Which of the following statements is incorrect ?
Correct Answer :- B
Explanation : The sag is reduced at low temperatures and is increases at higher temperatures.
Sag is directly proportional to the temperature.
A relay used on short transmission lines is
Reactance relay used for the small transmission line.
Mho relay used in the long transmission line.
Impedance is non-directional and used in medium transmission lines.
Reactance relay is non directional and used in short transmission lines.
The main advantage of AC transmission system over DC transmission system is
Correct Answer :- b
Explanation : Some advantages of AC over DC such as less loss in long transmission lines , the voltage can be changed easily ( step up / step down) using transformers.
Almost every electronic device that we use in our home and plug in to AC 230v outlets are working in DC . LED TV, home theater, disk players, electronic gadgets, laptop, computer , set top box etc all are working in DC. Though they are connecting to AC outlets, they are not working in AC, an AC to DC converter is used inside.
Usually electrical devices like air conditioner , refrigerator , mixer grinder, fan etc are designed to work in AC since we already have an AC connection in our home. Most of these devices can design in DC 12V/ 24V but it is not easy or good to design a computer motherboard or microcontroller circuit to work in 230v AC directly.
In any case, where the height of transmission tower is increased
If the height of the transmission tower is increased, inductance won't change, that is a function of wire size. The increased height will decrease line to ground capacitance, but the line to line capacitance will be unchanged, unless you also change the spacing between lines.
Series capacitors on transmission lines are of little used when
VAR load is small which means reactive power is less or use of inductive loads are small. When reactive power is increases then power factor decreases. To maintain power factor as 1 , We use series capacitors in transmission lines. When the series capacitors are of little used in transmission line, VAR requirement is small.
Which of the following is not a standard transmission voltage?
STANDARD TRANSMISSION VOLTAGES
Voltages adopted for transmission of bulk power have to conform to standard specifications formulated in all countries and internationally. They are necessary in view of import, export, and domestic manufacture and use. The following voltage levels are recognized in India as per IS-2026 for line-to-line voltages of 132 kV and higher.
Voltage kV 132 220 275 345 400 500 750
Voltage, kV 145 245 300 362 420 525 765
For the transmission of same power
For the transmission of same power AC line requires more copper than a DC line
The bedding of a cable consist of
Bedding - Over the metallic sheath is applied a layer of bedding which consists of a fibrous material like jute or hessian tape. The purpose of bedding is to protect the metallic sheath against corrosion and from mechanical injury due to armouring.
The material for armouring on cable is usually
Materials are also used to provide armoured protection to cables, including aluminium, but steel is the most common. SWA cable is made by winding solid steel wires of between 0.9mm to over 3mm diameter around the bedded cable in a spiral form.
If the length of a cable is double , its capacitance
1. Capacitance exists between two things with different electric charge and a dielectric in between.
2. The transmission line and the earth below it, have a charge difference and the air between them is dielectric. This constitutes a capacitance.
3. The longer the cable, the more part of it runs parallel to the earth and hence, more capacitance between them since the length of the cable and the capacitance of the cable are directly proportional to each other.
HT cables are generally used upto
The main source of hydro electric power station is
A hydroelectric power station consists of turbines that rely on a gravity flow of water from the dam to turn a turbine to generate electricity. The water can be either released to the river downstream of the dam or pumped back into the reservoir and reused.
In a transmission line insulators are used
In higher voltage, beyond 33KV, it becomes uneconomical to use pin insulator because size, weight of the insulator become more. Handling and replacing bigger size single unit insulator are quite difficult task. For overcoming these difficulties, suspension insulator was developed.
In suspension insulator numbers of insulators are connected in series to form a string and the line conductor is carried by the bottom most insulator. Each insulator of a suspension string is called disc insulator because of their disc like shape.
Porcelain insulators are glazed because
Porcelain in most commonly used material for over head insulator in present days. The aluminium silicate is mixed with plastic kaolin, feldspar and quartz to obtain final hard and glazed porcelain insulator material. The surface of the insulator should be glazed enough so that water should not be traced on it.
In an underground cable, insulating material is used
The principal insulating materials used in cables are rubber, vulcanised India rubber,impregnated paper, varnished cambric and polyvinyl chloride.
The function of circuit breaker is
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by excess current from an overload or short circuit. Its basic function is to interrupt current flow after a fault is detected.
What is the type of insulator used for holding the HT overhead conductor on the straight running of poles?
Pin Insulator is earliest developed overhead insulator, but still popularly used in power network up to 33 KV system. Pin type insulator can be one part, two parts or three parts type, depending upon application voltage. In 11 KV system we generally use one part type insulator where whole pin insulator is one piece of properly shaped porcelain or glass.
What is the types of insulators used at dead ends and on straight lines as suspension type for voltage 3.3 kV and above ?
Strain and shackle insulators are used at dead ends in low voltage distribution lines (less than 11 kV).
A 11 kV underground cable is layed at a depth of
The desired minimum depth of laying from ground surface to the top of cable is as follows:
1. High voltage cables, 3.3 kV to 11 kV rating = 0.9 m
2. High voltage cables, 22 kV, 33 kV rating= 1.05 m
3. Low voltage and control cables = 0.75 m
4. Cables at road crossings = 1.00 m
Rewirable fuse is also known as
Rewirable or Kit – Kat Type Fuses are a type of Low Voltage (LV) Fuses. They are most commonly used in house wiring, small industries and other small current applications.
The fusing factor of HRC fuse is
Fuse is a safety device in a circuit
A fuse is nothing more than a short length of wire designed to melt and separate in the event of excessive current. Fuses are always connected in series with the component(s) to be protected from overcurrent, so that when the fuse blows (opens) it will open the entire circuit and stop current through the component(s). A fuse connected in one branch of a parallel circuit, of course, would not affect current through any of the other branches.
Time delay relay is used in which relay type
Single bare copper wire having voltage of
Two pin sockets should not be used in domestic wiring unless the appliance to be connected is
Correct Answer :- b
Explanation : Two pin sockets should not be used in domestic wiring unless the appliance to be connected is double insulated.