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

In India, wires have a 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 signify neutral wire in the electric circuit. The neutral wires are connected to a 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. The following are functions :

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

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

Capital costs, of nuclear power plants, include the cost of site preparation, construction, manufacture, commissioning, and financing of the nuclear power plants. 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 costs relative to alternative power generation systems.

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 the conductor carries an 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 the skin effect.

The skin effect increases the effective resistance of the metal to the passage of the large current hence increasing 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 the proximity effect.
• The proximity is more in the case of power cables and underground lines where the distance between the conductor is small.
• This effect is negligible in the case of overhead transmission lines because the distance between the conductors is large.
• The proximity effect is absent in the case of DC transmission because the frequency of DC transmission is zero.
• The proximity effect depends upon the size of the conductor, spacing between the conductor, frequency, and permeability of the conductor material.

• 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 the 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, normal iron loss will occur. Hence the iron loss is maximum at the rated voltage. This maximum iron loss is measured using the wattmeter.

Integral Slot Winding gets better performance than 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 an integral slot Winding because m = 36/(3 x 4) = 3

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

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.

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 a paper belt, is wound around the grouped insulated cores.

All three cores are grouped 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 fibrous insulating material (jute, etc.).The cores are generally stranded and may be of a non-circular shape to make better use of available space.

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.

Moving-iron instruments are generally used to measure alternating voltages and currents. The deflection of the needle of the moving iron instrument is given in terms of the RMS value of voltage or current.

As the angular deflection of the Moving Iron Instrument is proportional to the square of the operating current, therefore the instrument has basically a square-law response. Due to this square law response, the Moving Iron Instrument Scale is non-uniform.

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 lightweight, 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.