Table of Contents
What is AC System
The ac system is mainly used for transmission of power supply. The ac transmission line transmits alternating current over a long distance. The universally adopted AC system is three phase Four wire system. In this system high voltage drop and skin effect is occurs. The ac system is more expensive. AC supply can be transmits over a long distance.
Types of AC System
- Single phase two-wire system
- Single phase three-wire system
- Two phase three-wire system
- Two phase four-wire system
- Three phase three-wire system
- Three phase four-wire system
1. Single Phase Two Wire System
These system is consist of two wires i.e. Phase & Neutral wire. The voltage difference between these two lines is about 230-240 V.These system is commonly used for short distance distribution. Single phase system is easy to balance the electrical loads. The single line diagram is shown as :
2. Single Phase Three Wire System
These system is similar to 3 wire dc distribution system. In this the neutral wire is centred tapped from secondary winding of transformer and then earthed for protecting personal from electrical shock.
3. Two Phase Three-Wire System
In this system two phase wires is connected in such a way that the neutral wire is taken out from the junction point of two windings. Before moving on the three phase system we used, two phase system for a short time period. In electrical two phase system means two voltages 90′ apart.
4. Two Phase Four-Wire System
In this system, four wires are brought out from two phase windings. Whose voltages are 90′ electrical apart with each other. Then the mid point of these two windings are connected together to form two phase four wire system.
5. Three Phase Three-Wire System
These system may be star or delta connected. The neutral is grounded if it is star connected. The large consumers which need large power are directly supplied from the substation. The diagram of three face three wire star connected & three phase three wire delta connected is shown in fig.
6. Three Phase Four-Wire System
In this system four wires are used to distribute the supply. The fourth wire of this system is neutral due to this the secondary of three phase four wire system is always in star connected. This system is generally preferred for secondary distribution. The voltage between any face & neutral is 230 v. while the voltage between any two faces is 400 v. The diagram of three face four wire system is shown in fig.
What is DC System
We know that AC system is very efficient although DC system is also required where ac can’t used. There are few applications where DC system is must like operation of DC motors, batteries, charging etc. It can be obtained by using dc rectifiers or by dc generators at substation. DC system can’t be stepped up easily due to this it is less used in transmission system.
Types of DC System
- Two wire DC system
- Two wire with mid point earthed
- Three wire DC system
1. Two Wire DC System
This system consist of two wires i.e. one positive & other negative. The current going through positive terminal & return back through negative terminal. The two wire DC system is shown in fig.
2. Two Wire With Mid Point Earthed
In these system two line conductors are used & earth wire is taken out from the middle point of the two conductors. No connection is taken out from the mid point. The copper required is less. The diagram is shown as.
3. Three Wire DC System
These system is exactly similar to the two wire with mid point earthed dc system. It consist of two outers and a middle or neutral wire which is earthed. when the load is balanced, no current is flows through the neutral wire. The copper requirement is higher then two wire mid point earthed system. The diagram of three wire DC system is shown as.
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