Electrical Daily Quiz 22nd January (UPRVUNL JE 14th Oct 2021 Solution)
1. What does the above symbol represents?
A. OR Gate
B. XOR Gate
C. NOR Gate
D. XNOR Gate
Explanation-The given symbol represents the XNOR Gate.
The output is high when both inputs A and B are high and when neither A nor B is high.
2. The effective resistance of an 2200 V, 50 Hz, 440 KVA single phase alternator is 0.6 ohm. A field-current of 40 A on a short circuit gives a full load current of 200 A. The emf on the open circuit with the same field-current excitation is 800 V. Calculate the synchronous reactance.
A. 3.95 ohm
B. 4.6 ohm
C. 4.04 Ohm
D. 4 Ohm
Explanation-Given emf=800V, I= 200A R=0.6
Z = V/I = 800/200 = 4 ohms
Now synchronous Reactance XL
3. When a conductor is carrying AC current, the current is not distributed in the conductor uniformly. Rather it has tendency to concentrate near the surface of the conductor. What is this effect known as?
A. Corona effect
B. Inductance effect
C. Skin effect
D. Ferranti effect
Explanation- Skin effect-The non-uniform distribution of electric current over the surface or skin of the conductor carrying a.c is called the skin effect.
Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor, and decreases with greater depths in the conductor.
Factors affecting skin effect
- Frequency – Skin effect increases with the increase in frequency.
- Diameter – It increases with the increase in diameter of the conductor.
- The shape of the conductor – Skin effect is more in the solid conductor and less in the stranded conductor because the surface area of the solid conductor is more.
- Type of material – Skin effect increase with the increase in the permeability of the material (Permeability is the ability of material to support the formation of the magnetic field).
4. Which of the following is the TRUE comparison of Copper and aluminum conductor for high voltage power transmission?
A. Conductivity of copper is less than that of aluminum
B. Tensile strength of aluminum is more than that of copper
C. Cost aluminum is more compared to copper
D. Specific gravity of copper is more than that of aluminum
Explanation-Copper has much greater radius than aluminium, so the outer electrons are less strongly attracted as compared to aluminium.
Aluminium wires expand in high temperatures and contract in low temperatures when compared to copper, which can withstand thermal changes.
The conductivity of aluminium is about 60 percent of the conductivity of copper.
Electrical resistivity of aluminium is higher than copper.
Specific gravity of copper (8.89) is more than that of aluminum (2.55).
5. Which of the following is NOT true for RAM, used in information technology
A. It stands for Random Access Memory
B. It is known as Read/write Memory
C. It is not a primary storage device
D. It is also called as volatile memory
Explanation-A primary storage device is a medium that holds memory for short periods of time while a computer is running.
RAM (random access memory) and cache are both examples of a primary storage device.
It stands for Random Access Memory.
It is known as Read/write Memory.
It is also called as volatile memory.
6. The angle of deflection of the pointer in a moving iron instrument is
A. Inversely proportional to the square of the current through the coil
B. Proportional to the current through the coil
C. Proportional to the square of the current through the coil
D. Inversely proportional to the current through the coil
Explanation-MI Instruments-The instrument in which the moving iron is used for measuring the flow of current or voltage is known as the moving iron instrument.
Angle of deflection ⇒ Ɵ = (1/2)(I2/K)(dL/dƟ)
From the above torque equation, we observe that the angular deflection of needle of moving iron instruments is square of rms current flowing through the coil.
Advantages of the MI Instruments
- Universal use – The MI instrument is independent of the direction of current and hence used for both AC and DC.
- Less Friction Error – The friction error is very less in the moving iron instrument because their torque weight ratio is high. The torque weight ratio is high because their current carrying part is stationary and the moving parts are lighter in weight.
- Cheapness – The MI instruments require less number of turns as compared to PMMC instrument. Thus, it is cheaper.
- Robustness – The instrument is robust because of their simple construction. And also because their current carrying part is stationary.
Disadvantages of Moving Iron Instruments
- Accuracy – The scale of the moving iron instruments is not uniform, and hence the accurate result is not possible.
- Errors – Some serious error occurs in the instruments because of the hysteresis, frequency and stray magnetic field.
- Waveform Error – In MI instrument the deflection torque is not directly proportional to the square of the current. Because of which the waveforms error occurs in the instrument.
- Difference between AC and DC calibration – The calibration of the AC and DC are differed because of the effect of the inductance of meter and the eddy current which is used on AC. The AC is calibrated on the frequency at which they use.
7. Which type of wiring Is suitable for places exposed to sun or rain?
A. Battery wiring
B. Lead sheathed wiring
C. Wooden casing and capping wiring
D. PVC casing and capping wiring
Explanation-Lead Sheathed Wiring
In this system of wiring lead covered cables are used on a batten or sometimes without batten, so it is known as Lead sheathed cable wiring. The wire is supported by means of the clips. An earth wire runs along to maintain the earth continuity. The wires can be single or twin core.
Advantages of Lead Sheathed Wiring
- These wires are safe from fire, moisture and mechanical damages.
- It has long life.
- It can be done in damp places, open areas even which are exposed to sun and rains also.
- It has good appearance.
Disadvantages of Lead Sheathed Wiring
- Skilled worker required so the labour is costly.
- It is costly because of lead covering.
- Extension is not so easy.
- Fault location is not easy.
The power wiring should be carried out separately from the lighting circuit. In this wiring all the joint boxes and ends of the wires are sealed with compound, so that moisture may not enter in the cable or wires.
Uses of Lead Sheathed Wiring
It is not a common type of wiring. It is used in the places where dampness, exposing to run and rain etc. are there. It should not be used the places, where in chemical corrosion may occur.
8. Two diametrically opposite holes are drilled in the disc of the single phase induction type energy meter to overcome __ error.
Explanation-Sometimes the disc of the energy meter makes slow but continuous rotation at no load i.e. when the potential coil is excited but with no current flowing in the load; This is called creeping.
This error may be caused due to overcompensation for friction, excessive supply voltage, vibrations, stray magnetic fields, etc.
In order to prevent this creeping on no-load two holes or slots are drilled in the disc on opposite sides of the spindle.
This causes sufficient distortion of the field; The result is that the disc tends to remain stationary when one of the holes comes under one of the shunt magnets.
9. Identify the software SCADA (SCADA) useful HMI (HMI) (Human Machine Interface) software package to do It.
A. Intelligence iFIX
C. RS View
Explanation-Supervisory control and data acquisition (SCADA) is a system of software and hardware elements that allows industrial organizations to:
- Control industrial processes locally or at remote locations
- Monitor, gather, and process real-time data
- Directly interact with devices such as sensors, valves, pumps, motors, and more through human-machine interface (HMI) software
- Record events into a log file
A Human Machine Interface, or HMI for short, is a device that allows a human to give directions and receive feedback from the PLC that is controlling the manufacturing process.
HMI (Human Machine Interface) software package include following
Mozilla Firefox or simply Firefox is a free and open-source web browser.
10. Find the true statements for inductive and capacitance reactance.
A. Inductive reactance and capacitive reactance decrease with increase in frequency.
B. With increase in frequency the inductive reactance increases and the capacitive reactance decreases.
C. With increase in frequency the inductive reactance decreases and the capacitive reactance increases.
D. Inductive reactance and capacitance reactance increase with increase in frequency.
Explanation-The reactance of an inductor is given by, XL = jωL = 2πfL
Where f is the frequency and L is the inductance.
The reactance of an capacitance is given by, XC = 1/jωL = 1/2πfC
Where f is the frequency and C is the capacitance.
So it clear with increase in frequency the inductive reactance increases and the capacitive reactance decreases.