DC Generator.ppt
- 1. DC GENERATOR & DC MOTORS By Dr. M. Ajay Kumar Associate Professor, EEE. 1 Basic Electrical Engineering
- 2. A DC generator converts mechanical energy into electrical energy (DC). The working of a DC generator is based on the principle that, when a conductor cuts a magnetic field, an e.m.f. is induced in the conductor. A dynamically induced e.m.f. will be produced in the conductor when it will cut the magnetic flux as per the laws of electromagnetic induction 2 Basic Electrical Engineering
- 3. If the circuit is closed this induced e.m.f. will cause a current to flow through circuit. Basically a D.C. machine is an alternating current machine. The e.m.f. generated in the conductor is alternating in nature. With the help of the commutator segments this alternating e.m.f. is converted into a direct one. 3 Basic Electrical Engineering
- 8. There are two types of windings Lap winding • A = P • The armature windings are divided into no. of sections equal to the no of poles Wave winding • A = 2 • Used in high voltage low current output. • Requires 2 brushes 8 Basic Electrical Engineering
- 11. Let, Ø= flux per pole in weber Z = Total number of conductor P = Number of poles A = Number of parallel paths N =armature speed in rpm Eg = emf generated in any on of the parallel path 11 Basic Electrical Engineering
- 12. Flux cut by 1 conductor in 1 revolution = P * φ Flux cut by 1 conductor in 60 sec = P φ N /60 Avg emf generated in 1 conductor = PφN/60 Number of conductors in each parallel path = Z /A Eg = PφNZ/60A 12 Basic Electrical Engineering
- 13. •Separately excited DC machine •Self excited DC machine Shunt wound DC generator Series wound DC generator Compound wound 13 Basic Electrical Engineering
- 14. In this type of machine, the field of the machine is excited by an independent external source. This source can be a battery, rectifier circuit or a D.C. generator 14 Basic Electrical Engineering
- 15. Basic Electrical Engineering 15
- 16. V be the field excitation voltage Rf be the field resistance. If be the field current Eg be the generated e.m.f. in the armature Ra be the armature resistance Ia be the armature current IL be the load current VL be the load voltage 16 Basic Electrical Engineering
- 17. In this type of machine the field winding is connected in series with the armature winding of a DC generator 17 Basic Electrical Engineering
- 18. In this type of machine, since the field winding carry the full armature current, the field winding has less number of turns of wire of large cross sectional area. From the machine circuit shown, 18 Basic Electrical Engineering
- 19. In this type of machine, the field winding is connected in parallel with the armature winding. 19 Basic Electrical Engineering
- 21. In this type of DC machine the poles are having two separate windings. That is for a compound wound DC machine there are two field windings, namely, the shunt field winding and the series field winding. 21 Basic Electrical Engineering
- 22. Depending upon how these two windings are connected with the armature of the DC machine, they are classified as, •Long shunt compound DC machine. •Short shunt compound DC machine. 22 Basic Electrical Engineering
- 23. Long shunt Short shunt 23 Basic Electrical Engineering
- 24. This characteristic is called the magnetic characteristic or the Open Circuit Characteristic (O.C.C.) of a separately excited D.C. generator. 24 Basic Electrical Engineering
- 25. • Open Circuit Characteristic • Internal characteristic • The external characteristic 25 Basic Electrical Engineering
- 26. The voltage buildup in a DC generator depends on the presence of a residual flux in the poles of the generator. 26 Basic Electrical Engineering
- 27. • Internal characteristic • External characteristic 27 Basic Electrical Engineering
- 28. • Line OA represent the field resistance • Line OB is called the critical field resistance. 28 Basic Electrical Engineering
- 29. •DC shunt generator is used for such applications where constant voltage is required. •DC series generators are used as Boosters and also as a supply for arc lamps. •Differential Compound generators are used to supply dc welding machines. •Level compound generators are used to supply power for offices, hostels and Lodges etc. 29 Basic Electrical Engineering
- 30. •Over compound generators are used to compensate the voltage drop in Feeders. • Separately excited generator are used as a supply for DC Motors ,it is also used for such applications where a wide range of voltage is required for the testing purposes. 30 Basic Electrical Engineering