Introduction:
~ In day to day life, we use electrical power for various applications including the domestic and industrial applications.
~ For most of the domestic applications we use a single phasei ac (alternating) supply.
~ For high power industrial applications, the three phase aci supply is used.
~ For certain domestic applications such as telephones, the dci (direct) supply is used.
~ For certain applications such as electric trains a high voltagei DC (HVDC) system is used.
~ Difference between AC and DC Quantities:
~ The long form of ac is alternating current. What is alternating in the ac ? The answer is both the magnitude and direction of the alternating current changes as shown in Fig. 1.2.1(b). No such changes take place for the direct current (dc) as showni in Fig. 1.2.1(a).
Pure dc quantity :
~ We can define a pure dc quantity (voltage, current or power) as the one which does not change its value or polanity with respect to time.
~ As shown in Fig. 1.2.1(b) the alternating current changes its value with respect to time. It's value can be positive, zero, negative, maximum or in between zero and maximum. This is called as change in magnitude.
~ Look at Fig. 1.2.1(b), the alternating current can be positive, negative or zero. The current is that changes its polarity is called as alternating current.
Definition of an ac quantity :
~ An alternating (ac) quantity (voltage, defined as the one which changes its value as well asi direction (polarity) with respect to time.
~ Thus it is important to note that a quantity is called as an aci quantity if and only if both its values as well as polarity changes with respect to time.
Pulsating DC:
~ In practice we may not always use the pure dc quantities. Thei practical dc quantities may change their magnitude (value) with respect to time. But the polarity does not change.
~ Such dc quantities are called as pulsating dc quantities.
~ Fig. 1.2.2 shows the waveforms for pulsating dc currents. Only ohange in magnitude.
Practically what type of circults are more popular ?
~ Practically about 90% of the circuits use the "ac" energy for their operation. The voltage supplied to us by the electricity board is also ac voltage.
~ All our appliances such as TV, refrigerators, washing machines, air conditioners, fans etc. operate on the alternating voltage (ac voltage).
Why is ac more popular and widely used?
The ac source of energy is more popular and widely used duei to its following advantages over dc:
~ In ac systems we can use transformers to reduce or increasei the voltage levels. Transformers cannot be used in the dci circuits, hence changes in the voltage levels are difficult to achieve.
~ The distribution of AC voltage is more efficient than thei distribution of dc voltage. This is because distribution at higher level is possible.
~ The construction of ac motors and ac generators is simpler as i compared to that of dc motors.
~ It is possible to obtain a dc voltage from ac by means of rectification and filtering, rather than using the dc generators.
What is meant by the term single phase circulit ?
~ If we apply only one alternating voltage to a circuit then it isi called as the single phase ac circuit. The ac supply coming from the electricity board for the domestic applications is single phase ac voltage supply.
~ A polyphase circuit has more than one ac voltages applied simultaneously.
~ In day to day life, we use electrical power for various applications including the domestic and industrial applications.
~ For most of the domestic applications we use a single phasei ac (alternating) supply.
~ For high power industrial applications, the three phase aci supply is used.
~ For certain domestic applications such as telephones, the dci (direct) supply is used.
~ For certain applications such as electric trains a high voltagei DC (HVDC) system is used.
~ Difference between AC and DC Quantities:
~ The long form of ac is alternating current. What is alternating in the ac ? The answer is both the magnitude and direction of the alternating current changes as shown in Fig. 1.2.1(b). No such changes take place for the direct current (dc) as showni in Fig. 1.2.1(a).
Pure dc quantity :
~ We can define a pure dc quantity (voltage, current or power) as the one which does not change its value or polanity with respect to time.
~ As shown in Fig. 1.2.1(b) the alternating current changes its value with respect to time. It's value can be positive, zero, negative, maximum or in between zero and maximum. This is called as change in magnitude.
~ Look at Fig. 1.2.1(b), the alternating current can be positive, negative or zero. The current is that changes its polarity is called as alternating current.
Definition of an ac quantity :
~ An alternating (ac) quantity (voltage, defined as the one which changes its value as well asi direction (polarity) with respect to time.
~ Thus it is important to note that a quantity is called as an aci quantity if and only if both its values as well as polarity changes with respect to time.
Pulsating DC:
~ In practice we may not always use the pure dc quantities. Thei practical dc quantities may change their magnitude (value) with respect to time. But the polarity does not change.
~ Such dc quantities are called as pulsating dc quantities.
~ Fig. 1.2.2 shows the waveforms for pulsating dc currents. Only ohange in magnitude.
Practically what type of circults are more popular ?
~ Practically about 90% of the circuits use the "ac" energy for their operation. The voltage supplied to us by the electricity board is also ac voltage.
~ All our appliances such as TV, refrigerators, washing machines, air conditioners, fans etc. operate on the alternating voltage (ac voltage).
Why is ac more popular and widely used?
The ac source of energy is more popular and widely used duei to its following advantages over dc:
~ In ac systems we can use transformers to reduce or increasei the voltage levels. Transformers cannot be used in the dci circuits, hence changes in the voltage levels are difficult to achieve.
~ The distribution of AC voltage is more efficient than thei distribution of dc voltage. This is because distribution at higher level is possible.
~ The construction of ac motors and ac generators is simpler as i compared to that of dc motors.
~ It is possible to obtain a dc voltage from ac by means of rectification and filtering, rather than using the dc generators.
What is meant by the term single phase circulit ?
~ If we apply only one alternating voltage to a circuit then it isi called as the single phase ac circuit. The ac supply coming from the electricity board for the domestic applications is single phase ac voltage supply.
~ A polyphase circuit has more than one ac voltages applied simultaneously.
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