MCQ . electrical Cable

24. Which of the following protects a cable against mechanical injury ?
(a) Bedding
(b) Sheath
(c) Armouring✔
(d) None of the above


23.  Which of the following insulation is used in cables ?
(a) Varnished cambric
(b) Rubber
(c) Paper
(d) Any of the above✔


 22. Empire tape is
(a) varnished cambric✔
(b) vulcanised rubber
(c) impregnated paper
(d) none of the above


21. The thickness of the layer of insulation on the conductor, in cables, depends upon
(a) reactive power
(b) power factor
(c) voltage✔
(d) current carrying capacity

20. The bedding on a cable consists of
(a) hessian cloth
(b) jute
(c) any of the above✔
(d) none of the above


19. The insulating material for cables should
(a) be acid proof
(b) be non-inflammable
(c) be non-hygroscopic
(d) have all above properties✔


18. In a cable immediately above metallic sheath _____ is provided.
(a) earthing connection
(b) bedding✔
(c) armouring
(d) none of the above


17. The current carrying capacity of cables in D.C. is more thanthat in A.C. mainly due to
(a) absence of harmonics
(b) non-existence of any stability limit
(c) smaller dielectric loss
(d) absence of ripples✔
(e) none of the above


16. In case of three core flexible cable the colour of the neutral is
(a) blue✔
(b) black
(c) brown
(d) none of the above


15. cables are used for 132 kV lines.
(a) High tension
(b) Super tension
(c) Extra high tension
(d) Extra super voltage✔

14. Conduit pipes are normally used to protect _____ cables.
(a) unsheathed cables✔
(b) armoured
(c) PVC sheathed cables
(d) all of the above

13. The minimum dielectric stress in a cable is at
(a) armour
(b) bedding
(c) conductor surface
(d) lead sheath✔


12. In single core cables armouring is not done to
(a) avoid excessive sheath losses✔
(b) make it flexible
(c) either of the above
(d) none of the above

11. Dielectric strength of rubber is around
(a) 5 kV/mm
(b) 15 kV/mm
(c) 30 kV/mm✔
(d) 200 kV/mm

10. Low tension cables are generally used up to
(a) 200 V
(b) 500 V
(c) 700 V
(d) 1000 V✔


9. In a cable, the maximum stress under operating conditions is at
(a) insulation layer
(b) sheath
(c) armour
(d) conductor surface✔


8.High tension cables are generally used up to
(a) 11kV✔
(b) 33kV
(c) 66 kV
(d) 132 kV

 7.The surge resistance of cable is
(a) 5 ohms
(b) 20 ohms
(c) 50 ohms✔
(d) 100 ohms

6.PVC stands for
(a) polyvinyl chloride✔
(b) post varnish conductor
(c) pressed and varnished cloth
(d) positive voltage conductor
(e) none of the above


5.In the cables, the location of fault is usually found out by comparing
(a) the resistance of the conductor
(b) the inductance of conductors
(c) the capacitances of insulated conductors✔
(d) all above parameters

4.In capacitance grading of cables we use a ______ dielectric.
(a) composite✔
(b) porous
(c) homogeneous
(d) hygroscopic


 3.Pressure cables are generally not used beyond
(a) 11 kV
(b) 33 kV
(c) 66 kV✔
(d) 132 kV

2.The material for armouring on cable is usually
(a) steel tape
(b) galvanised steel wire
(c) any of the above✔
(d) none of the above

1.Cables, generally used beyond 66 kV are
(a) oil filled✔
(b) S.L. type
(c) belted
(d) armoured

What is Electricity?
 
So what is electricity and where does it come from? More importantly, why is carpet, socks and a doorknob a bad combination? In its simplest terms, electricity is the movement of charge, which is considered by convention to be, from positive to negative. No matter how the charge is created, chemically (like in batteries) or physically (friction from socks and carpet), the movement of the discharge is electricity.


Understanding Current

This flow of electrical charge is referred to as electric current. There are two types of current, direct current (DC) and alternating current (AC). DC is current that flows in one direction with a constant voltage polarity while AC is current that changes direction periodically along with its voltage polarity. Thomas Edison and Alessandro Volta were pioneers in DC current and wrote much of electricity’s history. But as societies grew the use of DC over long transmission distances became too inefficient. Nikola Tesla changed all that with the invention of alternating current electrical systems. With AC it is possible to produce the high voltages needed for long transmissions. Therefore today, most portable devices use DC power while power plants produce AC


Ohms Law

The most fundamental law in electricity is Ohm’s law or V=IR. The V is for voltage, which means the potential difference between two charges. In other words, it is a measurement of the work required to move a unit charge between two points. When we see a value such as 10 Volts, it is a measurement of the potential difference between two reference points. Normally the two points will be +10V and 0V (also known as ground), but it can also be the difference between +5V and -5V, +20V and +10V, etc. In the field, you might hear the term “common grounds” which refers to each device in a system using the same zero-point reference (or ground) to ensure the same potential difference ( or voltage) is applied throughout the system. The next component of Ohm’s law is current, the units of which are Amperes; in the formula, current is represented by the very logical choice of the letter I. As mentioned previously, current is the measurement of the flow of charge in a circuit. This leaves us with the letter R which represents Resistance. Electrical resistance, measured in Ohms, is the measure of the amount of current repulsion in a circuit. Simply, resistance resists current flow. When electrons flow against the opposition offered by resistance in the circuit, friction occurs and heat is produced. The most common application for resistance in a circuit is the light bulb. The light bulb introduces enough resistance in a circuit to heat up the filament inside, causing light to be emitted. Resistance in a circuit can also be helpful when needing to alter voltage levels, current paths, etc. Resistors are self-contained packages of resistance that can be added to a circuit and are commonly used to divide voltage levels.