Controlled Switching suitability check for already installed HVAC circuit breakers

Transkript

1 Controlled Switching suitability check for already installed HVAC circuit breakers Dipl. El.-Ing. Urs Krüsi Swiss Federal Institute of Technology, Zurich, CH

2 STRUCTURE INTRODUCTION IMPORTANT CHARACTERISTICS IDENTIFICATION OF RDDS CASE STUDY: CAPACITOR BANK QUESTIONS

3 INTRODUCTION Reduction specifies the CB Transformer inrush Uncontrolled Need for methods to identify the characteristics of already-installed circuit breakers Controlled Circuit breaker characteristics are often unknown CB specifies the reduction

4 Suitable or not? Depends on the switching case (reactor, capacitor bank, line, transformer, etc. ) Defined by the power utility and/or its customers -> a methodology to calculate the numbers as a base for the decision pro or contra controlled switching

5 IMPORTANT CHARACTERISTICS Rate of decrease of dielectric strength RDDS Mechanical closing time in dependence of: -Idletime - Auxillary voltage - Temperature -Drive energy Scatter Work is in progress No results can be presented for the time being

6 CAPACITORBANK ENERGIZATION Optimal closing instant: system voltage = capacitor bank voltage small prestrike voltage leads to small transients Main parameters that affect prestrike voltage?

7 INFLUENCE OF RDDS ON PRESTRIKE VOLTAGE Rate of Decrease of Dielectric Strength=Slope U [p.u.] RDDS>p.u. U ct RDDS<p.u. RDDS=p.u. U prestrike t

8 STATISTICAL MODEL OF THE DYNAMIC U [p.u.] DIELECTRIC STRENGTH U ct t Nominal Beginning of the movement Contact velocity Dielectrical scatter

9 INFLUENCE OF RDDS ON prestrike voltage [p.u.] PRESTRIKE VOLTAGE zero voltage switching theoretical optimum (no scatter) % of all prestrike voltages below Median, 50% of all prestrike voltages below scatter RDDS [p.u.] Assumptions: 3σ Tb=ms 3σ V=5% 3σ D=5%

10 CHARACTERISTIC PATTERN prestrike voltage time (half a period) RDDS n 2.0 Computer generated patterns using the statistical model of the dynamic dielectric strength of a circuit breaker 00 patterns are available for identification

11 IDENTIFICATION ALGORITHM Closing command is synchronized and delayed in 20 steps over one half-cycle U [p.u.] U ct delay U ps Closing command t Prestrike voltages are measured U ps delay The algorithm evaluates the best pattern 0.5 prestrike voltage.0 time (half a period) RDDS n 2.0

12 TEST SETUP ~ Oscilloscope Controller Measures the prestrike voltage Synchronizes the close command with the system voltage Delays the command in 20 steps over half a period

13 MEASUREMENTS prestrike voltage (absolute value) [p.u.] t[ms]

14 VISUALIZED RESULT prestrike voltage [p.u.] RDDS/pattern: 2.25; time shift: time [T]

15 CASE I Inrush current ~ Overvoltage

16 SUITABILITY CHECK Single capacitor bank overvoltage (p.u.) prestrike voltage (p.u.) inrush current (p.u.)

17 CASE II Simple back-to-back situation: Inrush current ~ Overvoltage

18 SUITABILITY CHECK Back-to-back.4 40 overvoltage (p.u.).2 20 inrush current (p.u.) prestrike voltage (p.u.)

19 U [p.u.] Statistical model of dynamic dielectric strength SUMMARY Case Study Inrush current U ct ~ Overvoltage t prestrike voltage [p.u.] RDDS [p.u.] RDDS overvoltage (p.u.) inrush current (p.u.) Inrush current Identification. Overvoltage prestrike voltage (p.u.).25