module g1 electric power generation and machine controls l.
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Module G1 Electric Power Generation and Machine Controls. James D. McCalley. Overview. Energy transformation into electrical form Generation operation Revolving magnetic field Phasor diagram Equivalent Circuit Power relationships Generator pull-out power Excitation control

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Presentation Transcript
overview
Overview
  • Energy transformation into electrical form
  • Generation operation
    • Revolving magnetic field
    • Phasor diagram
    • Equivalent Circuit
    • Power relationships
    • Generator pull-out power
  • Excitation control
  • Turbine speed control
energy transformation
Energy Transformation
  • Transformation processes:
    • Chemical
    • photovoltaic
    • electromechanical
  • Electromechanical: conversion of energy from coal, petroleum, natural gas, uranium, water flow, geothermal, and wind into electrical energy
  • Turbine-synchronous AC generator conversion process most common in industry today
slide4

Click on the below for some pictures of power plants

and synchronous generators

ISU Power Plant

http://powerlearn.ee.iastate.edu/library/html/isupp39.html

ISU Power Plant synchronous generator

http://powerlearn.ee.iastate.edu/library/html/isupp1.html

Ames Power Plant

http://powerlearn.ee.iastate.edu/library/html/amespp34.html

Ames Power Plant synchronous generator

http://powerlearn.ee.iastate.edu/library/html/amespp1.html

feedback control systems for synchronous generators
Feedback Control Systems for Synchronous Generators
  • Turbine-generator basic form
  • Governor and excitation systems are known as feedback control systems; they control the speed and voltage respectively
synchronous machine structure
Synchronous Machine Structure

Phase A

STATOR

(armature

winding)

ROTOR

(field

winding)

+

N

Phase B

+

DC

Voltage

S

The negative terminal

for each phase is

180 degrees from

the corresponding

positive terminal.

+

Phase C

A Two Pole Machine (p=2)

Salient Pole Structure

slide7

Salient Pole

Construction

Smooth rotor

Construction

synchronous machine structure8
Synchronous Machine Structure

N

S

S

N

A Four Pole Machine (p=4)

(Salient Pole Structure)

generation operation
Generation Operation
  • The generator is classified as a synchronous machine because it is only at synchronous speed that it can develop electromagnetic torque
  • = frequency in rad/sec
  • = machine speed in RPM
  • p = number of poles on the rotor of the machine
slide11

For 60 Hz operation (f=60)

No. of Poles (p) Synchronous speed (Ns)

------------------- -----------------------------

2 3600

4 1800

6 1200

8 900

10 720

12 600

14 514

16 450

18 400

20 360

slide12

Fact: hydro turbines are slow speed,

steam turbines are high speed.

Do hydro-turbine generators have few poles or many?

Do steam-turbine generators have few poles or many?

Fact: salient pole incurs significant

mechanical stress at high speed.

Do steam-turbine generators have salient poles or smooth?

Fact: Salient pole rotors are cheaper to build than smooth.

Do hydro-turbine generators have salient poles or smooth?

generation operation13
Generation Operation
  • A magnetic field is provided by the DC-current carrying field winding which induces the desired AC voltage in the armature winding
  • Field winding is always located on the rotor where it is connected to an external DC source via slip rings and brushes or to a revolving DC source via a special brushless configuration
  • Armature winding is located on the stator where there is no rotation
  • The armature consists of three windings all of which are wound on the stator, physically displaced from each other by 120 degrees
synchronous machine structure14
Synchronous Machine Structure

Phase A

  • voltage induced in phase
  • wdgs by flux from
  • field wdg
  • current in phase wdgs
  • produces flux that
  • also induces
  • voltage in phase
  • wdgs.

+

N

Phase B

+

DC

Voltage

S

+

Phase C

generation operation the revolving magnetic field
Generation Operation: The revolving magnetic field
  • = flux associated with the revolving magnetic field which links the armature windings. It will have a flux density of B.
  • At any given time t, the B-field will be constant along the coil.
  • By Faraday’s Law of Induction, the rotating magnetic field will induce voltages phase displaced in time by 120 degrees (for a two pole machine) in the three armature windings
  • Let’s consider just the A-phase.
generation operation the revolving magnetic field cont d
Generation Operation: The revolving magnetic field (cont’d)

If each of the three armature windings are connected across equal

impedances, balanced three phase currents will flow in them

producing their own magnetic fields = =

  • = resultant field with associated flux obtained as the sum of the three component fluxes is the field of armature reaction
  • The two fields represented by and are stationary with respect to each other
  • The armature field has “locked in” with the rotor field and the two fields are said to be rotating in synchronism
  • The total resultant field = +
generation operation the phasor diagram
Generation Operation:The phasor diagram
  • From Faraday’s Law of Induction, a voltage is induced in each of the three armature windings:

where N = number of winding turns

  • All voltages, ,lag their corresponding fluxes, ,by 90 degrees
  • The current winding a, denoted by , is in phase with the flux it produces
generation operation the equivalent circuit model
Generation Operation: The equivalent circuit model
  • Develop equivalent model for winding a only; same applies to winding b and c with appropriate 120 degree phase shifts in currents and voltages given a balanced load
generation operation the equivalent circuit model cont d26
Generation Operation: The equivalent circuit model (cont’d)

You can perform per-phase equivalent analysis

or you can perform per-unit analysis.

In per-phase, Ef and Vt are both line to neutral voltages,

Ia is the line current, and Z is the impedance of the

equivalent Y-connected load.

In per-unit, Ef and Vt are per-unit voltages,

Ia is the per unit current, and Z is the per unit load

impedance.

leading and lagging generator operation
Leading and Lagging Generator Operation

Let

From the equivalent circuit,

So here we see that

leading and lagging generator operation28
Leading and Lagging Generator Operation

Assign Vt as the reference:

Then,

So here we see that

This gives an easy way to remember the relation

between load, sign of current angle, leading/lagging,

and sign of power angle.

leading and lagging generator operation29
Leading and Lagging Generator Operation

Circle the correct answer in each column

Inductive load Capacitive load

----------------------------------------------------------------

phasor diagram for equivalent circuit31
Phasor Diagram for Equivalent Circuit

This equation gives directions for

constructing the phasor diagram.

1. Draw Vt phasor

2. Draw Ia phasor

3. Scale Ia phasor magnitude by Xs and

rotate it by 90 degrees.

4. Add scaled and rotated vector

to Vt

Ef

jXsIa

jXsIa

Vt

Ia

Try it for lagging case.

XsIa

phasor diagram for equivalent circuit32
Phasor Diagram for Equivalent Circuit

This equation gives directions for

constructing the phasor diagram.

1. Draw Vt phasor

2. Draw Ia phasor

3. Scale Ia phasor magnitude by Xs and

rotate it by 90 degrees.

4. Add scaled and rotated vector

to Vt

You do it for leading case.

phasor diagram for equivalent circuit33
Phasor Diagram for Equivalent Circuit

Let’s define the angle that Ef makes with Vt as

For generator operation (power supplied by machine),

this angle is always positive.

For motor operation, this angle is negative.