08f - MOD-033 Guideline Guidelines for... · Web viewThe NERC Steady-State and Dynamic System Model Validation Standard, MOD-033-1, was created to establish consistent validation

Guidelines for Validation of Powerflow and Dynamic Cases for MOD-033-1

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Salt Lake City, Utah 84103-1114

MOD-033-1 Guideline 2

Table of Contents

1 Introduction................................................................................................................................4

1.1 Purpose....................................................................................................................................4

1.2 Definitions............................................................................................................................... 4

2 Overview of MOD-033-1............................................................................................................53 Discussion.................................................................................................................................54 Monitoring Equipment..............................................................................................................65 Methodology..............................................................................................................................8

5.1 Selection of Events.................................................................................................................. 9

5.2 Data Acquisition.....................................................................................................................10

5.3 Real-time WSM Validation (Peak RC best practice)...............................................................11

5.4 Steady-state Model Validation (using the WECC power flow base case)...............................12

5.5 Dynamic Model Validation (WECC base case).......................................................................13

5.6 Review of Steady State and Dynamic Model.........................................................................15

5.7 Comparison............................................................................................................................15

6 References...............................................................................................................................197 Approval...................................................................................................................................198 Appendix A...............................................................................................................................209 Appendix B...............................................................................................................................26

W E S T E R N E L E C T R I C I T Y C O O R D I N A T I N G C O U N C I L


1 Introduction

The NERC Steady-State and Dynamic System Model Validation Standard, MOD-033-1, was created to establish consistent validation requirements to facilitate the collection of accurate data and building of planning models to analyze the reliability of the interconnected transmission system. One of the requirements in this standard is that each Planning Coordinator shall implement a documented data validation process. WECC created the System Model Validation Task Force (SMVTF) under the WECC Modeling and Validation Work Group (MVWG) to facilitate the MOD-033-1 validation process and to enhance the model validation.

1.1 Purpose

This guideline is meant to provide basic information on how WECC staff and Peak RC prepare the study cases for model validation and performs steady-state and dynamic system model validation. The cases may be leveraged for use by its members, as applicable, to meet the MOD-033-1 compliance.

This guideline also includes a description of monitoring equipment requirements, how members can use these cases for model validation, and provide some guidance on identifying unacceptable differences and how to resolve those differences. This is intended to provide some consistency for members across WECC.

1.2 Definitions

Term or Acronym Definition

SMVTF System Model Validation Task Force

RC Reliability Coordinator (Peak RC)

SE State Estimator

PC Planning Coordinator

WSM West-wide System Model



2 Overview of MOD-033-1

The NERC MOD-033-1 standard becomes effective on July 1, 2017. Here is a brief overview of MOD-033-1: requirements (for the complete requirements, see the NERC MOD-033-1 standard):

R1. Each PC shall implement a documented data validation process that includes the following attributes:

1.1 Comparison of the performance of the PC’s system in a planning power flow model against actual system behavior represented by State Estimator (SE) case or other Real-time data sources;

1.2 Comparison of the performance of the PC’s system in a planning dynamic model against actual system response;

1.3 Guidelines the PC will use to determine unacceptable differences in performance under 1.1 and 1.2;

1.4 Guidelines to resolve unacceptable differences identified under 1.3;

R2: Each RC and TOP shall provide actual system data necessary to the PC to perform validation under Requirement R1 within 30 calendar days of a written request.

Validation of the planning power flow and dynamic models are to be performed at least once every 24 months.

3 Discussion

The focus of MOD-033-1 is comparison of the performance of the PC’s portion of the existing system for steady-state and dynamic response for a local event. Additionally, it is specified in the standard that a dynamic local event could also be a subset of a larger disturbance involving large areas of the grid. NERC’s main emphasis is the utilization of local disturbances for the evaluation of the model; however, there are numerous advantages in the use of large disturbance events within WECC, if available and relevant to the PC’s validation of its system model. Following arguments emphasize importance and advantages of using large interconnection wide disturbance instead a local one:

o Dynamic system model validation requires full knowledge of which units are on-line within the interconnection during the event used for validation.

o Interconnection dynamic response including frequency response (initial and primary) depends on all units within a system and the planner must know which units are on line in the remote parts of the system in order to validate the simulated frequency response.;

o After a disturbance occurrence, real and reactive power flows on major transmission lines and paths are directly affected by the response of many generating unit. If the status and outputs of on-line generating units in areas remote from the actual



disturbance are not known, the results of the event simulation may significantly differ from the actual measurements.

o Correct dynamic modeling of generators is essential to properly simulate its behavior. Dynamic oscillatory behavior of the system depends on available rotational masses and excitation system response of the generators within the system. For example, after a system disturbance, the generating units in California may oscillate against generating units in Alberta. Hence, unless the generating units in Alberta are represented accurately, the resultant simulation response may significantly differ from the measurements.

o Usage of large interconnection events for system validation has the benefit that all affected PCs within WECC may be able to use the same power flow base case and dynamic model. Using the system common case may significantly reduce time needed for base case preparation and potentially could enhance the model validation process. In the case that a system event does not cause a significant impact on a PC footprint, the PC may choose to evaluate local events that could provide better validation of its power flow and dynamic models.

o The adjustment of the WECC base case utilizing exclusively local events may lead to an over-tuning of the models in an attempt to match the simulation to the field measurements. For instance, if all PCs modify the modeling parameters within their area based only on local events, the sum result may lead to the incorrect validation of the WECC-wide system model, particularly the dynamic response.

4 Monitoring Equipment

Sources of actual measurement data that can be used for power flow model validation include:

EMS/State Estimator (SE) SCADA/PI Historian West-wide Model (WSM) case (from WECC EMS) Phasor Measurement Units (PMUs)

This is not a complete list of possible sources. As long as the data provided is a time synchronized snapshot of the system (includes voltage, real and reactive power flow, status, settings, etc.), it could be used for power flow model validation.

Sources of actual measurement data that can be used for dynamic model validation include:

PMUs DFRs (Digital Fault Recorder) Relays



This is not a complete list of possible sources. As long as the data provided is time synchronized and can provide the data with at least 30 samples per second of the positive sequence data (including voltage, real and reactive power flow, frequency, phase angle), it could be used for dynamic model validation. It is better if the sampling rate is 30-60 samples per second, especially if new equipment is being installed. The input sampling rate is typically much faster (typically in kHz) than the data in the output file.

If continuous monitoring (which is preferred) is not available, a suggested starting point for trigger settings are as follows:

Voltage < 0.9 pu (note: may be in reference to either normal operating voltage (e.g. 117 kV) or nominal voltage (e.g. 115 kV), depending on whether it’s relevant and applicable to the PC’s existing system)

Voltage change +/- 5-10% Frequency < 59.9 Hz or > 60.1 Hz Event recordings to include a minimum of 2 second pre-event and 5 seconds post-event

conditions. The ideal recommended recording times, if possible, should be 10 second of the pre-event conditions and 60 seconds of the post-event conditions.

These may be adjusted further based on the PC’s knowledge of its own system and engineering judgement.

Monitoring equipment for dynamic local events are located based on what is appropriate for each PC’s existing system. The number of devices will vary depending on the entity. The following considerations for locations of dynamic monitoring devices include:

At and/or near generation facilities At major transmission facilities At major load centers At major interconnection points Bulk Electric System (BES) buses with large reactive power devices

Most non-PMU recording devices will provide data as a point-on-wave quantity, at multiple samples per cycle. To effectively perform model validation, those recordings will need to be converted to RMS quantities in post-processing.

The high sampling rates necessary to capture the dynamic behavior of the system imposes a burden on the storage capacity of the recording devices; specifically, DFRs, relays, and PQ meters. For this reason, PCs will need to implement manual or automated systems to avoid event data over-writing.



Multiple software tools exist that can automatically poll DFRs/relays for new events, usually stored in COMTRADE format, and downloaded to a more permanent location. These tools can be installed within a substation (on a hardened PC, for example), which requires manual retrieval by someone at the station. Alternatively, if the communication system allows, it’s possible to install a central retrieval unit to poll field devices and download event records to a central location for storage and analysis.

5 Methodology

There are essentially two components of planning model validation for the MOD-033-1 standard: steady-state (R1.1.1) and dynamics (R1.1.2). Both require adjustments of the WECC power flow base case, either to the selected date and time or to pre-contingency event conditions. While the steady-state and dynamic system models can be validated separately, it may be more logical and efficient to use the same event and power flow case for validation of both (R1.1.1 and R.1.1.2). Note that an accurate steady-state model is needed for dynamic validation but a steady-state model validation does not require having a system event. Both of these topics are tightly linked but will be discussed separately.

This guideline is not meant to be perceived as the only acceptable document to be used for model validation. Additional information is provided in references [1, 2].



5.1 Selection of Events

The first step in MOD-033-1 model validation is to select an event against which system response will be validated. Large system event occurs infrequently and unplanned and the one to be used for model validation must be selected carefully.

An example of a useful large event for system model validation is the loss of PDCI and associated RAS that include multiple generation tripping. This type of event and corresponding impacts are observed and recorded widely within the interconnection. Other useful events are transmission line faults followed by the loss of a large amount of generation. SMVTF will choose and prepare at least two WECC-wide system event cases annually. If time permits, and should other interesting event(s) occur, SMVTF may decide to prepare additional study cases. Another potential case that may be selected is a case for steady-state validation only, such as heavy winter peak or heavy summer peak scenario or choosing disturbance that eventually occurred during system conditions close to heavy winter or peak summer conditions.

Some events may not be suitable for MOD-033-1 validation purpose. These events may include, for example, asymmetric events that include highly unbalanced flows such as single pole reclosing or an event that occurred at the top of the hour when generating units are ramping up or down. In study simulation, during initialization process, we assume that all generating units are static with fixed outputs, but over the course of the simulation progress, where the timeframe typically lasts 60 to 120 seconds, some of the units may ramp up or down and they would need additional modeling efforts to simulate. Such effort is unlikely to add value to model validation.



Fig.1 Example of path flow decreasing due to generation ramping down. In this case the units that ramp down need to be scaled down during the simulation.

5.2 Data Acquisition

Once a system event is selected, the data (i.e., from state estimator, SCADA and PMU) for the system and the time duration being simulated should be acquired. The data can be requested through the Reliability Coordinator (RC) and/or TOPs (per MOD-033-1 R2). The RC in WECC is Peak Reliability (Peak RC). Peak RC can provide a snapshot from their State Estimator (SE) data prior to and immediately after the event.

The Peak RC archives SE cases every 5 minutes. For that reason there is a need to verify if there were additional switching actions within the time of the saved SE case and the time of the event (theoretically this time interval can be a maximum of up to 5 minutes).

The Peak RC receives over 130,000 real-time measurements that are mapped to the West-wide System Model (WSM). The measurements include analog data (MW, MVARs, kV) and status of the equipment. These measurements allow the model to be adjusted to match real-time conditions. These measurements are received every 10 seconds via ICCP links.

Event sequence should be requested from the TOP(s) in the area that the event occurred. The TOPs would have the most accurate information for the event.

Peak RC will use PMU data available from different part of BES to validate general dynamic response. Individual PCs will use their own data for validation of their portion of the system dynamic response



5.3 Real-time WSM Validation (Peak RC best practice)1

To enhance the process and data accuracy, Peak RC staff will simulate the selected event using WSM directly and compare the simulation results to available PMU data. The following are two reasons for this process:

To validate WSM itself for Peak Reliability;

To make sure that WSM snapshot provided for model validation represents event accurately since this snapshot is used as modeling inputs to the WECC power flow base case for pre-contingency operational conditions;

The process of WSM validation is relatively quick since the WSM case is a representation of the pre-event conditions adjusted by real-time SCADA measurements. Only event sequence needs to be investigated, prepared and then included in the study. Since the WSM case uses the same dynamic model as the WECC power flow case, all modeling issues found in this process will be reported to the WECC staff.

1 This is above and beyond requirement for MOD-33. It does not require PC to do any additional work.



5.4 Steady-state Model Validation (using the WECC power flow base case)

After WSM validation is performed, the WECC power flow case needs to be adjusted and prepared based on the pre-contingency operating conditions. This process will be performed by the WECC staff and it may require a few weeks to prepare the power flow study case. This is the most time consuming part of the process.

For the preparation of the event base case, the WECC steady state planning model must be modified with generation dispatch, topology and load changes based on the real-time data noted above in order to achieve a close match to actual system condition for the selected time. Reference [1] from the NERC MWG document provides more details on this process. There could be some limitations on the part where the WECC staff can modify the power flow study case for the overall WECC-wide footprint. Additional refinement of the power flow study case may be required by the PC for their own planning area.

The main intent for validating a steady-state power flow model is to compare the pre-disturbance measurement (e.g. bus voltages, real and reactive power flow on system elements and paths, generation dispatch, phase shifter settings, LTC tap positions, etc.) to the power flow solution from the WECC study case that is adjusted to the pre-disturbance operating conditions. The desired outcome would be a close match of the results obtained between the power flow simulation and the real-time measured data.



If the results are not a good match, based on engineering judgement, it is necessary to investigate the cause(s) of the discrepancies. Therefore, it is recommended to adjust voltages by allowing LTC taps, SVCs and generators to adjust automatically based on measured conditions (AVR selection for power flow solution) and then to compare simulated tap positions and MVAr values to the actual values. This process is helpful to pinpoint the issues and to correct transformer tap positions, controlled points and transformer impedances. Note that there will be differences between the WECC power flow case and WSM (State-estimator snapshot) study case. The difference is mainly due to mismatches that are introduced to the SE power flow case during the process of state estimations. The mismatches appear as small MW and MVAr loads that are added to the study case.

Process described above is used for events selected by SMVTF. If PC(s) decide to use other event than one chosen by SMVTF then they will need to adjust basecase by themselves. Below is brief procedure on how basecase is adjusted:

In order to create an event case using a WECC base case the following will need to be adjusted in the WECC base case, generation dispatch, voltage, load dispatch, transmission line status and adjusting the flows on the Phase shifting transformers to match the WSM case.

In mapping the WSM2 to the WECC base case start on the outer rim of the WECC footprint such as Alberta. Set the generation dispatch from the WSM into the WECC base case. This can be done by running a script that will use the WSM generator ID that will match the same ID in the WECC base cases. Next adjust the load dispatch to match the net MW interchange in or out of Alberta. The load dispatch is typically a little different due to different losses between the WSM and WECC base cases. Repeat these steps for all areas in the WECC base cases.

Setting the Voltage in the WECC planning case to match the WSM case is a manual process. Starting with the area that has been affected by the disturbance take the actual voltage of a bus from the WSM and adjust the schedule voltage parameter in the WECC base case.

2 Instead of using WSM PC may use SCADA data.



Adjusting the transmission line status is another manual process. In the WSM case under the SECDD record you can display a field called DST and filter for values of 0. This is the lines that are off in the case and adjust the WECC base case according. Set the Phase Shifting transformers to match the same flow that the WSM is showing across it.



5.5 Dynamic Model Validation (WECC base case)

5.5.1 Creation of Dynamic Data File

Once an acceptable steady-state model has been developed, the next step is to create a good dynamic data file. To begin, we will need to select the dynamic data file that is available with the approved WECC power flow base case that was selected in Section 5.4 above. For the process of adjusting generation dispatch, load modeling, etc., in the preparation of the steady-state model, it may be necessary to have additional steady-state model adjustments as well as dynamic model adjustments. For example, individual generator outputs may need to be lowered in the steady-state power flow case or generator real power capability parameter may need to be incremented in the dynamic model to achieve a clean dynamic initialization result. There are multiple reasons for that such as no plant load modeled in WSM, state estimator mismatches that are not presented in basecase but they exist in WSM as additional positive/negative loads or not having matching of some generators one to one. , Additionally, new composite load models may need to be modeled if they are missing in the original dynamic data. It is important that the adjusted dynamic data file is initialized properly with the steady-state power flow model. In other words, generators must initialize within governor limits, missing dynamic models must be created appropriately, and initialization warning/error messages must be addressed.



After the power flow case and dynamic data are prepared, a few transient runs should be performed using the new dynamic data. A no-disturbance simulation should produce flat lines, a ring-down simulation (insertion of the Chief Joseph Braking Resistor) should produce traces that initially oscillate but damp out acceptably. In addition, a few additional disturbances should be simulated (such as the double Palo Verde generation loss) with acceptable transient results. All netted generating units in the dynamic model in a specific PC’s footprint should be addressed and corrected by the PC.

5.5.2 Creation of Event Sequence

The next step is to create an accurate sequence of events and switching file. The TOPs of the system where the event happened should have the most accurate time sequence data. The switching sequence is created based upon the sequence of event data, such as from DFRs, relays, and other information such as SCADA or dispatcher’s logs. Sequence component currents and voltages are recorded by relays.

Example

The following is an example of a switching file in GE-PSLF format. The contingencies can be defined based upon the bus number or the EMS labels. Note that switching times need to be accurate within fraction of the second.



Fig.2



5.6 Review of Steady State and Dynamic Model

After the WECC study case (steady-state model and dynamic) has been created, the case will be posted on peakrc.org. Email notice will be sent to PCs, and feedback will be sent back to Peak RC and WECC. The parameters that should be reviewed include bus voltages and reactive sources (to ensure an acceptable voltage profile), generation levels, power flow on transmission system elements (including paths), loads, etc. The objective of this review is to improve quality of steady state case that then can be used as starting point for system model validation.

After the review comments have been addressed, the case will be posted on peakrc.org.

5.7 Comparison

After preparation of disturbance case and clean dynamic data initialization and flat no-disturbance dynamic test is achieved, and the event disturbance simulated, the PCs can use this case for MOD-33-1. The PCs should develop their own guidelines for R1.1.3 and R1.1.4. In R1.1.3 (development of guidelines to determine unacceptable differences) as they should take into account the accuracy of available measurements (accuracy class of PTs and CTs). This effort can be coordinated with the TPs where the recorders are installed. Also some PMUs have large offset compared to SCADA measurements which should be taken into account while comparing with simulation responses.

5.7.1 AGC Limitation

Traditionally, dynamic simulation duration is 10 to 20 sec. For that reason Automatic Generation Control (AGC) action is not simulated. During frequency events (loss of generation) for runs longer than 20 sec. AGC will act to try to restore Area Control Error (ACE). For that reason AGC action might be needed in order to match simulation results to PMU measurements. Following example illustrates the above mentioned remark:



Example:

Simulation is performed for tripping of BC-Hydro 525 MW unit.

Fig. 3.1 illustrates currents through some of the WECC major 500 kV lines. Within first 20 sec. (initial and primary response) current waveform from simulation and PMU measurements match remarkably. After 20 seconds current through the line builds up due to generation secondary response (AGC action). In simulation the post-disturbance current approaches a constant value since there is no AGC action modeled.

Fig.3.1 Impact of AGC action is reflected in increasing current over the line (blue trace). AGC action is not modeled and in simulation, after primary response current becomes constant (orange trace).



Figures 3.2 show voltage profile on buses at the end of this lines. First 20 sec. voltage profile of simulation and measurements match remarkably. After 20 seconds the voltage profile in simulation becomes constant but in fact the measured voltage depresses due to increase current through the line (AGC action).

Fig.3.2 increasing current over the line sag voltage (blue trace). Simulation does not model AGC action (no current increase over the line) so voltage drop remains constant (orange trace).

Appendix A illustrates, using an example, the above procedure. Appendix B illustrates how a PC (Arizona Public Service (APS)) used the case available from the Appendix A to perform model validation.



Alternatives to the above process could be using local disturbance event for a PC’s model validation. The process should be similar as with WECC wide disturbance. The difference is in how much PC needs to tune basecase outside of its own footprint to correctly capture impact of the external system on disturbance dynamic. The procedure for using WSM directly for system dynamic model validation is provided in reference [2].This procedure might be useful if PC want to separate validation of powerflow and dynamic model as discussed in 5.1.

6 References

[1] Procedure for Validation of Powerflow and Dynamic Cases, NERC http://www.nerc.com/comm/PC/Model%20Validation%20Working%20Group%20MVWG/Model_Validation_Procedures_2011_12.pdf update to the newer version

[2] A New Framework to Facilitate the Use of Node-Breaker Operations Model for Validation of Planning Dynamic Models in WECC- PES GM 2016, Boston, MA

7 Approval

Approving Committee, Entity or Person Date



8 Appendix A

Example: January 21th 2016 – Event ATR RAS action and loss of two Colstrip units

1 Event sequence obtained from Northwestern:

2 WSM case snapshot from Peak Reliability archive retrieved (case representing system conditions closest to moment before occurrence of the event)

3 Event sequence was replicated by Peak RC using the WSM directly (Note: Line fault and line relaying is simulated as a contingency and ATR RAS model disconnected units 3 and 4. This event was used to validate RAS model at the same time)



4 RAS model validated:

5 Major WECC Paths and voltages plotted against PMU signals:



Note: results match within less than 1%

6 WSM Case and switching sequence provided to WECC staff7 WECC staff adjusted WECC base case and run dynamic simulation (see results)







8 Case posted on peakrc.org for PCs use





9 Appendix B

Example of a PC Model validation process

Steps taken by PC:

1. Downloaded the case from peakrc.org2. Ran the disturbance case to make sure it runs3. Downloaded the PMU data for the event 4. Time synchronized the PMU and simulation data5. Compared various quantities such as voltage, frequency, flow at various significant

buses where the PMU data was available6. Compared generator response where data is available from PMU7. Adjusted the initial generator voltage and power in the Peak RC-provided study case

where it was significantly different than what was measured by the PMUs8. Checked for reasonable steady state comparison 9. Reran the revised case and compared the simulation and measurements.10. Following are some of the sample plots11. Based upon the following plots it is judged that the validation is reasonable.






Documents

08f - MOD-033 Guideline Guidelines for... · Web viewThe NERC Steady-State and Dynamic System Model Validation Standard, MOD-033-1, was created to establish consistent validation