1. Power System Fundamentals EE 317 Lecture 9 27 October 2010

2. Aims  Chapter 6 – Parallel Operation of Synchronous Generators

3. Chapter 6  Rationale for paralleling  Conditions for paralleling  Procedure for paralleling  Characteristics of a Synchronous Generator  Operation with an Infinite Bus  Operating with another of similar size

4. Paralleling generators  Why? Higher loads Increased reliability under failure Maintenance More efficient operation of the fleet

5. Conditions for paralleling  Rms line voltages must be equal  Same phase sequence  Phase angles must be equal  Frequency of new generator (oncoming unit) must be slightly higher the frequency of the running system

6. procedure  First – verify terminal voltage of oncoming generator equals line voltage of system  Second – verify that the phase sequence of the oncoming generator is the same as the phase sequence of the running system (motor, bulbs)  Third – adjust the frequency of the oncoming unit to be slightly higher than the frequency of the running system (synchroscope)  Close circuit breaker when 1-3 are satisfied and the generator is in phase with the power system

7. synchroscope  Measures the difference in phase angle between the phases of two systems  Dial shows the difference between two a or b or c phases  Faster (desirable) means clockwise from straight up (which means in phase)

8. Characteristics of a Synchronous Generator  When operating alone its P&Q supplied will depend entirely on the P&Q demanded by the load  Governor – sets the frequency and resulting Real Power output of the synch. Generator  Field Current – controls the output terminal voltage V T and resulting Reactive Power

9. Operation with an Infinite Bus  Infinite bus – a power system so large that any draw of reactive and real power will not affect frequency and voltage  Result: no reasonable action on the part of one generator will cause an observable change in system overall  Imperative that frequency of connected devices be higher than system frequency when connecting

10. Reverse-power trip  Most real generators are equipped with a reverse power trip so that if they do begin to consume power they will disconnect automatically.

11. Operating with another of similar size  Sum of load P&Q is supplied by the n generators  Increase in governor set-point on one generator: Increases system frequency Decreases power supplied by other, up on this one  Increase in field current of one generator: System terminal voltage is increased Reactive power supplied by other is decreased

12. Paralleling Generators

13. Ch. 7 - Induction Machines  Motors and generators whose magnetic field current is supplied by magnetic induction (transformer action) into the field windings of the rotor (a DC power source is not required)  Although induction machines can be motors or generators they have many disadvantages as generators. Thus, they are referred to typically as induction motors. Most popular type of AC motor