Transcript Lecture 9
Power System Fundamentals EE 317 Lecture 9 27 October 2010 Aims Chapter 6 – Parallel Operation of Synchronous Generators 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 Paralleling generators Why? Higher loads Increased reliability under failure Maintenance More efficient operation of the fleet 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 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 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) 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 VT and resulting Reactive Power 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 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. 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 Paralleling Generators 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