Power Plant Construction and QA/QC

Section 4.1 AC Generators and Generator Protection

Engineering Technology Engineering Technology DivisionDivision

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Section 4.1 AC Generators and Generator Protection

Overview

• Generators are the production point for electricity• Both Alternating and Direct Current is generated• Alternating Current travels both directions• Direct Current travels in only one direction• DC was developed first in the mid – 1870• DC has a limited travel distance – requires high

current• AC has “no” distance limits in comparison• Prime movers are needed to turn generators• Prime movers are geared to match generator

design• 99.2% of the power generated today is AC

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Section 4.1 AC Generators and Generator Protection

AC vs. DC

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Section 4.1 AC Generators and Generator Protection

Generator Types - Synchronous

3 Phase AC 2 Pole, 3 Coil

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Section 4.1 AC Generators and Generator Protection

Generator Types - Synchronous

Synchronous Generators are common for Power Plants

Exciter

Stator

Rotor

Voltage and current from Stator

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Section 4.1 AC Generators and Generator Protection

Generator Types - Synchronous

Stator

Rotor

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Section 4.1 AC Generators and Generator Protection

Generator Types - Induction

Voltage and current from Rotor

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Section 4.1 AC Generators and Generator Protection

Generator Cooling

Direct – Gas (Hydrogen) Indirect – Water, Oil

Liquid Hydrogen = -423.17º F

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Section 4.1 AC Generators and Generator Protection

Generator Rating

Over Excitation Under

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Section 4.1 AC Generators and Generator Protection

Exciters

DC Generator, Rotating AC, Brushless

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Section 4.1 AC Generators and Generator Protection

Exciters

DC Generator, Rotating AC, Brushless

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Section 4.1 AC Generators and Generator Protection

Exciters

DC Generator, Rotating AC, Brushless

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Section 4.1 AC Generators and Generator Protection

Generator Synchronizing

Generator 2Generator 1

Exciter Control

Breaker Switch

Exciter Control

Breaker Switch

Speed Control

Speed Control

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Section 4.1 AC Generators and Generator Protection

Generator Protection

Differential Current – fault between phases

Voltage Regulation – generator control

Stator Overcurrent – high operating levels

Negative Sequence Current - phase imbalance

Stator Ground Fault – stator ground

Field Ground – rotor ground

Loss of Excitation Protection – synchronization loss

Motoring protection – loss of prime mover

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Questions?

Section 4.1 AC Generators and Generator Protection