UPPCL JE 2016 Electrical question paper with Solution (Evening Shift)

Ques 51. According to the IS code, the color of earth wire is usually

  1. Red
  2. Green
  3. Yellow
  4. Black

These electrical color codes dictate what role each wire has in an electrical system that is important to know for safety purpose.

In India, wires have standard color code as RGB i.e. Red- Green- Black. Each of these wires has different functions. But, it is the old color coding, where

  • RED: Red wire signifies the phase of an electric circuit. It is the live wire.
  • BLACK: Black wires signifies neutral wire in the electric circuit. The neutral wires are connected to neutral bus bar inside an electric panel.
  • GREEN: Green wire stands for grounding/ earthing in the electric circuit.

The new color-coding consists of Brown, Blue and Green wires. Following are functions :

  • BROWN: It is a live wire.
  • BLUE: It is neutral wire.
  • GREEN: It is earthing wire.

In case of a three-phase power supply, the combination of Red, Yellow and Blue are used for the active line power conductors, Black color for the neutral conductor and Green or Green – Yellow for protective ground.

 

Ques 52. Capital cost of a nuclear plant is

  1. Very Low
  2. Low
  3. Moderate
  4. Very High

Capital costs, of nuclear power plant include the cost of site preparation, construction, manufacture, commissioning and financing a nuclear power plant. Building a large-scale nuclear reactor takes thousands of workers, huge amounts of steel and concrete, and several systems to provide electricity, cooling, ventilation, information, control, and communication.

Nuclear power plants have relatively high capital costs for building the plants, but low fuel cost relative to alternative power generation system.

 

Ques 53. Which of the following is an effect of non-uniform current distribution in a conductor?

  1. Ferranti effect
  2. Skin effect
  3. Proximity effect
  4. Skin effect or Proximity effect

Skin Effect

When a conductor carries a steady or d.c. current, this current is uniformly distributed over the whole cross-section of the conductor. However, the current distribution is non-uniform if conductor carries alternating current. The current density is higher at the surface than at its center. Thus the current is concentrated near the surface of the conductor. This effect becomes predominant with an increase in frequency. Hence the phenomenon of the non-uniform current distribution within the conductor cross-sectional is called skin effect.

The skin effect increase the effective resistance of the metal to the passage of the large current hence increases the heating.

The skin effect depends upon the following factor.

  1. Frequency
  2. Diameter of wire
  3. Nature of material
  4. Shape of wire

Proximity effect

  • The alternating magnetic flux produced in the conductor due to the current flowing through the neighboring conductor gives rise to the non-uniform circulating current which increases the resistance of the conductor. This phenomenon is called as the proximity effect.
  • The proximity is more in the case of power cable and underground line where the distance between the conductor is small.
  • This effect is negligible in case of overhead transmission lines because the distance between the conductors is large.
  • Proximity effect is absent in case of DC transmission because the frequency of DC transmission is zero.
  • Proximity effect depends upon the size of the conductor, spacing between the conductor, frequency, and permeability of the conductor material.

 

Ques 54. Open Circuit Test on a transformer is used to find

  1. No load current
  2. Full load copper loss
  3. Equivalent resistance referred to metering side
  4. Equivalent resistance referred to metering side and no load current both

  • Open circuit test or no load test on a transformer is performed to determine ‘no-load loss (core loss)’ and ‘no-load current I0‘ in the transformer.

  • At load, the primary current has two components: Shunt branch current & secondary current when referred to the primary side.

  • At no load, the secondary current becomes zero due to open circuited at secondary.

  • Therefore, only shunt branch component is left which is used to magnetize the transformer coils. The current flowing in coils leads to winding losses. Hence, the current supplied by the source at no load is shunt branch current which is known as No Load Current.

  • No load current has two components (a)Iron loss component (b) Magnetizing Component.
  • Iron loss component: It is the component of no-load current responsible for the resistive loss in the core.
  • Magnetizing Component: It is the component of no-load current responsible for hysteresis loss in the core
  • In this method, the secondary of the transformer is left open-circuited.
  • A wattmeter is connected to the primary.
  • An ammeter is connected in series with the primary winding. A voltmeter is optional since the applied voltage is the same as the voltmeter reading.
  • Rated voltage is applied at primary.
  • If the applied voltage is normal voltage then normal flux will be set up. Since iron loss is a function of applied voltage, the normal iron loss will occur. Hence the iron loss is maximum at rated voltage. This maximum iron loss is measured using the wattmeter.

 

Ques 55. An integral number of slots per pole is often used in an alternator in order to

  1. Eliminate harmonics in the waveform
  2. Provide insulation
  3. Permit easy installation of stator coils
  4. Provide easy removal in case of repair

Integral Slot Winding gets better performance of the alternator, flux should be uniform throughout the surface of the armature. For this purpose, the armature conductors should be properly distributed. The number of slots in an AC machine should always be an integral multiple of three. When the number of the slots per pole per phase (m) is an integer, the winding is called integer slot winding. For example, a 3-phase Winding with 36 slots and 4-poles is integral slot Winding because m = 36/(3 x 4) = 3

The main advantage of integral slot winding is it reduces the harmonic of phase EMF and MMF in an alternator.

 

Ques 56. Which of the following is used to make bus bars and transmission line conductors?

  1. Lead
  2. Aluminium
  3. Nichrome
  4. Cadmium

Aluminium is next to copper in electrical conductivity.It is a low-cost metal and also is the most abundant of all the elements in the earth’s crust. Alloys of aluminum have greater mechanical strength, so they find application as overhead transmission lines, domestic wiring, flexibility wires busbars rotor bars etc.

 

Ques 57. Core is insulated by ___________ in a belted cable.

  1. Impregnated paper
  2. VIR
  3. PVC
  4. Gutta Percha

Belted core cables are used for voltages up to 11 kV.The cores are insulated from each other by layers of impregnated paper. Another layer of impregnated paper tape, called paper belt, is wound around the grouped insulated cores.The all three cores are group together and belted with the help of the paper belt. The belt is covered with the lead sheath to protect the cable against ingress of moisture and mechanical injury. The lead sheath is covered with one or more layers of armoring with an outer serving.The gap between the insulated cores is filled with the fibrous insulating material (jute, etc.).The cores are generally stranded and may be of the noncircular shape to make better use of available space.

 

Ques 58.  From no-load to full-load, synchronous motors give

  1. Constant speed
  2. Variable speed
  3. Gradually increasing speed
  4. Gradually decreasing speed

The synchronous motor is the one type of 3-phase A.C. motors which operates at a constant speed from no-load to full load.

 

Ques 59. Scale of Moving Iron instruments is

  1. Linear
  2. Non-uniform
  3. Exponential
  4. Logarithmic

Moving-iron instruments are generally used to measure alternating voltages and currents.The deflection of the needle of moving iron instrument is given in terms of RMS value of voltage or current. As the angular deflection of Moving Iron Instrument is proportional to the square of the operating current, therefore the instrument has basically square law response. Due to this square law response, the Moving Iron Instrument Scale is non-uniform.

 

Ques 60. ____________ has the maximum life tenure

  1. Wooden Poles
  2. Steel Poles
  3. Concrete Poles
  4. Steel Towers

Steel Poles. They are used for system voltages up to 33 kV in low and high-voltage distribution systems. These are costlier than wooden and RCC poles. When compared to wooden poles, tubular steel poles have advantages like light weight, long life, and greater strength. These are used for a longer span, i.e., from 50 to 80 m. All steel supports should be well-galvanized and should have a life of at least 30 years.

Steel Towers: These towers are robust in construction. They can be used for spans 300 m or above. They are used for the transmission of power above 66 kV and are more useful for valleys, railway lines, rivers, etc. They are mechanically very strong and have a longer life than steel poles. They are capable of withstanding the most severe climatic conditions and cannot be destroyed by forest fires.

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