
A good fuse wire must have:
A fuse is a short length of wire designed to melt and separate in the event of excessive current. It must have low resistance, high conductivity, low ohmic losses and low melting point.
Resisting capacity of Vacuum circuit breaker is
A vacuum circuit breaker is such kind of circuit breaker where the arc quenching takes place in vacuum. This is suitable for medium voltage application. Resisting capacity of this type of circuit breaker is very high.
Air Blast Circuit breaker is employed among which of the following?
i. Arc furnace duty
ii. Traction system
Air blast circuit breakers are used in arc furnace duty, traction systems, and used for the railway electrification. Because they are suitable for repeated duty.
For Average values of load current, current chopping occurs more frequently in
When low inductive currents such as magnetizing current of transformer, shunt reactors are interrupted by breaker, there is rapid deionization of contact space and may cause the current to be interrupted before its neutral zero. This phenomena is called current chopping. For average values of load current, it occurs frequently in Air blast circuit breakers.
Earth fault relays are
The directional relay recognizes the direction in which fault occurs with respect to the location of relay. It is set such to actuate for faults occurring in one particular direction only.
The earth fault relay is basically a protection device used selectively for earth fault protection, can be used for both primary and backup protection in an electrical system. It is a directional relay.
Which of the following is not a kind of relay on the basis of constructional features?
According to the principle of operation and construction, the relay may be classified as follows
1) Electromagnetic Relays
2) Electromagnetic Induction Relays
3) Electrodynamic Type Relays
4) Moving Coil Type Relays
5) Electro-thermal Relays
6) Static Relays
Reactance relays are generally deployed for the phase faults in
1) Short lines
2) Medium lines
3) Long lines
Impedance relay is used for the phase faults in medium transmission line
Reactance relay is used for the phase faults in short transmission line
Mho relay is used for the phase faults in long transmission line
An equipment has an impedance of 0.9 p.u. to a base of 20 MVA, 33 kV. To the base of 50 MVA, 11 kV, the p.u. impedance will be
In differential protection of busbars, the CT ratio is
Correct Answer :-D
Explanation : The CT ratio is the ratio of primary current input to secondary current output at full load.
A thermal protection switch provides protection against
A thermal switch is a device which normally opens at a high temperature and re-closes when the temperature drops. The thermal switch may be a bimetallic strip, often encased in a tubular glass bulb to protect it from dust or short circuit.
A thermal switch is usually reusable, and is therefore suited to protecting against temporary situations which are common and user-correctable. Thermal switches are used in power supplies in case of overload, and also as thermostats in some heating and cooling systems.
The daily energy produced in a thermal power station is 600 MWh at a load factor of 0.8. What is the maximum demand of the station?
We know that,
Here t = 24 hours.
Peak load or maximum demand,
The value of diversity factor is:
Electrical diversity factor is the ratio of the sum of the individual maximum demands of the various electrical components of a grid to the maximum demand of the grid. The value of the diversity factor of an electrical grid usually exceeds one.
Which of the following method is used for changing power factor from leading to lagging
Under no load condition or light load condition, medium and long transmission lines may operate at leading power factor due to capacitance effect. This leading power factor can be changed to a lagging power factor by using a shunt reactor. By using a shunt reactor, it will compensate the effect of capacitance and changes the power factor.
When the spacing between the conductors in an overhead line is increased
The spacing between the conductors in an overhead line is directly proportional to inductance and inversely proportional to capacitance. Hence as spacing of overhead line is increase, the line capacitance decreases but line inductance increases.
Which of the following is true with respect to a breeder reactor?
A breeder reactor is a nuclear reactor that generates more fissile material than it consumes. These devices achieve this because their neutron economy is high enough to breed more fissile fuel than they use from the fertile material, such as uranium-238 or thorium-232. Its conversion ratio is greater than one.
The main objective of the governor system in power systems for all types of turbines is to control the:
The main objective of the governor system in power systems for all types of turbines is to control the frequency. A governor protects the prime mover from over speed and keeps the prime mover speed at or near the desired revolutions per minute. When a prime mover drives an alternator supplying electrical power at a given frequency, a governor must be used to hold the prime mover at a speed that will yield this frequency.