1. NUE046: Alternating Current Machines - Synchronous Machines section

6. 500 KW Genset / Generator Set, powered with a Cummins VTA28G1 Engine

9. 2 x 14MW Synchronous Motors … apparently, they use permanent magnets!

11. 3 phase Dunlite machine

13. Synchronous machines are not just the big units, but they can be small also.

14. R, L, and C on AC Revision of...

15. Resistance on AC Current is in phase with voltage. Time-> V AC Supply R V I I

16. Inductance on AC L AC supply Current lags the Voltage by 90 o V I V I

17. Capacitance on AC But if an ammeter were placed in series it would most definitely read a current. Current appears to pass through the capacitor. In reality, it is charging in one direction, and then discharging and recharging in the other direction. C AC Supply

18. Capacitance on AC V Current leads the Voltage by 90 o I C AC Supply V I

19. Inductive and Capacitive Reactance This opposition to current flow is called: Inductive reactance, in inductors. (X L ) Capacitive reactance in capacitors. (X C ) Both Inductors and Capacitors oppose, or “resist” current flow when connected to AC supplies. While it opposes current flow, it is NOT called resistance. Current flow through resistance produces HEAT. Current flow in inductors and capacitors doesn’t!

20. Star and Delta Connections Revision of...

21. Star Generator / Transformer / Motor A C B S F S F S F S F S F S F B A C

22. A C B Motor Star Why isn’t a neutral run to a balanced three phase Star connected load? A B C N ?????

23. A C B Motor Star Because the Star point is at 0V A B C And the neutral is at zero volts also. So if they were joined no current would flow. So why join it? 0V 0V N 0A

24. A C B Motor Star A B C The neutral is not connected to a balanced three phase star connected load. Only connected to unbalanced loads!!!

25. Transformer Delta Generator / Transformer / Motor S F B S F C A B C F S F S F S S F A

26. Transformer Delta Generator / Transformer / Motor S F B S F C A B C S F S F S F S F A Swapped

27. 3-phase Transformer Secondary Delta S F B C S F A S F Note that all windings are connected in series, with the two ends joined together. A B C

28. Delta If we did that with three batteries, there would be major problems!

29. Delta The voltmeter should read the sum of the three voltages? Right? Transformer The voltmeter reads the phasor sum of the voltages. V A V B V C A C B F S F S F S V

30. Delta The voltmeter reads, in effect, the distance between the beginning of V A and the end of V C . ie. 0V We can connect the two ends together because the phasor sum adds up to zero! V A V B V C A C B F S F S F S Transformer V

31. Delta Transformer No Arc! V A V B V C A C B F S F S F S The voltmeter reads, in effect, the distance between the beginning of V A and the end of V C . ie. 0V We can connect the two ends together because the phasor sum adds up to zero!

32. Three Phase Power Equation Revision of...

33. Generator Load P = 3 x V PH x I PH x Cos  = 3 x V L /  3 x I L x Cos  = 3/  3 x V L x I L x Cos  =  3 V L x I L x Cos  P = 3 x V PH x I PH x Cos  = 3 x V L x I L /  3 x Cos  = 3/  3 x V L x I L x Cos  =  3 V L x I L x Cos  Three Phase Power STAR V L =  3 V PH I L = I PH DELTA I L =  3 I PH V L = V PH

34. P =  3 V L x I L x Cos  NOT: P = 415 x I x pf. Three Phase Power

35. Three Single Phase Power Equations: True Power = Watts = V x I x Cos  Apparent Power = VA = V x I Reactive Power = VAR’s = V x I x Sin  Power Factor = Cos  where Cos  = Cosine of the angle between Voltage and Current

36. VA Watts Var’s  Phase angle between current and volts This can be put as a triangle: VA 2 = Watts 2 + Var’s 2

37. Alternators, where the windings are limited by the current through them , are rated in VA. To rate them in watts, (ie. watts delivered to the load) would give no idea of the current through them. Load 3 = 14.14A at 45º Load 1 = 10A Load 2 = 20A at 60º P = V x I x Cos 45º = 240 x 14.14 x 0.707 = 2.4kW P = V x I x Cos 0º = 240 x 10 x 1 = 2.4kW P = V x I x Cos 60º = 240 x 20 x 0.5 = 2.4kW V=240V

38. Q What dictates the phase angle of the current supplied by a single alternator supplying a single load? A The load V=240V Load 3 = 14.14A at 45º Load 1 = 10A Load 2 = 20A at 60º P = V x I x Cos 45º = 240 x 14.14 x 0.707 = 2.4kW P = V x I x Cos 0º = 240 x 10 x 1 = 2.4kW P = V x I x Cos 60º = 240 x 20 x 0.5 = 2.4kW

39. V Al currents here take the same power Constant power line

40. Al currents here take the same power Higher power V

41. Al currents here take the same power Constant power line V

42. Al currents here take the same power Lower power V

43. So much for revision...

44. Synchronous Machines

45. Alternator - Diesel Engine - Steam Turbine - Small petrol engine Mechanical Energy Electrical Energy Losses Alternator Prime Mover Alternator: Pout Eff% = x 100 Pin Alternator: Pin = Pout + Losses

46. Synchronous Motor Losses Mechanical Energy MSB Electrical Energy Motor: Pout Eff% = x 100 Pin Motor Pin = Pout + Losses Motor Load

47. Synchronous Machine Stator - Identically wound to an induction motor. - Connected to supply. Rotor - Constant DC field - Connected to supply via sliprings. Electrical Power DC Supply

49. Synchronous Machine If a synchronous motor is OVER driven by the load (eg electric train going down a hill), then it will generate power, still at synchronous speed. If an alternator coupled to the grid is UNDER driven by the prime mover (eg steam stops), then it will motor, and drive the turbine at synchronous speed. Electrical Power DC Supply

50. Synchronous Machine In other words, the two machines are identical in construction. Electrical Power DC Supply

51. Synchronous Motors

54. Construction

57. 2 basic types: Cylindrical rotor Salient Pole -Low speed -Diesel Prime Mover -Hydro systems -High speed -Steam Turbine Salient Pole Rotor Cylindrical Rotor

64. www.tecowestinghouse.com Small salient pole synchronous machine rotor

75. Synchronous Motor Losses Mechanical Energy MSB Electrical Energy Motor: Pout Eff% = x 100 Pin Motor Pin = Pout + Losses Motor Load

76. Stator Construction Same as an induction motor.

77. 2-Pole Machine ie. 3000RPM Stator Construction A1 A2

78. Stator Construction Stator Construction

79. 2-Pole Machine ie. 3000RPM In reality, the coils span more slots in a 2-pole motor. Stator Construction Notice that for a two pole stator we have a 2-pole rotor A1 A2 B1 B2 C1 C2 N S

80. Stator Construction N N S S A A A A B B B B C C C C 4-pole machine A four pole stator must have a four pole rotor

81. Time-> S Stator Construction N Flux + - 1 Resultant flux = 1.5 x flux of one phase N S N S

82. Time-> Resultant flux = 1.5 x flux of one phase Stator Construction Flux + - 2 N S N S N S

83. Time-> Stator Construction Flux + - 3 4 5 6

84. Time-> So the flux rotates one full rev in one cycle, for our two pole machine. Stator Construction Flux + - 3 4 5 6 1 2

85. Time-> Because the flux is a constant value, it gives: 1. Very quiet operation 2. Constant torque as the rotor rotates. Stator Construction Flux + - 3 4 5 6 1 2

86. Time-> This rotating magnetic field rotates at: 3000RPM for a 2-pole motor 1500RPM for a 4-pole motor Stator Construction Flux + - 3 4 5 6 1 2

87. Time-> To reverse the direction of rotation: reverse any two phases to the motor. Stator Construction Flux + - 3 4 5 6 1 2

88. where N = RPM f = frequency P = Number of poles (per phase). N = 120f/P So the speed of the rotating magnetic field is affected by: Frequency, and Number of poles. Stator Construction

89. As the rotating magnetic field rotates, the rotor is locked in synchronism with it and is dragged along for the ride. Stator Construction

90. As the rotating magnetic field rotates, the rotor is locked in synchronism with it and is dragged along for the ride. Construction N S

91. What will happen as a load is put on the shaft? Construction N S

92. What will happen as a load is put on the shaft? Construction N S

93. The load tries to slow it down. But it must do synchronous speed! So it stretches the lines of flux. Construction N S

94. Construction C/L of RMF C/L of Rotor Field Torque Angle  N S

95. If the lines stretch to breaking point (ie too much load), then the rotor stalls This is referred to as “Pull Out Torque”. N S Construction

96. What would the Torque Curve look like? RPM Ns 0 Torque Curve for an induction motor Torque

97. What would the Torque Curve look like? Torque RPM Ns 0 Torque “Curve” for a Synchronous Motor Zero Torque below synchronous speed Pull out Torque

98. Starting a Synchronous Motor? 1. Amortisseur winding

100. Induction Motors Rotor Construction Squirrel Cage

103. Starting a Synchronous Motor? 1. Amortisseur winding This gets the motor up to speed as an induction motor. When it is close to synchronous speed it will lock in. 2. Shorting the rotor DC winding and starting it as a wound rotor motor. When it is close to synchronous speed, the short is removed and DC is applied to the rotor. It will (hopefully) lock in.

104. 3. Using a pony motor to get the synchronous motor up to speed, then applying AC to the stator and DC to the rotor. (Not applicable if there is a high starting torque load connected) Note that these starting methods will only work if the load on the motor at start can be reduced or eliminated. Starting a Synchronous Motor?

105. • Amortisseur windings also reduce hunting. • Hunting is rhythmic fluctuations of the RPM around an average value. • If not subdued, hunting can cause the rotor to swing out of synchronism. Hunting

106. Revs Time Hunting

107. And all this while it is whizzing around at synchronous speed! Hunting N S N S N S N S N S

108. And all this while it is whizzing around at synchronous speed! Hunting N S

109. Electrical Operation

110. V supply V induced Phasor Diagram of Synchronous Motor Induced in the stator from the rotor

111. V supply V induced V R Phasor Diagram of Synchronous Motor Torque angle  I supply

112. Phasor diagram for increased load: (Excitation current held constant) V supply V R Increased load = Increased Torque Angle Increasing the load increases the power taken from supply V induced  I supply V induced

113. V supply Phasor diagram for increased excitation: (Constant Load)  Constant load = Constant Power line V induced V induced

114. Phasor diagram for increased excitation: (Constant Load) V supply  Constant load = Constant Power line V induced

115. V supply Phasor diagram for increased excitation: (Constant Load) So to force the supply current leading, we INCREASE excitation  Constant load = Constant Power line V induced V R I supply

116. V supply Phasor diagram for decreased excitation: (Constant Load)  Constant load = Constant Power line V induced I supply V R

117. V supply  Phasor diagram for decreased excitation: (Constant Load) So to force the supply current lagging, we DECREASE excitation Constant load = Constant Power line I supply V R V induced

118. V supply V induced I supply V R   Constant load = Constant Power line V supply V supply  I supply V R V induced V induced I supply V R

119. V supply With a constant load, changing excitation changes the phase angle and value of supply current. I supply By increasing the DC excitation current to the rotor, the synchronous motor can act as a capacitor It can be used for power factor correction. Constant load = Constant Power line

120. Excitation Current Stator Current 50% load Unity pf Lag Lead

122. Excitation Current Stator Current 50% load Lag Lead 75% load Stability limit pf=1

123. 0.8 pf lag Unity 0.8 pf lead Per unit Power output

131. Alternators

132. Why generate AC?… Why not DC? DC cant be “transformed” through a transformer. AC can go through a transformer. Large brushless DC generators are not possible Large brushless AC alternators are! Why do we want to transform it? It is easier to transmit to distant places at higher voltages as the current will be lower. (P=V x I) Induction motors are simpler and cheaper than DC motors

133. Voltage Generation

134. N S V Generating an AC Voltage

135. N S Generating an AC Voltage Time-> Volts + -

136. Generating an AC Voltage Time-> N S Volts + -

137. Generating an AC Voltage Time-> N S Volts + -

138. Generating an AC Voltage Time-> N S Volts + -

139. N S Generating an AC Voltage Time-> Volts + -

140. Generating an AC Voltage Time-> N S Volts + -

141. N S V Generating a AC Voltage 3-Phase

142. N S Time-> Require: Three sets of coils physically displaced from each other by 120º electrical . Volts + - Generating a AC Voltage 3-Phase

143. N S V A V C V B Generating a AC Voltage 3-Phase

144. A1 A2 Generating a AC Voltage 3-Phase N S

145. Generating a AC Voltage 3-Phase N S A1 A2 B1 B2 C1 C2

146. N N S S A A A A B B B B C C C C 4-pole machine A four pole stator must have a four pole rotor Generating a AC Voltage 3-Phase

148. Alternator Stator - Connected to load . Rotor - Constant DC field - Connected to its own DC supply via sliprings. Electrical Power Mechanical Power Magnetic Field

149. Alternator Q: What keeps an alternator producing 50Hz under all load conditions? A: The governor on the prime mover. It detects any drop in speed, and tries to speed the unit up. Alternator Petrol Engine

150. Electrical Operation

151. I FIELD V OUT Alternator Excitation Curve (No Load)

152. Alternator Alt Load R X L Internal Impedance

153. Resistive Load V OUT V Z = Internal Impedance of the alternator V R = Internal Resistance of the alternator V L = Internal Reactance of the alternator I LOAD V R V Z V L V GEN

154. Resistive Load  Load current and p.f. are dictated by the LOAD! V OUT I LOAD V R V Z V L V GEN  Notice that terminal volts DROP as load increases

155. Inductive Load V OUT I LOAD V R V Z V L V GEN Parallel

156. Inductive Load  Now there is a greater voltage drop under load V OUT I LOAD V R V Z V L V GEN

157. Capacitive Load V OUT I LOAD  Now there is a voltage RISE under load  Because of the voltage rise under load, it is not desirable to run alternators at a leading power factor. V R V Z V L V GEN Parallel

158. Effect of Power Factor on Output Voltage Leading pf Unity pf Lagging pf Load Current Output Voltage

160. Summary: When an alternator is standing by itself with a single load: Output voltage is affected by excitation current Output frequency is affected by input power to the alternator. Alternators - stand alone

161. When an alternator is tied to the grid, you cannot change: Grid voltage Grid frequency So the output voltage of the alternator will not change, and the output frequency of the alternator will not change. Notice that, for a stand alone alternator with stand alone load, these are the two things that changed when: (a) the excitation was altered, and (b) the power input to the alternator was increased (ie. Put the foot down on the prime mover) Alternators tied to the Grid

162. Alternators tied to the Grid V OUT V GEN If excitation is increased , and V OUT cannot alter, V GEN will increase and push the triangle over. I LOAD 1. Altering Excitation. V R V Z V L

163. V OUT I LOAD V GEN If excitation is increased , and V OUT cannot alter, V GEN will increase and push the triangle over. Alternators tied to the Grid 1. Altering Excitation. Note that input power to the alternator is not changing, so output power does not change either. V R V Z V L Constant Power Line (Output power of the alternator has not Changed)

164. V OUT I LOAD If excitation is reduced , and V OUT cannot alter, V GEN will reduce and pull the triangle back. Alternators tied to the Grid 1. Altering Excitation. V GEN This drives the load current lagging V R V Z V L

165. V OUT I LOAD V GEN If excitation is reduced , and V OUT cannot alter, V GEN will reduce and pull the triangle back. Alternators tied to the Grid 1. Altering Excitation. This will drive the load current leading V R V Z V L

166. If input power is reduced , and frequency and V OUT cannot alter, output power will reduce . Alternators tied to the Grid 2. Altering input power to the alternator. V OUT V GEN I LOAD V R V Z V L

167. If input power is reduced , and frequency and V OUT cannot alter, output power will reduce . Alternators tied to the Grid 2. Altering input power to the alternator. V OUT V GEN I LOAD V R V Z V L

168. If input power is reduced , and frequency and V OUT cannot alter, output power will reduce . Alternators tied to the Grid 2. Altering input power to the alternator. V OUT V GEN I LOAD Size of triangle reduces V R V Z V L

169. If input power is reduced , and frequency and V OUT cannot alter, output power will reduce . Alternators tied to the Grid 2. Altering input power to the alternator. V OUT V GEN I LOAD Size of triangle reduces V R V Z V L

170. If input power is increased , and frequency and V OUT cannot alter, output power will increase . Alternators tied to the Grid 2. Altering input power to the alternator. V OUT V GEN I LOAD V R V Z V L

171. If input power is increased , and frequency and V OUT cannot alter, output power will increase . Alternators tied to the Grid 2. Altering input power to the alternator. V OUT V GEN I LOAD V R V Z V L

172. If input power is increased , and frequency and V OUT cannot alter, output power will increase . Alternators tied to the Grid 2. Altering input power to the alternator. V OUT V GEN I LOAD V R V Z V L

173. If input power is increased , and frequency and V OUT cannot alter, output power will increase . Alternators tied to the Grid 2. Altering input power to the alternator. V OUT V GEN I LOAD V R V Z V L

180. Single Phase Alternators Electrical Power Mechanical Power Regulator Stator Magnetic Field

184. Brushless Alternators Note: Self Excited Rotor AC is sampled Regulator DC Field P.S . 3-phase out

185. Brushless Alternators Rotor Regulator 3-phase out Prime Mover 3-phase out

187. T E N D h e