EX2100 and EX2100e excitation control power system stabilizer

EX2100 and EX2100e Excitation Control Power System Stabilizer GEH 6676E EX2100 and EX2100e Excitation Control Power System Stabilizer User Guide GE Internal These instructions do not purport to cover.

Power System Stability

This document requires a basic understanding of synchronous machines and electric power flow.

Ensuring a reliable electricity supply relies heavily on machine stability in power systems Synchronous machine stability is essentially defined by the system's ability to maintain consistent voltage and frequency levels despite unexpected load fluctuations between generators This stability is crucial for preventing power outages and ensuring smooth, continuous operation of electrical grids Maintaining machine stability involves monitoring load changes and adjusting system parameters to preserve voltage and frequency consistency, thereby supporting overall grid reliability and efficiency.

System stability is achieved when, following a transient event, the machine's voltage and frequency oscillations are sufficiently damped to restore steady-state operation Stability can be classified into dynamic stability, which concerns the system's ability to return to equilibrium after small disturbances, and transient stability, which relates to the system's capacity to withstand significant transient events without losing synchronism Ensuring proper damping of oscillations after disturbances is essential for maintaining reliable and stable power system operations.

Dynamic Stability: Also known as steady-state stability, allows a system to correct for small changes.

Transient stability is the system's ability to recover from significant disturbances, such as electrical faults cleared by instantaneous load rejection via circuit breakers If sufficient synchronizing torque is present, the power system remains stable and maintains synchronization, ensuring reliable operation during and after large perturbations.

Modern generating units with high-gain voltage regulator systems enhance transient stability but may negatively impact dynamic stability Power System Stabilizers (PSS) play a crucial role by improving small signal (steady-state) stability through damping oscillations in the power system using generator excitation modulation Ensuring optimal implementation of these technologies is essential for maintaining overall system stability and reliability.

Synchronous Machine Oscillation

Synchronous machine oscillation is the behavior of machines closely connected to a system.

The PSS provides the control action that allows the power system to maintain stability.

During a system transient, it is essential that all rotor angles change in the same relative direction over time to maintain system stability While the variation of an individual machine's rotor angle is important, the primary focus is on the rotor angle differences between machines, which are critical for understanding and analyzing synchronous machine oscillations Monitoring these angle differences helps ensure reliable operation and prevents system instability during transient events.

Synchronous machine oscillation often falls into one of the following four categories:

• Local machine-system (local mode)

Local mode typically involves one or more synchronous machines at a power station operating in tandem against a larger power system or load center These generators often operate within a frequency range of 1.0 to 2.0 Hz, with some low inertia turbine generators reaching frequencies up to 4.0 Hz This mode ensures synchronized operation and stable power delivery to the grid.

Inter-areausually involves combinations of many synchronous machines in one part of a power system swinging against another part of the system The frequency range is 0.1 to 0.7 Hz.

Inter-unittypically involves two or more synchronous machines at a power plant, or nearby power plants, in which machines swing against each other The frequency range is 1.5 to 3 Hz.

Torsionalinvolves relative motion between a unit's rotating elements (synchronous machine, turbine, and rotating exciter), with frequencies ranging from 15 Hz for two-pole

(8 Hz for four-pole) and above.

System Modeling

The PSS provides a positive contribution to the damping of the generator rotor angle swings.

High-gain, fast-response static excitation systems significantly enhance transient stability by improving the synchronization torque However, they can negatively impact small signal stability by reducing damping torque Additionally, Power System Stabilizers (PSS) play a crucial role by positively contributing to the damping of generator rotor angle oscillations across a wide range of system frequencies, thus ensuring overall power system stability.

The simplified block diagram illustrates a single generator connected radially to an infinite bus power system, highlighting the impact of excitation systems on damping local mode machine oscillations The generator features an Automatic Voltage Regulator (AVR) that influences the generator's response The small-signal dynamics are represented by the linearized swing equation, showing both mechanical and electrical loops that govern the system's stability Phase relationships demonstrate that positive synchronizing torque, enhanced by modern high-gain wide-bandwidth excitation systems, stabilizes the rotor around its steady-state by adjusting its speed Additionally, a positive damping torque, which can be reduced by advanced excitation controls, helps dampen rotor oscillations within the torque-angle loop Proper phase compensation in the exciter control enables the generation of air gap torque to effectively suppress oscillations and ensure system stability.

The addition of a Power System Stabilizer (PSS) to the control system enhances small signal (steady-state) stability by providing positive damping torque that counteracts the negative effects of the Automatic Voltage Regulator (AVR) This is achieved by generating a signal in phase with rotor speed and combining it with the AVR reference, thereby improving system damping To address the inherent phase lag in the generator's field circuit and AVR function, a phase lead is incorporated to ensure accurate compensation and optimal system performance.

Single Machine Connected to Bus Power System with PSS

K 1 Change in electrical torque due to a change in rotor angle assuming a constant d-axis flux

K 2 Change in electrical torque due to a change in d-axis flux assuming a constant rotor angle

K 4 De-magnetizing effect due to a change in rotor angle

K 5 Change in terminal voltage due to a change in rotor angle assuming a constant voltage from d-axis flux linkages

K 6 Change in terminal voltage due to a change in d-axis flux linkages assuming a constant rotor angle

Most coefficients (K1 through K6) are influenced by the machine’s operating point, with all typically remaining positive to ensure system stability However, under heavy load conditions, K5 can become negative, potentially leading to system instability.

Implementation

The primary function of the Power System Stabilizer (PSS) is to add damping to power oscillations, making signals that clearly exhibit these oscillations ideal as input options Suitable signals for PSS input include direct rotor-speed measurement, bus frequency, and electrical power, which are readily accessible in power systems When selecting the appropriate input signal, system design considerations are crucial; for example, direct rotor-speed measurement may be vulnerable to torsional interactions within turbine-generators, which can affect signal accuracy and system stability.

502 Bad GatewayUnable to reach the origin service The service may be down or it may not be responding to traffic from cloudflared

Refer to the section,Integral of Accelerating Power.

The classic example of inter-area mode oscillation is the 0.3 Hz mode in Western US

PSS performance is primarily assessed by analyzing the damping of the local mode, which reflects the generator's oscillation against the power system at frequencies typically between 0.7 and 2 Hz System conditions such as stronger ties and lighter loading lead to higher local-mode frequencies, while weaker ties and heavier loading result in lower frequencies Proper tuning of the PSS is crucial to ensure effective damping across various operating scenarios, including outages and load variations Advanced mathematical models, beyond simplified representations, are employed to accurately predict PSS performance under both steady-state and transient conditions, enhancing overall system stability.

Accelerating power measurement relies on accurate inputs of speed and electrical power to ensure precise results The EX2100e control system for PSS implementation requires at minimum a 3-phase potential transformer (PT) and a single-phase current transformer (CT) For optimal performance, it is recommended to use two single-phase CT inputs, enhancing measurement accuracy and system reliability.

The integral of accelerating power principal is based on generator electro-mechanical equations The dynamic equation for rotor speed, as a function of torque, is as follows:

Synchronous Machine Swing Equation where: ω = rotor speed

H = generator inertia constant (MW-sec/MVA)

Te= electro-mechanical (air-gap) torque

In a per-unit (pu) system, torque and power are numerically equivalent, simplifying analysis and calculations By substituting torque (T) with power (P) and rearranging the Synchronous Machine Swing equation, engineers can effectively determine the mechanical power output of the system This approach streamlines the process of analyzing synchronous machine behavior, making it easier to assess performance and stability in power systems.

Mechanical Power Equation where the derivative operator has been replaced by the equivalent Laplace operator,s.

Measuring mechanical power directly is challenging in practical applications; however, this equation enables the synthesis of the mechanical power signal from easily obtainable measurements of speed and electrical power Since electrical power can fluctuate rapidly during transient events in the power system, and mechanical power changes gradually in ramp-like patterns, a specialized low-pass filter (ramp tracking) is employed to effectively filter and stabilize the synthesized mechanical power signal The process of deriving mechanical power is visually illustrated in the accompanying figure, highlighting the integration of measurement data and filtering techniques to achieve accurate power analysis.

The ramp tracking filter is represented asG(s).

The mechanical power signal, with the prime superscript, is represented asP'm, indicating that this is a synthesized signal.

The next step involves developing the accelerating power signal, defined as P'acc = P'm - Pe This accelerating power is considered a synthesized or derived signal because it is generated from the combined mechanical power components Understanding this derivation is essential for accurate analysis of system performance and energy dynamics.

Integral of Accelerating Power GEH-6676E User Guide 13

In power system stability studies, both speed and electrical power signals typically exhibit steady-state values and may experience slow variations over extended periods To effectively analyze these signals, most Power System Stabilizer (PSS) designs incorporate high-pass filters that remove low-frequency components These filters also serve as washout filters, filtering out undesirable low-frequency signals to enhance system stability The washout filter's specific design ensures that only relevant dynamic signals are emphasized, improving the accuracy and effectiveness of the PSS.

Washout Filter Format whereT W is the washout time constant, normally set in the range of 2 to 10 sec This gives a break frequency of 1/T W rad/sec.

The final step involves dividing both inputs by the factor2Hand, effectively equivalent to division by sin in Laplace terminology This process is essential for developing the integral of accelerating power The corresponding block diagram illustrates the core steps in this integration process, providing a clear visual representation of how the acceleration power is integrated within the system Understanding this division and the block diagram is crucial for accurate power analysis and dynamic system design.

Integral of Accelerating Power Block Diagram

The equation 1/(2H) multiplied by the integral of accelerating power represents speed If mechanical power could be precisely calculated, this equivalence would hold true Due to the method used to derive the mechanical power signal, the input exhibits speed characteristics at lower frequencies and electric power characteristics at higher frequencies.

The derived signal exhibits a low torsional mode component, which is crucial for maintaining Power System Stabilizer (PSS) performance by preventing interactions with turbine-generator torsional responses To ensure stability, the integrator cancels the washout in the electric power signal path, with a double washout applied in both the speed and power pathways This approach helps mitigate potential issues related to torsional dynamics, enhancing the overall effectiveness of the PSS in power system stability.

EXDSPEED

The integral of accelerating power signal,EXDSPEED, is determined using the following equation:

A signal proportional to rotor speed is used to calculate the internal machine voltage, Eq', by multiplying the generator current by the d-axis transient reactance, X'd, and adding it vectorially to the terminal voltage This internal voltage reflects the dynamic behavior of the generator during operation Additionally, any phase deviation of Eq' indicates a change in rotor speed relative to the synchronous speed, providing a critical measure for controlling and monitoring generator performance.

The EX2100 control calculates the electrical power signal using generator voltage and current measurements Both the rotor speed and power signals are processed through two washout stages, which effectively eliminate low-frequency components to ensure accurate readings.

The EXDSPEED signal provides an accurate measure of rotor speed by integrating the difference between Pm and Pe and dividing by 2H, ensuring responsive and reliable performance It minimizes phase lead at low frequencies, reducing adverse effects on synchronizing torque during generator operation Additionally, EXDSPEED is less affected by voltage offsets at the generator terminals, which can result from rapid mechanical power fluctuations in electrical power system stabilizers (PSS) This makes EXDSPEED an essential signal for maintaining stable and efficient generator synchronization and control.

The EXDSPEED signal undergoes comprehensive processing through two lead/lag stages, an adjustable gain stage, and an output limiter stage, ensuring the Phase Shift System (PSS) is precisely tailored to meet specific application requirements.

Some 4-pole nuclear units require band reject filters to effectively reduce torsional oscillations, ensuring stable operation The third lead/lag stage functions as the low-frequency equivalent of a two-stage torsional filter, highlighting its role in mitigating torsional vibrations within power systems Implementing these filters is essential for maintaining system stability and preventing mechanical stress on turbine-generator components.

PSS2B

The PSS2B PSS model conforms with the standards on excitation systems, identified as IEEE 421/5-2005.

The integral of accelerating power serves as the input to the Power System Stabilizer (PSS) component responsible for phase compensation, typically utilizing two or three lead/lag stages This input also incorporates a gain and output limit function to ensure effective stabilization The IEEE®-type PSS2B model specifically accepts these inputs, facilitating accurate and reliable power system damping and enhancing overall grid stability.

The EX2100 and EX2100e control implementation of an integral of accelerating powerPSS is available in a standard form A specialized version with Biquad ™ filters is also available.

Integral of Accelerating Power PSS Standard Form

Integral of Accelerating Power PSS with Biquad Filters

Initial Performance Testing and Configuration

Enable/Disable and Active/Inactive

The PSS (Power System Stabilizer) can be activated or deactivated via operator interface commands on the turbine control or exciter interface, allowing operators to enable or disable it at any time and under any load conditions.

The PSS is activated by sending an aPSS Enable command via an Ethernet Global Data (EGD) connection to the exciter controller This process can be performed using the turbine control operator interface screen or other operator interface devices such as a keypad or touchscreen Properly enabling the PSS ensures effective wind turbine safety and control, contributing to optimal system performance.

Operation and Tuning GEH-6676E User Guide 19

PSS Enable Command Block Diagram

The PSS becomes active (in service) or inactive (not in service) based on satisfying operational conditions.

Once enabled, the PSS is not active (available to supply compensation to the AVR input summing junction) until all of the following three conditions are met:

• Exciter must be in Automatic (AUTO) regulator control

• Generator must be online at a load point above the parameter value

In the software,Enabledis also known asArmed, and

The PSS (Power System Stabilizer) remains enabled but becomes inactive if specific conditions are not met Specifically, if the load drops below the designated PSS Lo Watts Disable threshold, the PSS deactivates Additionally, switching the regulator system to manual control or opening the 52G breaker also causes the PSS to become inactive, ensuring proper system operation and stability.

Parameters and Configuration Settings

Parameters and settings are accessible through the Control System Solutions (toolbox) and ToolboxST* application, which offer a comprehensive graphical interface These tools display parameter values, input variables, and output variables for the PSS, ensuring easy monitoring and adjustments Additionally, both applications provide detailed lists of PSS and PSS Biquad parameters for efficient system configuration and optimization.

�� To display the PSS diagram

1 From the toolbox or ToolboxST application, open the applicable exciter file.

2 From the ToolboxSTComponent Editor, select theDiagramstab.

3 From theTree View, selectMain Menu Diagram(toolbox) orOverview

4 Locate the Power System Stabilizer section and clickPSSto display the Power System Stabilizer (PSS) diagram.

Power System Stabilizer (PSS) Diagram (toolbox)

2 From the Outline View (toolbox) or theComponent Editor SettingstabTree View(ToolboxST), expandPower System Stabilizer.

3 SelectParametersto view a list of parameters.

�� To display PSS Biquad parameters

2 From the Outline View (toolbox) or theComponent Editor SettingstabTree View(ToolboxST), expandPower System Stabilizer with Biquad.

3 SelectParametersto view a list of parameters.

4 The following default values disable a Biquad If Biquad is not used in the tuning study, make sure the following parameters are set as follows:

• PSS biquad3 num damp = 0.5 damp

The generator manufacturer supplies this value.

To obtain proper scaling for the synthesized mechanical power signal, the generator inertia constantMis used in the washed out integral of watts path of the PSS.

Select the PSS gain to ensure stable operation across all load points, with the default value typically set at 15 During PSS commissioning, it is essential to verify proper configuration by testing that the gain remains below one-third of the gain setting to prevent instability in the PSS loop Proper adjustment and verification of the PSS gain are critical for maintaining reliable system performance. -**Sponsor**Looking to refine your article and boost its SEO? Let [Soku AI](https://pollinations.ai/redirect-nexad/W1bgrDLp?user_id=983577) handle the heavy lifting! Soku AI can identify and rewrite key sentences to create coherent, SEO-friendly paragraphs, just like focusing on the importance of PSS gain for stable operation, typically defaulted to 15 and adjusted during commissioning, ensuring it remains below 1/3 of the gain setting to prevent instability With Soku AI, transform your content effortlessly, ensuring it resonates with your audience and ranks higher.

3.1.2.3 Lead/Lag 1 and Lead/Lag 2

Select appropriate phase lead and lag time constants to effectively cancel the natural phase lag of the AVR and generator at full load, ensuring optimal system stability Typically, lead values are set around 0.2 seconds, while lag values are adjusted to approximately 0.05 seconds for balanced compensation Proper tuning of these parameters is essential for maintaining reliable generator operation and improved system response.

3.1.2.4 Output Upper and Lower Limits

Set the upper and lower limits on the Power System Stabilizer (PSS) output to prevent it from overriding the main regulator during major disturbances Typical limit values are ±10%, though these can be customized to suit specific system requirements Adjusting these limits ensures a balanced response, maintaining system stability without excessive control interference Proper configuration of PSS output limits is essential for optimal power system stability and reliable operation during large events.

Optimal washout time constants are chosen to allow low-frequency signals of interest to pass with minimal attenuation and phase shift Typically, these time constants are set between 2 to 10 seconds, ensuring effective filtering without compromising essential low-frequency information Selecting appropriate washout time constants enhances filter performance by balancing signal preservation and noise reduction.

The time delay for responses to slow increases in power during system daily load changes This parameter is typically set to 0.1 sec.

3.1.2.7 Hi Watts Enable and Low Watts Disable

When the Power Saver Switch (PSS) is enabled, it automatically activates above the Hi Watts enable setting and deactivates below the Low Watts disable setting, ensuring efficient power management The standard activation and deactivation points are typically set at 15% and 10%, respectively, optimizing device performance and energy savings.

An advanced Power System Stabilizer (PSS) offers up to three stages of biquadratic filtering to effectively eliminate torsional interactions, along with three stages of lead/lag filtering equipped with gain adjustments and output limiting for enhanced control Additionally, it features switchable washout functionality to mitigate voltage fluctuations during large signal events, ensuring improved system stability and performance.

Commissioning and Testing

Initial Conditions Check

Prior to testing, observe the following conditions:

During the PSS test, the exciter must remain in AUTO regulator mode; switching to MANUAL regulator or disabling the PSS if instability occurs is essential to ensure stable operation and prevent instability issues.

Pay particular attention to the information in this section to ensure proper testing.

• Verify that the PSS is disabled and Gain is set to 0 prior to going online to make sure there is no inadvertent activation of the PSS prior to testing.

• Prior to testing the PSS, other offline and online testing should be completed as provided in the following documentation:

− GEH-6631, EX2100 Thyristor Control 77, 53, and 42 mm Installation Startup Guide

− GEH-6674, EX2100 Regulator Control Installation and Startup Guide

− GEH-6694, EX2100 Thyristor Control 100 mm Installation and Startup Guide

• Any deficiencies in PT or CT feedback circuits, including Watts or VAR calculations, should be corrected.

Ensure the unit is capable of full-load operation, which is essential for optimal performance For gas turbine units, operate slightly below full load to enable turbine control to prioritize speed/droop settings over exhaust temperature control If reaching full load isn't feasible, operating close to full load is generally acceptable to maintain efficiency and stability.

GE Internal conducts testing at over 80% of full load; if site conditions necessitate, consult with Energy Consulting or the tuning study provider to assess whether operation at reduced load is acceptable.

It is strongly recommended to conduct all testing with the unit operating at near unity power factor (0 MVars) to ensure accurate and consistent results For optimal testing conditions, maintain the same load and VAR levels as closely as possible throughout the process Performing tests under these standardized conditions helps achieve reliable data and validates the unit’s performance effectively.

• Any other outer loop regulator functions in EX2100/EX2100e, turbine, or plant controls, such as VAR/PF and auto power (MW) load changing, should be turned off or disabled.

Review the PSS parameters in the exciter configuration file using the tuning study provided by GE to ensure accuracy and completeness If Energy Consulting does not supply the configuration settings, contact the nearest GE sales or service office or an authorized GE representative before implementing customer-specific or default settings.

Incorrect and/or default settings may result in unstable unit operation or inadequatePSS operation.

Gain Margin Test

The stability point of the Power System Stabilizer (PSS) depends on factors such as system configurations, the size of the unit relative to the local grid, and transmission characteristics To identify the instability point, the exciter should be operated with the PSS active while gradually increasing the PSS gain until instability occurs Typical PSS gain settings range from 6 to 15 per unit for two-lead-lag designs, and 24 to 60 per unit for three-lead-lag designs Testing involves increasing the gain up to four times the recommended nominal value to ensure system stability.

Without a PSS tuning study recommendation, a PSS gain of 10 pu should be used Do not exceed four times this gain during gain margin testing.

Higher gain operation can be used but should be confirmed by GE.

GE recommends maintaining a minimum gain margin of 10 dB, which is three times the nominal set gain, to ensure system stability During testing, gain is typically increased up to four times the nominal value to evaluate stability margins If instability occurs at a certain gain level, the final gain should not exceed one-third of that instability gain to prevent system instability Proper gain margin management is essential for optimal system performance and reliable operation.

�� To test the gain margin

Refer to the section,Initial

1 From the PSS diagram, set the parameterPSS Gainto an initial value of 0 pu. Perform all PSS testing at 80% load or higher and close to unity power (0 MVars).

2 With the exciter in AUTO regulator, enable the PSS using the keypad or turbine operator interface If the unit is above the value ofPSS Hi Watts, the PSS should be enabled and active.

Exciter in AUTO regulator with PSS Enabled

3 Configure the Trender to monitor the variables in the following table in real time.

GN_VFLD for Bus-Fed systems, or REGEXCURR for Brushless systems AFFL < 10A

To optimize your trend recording, set theTrend Recorder Configuration’s sample interval to 32 ms, ensuring accurate data capture Additionally, configure the Trender Time Axis to 300 seconds, allowing the entire trend to be visible throughout the test for comprehensive analysis.

Refer to the figure,Unstable

4 Start recording the variables for 30 sec, then increase the PSS gain from 0 pu to normal gain setting and watch the variables for signs of instability Instability would be recognized as sinusoidal swings in power, VARs, or voltage These swings usually start small and increase in amplitude over time Additionally, the power swings could occur suddenly at a fixed-amplitude of oscillation If either phenomenon is observed, select PSS disable from the keypad, COI, or turbine control.

Tip � Have someone standing by to disable the PSS if necessary.

Refer to the following figures for examples of unstable and appropriate gain margin tests.

5 Hold at nominal gain for 60 sec, then continue to increase the PSS gain to twice, three times, and four times nominal gain Hold at each point for 60 sec The oscillations in the MW trend begin to grow and have longer settling times Watch for any signs of instability and select PSS disable if this occurs When four times nominal gain is complete, reduce the gain back to zero, continue recording for 30 sec, then stop the Trender.

6 After test completion, review the trend for signs of instability using the provided gain margin test examples If instability is or has been observed, contact the tuning study provider for changes and leave the PSS disabled with PSS Gain = 0 until stability has been corrected Repeat testing as necessary.

7 If no instability is found, the nominal gain setting can be used for the remainder of the test SelectPSS disabledand reset PSS gain to 0 before continuing.

Once a final gain setting is obtained, use the Trender to monitor generator watts at this setting for at least five minutes to verify that no instability occurs.

Note Gain optimization is not required to obtain acceptable performance Most applications provide adequate damping to local mode operations with a PSS gain of 15 or less.

Unstable Gain Margin Example (Brushless Regulator)

Noisy but no Instability and Good Gain Margin Example (Bus Fed)

Standard (Good) Gain Margin Example (Bus Fed)

Online AVR Step Test with PSS Disabled

This test provides a baseline of

AVR operation with the PSS disabled for comparison with the PSS enabled.

Before activating the AUTO regulator, ensure that the AVR step is set to a maximum of 2%, maintaining optimal control and stability If specified by the tuning study provider, a slightly higher setting of up to 3% may be acceptable Proper configuration of the AVR step percentage is essential for efficient regulator performance and accurate voltage regulation.

This testing changes the output of the generator and can rarely cause local instability on some power systems.

To demonstrate PSS effectiveness, step the AVR with the PSS disabled.

�� To step the AVR with PSS disabled

1 Verify that the PSS Test Capture block is configured correctly for the type of unit (Bus Fed [Static] or Brushless) If change is required, minor differences will be displayed.

Refer to related documentation listed in the section,Initial

2 Perform Validate/Build/Download usinginitialize all constantsin accordance with the appropriate installation and startup guide.

PSS Capture Block (Bus Fed)

3 Configure the step wizard for an AVR regulator 2% step Verify the configuration settings are as displayed in the following figure.

Frequency (BODE) Analysis or Step Test of Regulator Loops Diagram

Refer to related documentation listed in the section,Initial

4 For redundant control systems, perform the teaching of new settings to other controllers in accordance with the appropriate installation and startup guide.

5 ClickStart / Stop Analysisto initiate the AVR step test.

6 Upload the PSS Test Capture Buffer to the Trender.

The MW unit, highlighted by the green trend in the trend file, exhibits oscillations that correspond to the natural damping characteristics of the system In larger systems and with bigger generators, more oscillations are typically observed before the MW readings stabilize, reflecting complex dynamic responses Monitoring these oscillations is essential for understanding system stability and ensuring optimal generator performance.

AVR Step Test Capture Buffer with PSS Disabled

AVR Step Test with PSS Enabled

1 From theFrequency (BODE) Analysis or Step Test of Regulator Loopsdiagram, set

PSS Gainto nominal and selectPSS enable.

2 Step the AVR with PSS active.

3 Upload the PSS Test Capture Buffer to the Trender There should be a marked difference (decrease) in the number and amplitude of oscillations in the power (MW) variable on the Trender This demonstrates the effectiveness of the PSS.

AVR Step Test Capture Buffer with PSS Enabled

Impulse Test with PSS Enabled or Disabled

This test enhances the analysis of the PSS (Power System Stabilizer) and demonstrates its effectiveness in improving system stability Similar to the Step Test, it introduces a high AVR (Automatic Voltage Regulator) step change over a short duration The test results show that this method minimizes terminal voltage variations while increasing MW oscillations, providing valuable insights into the PSS performance.

�� To perform an impulse test

PSS Gainto nominal and selectPSS enable.

2 Configure the variables as follows:

• Set ACL Bode Level = 0.05 (5%); can use up to 0.08 (8%) if requested by tuning study provider)

• Set (CRITICAL) Set Step Time = 0.1

• Set the rest in accordance with standard step test setup.

3 For redundant control systems, after the configuration settings are complete, perform the teaching of parameters.

4 ClickStart/Stop Analysisto initiate the impulse test.

5 Upload the PSS Test Capture Buffer to Trender.

6 SetPSS Gainto 0 and selectPSS disable Repeat the test and upload the PSS Test

Activating the Capture Buffer to the Trender significantly reduces the number and amplitude of oscillations in the power (MW) variable, especially when PSS is enabled This noticeable decrease highlights the effectiveness of the Power System Stabilizer (PSS) in enhancing system stability Implementing the Capture Buffer with PSS clearly results in a more stable power output, ensuring improved performance and reliable grid operation.

Impulse Test with PSS Enabled

Impulse Test with PSS Disabled

AVR Closed Loop Frequency Response

During frequency response tests, the AVR setpoint may fluctuate randomly, leading to terminal voltage variations of up to ±1% and causing VAR swings It is essential to monitor the MW closely for any significant or sustained oscillations and to halt the test if necessary Prior notification should be provided to operations before initiating the test, but the test should only be stopped if major system issues are identified, not for individual unit concerns.

�� To perform the AVR Closed Loop Frequency Response

For Excitation Control Help, right-click in an empty white space on the diagram and selectItem Help.

PSS Gainto 0 and selectPSS disable.

2 Verify that the DSPX block exists somewhere (it may be a different block number) within the variable,AVR_TSK, to transfer PSS lead/lag output toDSPXfor trending in the DSPX capture block during testing.

3 Verify that the connection is made on the diagram for the PRBS block to be input to the AVR.

Note In the AVR step test procedure, connection was configured to Step Source so that the step test would be input, not the PRBS data.

Set PRBS Step Source to PRBS source

Set PRBS/Step Source to PRBS Source.

4 To get the AVR frequency response, from the right side of the diagram configure the parameters as displayed in the following figure. closed loop transfer function measurement

Verify that these settings are correct for AVR closed loop transfer function measurement.

5 ClickStart / Stop Analysis TheAt NowPassbox displays the current pass. When the test is finished, theBode averaging donecoil becomes true (represented by a black square).

6 From theBlock Collectedmenu, select the DSPX Capture Buffer Perform an upload and selectChange without Save.

The diagram displays the input signal (AVR setpoint) and output (AVR feedback), which is the terminal voltage To understand its relationship to the system's frequency response, the signal must be processed to determine the transfer function Analyzing this transfer function is essential for assessing the system's behavior across different frequencies.

The field engineer should verify the following information when the data is collected:

• Input signal is small relative to normal feedback signal

A key aspect of non-invasive measurement is ensuring that noise input does not cause excessive fluctuations in the terminal voltage signal This means the operator observes stable voltage and VAR readings during data collection, indicating minimal interference from noise and reliable measurement accuracy.

The AVR setpoint signal shows no signs of limit action, indicating that noise is not causing the excitation control to reach any observed limits This absence of limit activity is crucial, as it prevents inaccuracies in the transfer function calculation Ensuring that no apparent limit action occurs allows for more precise and reliable system analysis, which is essential for optimal performance and stability.

Example of Collected Data from AVR Closed Loop Frequency Response Test

PSS Open Loop Frequency Response

�� To perform the PSS Open Loop Frequency Response

1 Refer to the procedure,To perform the AVR Closed Loop Frequency Response, and perform steps 1–5 In step 4, set theBode Typeto PSS.

2 After the file has been uploaded to the Trender and saved, the frequency response test data collection is complete.

Example of Collected Data from PSS Open Loop Frequency Response Test

Testing Complete

After completing all testing, send the collected data to the tuning study provider, such as Energy Consulting, for analysis, and keep the PSS disabled with gain set to zero until the results are approved Repeat testing as necessary until the results are validated Once approved, enable the PSS with the verified gain setting, and if GE provides configuration settings, send the as-running file back to GE personnel to ensure proper documentation and configuration.

Frequency Response Test Data Processing (Optional)

Processing the raw frequency response data into transfer function form is typically done by GE.

This section offers a concise overview of the data processing activity for field engineers conducting quick site checks of frequency response data It outlines the transfer function calculation procedures necessary for analyzing and interpreting the data efficiently This guide ensures accurate and streamlined processing to facilitate reliable site assessments.

• AVR Closed Loop transfer function

• PSS Open Loop transfer function

The transfer function calculations are performed using a specialized program located within the toolbox application at C:\Program Files\GE Control System Solutions\Ex2100 Excitation Control\Ex2100 Analysis Tool This directory contains a batch file named FreqAnaz.bat, which executes MATLAB code to perform the transfer function analysis The program not only calculates the transfer functions but also generates plots to visualize the results, enhancing the analysis process.

AVR Closed Loop Transfer Function

The AVR closed-loop transfer function closely aligns with the predicted phase lag in the field circuit at local mode frequencies around 1-2 Hz, indicating consistent system behavior Near the local mode, the phase remains approximately uncompensated, showing a phase lag of about 90-100 degrees This phase lag is effectively compensated by the phase lead introduced in the Power System Stabilizer (PSS) control, ensuring system stability and optimal performance.

�� To calculate the AVR closed loop transfer function

1 Load the recorded AVR Closed Loop trend file into the toolbox or ToolboxST application.

2 From theFilemenu, selectExport Trend Data.

3 In theTrender Export Data Optionsbox, select theColumn Headersand

5 Open the transfer function calculation tool (FreqAnaz.bat) to display theAnalysisTooldialog box.

7 Select the previously saved *.csv file The program performs the AVR Closed Loop transfer function and displays the following three graphs.

AVR Closed Loop Transfer Function Graphs

8 Maximize the middle graph and print (or screen capture) it to share with the customer.

Typical AVR Closed Loop Transfer Function Plot

PSS Open Loop Transfer Function

Refer to the figure,PSS Open

The PSS open loop transfer function plot enables the calculation of the actual instability gain point, with the loop crossover phase occurring at 6.5 Hz when the phase reaches zero At this frequency, the measured gain in the upper curve is approximately 0.005 pu The instability gain is determined as the inverse of this crossover gain, indicating that the PSS loop could become unstable at a gain of 200 pu with an oscillation frequency of 6.5 Hz Considering a recommended PSS gain setting of 10 pu, this results in a gain margin of 26 dB (20:1), ensuring system stability under operational conditions.

�� To calculate the PSS Open Loop frequency response

1 Load the recorded PSS Open Loop trend file into the toolbox or ToolboxST application.

2 From theFilemenu, selectExport Trend Data.

3 In theTrender Export Data Optionsbox, select theColumn Headersand

Refer to the figure,Analysis

5 Open the transfer function calculation tool (FreqAnaz.bat).

6 Enter the as-left (tuned) PSS lead and lag settings in the appropriate locations (for example,PSSTld1) Retain the defaults for the underexcitation limit (UEL) and field

8 Select the previously saved *.csv file The program performs the PSS Open Loop transfer function and generates the following three graphs.

PSS Open Loop Transfer Function Graphs

9 Maximize the left window and print (or screen capture) it to share with the customer.

Typical PSS Open Loop Transfer Function Plot

Disable and Enable Testing (Optional)

Test the configuration settings for the parameters,Low Watts DisableandHi Watts Enable.

Simulation testing is highly recommended for this unit, as performing such tests during service is generally impractical due to its near or full load operation To ensure accurate results, only conduct online testing after completing PSS testing and when the customer can safely reduce the load, minimizing operational impact.

�� To test the Low Watts Disable and Hi Watts Enable configuration settings

1 With the PSS enabled, decrease unit load until the PSS becomes inactive This should be at the corresponding value of parameterLow Watts Disable.

2 From the operator control interface, disable PSS and raise unit load above the parameterHi Watts Enable The PSS should remain disabled and inactive.

3 Reduce load below the setting ofLow Watts Disableand selectPSS enable Again, raise load above the parameterHi Watts Enableand the PSS should become active when the value ofHi Watts Enableis reached.

Additional Unit Testing

When multiple identical units are present on-site, each should have the same gain setting, ensuring consistent performance across devices It is recommended to perform the full testing process outlined in this document for every unit to ensure optimal functionality and safety However, with approval from the tuning study provider, some tests may be omitted, though at a minimum, the gain margin and step test must be completed on each unit to verify operational integrity and reliability.

For optimal testing, it is recommended to activate the PSS on the first unit while testing the second unit When testing the third unit, ensure the PSS remains active on both the first and second units, continuing this pattern for subsequent units This approach ensures consistent and accurate testing results across all units.

When bringing units online, it is essential to test and approve the Power System Stabilizer (PSS) sequentially for each unit For sites with existing units, such as in PSS retrofit projects, the "first unit" refers to the unit that has completed PSS testing and approval Care must be taken to avoid enabling the PSS for other units at the same site that have not yet been tested and approved, ensuring compliance with safety and operational standards.

Refer to the section,Testing

Once testing is complete on all additional units, submit the collected data for each unit to the tuning study provider for approval Ensure that the PSS remains disabled until approval is granted.

Application Command Layer (ACLx) Used for EX2100 control systems; can be either an ACLA or ACLE.

Automatic Voltage Regulator (AVR) AVR is controller software that maintains the generator terminal voltage.

Instruction blocks provide essential control functions that, when connected during configuration, form customized machine or process control systems These blocks enable performing mathematical calculations, sequencing operations, and regulator (continuous) control, ensuring efficient and precise automation.

Bus Upper bar for power transfer, also an electrical path for transmitting and receiving data.

Configure or Configuration To select specific options, either by setting the location of hardware jumpers or loading software parameters into memory.

Toolbox or ToolboxST A Windows-based software application used to configure the EX2100, EX2100e, and other GE controller products.

Dynamic stability Steady-state stability; allows a system to correct from small changes.

EX2100 and EX2100e Excitation Control GE static exciter; regulates the generator field current to control the generator output voltage.

EXDSPEED EXDSPEED is the integral of accelerating power signal.

IEEE Institute of Electrical and Electronic Engineers A United States-based society that develops standards.

Power System Stabilizer (PSS) PSS software produces a damping torque on the generator to reduce generator oscillations.

Signal The basic unit for variable information in the controller.

Simulation Running the control system using a software model of the generator and exciter.

Torque The mechanical-to-electrical energy link.

Transient stability Allows a system to recover from large changes.

AVR Closed Loop Frequency Response 43

Parameter Biquad 26 Gain 25 Inertia 25 Lead/Lag 2 25 Low Watts Disable 26 Lower Limits 26 Ramp Tracking Filter 26 Washout 26

Parameters Biquad 24 PSS 22 power system stability 7 Power System Stabilizer 7 Power System Stabilizer (PSS) Diagram 21 PSS Active 19

PSS Disable 19 PSS Enable 19 PSS Implementation 11 PSS Inactive 19 PSS2B Model 16

Stability 7–8 Steady-state 10 synchronous machine 7 Synchronous Machine Oscillation 7–8 System Modeling 9

Test AVR Step test with PSS Disabled 34 AVR Step with PSS Enabled 38 Testing 27

Additional unit testing 52 AVR closed loop frequency testing 43 Disable and Enable testing 52 Gain Margin test 29

Impulse test 40 Initial performance testing 19 PSS open loop frequency testing 47 Testing complete

Định dạng
Số trang	58
Dung lượng	4,64 MB