Generator fundamentals 2

GE Power Systems

Revision Date: 02/10/2000Revision Date: 02/10/2000 Property of Power Systems University- Proprietary Information for Training Purposes Only!Property of Power Systems University- Proprietary Information for Training Purposes Only!

Introduction to GE Generators

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Objectives

• Understand the basic GE generator.• Understand what the following components do:

– Rotor

– Collector Rings

– Brushes

– Stator Frame

– Stator Core

– Stator Windings

– Stator Connections

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• GE electrical generators are totally enclosed units that use Hydrogen or Air as the cooling medium.

GE Generators

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GE Generators

• The generator is supplied with:– a self contained

ventilation system that includes gas coolers, fans, and filters..

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GE Generators

• GE machines are designed for continuous operation.

• Temperature Detectors (RTD’s) permit the measurement of winding and gas stream temperatures.

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GE Generators

• The generator is constructed to withstand all normal conditions of operation as well as short circuit faults.

• Hydrogen cooled units are capable of containing an internal explosion.

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Generator Rotor

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The “Rotor” is a simple bar magnet that has DC flowing through it and is turned by either a steam or gas turbine.

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• DC current is supplied to the rotor by an excitation system or “Exciter” (aka Voltage Regulator).

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• Longitudinal slots cut into the rotor body hold the field coils.

• Additional slots provide rotor ventilation.

The Rotor

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• The rotor receives DC current from the exciter and creates a rotating magnetic field.

• The rotor is machined from a single alloy steel forging.

The Rotor

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The Rotor

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• DC is applied to the rotor through slip rings (collector rings) and carbon brushes.

The Rotor

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• Collector Rings are made from copper, brass or steel and are insulated from the generator shaft.

The Collector Rings

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• Larger generators will use steel collector rings to compensate for large amounts of heat that can be generated.

• Rings are orientated such that the (-) negative ring is inboard (closest to the generator) and the (+) outboard.

The Collector Rings

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• Steel collector rings will have a groove cut into the face for cooling and for proper brush wear.

The Collector Rings

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• 48 Brushes are used in 7FA applications.

• Carbon is chosen because:– Excellent Conductor– Cheaper– Natural Lubricant

The Brushes

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Current into the page

Current out of the page

Centerline of Poles

A

A

View A - A

ROTOR w/Field Windings

+

-

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The Stator

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The stator is composed of three major elements:

The Frame

The Core

and

The Windings

The Stator

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The Stator

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The Outer Frame

• The Outer Frame:– Gas Guide

– Explosion Proof Barrier

– Sound Proof Enclosure

– Grounded

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The Inner Frame

• The Inner Frame:– Supports the Core

and Windings

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Stator Frame

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Stator Core

Up to 350,000 individual laminations.

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Stator Core

Laminations or punchings are assembled on machined key bars (ribs) and are separated into packets by small space

blocks to provide ventilation ducts.

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Stator Core

The laminations must be carefully aligned and checked to ensure that the stator bars will fit accurately into the

slots and maintain the required specific clearances.

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Stator Core

Once assembled tightening is accomplished with a hydraulic ram which can apply a total load of up to

1200 tons.

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Stator Core

The end result is that the core behaves similar to that of a solid cylinder.

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Stator Core

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Stator Core

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Stator Windings

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Stator Windings

• Each phase is split into groups of windings 180o apart.

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The Stator• The stationary component of

the generator.

• The stator or “armature” is where generator voltage and current is induced.

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Stator Windings

• The stator windings are composed of insulated bars assembled in the stator slots, joined at the ends to form coils, and connected to the proper phase belts by bus rings.

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Stator Windings

• The stator bars are composed of insulated copper conductors (strands) transposed by the “Roebel” method.

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The Stator

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• In a simple generator, the field winding or “Rotor” is rotated under 3 sets of armature or “Stator” windings.

• These windings produce 3 distinct outputs that are 120o apart.

Three Phase AC Generation

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• Each stator winding or phase is actually several windings connected in series.

• Windings connected in series increase the voltage in each phase. This is desirable to limit the strength of the excitation current.

Three Phase AC Generation

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Stator Arrangement

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A

AView A-A

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Centerline of Poles

Centerline of Flux

Flux Pattern inside the generator when the unit is:

OFF LINE

@ RATED Terminal volts

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A

AView A-A

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Draw the AC WaveformIn

duce

d V

olta

ge

TB1-06

Education

Generator fundamentals 2