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What is the lowest acceptable insulation resistance for a cable?

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Description : If the insulation resistance of a cable of length 10 km is 1 mega ohm, its insulation resistance for 50 km length will be

Answer : If the insulation resistance of a cable of length 10 km is 1 mega ohm, its insulation resistance for 50 km length will be 0.2 mega ohm

Description : What is an insulation resistance test?

Description : Write measures to be taken to maintain the insulation resistance of electrical machines to healthy levels.

Description : Name the method used to measure following resistances:- (i) Low resistance (ii) Medium resistance (iii) Insulation resistance (iv) Earth resistance.

Answer : Following are the methods used to measure resistances:-  (i) Low resistance: 1.Voltmeter-Ammeter Method 2. Kelvin's Double bridge Method  (ii) Medium resistance: 1.Voltmeter-Ammeter Method 2. ... of Charge Method  (iv) Earth resistance : 1. Fall of Potential Method 2. Earth tester

Description : When measuring insulation resistance of cables using d.c. source, the galvanometer used should be initially short circuited because  (A) Cables have a low value of capacitance which draws a high ... high value of charging current (D) Cables have a low value of capacitance and initial resistance

Answer : When measuring insulation resistance of cables using d.c. source, the galvanometer used should be initially short circuited because Cables have a high value of capacitance which draws a high value of charging current

Answer : Meggar is an instrument which measures the insulation resistance of an electric circuit relative to earth and one another.

Answer : Insulation resistance of high voltage circuit breakers is more than 100 mega ohms.

Description : What do you mean by insulation coordination?

Description : What is double or reinforced insulation?

Description : What is basic insulation level?

Description : The lowest eigenvalue of the 2x2 matrix 

Answer : Linear Algebra Problem The lowest eigenvalue of the 2x2 matrix https://youtu.be/QatcRTzF7EA

Description : Which of the following has the lowest electrical conductivity? A) Mercury B) Silver C) Copper D) Gold

Answer : Which of the following has the lowest electrical conductivity? A) Mercury B) Silver C) Copper D) Gold

Description : Which of the following waveforms has the lowest form factor? A) Sine wave B) Square wave C) Sawtooth wave D) Triangle wave

Answer : Which of the following waveforms has the lowest form factor? A) Sine wave B) Square wave C) Sawtooth wave D) Triangle wave

Description : Which configuration has the lowest current gain ?

Answer : Common base configuration has the lowest current gain.

Description : State the procedure for laying / installation of underground cable.  

Answer : 1) Direct laying Cable: or Trench laying method: Procedure: * For laying of a cable trench about 1.5m deep and 0.5m wide is made along the cable route. * A ... over. * Cables laid in this manner are usually plain lead covered because troughing affords good mechanical protection. 

Description : How rating of main switch and cable is selected for Industrial Installation.

Answer : 1. Rating of Main Switch or Fuse Rating is decided in industrial installation: Rating of main switch or fuse is based up the starting current of motor. For calculating starting current is considered 2 ... take 1.5 times the rated current or full load current. & thus cable rating is decided.

Description : A single core cable is designed to work for a single phase system with a peak voltage of 220 kV. The maximum permissible stress in the dielectric is not to exceed 20 kV/mm. For economical size, the overall core diameter of the cable is (A) 28.2 mm (B) 26.4 mm (C) 24.4 mm (D) 22.0 mm

Answer : A single core cable is designed to work for a single phase system with a peak voltage of 220 kV. The maximum permissible stress in the dielectric is not to exceed 20 kV/mm. For economical size, the overall core diameter of the cable is 22.0 mm

Description : State the four methods of laying of cable. State precautions while laying of underground cable in the situation : (i) Minimum clearance between cable and water pipe line when running in parallel. (ii) ... is to be laid in the same trench, what should be minimum spacing between two cables ?  

Answer : (i) Minimum clearance between cable and water pipe line when running in parallel:- 0.5 mtr. (ii) Minimum clearance between cable and water pipe line when running in parallel:- 0.5 mtr ... should be minimum spacing between two cables :- Then minimum 30 cm spacing is provided between 2 cables 

Description : What is the difference between a cable and a conductor?

Description : what is the use of bedding on underground cable?

Answer : Bedding is the layer above the lead sheath it protects the lead sheath from corrosion that means it gives chemical protection to metallic sheath(lead sheath)

Description : The thickness of insulation provided on the conductor depends on?

Answer : The thickness of insulation provided on the conductor depends on the magnitude of voltage on the conductor.

Description : The insulation on a current carrying conductor is provided?

Answer : The insulation on a current carrying conductor is provided to prevent leakage of current, to prevent shock.

Description : desirable properties of Cable

Answer : Following are the main properties of cables:  1. Stranded Conductor: The conductor used for cable should be stranded specially for large size of cable because,  To increase the flexibility ... and mechanical injury.  7. Life: The material used for cable should have long life. 

Description : Why is "RJ-45" cable called "RJ-45" ?

Answer : rj = registered jack 45 = is number of standard interface and contains 8 separate wires

Description : Why cable outer sheath is black in color?

Answer : There are cables with different colors, for example, red, orange, grey. PVC or HDPE, the plastics that the jacket of the cable is made of, have to be UV-stabilized. Carbon black is a common and cheapest additive for it purpose

Description : State functions of ; i) Cable box ii) Guard wire iii) Shackle insulator iv) Stay wire used in service connection

Answer : i) Function of Cable box: To hold and inspect incoming and outgoing terminals  ii) Function of Guard wire : A grounded conductor placed beneath an overhead transmission line in order to ground ... in service connection: To give mechanical Support to pole, line and prevent leakage current if any

Description : The velocity of travelling wave through a cable of relative permittivity 36 is

Answer : The velocity of travelling wave through a cable of relative permittivity 36 is 0.5 x 108 m/sec

Description : A single core lead sheathed cable with two dielectrics of permittivity 4 and 3, respectively, are subjected to same maximum stress. If the conductor diameter is 1.5 cm, the outer diameter of the first dielectric is (A) 1.125 cm (B) 1.5 cm (C ) 2 cm (D) 8 cm

Answer : A single core lead sheathed cable with two dielectrics of permittivity 4 and 3, respectively, are subjected to same maximum stress. If the conductor diameter is 1.5 cm, the outer diameter of the first dielectric is 2 cm 

Description : A megger is to measure insulation resistance of a cable. The cable should be connected to   (a) Battery (b) DC supply (c) AC supply (d) No supply  

Answer : Battery

Answer :  In RE cable the insulation resistance will be above 20 mega ohms.

Description : State the procedure for testing of earth pit resistance with necessary diagrams.

Answer : Following procedure (Method) for testing of earth pit resistance with necessary diagrams. 1) Earth Tester : i) Three point method ii) Four point method 2) By Potential drop method 3 ... of that earthing pit. In this test the accuracy is less but electrical rods are not required. 

Description : Name two methods for measurement of low, medium and high resistance. Give one advantage and one limitation of V- I method.

Answer : Methods for measurement of low resistance:  1. Ammeter voltmeter method  2. Kelvin's bridge method  3. Ohm meter method  4. Potentiometer method  5. Digital/analog multi-meter ... must be infinity for perfectly accurate measurement which is not possible.  2. Connection errors.

Description : State the range for low and medium resistance.

Answer : Low resistances: less than 1 ohm.  Medium resistances: 1 ohm to 0.1 Mega ohm. 

Description : Resistance grounding is normally used for :  (A) high voltage long over head transmission lines  (B) low voltage short over head transmission lines  (C) extra high voltage long over head transmission lines  (D) all the above

Answer : Resistance grounding is normally used for : low voltage short over head transmission lines

Description : Ratio of the rotor reactance X to the rotor resistance R for a two-phase servo motor (A) is equal to that of a normal induction motor (B) is less than that of a normal induction motor (C) ... than that of a normal induction motor (D) may be less or greater than that of a normal induction motor

Answer : C

Description : For maximum transfer of power, internal resistance of the source should be?

Answer : For maximum transfer of power, internal resistance of the source should be equal to load resistance.

Answer : For measuring a very high resistance we should use Meggar.

Answer : Yes we can use potentiometer for measuring resistance.

Description : What do you mean by exciting resistance and exciting reactance?

Description : what is equivalent resistance when four 4 Ohm resistors are connected in i) series ii) parallel

Answer : equivalent resistance

Description : What is the mathematical relationship between resistance and conductance?

Description : What is the resistance of a coil which draws 10 A and dissipates 1520 W? A) 152 Ω B) 15.2 Ω C) 1.52 Ω D) None of these

Answer : What is the resistance of a coil which draws 10 A and dissipates 1520 W? A) 152 Ω B) 15.2 Ω C) 1.52 Ω D) None of these

Description : What happens to the resistance of a wire when its length as well as the cross-sectional area are doubled? A) It doubles B) It becomes 4 times C) It becomes 2π times D) It remains the same

Answer : Automatically the resistivity will increase as they are the factors affecting the resistivity 

Description : Consider a cube of material of sides 1 cm with a resistance of 0.003 Ω between its opposite faces. What is the resistance if the same volume of the material is drawn into a length of 50 cm with a uniform cross – section? A) 0.003 Ω B) 0.15 Ω C) 7.5 Ω D) None of these

Answer : Consider a cube of material of sides 1 cm with a resistance of 0.003 Ω between its opposite faces. What is the resistance if the same volume of the material is drawn into a length of 50 cm with a uniform cross – section? A) 0.003 Ω B) 0.15 Ω C) 7.5 Ω D) None of these

Description : What is the resistance of a 160 m wire with a uniform diameter of 0.28 mm, if the specific resistance is 12.32 μΩ-cm? A) 3.2 Ω B) 3.2 μΩ C) 0.8 Ω D) None of these

Answer : What is the resistance of a 160 m wire with a uniform diameter of 0.28 mm, if the specific resistance is 12.32 μΩ-cm? A) 3.2 Ω B) 3.2 μΩ C) 0.8 Ω D) None of these

Description : What is the total resistance if 5 resistors of 20 Ω each are connected in series? A) 100 Ω B) 4 Ω C) 20 Ω D) None of these

Answer : What is the total resistance if 5 resistors of 20 Ω each are connected in series? A) 100 Ω B) 4 Ω C) 20 Ω D) None of these

Description : What is the relationship between power and resistance?

Answer : P = I2R Where P = power I = Current R = Resistance

Description : What happens to the resistance when the current increases?

Answer : Resistance  reduces  when  current  increases.

Description : What is meant by resistance heating?

Description : What should be the ideal resistance of ammeter ?

Answer : Ideal resistance of ammeter should be zero.

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