bdpp

DIGITAL EXCITATION SYSTEM IN BDPP

By Group :12Under the Guidance of Ms:-SOUMYA.C

Group Members

1. ANN MERIN TONY (JYAJEEE-010)

2. CHACKO J CHEMBUKKAVU (JYAJEEE-013)

3. DITTO DAVIS (JYAJEEE-019)

4. RIMA JOY (JYAJEEE-050)

5. SHIBIL DAVID (JYAJEEE-055)

OVERVIEW• Objective of project• Base paper• Reference paper• Brushless excitation• Automatic voltage regulator• Digital excitation• Improvements in diagnostics• Literature survey• Conclusion• References

Objective of Project

• Elaborate study of brushless excitation system at BDPP• To improve the overall efficiency• Brushless excitation system as the name indicate does not

require any sliding contacts or brushes• It can be used for all type of alternators; temperature control

is possible, fast response to load changes. • The regulation system ensures through its electronic circuit

the generator voltage regulation, the control of the thyristor and protection of the excitation system

• The regulation is done using automatic voltage regulator (AVR) which includes use of many electronic cards.

BASE PAPER:-

“DIAGONOSTIC EXCITATION ENHANCES PERFORMANCE AND DIAGONOSTICS”• This paper presents new digital excitation systems are being introduced that provide many advantages over existing systems•some of the previous limiter functions modifies the pickup point based on external conditions• It allow the generator to operate closer to its design limit and help keep the unit online during adverse conditions, increasing reliability and reducing down time• In the past, only a limited amount of information was available to help the user diagnose problems in the excitation system.• Other improvements include internal transducers, digital control relay

logic, enhanced communication capabilities, internal simulators, and improved thyristor firing- control algorithms,

Reference paper:-

Commissioning Experiencewith a Modern Digital Excitation System

• This paper presents design,testing,commisioning and operational experience related to a modern digital excitation system.

• It compares the digital and analog regulators in terms of efficiency of commissioning and the resulting system performance.

• Digital regulator allows ease of custom design of the regulator settings to match the exciter and the generator, resulting in efficient commissioning.

BRUSHLESS EXCITATION

BRUSHLESS EXCITATION

• The pilot exciter is a permanent magnet alternator

• After rectification, the controlled dc output is supplied to the stationary field winding of the main exciter

• A signal,picked from alternator terminals through CT and PT,controls the firing angle of the thyristor bridge

• Does not require any sliding contacts and brushes

DISADVANTAGES:-

• Brushless excitation systems is slow in response to fast load changes. 

• Utilities require large generators need to have fast acting voltage regulation.  The inherent delay of the brushless system and the inability to reverse the field voltage was not acceptable to many utilities  

• A large generator required a large (heavy) field winding and diode assembly that created mechanical design problems.  

• The present excitation system will not measure the temperature of the rotor.

•   It can be used only in medium type alternators.

AUTOMATIC VOLTAGE REGULATOR

• A voltage regulator is defined as a device for varying the voltage of a circuit or for automatically maintaining it at or near a prescribed value.

• The term automatic voltage regulator covers the apparatus used in the methods of obtaining a constant voltage.

• There are two general methods of obtaining a constant direct or alternating voltage is :

1. By the control of the output voltage of the generator

2. By the corrections of the normal supply voltage

REQUIREMENTS FOR AUTOMATIC VOLTAGE REGULATOR

Voltage regulators for synchronous generators must satisfy the following conditions

1. Regulation to counter the disturbances must take place as rapidly as possible

2.  The revolving field must be protected against overload by a limit device in the regulator.

3. The rated voltage must be easily adjustable on the regulator

4. Proper sharing of reactive load must be assured were several generators are connected in parallel Supply-type automatic voltage regulator.

GENERATOR TYPE AUTOMATIC VOLTAGE REGULATOR

• It is a control device which automatically regulates the voltage at the exciter of an alternator , to hold the output voltage constant with in specified limits.

• The characteristics of the driving source since changes in speed cause variations of voltage.

• In the case of alternating current, the power factor of the load , since this in conjunction with maximum and minimum load on the generator will determine the range of field current required.

DIGITAL EXCITATION

• New digital excitation systems are being introduced that provide the user with many advantages over the existing excitation systems.

• New limiter functions and monitoring capabilities have been added.

• These enhancements allow operation of the generator closer to its design limit and help keep the unit on line during adverse conditions thus increasing reliability and reducing down time.

• With the new systems, this information is readily available internally and can be stored digitally and retrieved later for analysis.

CONTD:-

• This systems include a variety of functions 1. Overexcitation limiter

2. Under excitation limiter

3. Volts per hertz (overvoltage) limiter

4. Ground detector

Fig. for Digital excitation

Description for the fig.:-

• The controller parameters are determined with several excitation system parameters, such as voltage loop gain and open-circuit time constants.

• input power voltage via power potential transformer (PPT) to the bridge rectifier as shown in Fig.

• To tune the digital controller, two methods are used:-

1.pole-placement method

2. cancellation approach• Every PID controller contains one pole and two zero

terms with low-pass filter .

CONTD:-

• For generators containing rotating exciters, the machine contains two open-loop poles, one from the main field and the other from exciter field.

• A pole represents a phase lag in the system while the zero tends to provide a phase lead component.

• The location of poles and zeros with relation to the exciter and generator field poles determines the performance of the excitation control system.

MAIN FEATURES:-

Four excitation control modes

1 Automatic Voltage Regulation (AVR)

2 Field Current Regulation (FCR)

3 Power Factor (PF)

4 Var

1. VOLTAGE REGULATION:-

By using DSP and regulation algorithms, it regulates the Generator rms voltage to within 0.2% of the set point from no-load to full-load.

  2.CONTROL OUTPUT:-

  The DECS supplies an isolated control output signal of 4 to 20 mA DC, 0 to 10 V DC, or ±10 Vdc to the firing or control circuits of external power stages. The DECS can control virtually any bridge that is capable of accepting these signals and is suitable for use on synchronous generators or motors.

3.STABILITY:-

PID stability control is utilized by the DECS Preprogrammed stability (PID) settings are provided for both main field and exciter field applications. Additional stability adjustments are provided for customizing the stability and transient performance of the minimum and maximum excitation

limiters and power factor controllers.  4. POWER SYSTEM STABILIZER :-

The PSS can also be set up to respond only to frequency if required for unusual applications. Inputs required for PSS operation include three phase voltages and two or three phase

line currents.

5.REGULATOR

• The regulator is made up of two racks equipped with electronic parts. The front plates of these cards include test points and LED lights.

• The regulation system ensures through its electronic circuits the generator voltage regulation, the limits, the control of the thrusters and the protection of the excitation system.

• All operation sequences are ensured by relays.• Controls are performed by local or remote action.• Two channels are provided in the regulator:

1. AUTOMATIC channel(generator voltage regulation)

2. MANUAL channel(exciter field regulation) 

 IMPROVEMENTS IN DIAGNOSTICS

1.EVENT RECORDERS:-• These recorders are of particular use in diagnosing problems or

mis operations that may occur.• The event can include generator terminal voltage, line current,

watts and vars, field current, and key internal exciter signals. • Another benefit of the internal recorder is that separate

transducers are no longer needed.

2. DATA LOGGERS•  The newer digital excitation systems contain internal recorders

that permit the gathering of data over longer periods of time. •  The logged data can then be saved in a file for storage or use

in a database.

3. FIELD GROUND DETECTORS• A field ground detector checks the integrity of the

insulation between the field conductors and earth ground

4. FIELD TEMPERATURE MONITORS• On some turbine generator units, a field temperature

monitor is used to help assure that the thermal capability of the rotor is not exceeded.

5 . BRIDGE TEMPERATURE MONITORS• The newer digital excitation system contains RTDs

mounted in the thyristor bridges, internal transducers

Literature Survey

DECS- Godhwani,A.Southern Illinois Univ., Edwardsville, IL Basler, M.J. “A digital excitation control system for use on brushless excited synchronous generators”, IEEE Trans , Volume: 11  , Issue: 3 Page(s): 616 - 620  Sep 1996

AVR-“A novel digital Automatic Voltage Regulator for synchronous generator” Weilin Li E.ON Energy Res. Center, RWTH Aachen Univ., Aachen, Germany Xiaobon Zhang, Huimin Li, IEEE Conference, Power System Technology (POWERCON), 2010 International Conference on 24-28 Oct. 201

“Tuning a PID Controller for a Digital Excitation Control System”-Kiyong Kim, Member, IEEE, and Richard C. Schaefer IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 41, NO. 2, MARCH/APRIL 2005

ConclusionNew digital excitation systems include a variety of

functions that existed before, but which have new and enhanced features incorporated into them.

These functions include the OEL, the underexcitation limiter, the volts/Hertz (overvoltage) limiter, and ground detector.

The newer excitation systems also include a variety of new functions. These include the bridge temperature limiters and temperature monitors.• These include transient event recorders, data loggers,

and field temperature monitors.

REFERENCES:-

• Maintenance manual Of B.D.P.P• Operational manual Of B.D.P.P • Chiu T. Law, Member, IEEE, Kalu Bhattarai, Member, IEEE,

and David C. Yu, Member, IEEE” Fiber optic based fault detection in power systems” ,” IEEE Trans. Power Del.,

• D. C. Yu, J. C. Cummins, Z. Wang, H.-J. Yoon, and L. A. Kojovic, “Correction of current transformer distorted secondary currents due to saturation using artificial neural networks,” C vol. 16, no. 2, pp. 189–194, Apr. 1996.

• W. F. Ray and C. R. Hewson, “High performance rogowski current transducers,” in Proc. IEEE Industry Application Conf., 2000, vol. 5, pp. 3083–3090