Submited by:Md Al-Beruni

Masters in Energy Systems

Matriculation No:3088591

A Presentation on

Excitation Systems for Hydro Alternators

Contents What is Alternator Excitation System Components of an Excitation System

Functions of Excitation System in a power plant Different Types of Excitation Systems

De-Excitation and Overvoltage Protection Conclusion.

What is it?

Input to the Alternator:1. Mechanical Energy to rotate the rotor2. Excitation current in field winding.

“Excitation System provides the DC electric power, which is necessary to magnetize the Generator Rotor. ”

Why DC current? To make the rotor magnet fixed polarity.

Power requirement: In large alternator : 0.3% to 0.6% of total

power. Around 250-500V, 10-15 Amp per MW normal load. Fig.1 : Rotor , Stator, field current

Source: http://www.alternative-energy-tutorials.com

1.Exciter2.Regulator3.Terminal voltage regulator and load compensator. 4.Power System stabilizer. 5.Limiters and protective circuits.

Components of Excitation System

Fig.2 : General Components of Excitation Systems

Source: Excitation Course, P. Kundur

Frequency, Induced Emf(volts), So, P=no of poles, n=r.p.m, Kw= Kc*Kd, =no. of turns in series per phase. = flux per pole

Permanent magnet can do the job ?Yes, but regulation not possible.

Main Functions:1. Supply direct current to synchronous generator

field winidng. 2. Control voltage and reactive power. 3. Perform protective function for the satisfactory

operaton of power systems.

Functions

Fig.3 : Block Diagram of Excitation Systems

Excitation Systems

DC Excitation

Self Excited(DC generators

shaft driven)

Seperately Excited

(DC Generators)

High Frequency AC Excitation Static Excitation Brushless

Excitation

Types

DC Generator system: Driven by prime mover..Shaft Driven system: Power generated by a DC generator driven by the shaft of main Alternator. This system is backdated. (1920-1960)

Large size, voltage regulation was complex. Very slow response.

Excitation controlled by automatic or manual voltage regulator.

Exciters Power comes from AC alternator which is also driven from the main alternator shaft.AC output : Rectified by rectifier. Frequency: 50-250 Hz (High frequency)

Suitable for Medium size hydro alternators. This system eliminates the commutator and brush. The high frequency output rectified by stationary diodes and delivered via slip rings.

DC and AC Excitations

Fig.4 : DC Excitation Systems Fig.5 : AC (high frequency)Excitation Systems

Source: IEEE std. 421.1-1986, IEEE standard definitions for excitation systems for synchronous machines

No rotating parts for Exciters.

Most commonly used for hydro Generators.

Thyristor rectifire to directly control alternator field current.

Advantage:1. Superior fast response.2. Low loss3. Relatively small size4. Suitable for large Synchronous

Machines.

Disadvantage:Brush and slip ring required.

Mechanism:Alternator Terminals(Auxiliary bus) Excitation power rectifier bridge slip ring rotor field.

Static Excitation System

Fig.6 : Static Excitation Systems

This system supplies rotor field current without using slip ring and carbon brush.How ? The exciter rotates on the rotor.

Operates in high-speed hydro generators. Diode rectifiers are mounted on Generator shaftAnd DC output directly connected to the field of Alternator. Two major part:1. Pilot Exciter.(PMG)2. Main exciter. (AC Generator)

The voltage regulator done by thyristor bridge controlling the field of AC exciter.

Advantages: no moving contact so less maintenanceDisadvantage: No fast de-excitation, slow response.

Brushless Excitation Systems

Fig.7 : Brushless Excitation Systems, Block Diagram

Source: https://www.gepower.com/, ABB Switzerland Ltd, GTSG Birr, Switzerland

What is De-excitation?De-excitation quickly cuts off power flow to the rotor and consumes the energy of magnatic field stored in excitation winding.

When operates ?Emergency shut down.

DE-Excitation for Alternator safety and safe operation of Power systems.

DE Excitation

Fig.8 : DE-Excitation System(Red Box)

Source: http://www.google.ch/patents/US20110298430

Conclusion

REFERENCES[1] VOITH: Thyricon™ Excitation System[2] GE Energy: Synchronous Hydro Generator

[3] ANDRITZ, “Excitation System: An essential component for generation of electrical energy,” International technology Group ANDRITZ, Austria, 2013.[4] ANL/DIS-13/05 Review of Existing Hydroelectric Turbine-Governor Simulation Models[5] Excitation System course. P. Kundur

Selection of Excitation System for hydro alternator widely depends on various factors. Alternator power, speed, size, maintenance cost, surrounding environment are some mainfactors for excitation systems selection criteria. Upgradation of old excitation system can lower operational cost and imporve efficiency of a power plant.