Synchronous Machines

Transcription

1 Synchronous machine

2 1. Construction

3 Generator Exciter View of a twopole round rotor generator and exciter.

4 A Stator with laminated iron core C Slots with phase winding B A B Rotor with dc winding B N S A C C Major components of a round rotor twopole generator

5 Crosssection of a large turbo generator. (Courtesy Westinghouse)

6 Metal frame Laminated iron core with slots Insulated copper bars are placed in the slots to form the threephase winding Details of a generator tor.

7 Rotor block of a large generator. (Courtesy Westinghouse)

8 Generator rotor with conductors placed in the slots.

9 Shaft Steel retaining ring Wedges DC current terminals terminals Large generator rotor completely assembled. (Courtesy Westinghouse)

10 C B Stator with laminated iron core Rotor with dc winding A B N S C A Slots with phase winding Twopole salient pole generator concept.

11 B A C N C B A B S N S C A C A B Fourpole salient pole generator concept.

12 Stator of a large salient pole hydro generator; inset shows the insulated conductors and spacers.

13 Large hydro generator rotor with view of the vertical poles.

14 Slip rings Pole Fan DC excitation winding Rotor of a fourpole salient pole generator.

15 Exciter rotor Rotating rectifier Exciter tor Generator Φ I dc Field winding Stationary Phase windings Rotates Concept of the brushless exciter system

16 Operating Concept

17 n sy Flux Φ f C B A N S A B C Operating concept of a synchronous generator

18 Maximum flux linkage with phase A No flux linkage with phase A A C B N S C A A B B C B N S C A (a) Flux is perpendicular to phase A (b) Flux is parallel to phase A Rotation produced flux linkage variation.

19 Φ rot ωt Φ link n sy C B N A 30 A S B C Rotating flux linkage to phase A.

20 Main rotating flux f n sy = p 2 ω = 2π Φ E link s n sy ( t) = Φ cos( ω t) ( t) = N rot d Φ dt link ( t) E s ( t) = N = E N = Φ N Φ rot rot ω sin( ω t) ω cos( ω t Φ 2 rot ω 90 ) The rotating flux generates the induced voltage

21 n sy C B Field flux Φ f N A 30 A S Armature flux Φ ar B C Field (Φ f ) and load generated (Φ ar ) rotating fluxes.

22 I Φ Armature flux arm ( t) = 2 I cos( ω t) arm ( t) = Φ cos( ω t) ar Load current generates a rotating flux reducing the main flux and induced voltage E ar dφ arm ( t) ( t) = N = N Φ ar ω sin ( ω t) dt E arm = N Φ 2 ar ω V t = E E arm

23 Armature flux ) sin( 2 ) sin( 2 ) cos( 2 ) ( ) ( t I X t I L t I dt d L dt t di L t E arm arm arm arm arm ar ω ω ω ω = = = = ar arm I N X 2 ω Φ = leakage arm syn X X X =

24 Single phase equivalent circuit E = I arm syn ( j X syn ) V t = E E arm syn = E I j X syn X syn R Flux E I V t DC Singlephase equivalent circuit of a synchronous generator.

25 The generator is loaded The load current produces a rotating flux This rotating flux induces a ac three phase voltage in the tor winding. This voltage is subtracted from the induced voltage. represented by a voltage drop on the synchronous reactance The equivalent circuit of a synchronous generator is a voltage source and a reactance connected in series

26 Generator Application Power angle: Angle between the dc excitation current generated induced voltage and the terminal voltage X ad X 1σ R I sp U b U V Z U I

27 U ˆ = U ˆ j X I ˆ ad j X 1 b σ I ˆ R I ˆ Synchronous Machines Phasor diagram of synchronous machine Uˆ = Uˆ j X Iˆ ad j X 1 b σ Iˆ R Iˆ

28 Generator Application Loading: power is less than angle 90 deg All generators in the system are connected in parallel All generators rotates with the synchronous speed The load can be increased by increasing the input mechanical power by regulating the turbine impute power The speed does not change, the power angle increases Maximum power angle is 90 degree, beyond that operation is unble Reactive power regulation When the excitation is: Increased, the generator reactive power also increases; Decreased, the generator reactive power also decreases

29 Load and excitation dependence 0 kap 0 ind U U n 1 0 0,8 ind ind 0,6 kap 0,2 kap 0,6 ind 1 0,6 kap I b 0 kap I (I sp ) I

30 Synchronization Verify that the phase sequences of the two systems are the same. Adjust the machine speed with the turbine that drives the generator until the generator voltage frequency is nearly the same as the frequency of the network voltage. Adjust the terminal voltage of the generator by changing the dc field (rotor) current until the generator terminal voltage is almost equal to the network voltage. Acceptable limit is 5%. Adjust the phase angle of the generator terminal voltage by regulating the input power until it is nearly equal with the phase angle of the network voltage. Acceptable limits are about 15.

31 Synchronization L1 L2 L3 V 1 f 1 V 2 f 2 A NAPÁJENÍ BUZENÍ SA

32 The generator and network power vs power angle δ := 0deg, 1deg.. 180deg 250 P g () δ kw P net () δ Stable operation Maximum power Unble operation kw Operation point δ deg