Error vs. Uncertainty Historical Perspective

Transcription

1 1 Error vs. Uncertainty Historical Perspective Jim McBride Chairman PSIM Committee Vice-Chairman HVTT Subcommittee IEEE PES SPDC Fall 2017 Clearwater, FL Discussions on Uncertainty PSIM - HVTT Subcommittee Wednesday, October 4 th, 2017

2 2 IEEE Standard 4 and GUM Revision History IEEE IEEE Standard Techniques for High Voltage Testing (Error = measured quantity value reference quantity value) NIST Technical Note Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results (Concept of Uncertainty is introduced) IEEE = IEEE Standard Techniques for High-Voltage Testing (Error = measured quantity value reference quantity value) GUM Revised 2008 and Amended in 2011 (GUM with minor corrections) IEEE IEEE Standard for High-Voltage Testing Techniques (Change from using Error to Uncertainty with NO limit changes)

3 3 AC Measurement System Requirements (same requirements for all revisions) Voltage Frequency = Hz Waveform V peak / V rms = ±5% Voltage Peak or RMS Amplitude = ±3% Voltage Harmonics Amplitude = ±10%

4 4 Impulse Measurement System Requirements (same requirements for all revisions) Lightning Impulse Waveforms Nominal: 1.2 µs X 50 µs V Peak = ±3% T Front = ±10% T Tail = ±10% Switching Impulse Waveforms Nominal: 250 µs X 2500 µs V Peak = ±3% T Front = ±10% T Tail = ±10% Current Impulse Waveforms Nominal: 4 µs X 10 µs or 8 µs X 20 µs V Peak = ±3% T Front = ±10% T Tail = ±10%

5 5 What did we historically mean by Error? Transformer Ratio Arm Bridge (Precision 100ppm or 0.01%)

6 6 What did we historically mean by Error? (continued) Guildline Current Transformer Test Set (Better Than 100ppm)

7 7 What did we historically mean by Error? (continued) 40 kv Electrostatic Voltmeter Measures Force Low Loading and Measures High Frequency

8 8 Sources of Error for Capacitive and Resistive AC Voltage Dividers Stray Capacitance Temperature Coefficient / Dielectric Ratio vs. Frequency Voltage Coefficient Partial Discharge Cable Loading

9 9 Stray Capacitance Example 700kV 5A Series Resonant Test Set (Divider Capacitance 3nF)

10 10 Stray Capacitance Example (Continued) 500kV 2A Series Resonant Test Set (Divider Capacitance 100pF)

11 11 Sources of Error for Capacitive and Resistive Impulse Voltage Dividers Temperature Coefficient / Dielectric Frequency Response Stray Capacitance Voltage Coefficient Damping Resistance Grounding System Impedance Matching High Frequency Signal Coupling

12 Resistive Impulse Voltage Divider 12

13 Damped Capacitive Impulse Divider 13

14 Stray Capacitance and Chopping Gap Voltage Divider Errors 14

15 15 Laboratory Grounding Improper Grounding (Measured Error 10-20%) Example of Proper Grounding

16 High-voltage leads and damping resistors For any particular measurement, the length of the lead should be stated, and it should be within the range of lengths for which the measuring system was calibrated. The position of the lead should be the same, to the extent that it is practically possible, for a test as during calibration. The high-voltage lead of the divider should normally be connected directly to the highvoltage terminal of the test object and not to the impulse generator or any point on the interconnecting lead. This avoids inclusion of the inductive voltage drop from the lead in the measurement. Since the test object and voltage measurement device are physically separated, it should be recognized that the voltages appearing across both are rarely identical. A resistor having very low inductance may be inserted in the high-voltage lead to the divider to damp excessive high frequency oscillations and reflections. If the damping resistor is located close to the divider, it is considered to be part of the divider, and the damping resistor shall be taken into consideration when the scale factor of the system is determined.

17 17 Importance of Damping Resistance and Voltage Divider Usage in Making Appropriate Measurements

18 18 IEEE Standard 4 and GUM Revision History IEEE IEEE Standard Techniques for High Voltage Testing (Error = measured quantity value reference quantity value) NIST Technical Note Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results (Concept of Uncertainty is introduced) IEEE = IEEE Standard Techniques for High-Voltage Testing (Error = measured quantity value reference quantity value) GUM Revised 2008 and Amended in 2011 (GUM with minor corrections) IEEE IEEE Standard for High-Voltage Testing Techniques (Change from using Error to Uncertainty with NO limit changes)

19 19 Why did the PSIM HVTT Subcommittee make this change to the wording from Error to Uncertainty? NOT to impose more stringent accuracy requirements. NOT to increase the difficulty of HV testing NOT to identify the best mathematicians at the lab IN ORDER TO PROVIDE A MORE CONSISTENT AND WELL DEFINED APPROACH TO SPECIFYING, QUANTIFYING, AND COMBINING THE SOURCES OF ERROR THAT HAVE BEEN CONSIDERED WHEN A PARTICULAR MEASUREMENT HAS BEEN MADE.