Comparison of SCADA and WAMS real-time data in dispatch center · Comparison of SCADA and WAMS...
Transcript of Comparison of SCADA and WAMS real-time data in dispatch center · Comparison of SCADA and WAMS...
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Comparison of SCADA and WAMS real-time data in dispatch center
Beijing Sifang Automation Co., Ltd.,CHINA
Qi Wenbin [email protected]
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Introduction
PMU has been widely used in power systems for more than ten years. Sifang Automation Co., Ltd. has over 50% of the WAMS and PMU market share in China. How is the PMU data quality? What is the relationship between the millisecond level
PMU data and the second level RTU data? whether PMU measurement data is accurate enough to
support better power system analysis and calculation?
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Diff =|(Vp-Vr)/Vr|
Comparison Method of PMU & SCADA Data
We have developed software to compare SCADA and WAMS real-time data in dispatching center.
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Comparison Method of PMU & SCADA Data
Take real-time measuring point with both PMU and RTU measurements, whose measurement status and state estimation error are all in normal state, as statistical objects, calculate the difference between PMU and RTU data, the equation as follows: Diff =|(Vp-Vr)/Vr| Where: Vr is real-time RTU data; Vp is real-time PMU data with the same time stamp from a physical point .
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Implementation of the Comparison Method
Get real-time measurement sample every second and compute the difference, get average difference every 5 minutes.
Abnormally large or small value (larger than 104 or smaller than 10-3) of PMU or RTU data is excluded from calculation.
Measurements with error greater than 10% after state estimation are excluded from calculation.
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Comparison of PMU & RTU Real Power Data Curve
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Comparison of PMU & RTU Voltage Data Curve (Average Difference 0.0036%)
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Comparison of PMU & RTU Real Power Data Curve
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Difference Between PMU & SCADA Real Power Measurements
1%<diff<5%
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Difference Between PMU & SCADA Real Power Measurements
1%<diff<3%
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Comparison of PMU & RTU Reactive Power Data Curve
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Comparison of PMU & RTU Real Power Data Curve
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Huge Difference Between PMU & SCADA Reactive Power Measurements
1%<diff<70%
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Huge Difference Between PMU & SCADA Reactive Power Measurements
10%<diff<18%
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Difference between PMU & SCADA real power measurement is small;
Difference between PMU & SCADA reactive power measurement is large.
Conclusions
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Difference Statistical Results (in 2011)
Measurement Type
No. of Measuring Points Diff > 1% Diff > 2% Diff > 5% Diff> 10%
Frequency 17 0 0 0 0
Voltage 33 1 0 0 0
Current 2 0 0 0 0
Real Power 164 95 48 15 5
Reactive Power 152 134 112 74 37
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Basic Conclusions
For a straight telemetered physical measurement, the time delay between RTU and PMU are less than 1 second, and the difference between RTU & PMU measurement curves is small.
For 70% of the active power measurements, difference between PMU and RTU data is less than 2%.
For reactive power measurements, difference between PMU and RTU data ranges from 5% to 50%; 50% of the measuring points have a difference larger than 5%, 24% of them have a difference larger than 10%. The reactive power meets a great measurement difference.
For the same measuring point, difference between RTU and PMU data remains almost the same for a period of time.
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Great Measurement Difference of Reactive Power
Q=
The reactive power measurement difference between RTU and PMU reflects the relative measurement error of current and voltage angle in PMU device.
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Power calculation in PMU device: P = IUcosφ Q = IUsin φ At certain φ0, the measurement error of φ will
lead to the following measurement errors of real power P0 and reactive power Q0:
⊿P/P0 = ⊿φ sinφ0/ cosφ0 ⊿Q/Q0 = ⊿φ cosφ0/ sinφ0
Great Measurement Difference of Reactive Power
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Φ0 is a decimal value close to 0. sinφ0 0,cosφ0 1 sinφ0/cosφ0 0 cosφ0/sinφ0 Max When error ⊿φ is fixed: ⊿P/P0 0 ⊿Q/Q0 Max
Great Measurement Difference of Reactive Power
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Difference between reactive power measurement of RTU and PMU reflects the relative measurement error of current and voltage angle in PMU device.
To obtain the same accuracy, PMU is more difficult.
Conclusion
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Effects of Advanced Algorithms Using PMU Data
State Estimation Transmission Line Parameter Identification
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State Estimation
There is no significant improvement on the accuracy of state estimation after adding PMU measurements. Measurements
Voltage
Real Power Reactive Power Total
Pass Rate No. Pass Rate No. Pass Rate No. Pass Rate
No.
SCADA data 79.38% 1411 81.57% 3488 89.64% 3542 84.59% 8441
PMU and SCADA 74.43% 1408 69.76% 2976 87.10% 3131 77.86% 7515
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Transmission Line Parameter Identification
Reliable parameters could be reached for some transmission lines.
Parameters of some transmission lines could not be identified reliably.
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Transmission Line Π-Model
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Parameter Identification Results of Line Taishun-2
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Parameter Identification Results of Line Wanshun-3 with Shunt Reactor at One End
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Transformer Parameter Identification
Reliable parameters could be reached for some transformers.
Parameters of some transformers could not be identified reliably.
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Transformer Parameter Identification
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Transformer Parameter Identification
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Conclusions
According to the PMU measurement quality of field data: the accuracy of active power, current magnitude and
voltage magnitude measurements of PMUs is equal to that of RTUs, indicating that these measurements can be used in power system analysis.
the reactive power, current angle and voltage angle
measurements of PMUs should not be used directly without selection. The accuracy of PMU phase angle measurements can be improved through periodically checking and
adjusting of the phase angle compensation parameters.
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Suggestions for Improving PMU Measurement Accuracy
According to the checking method for metering device, establish regular validation system for PMU data and check the angle compensation parameter of PMU device regularly, in order to decrease field measurement error to allowed level for standard products.
Improve calculation algorithm of reactive power in PMU
device. Reactive power calculation method used in RTUs , phase shifting method, could be applied to PMUs. Phase shifting method can avoid reactive power error caused by angle error. Real-time compensation algorithm for angle error could also be implemented in PMUs.
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Thank you!