Power System Fundamentals

1
Power System Fundamentals

• ECE 0909.402.05
• ECE 0909.504.05 - Lecture 10
• 8 April 2003
• Peter Mark Jansson PP PE MScEng

2
Aims

• Next Weeks Tour
• Chapter 6 Parallel Operation of Synchronous
  Generators
• Chapter 7
• Quiz 1 (Take Home or In Class 5.45 p.m. to 7 a.m.
  tomorrow)

3
Next Monday

• April 7, 2003
• 845 am
• Distribution Feeder Walk

4
Mid-Term Performance

• Very Good Performance To-Date 85.1 class
  average score with 38 of marks in
• Have provided a mid-term review for each student
  with HW 4
• Quiz 1 today is worth 5 - Take Home/In Class
• Quiz 2 Finals Week 10
• Technical Paper 20
• windings

5
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

6
Paralleling generators

• Why?
• Higher loads
• Increased reliability under failure
• Maintenance
• More efficient operation of the fleet

7
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

8
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

9
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)

10
Characteristics of a Synchronous Generator

• When operating alone its PQ supplied will depend
  entirely on the PQ 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

11
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

12
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.

13
Operating with another of similar size

• Sum of load PQ 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

14
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
• See pages 289-291