A short description of different types of excitation system of Alternator, mainly focused on Hydro Alternators.

1. Submited by:
Md Al-Beruni
Masters in Energy
Systems
Matriculation No:3088591
A Presentation on
Excitation Systems for Hydro Alternators

2. 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.

3. What is it?
Input to the Alternator:
1. Mechanical Energy to rotate the rotor
2. 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

4. 1.Exciter
2.Regulator
3.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

5. Frequency, 𝑓𝑒 =
𝑃
120
∗ 𝑛
Induced Emf(volts), 𝐸𝐴 = 4.44 ∗ 𝑓𝑒 ∗ 𝐾 𝑤 ∗ 𝑁𝑝ℎ ∗ 𝜑 𝑓
So, 𝐸𝐴 ∝ 𝜑 𝑓
P=no of poles, n=r.p.m, Kw= Kc*Kd, 𝑁𝑝ℎ=no. of turns in series
per phase. 𝜑 𝑓= 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

6. Excitation
Systems
DC Excitation
Self Excited
(DC generators
shaft driven)
Seperately
Excited
(DC Generators)
High Frequency
AC Excitation
Static Excitation
Brushless
Excitation
Types

7. 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

8. 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 loss
3. Relatively small size
4. 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

9. 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 shaft
And 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 maintenance
Disadvantage: 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

10. 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

11. 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 main
factors for excitation systems selection criteria.
 Upgradation of old excitation system can lower operational cost and imporve efficiency of
a power plant.