powertech - gentesting_brochure

7/27/2019 PowerTech - Gentesting_Brochure

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It is well known that accurate simulation models for generatorsand their controls are key for predicting plant and system

performance under various conditions and contingencies.

These models are critical in identifying operational problems,

conducting post-mortem analyses, and establishing secure

limits for system operations. In addition, these models are

used extensively in planning power system enhancements

and designing protection systems including generation

rejection and load shedding schemes. Recent power system

blackouts have highlighted the need for accurate models

and, as a result, many system reliability bodies have

implemented mandatory generator testing programs that

require the field testing of generating units to confirm their

dynamic performance, and to develop and validate

corresponding simulation models and parameters.

In addition to improving the predictability of system

performance, a significant economic benefit can also be

achieved by using the derived models for accurately

determining system security limits. System operating

security limits are generally determined based on

simulation studies. If the simulation models used produce

pessimistic results (simulated system is less stable than the

actual system), transfers or load serving capability may

have to be restrained unnecessarily. Unnecessary

generation or load shedding during a disturbance may

also be invoked. If, on the other hand, models produce

optimistic results (simulated system is more stable that the

actual system), system disturbances or even costly

system blackouts could occur under conditions which

were shown to be secure in simulations.

Other benefits of generator testing include identifying

and correcting equipment problems, tuning controls and

protections, both of which can increase the generating

units ability to withstand disturbances. Powertech has extensive experience in performing

generator tests and in developing and validating proper

simulation models. Powertech has tested hundreds of

hydro, gas and steam generating units, ranging in size

from large to small, manufactured by all majorequipment makers, and equipped with various types of

control and protection systems. Tests can be performed

to establish key system information related to,

• Generator machine parameters

• Speed governing system parameters

• Excitation system parameters

• Reactive power capabilities

• Protection and control performance



Test Procedures

After reviewing the plant documents such as unit design

data and curves, control diagrams and schematics of

excitation and speed governing systems, Powertech will

first develop a detailed test plan.

To minimize unexpected results during the site testing,

pre-test simulations will be conducted to examine theadequacy of proposed test conditions and disturbances

to be applied, and to assure safety and success of

testing. Powertech will then visit the plant to execute the

test plan with the assistance of plan personnel. For most

units, the compete tests can be completed in one or two

days, including tailboard meeting, test set-up and test

execution.

Once the field tests are completed, model validation will

be conducted based on the field measurements using

curve-fitting techniques.

Typical Tests

A number of tests can be performed on the generators

including the following,

Generator Tests are performed to validate generator

reactances and time constants provided by

manufacturer, or to derive model parameters for units for

which no manufacturer’s data is available. The tests

usually include, •

•

•

•

•

•

open-circuit saturation tests,

field short-circuit tests,

d- and q-axis current interruption tests.

Data provided by manufacturers are often design data,

or typical data which may have considerable variations

from actual field values.

Excitation System Tests are performed to derive gains

and time constants describing the voltage regulator,

over- and under-excitation limiters, and maximum field

forcing capabilities. Typical tests include, exciter step and frequency response tests

limiter functionality and performance tests,

reactive load rejection tests.

There is increasing number of older exciters being

retrofitted with newer digital controls, and control settings

may be modified from time to time. Therefore, the

excitation tests should be performed whenever changes

occur.

Governor Tests are performed to determine turbine and

governor time constants, speed droop settings, and gate

or valve opening and closing velocities. Depending on

the type of unit and governor, typical tests include,

•

•

•

partial load rejection tests

water starting time constant test for hydro units

frequency response tests.

Reactive Power Capability Test are performed to obtain

the generator’s maximum reactive power supplying and

absorbing capabilities. The test results are crucial for

determining system voltage security limits.

Power System Stabilizer Tests are performed to identify

power system stabilizer parameters and to assist in tuning

PSS for better performance. The tests usually include step

and frequency response tests, and exciter step response

tests.

13.6

13.7

13.8

13.9

14.0

14.1

0 2 4 6 8

Time in Seconds

G e n e r a t o r T e r m i n a l V o l t a g e i n k V

Simulated

Measured

+

VT

RMINV

1

K

+

+ E

FD

10

EsT

1

F

F

sT1

sK

+

KE

VREF

)(VS EE

RMAX

V

A

A

sT



Test and Model Validation Results Control Tuning

The figure below shows a case of incorrect under excitation

limiter (UEL) settings discovered from actual field testing. The

plot shows that the MEL settings are outside of the generator

capability curve; the limiter will never have a chance to act

as intended.

Once the field test are completed, they can be used to

develop and validate simulation models. The figure below

shows a typical exciter step response test for a generator with

a rotating DC exciter. Also shown is the response of the

model which was derived from the test.

Power system stabilizers (PSS) have been extensively used

in power systems as a very effective means to provide

damping of electro-mechanical oscillations. Successful

application of power system stabilizers depends on the

careful design of their functional structure and regular

tuning of its parameters in order to accommodate the

ever changing system characteristics and conditions.

In order to properly tune controls, detailed simulations

are performed using full power system models todetermine the best parameters for the excitation syste

including the PSS. In this approach, a wide number of

system conditions and contingencies can be examine

as well as the interaction with other generators and th

controls. The tuning process can be conducted

manually, using traditional control tuning methods, or

with Powertech’s Control Design ToolboxTM.

After suitable parameters are determined from

simulation, they can be applied and verified in the fiel

Some parameters may be further tuned in the field to

ensure that the settings provide the most damped

response.

Validated Model

IEEE Type ST1 Exciter Model & Parameters

Validated through Field Measurement

The final results of the model validation procedure are, for

each generator and it’s associated controls, a suitable set of

simulation model and parameters which best reflect the

actual performance of the devices. An example for an

exciter is shown below.

Results of Proper PSS Tuning

Powertech's Control Design Toolbox TM for PSS Tuning



Last modified June 2005 Powertech Labs inc. All Rights Reserved

www.powertechlabs.com

Other Powertech Services

• Evaluation of transfer capability and security limits

Powerflow analysis

Transient Stability analysis

Small-Signal Stability analysis

Voltage Stability analysis

• Post-mortem analysis of system disturbances

• Frequency control assessment

Islanding studies

AGC & governor performance

Design and evaluation of under-frequency load-shedding schemes

• Increasing transfer capability

Control-tuning and design

Load shedding schemes

Reactive compensation planning

Special protection system design and verification

• Assessment of planning alternatives

• Custom modelling & dynamic model reduction

• Reliability Assessment of power systems

• Generator field testing, model development &

validation

• Load characteristic measurement and modeldevelopment

• Custom software and model development

• Training

In addition to extensive power system study capabilities,Powertech has a $50 million lab and test facility which

includes high voltage, high current, and high powerlabs, as well as capabilities in hydrogen technologies,

chemistry, metallurgy, and materials engineering.

Tabula Data Acquisition System

TABULATM Data Acquisition System

Powertech has developed a specialized dataacquisition system for generator testing and other field

measurement tasks. The system is composed of a laptopcomputer with a data acquisition card, custom signalconditioning hardware, and a suite of software programs

designed to meet specific field-testing requirements . Themain features include,

• High resolution: 16 bit resolution, 16 channels at up to20 kHz total sampling rate

• High speed: 12 bit resolution, 16 channels at up to 200kHz total sampling rate

• Full signal conditioning and isolation modules

• Real-time display of RMS, raw waveforms of measuredquantities

•• Automatic calculation and logging of voltage,current, phase, power, frequency, etc.

• Full analysis, display, plotting and data-exportingcapabilities

• Timed or triggered recording, suitable for long-termunattended monitoring

For more information contact

Powertech Labs Inc.12388-88th AveSurrey, British ColumbiaCANADA V3W 7R7

Phone (604) 590-7470Fax (604) 590-8192Email [email protected] www.powertechlabs.cSoftware www.dsatools.com

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