Author: workhouse123
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ADVANTAGES OF THREE-PHASE SYSTEM OVER SINGLE-PHASE SYSTEM
The following are the main advantages of three-phase system over single-phase system:
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POLYPHASE SYSTEM
Poly means many (more than one) and phase means windings or circuits, each of them having a single alternating voltage of the same magnitude and frequency. Hence, a polyphase system is essentially a combination of two or more voltages having same magnitude and frequency, but displaced from one another by equal electrical angle. This angular displacement between the adjacent…
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INTRODUCTION
Although single-phase system is employed for the operation of almost all the domestic and commercial appliances, for example, lamps, fans, electric irons, refrigerators, TV sets, washing machines, exhaust fans, computers, etc. However, it has its own limitations in the field of generation, transmission, distribution, and industrial applications. Due to this, it has been replaced by…
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DIGITAL MULTIMETER
A digital multimeter (DMM) displays the AC or DC voltages being measured directly as discrete numerals in the decimal number system. Numerical readout of DMM is very convenient and it eliminates observational error. The use of digital multimeters increases the speed with which the readings can be taken. The DMM is a versatile and accurate instrument used…
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PERMANENT MAGNET MOVING COIL INSTRUMENTS
These instruments are very sensitive and accurate. These can be used only on DC as voltmeter and ammeter. The pictorial view of a voltmeter and ammeter is shown in Figures 9.19 and 9.20, respectively. The scale of such instruments is uniform, as shown in the Figure 9.20. Fig. 9.19 Voltmeter Fig. 9.20 Ammeter 9.9.1 Principle The basic principle of permanent magnet-type moving…
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MOVING IRON INSTRUMENTS
These instruments are quite cheap in cost, simple in construction, and reasonably accurate at fixed power supply frequency. These instruments can be used both on AC and DC. Therefore, these are widely used in laboratories and on switching panels. These instruments are used either as voltmeter or ammeter only. The pictorial view of these instruments is…
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ERRORS COMMON TO ALL TYPES OF INSTRUMENTS
The errors that are common to all types of instruments are given as follows:
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MEASURING ERRORS
Measurement is essentially an act by which a comparison is made between a given quantity and a quantity of the same kind chosen as a unit of measurement, that is, standard quantity. To make this comparison, a device is used called measuring instrument. When an unknown quantity is measured, the value thus obtained is considered…
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METHODS OF PROVIDING DAMPING TORQUE
To obtain critical damping (i.e., the value of damping that is sufficient to enable the point to rise quickly to its deflected position without overshooting), adjustments are made while designing the instruments. Damping torque or force can be provided by the following methods. 9.5.1 Air Friction Damping Two methods of air friction damping are illustrated in Figure…
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METHODS OF PROVIDING CONTROLLING TORQUE
The controlling or restoring or balancing torque is provided in the indicating instruments by two methods, namely spring control and gravity control. 9.4.1 Spring Control In this method, two phosphor bronze spiral hair-springs A and B are attached to the moving system (spindle) of the indicating instrument as shown in Figure 9.6(a). However, only one spring is used in moving iron…