Designing and Maintaining a Pollution-Resilient Electric Power System. Managing Pollution Issues

Transcription

1 Designing and Maintaining a Pollution-Resilient Electric Power System Tom McDermott IEEE/PES T&D Conference April 21-24, 2008 Chicago, IL Managing Pollution Issues Define the metrics, and measure them Use simulation to compare different designs and maintenance strategies validate with measurements how to value pollution? Implement system changes again, validate with measurements 4/23/2008 Pollution-Resilent Electric Power System 2 1

2 Harmonic Voltage Distortion Pollution Rank #1, PQ Rank #3 Standard: IEEE 519 Metric: THD 95 ; level exceeded 5% of time limit at MV is 5.0% total, 3.0% any component 4/23/2008 Pollution-Resilent Electric Power System 3 Voltage Flicker 100 Step-wise Flicker 50 Voltage Magnitude (%) Time (s) Pollution Rank #2, PQ Rank #4 Standard: IEEE 1453 Metric: P ST ; short-term flicker coefficient planning limit is 0.9 4/23/2008 Pollution-Resilent Electric Power System 4 2

3 Transient Overvoltages Pollution Rank #3, PQ Rank #5 Standard: IEEE 1159 (plus EPRI reports) Metric: SATMORI 1.7 ; annual frequency of voltage transients at least 1.7 per-unit typical value of 1 per day? 4/23/2008 Pollution-Resilent Electric Power System 5 RMS Variations (Sags & Swells) (Similar to voltage flicker) Pollution Rank #4, PQ Rank #2 Standard: IEEE 1159 (plus EPRI reports) Metric: SARFI 70 ; annual frequency of sags to 70% voltage or below typical value of 20 4/23/2008 Pollution-Resilent Electric Power System 6 3

4 Momentary Interruptions (Sags below 10% voltage; followed by a voltage recovery transient when the fault clears) Pollution Rank #5, PQ Rank #1 Standard: IEEE 1366 Metric: MAIFI; frequency of interruptions up to 1 or 5 min typical value of 6 annually 4/23/2008 Pollution-Resilent Electric Power System 7 Benefits of Source Strength Reduce voltage sag magnitudes Absorb more harmonic current injection Reduce flicker magnitudes Note: these are probably what you think of as pollution No inherent effect on interruptions (aka reliability) or transients (another type of pollution) 4/23/2008 Pollution-Resilent Electric Power System 8 4

5 Source Effect on Sags Fault on Adjacent Feeder Downstream Fault V PCC 1 = Z A Z + Z S A V PCC 2 = Z A Z + Z + Z S F A 4/23/2008 Pollution-Resilent Electric Power System 9 Source Effect on Flicker & Harmonics Pst* TDD [%] Pst Lim Sk [MVA] S K P ST 2 kv = Z + Z = S S F N cf S K 4/23/2008 Pollution-Resilent Electric Power System 10 5

6 Source Effect Parallel Resonance Parallel Resonance of 5 MVA, 13.8-kV Capacitor MVA Transformer 12-MVA Transformer 200 Voltage (V) Frequency (H pu) 4/23/2008 Pollution-Resilent Electric Power System 11 How To Increase Source Strength Increase conductor sizes Increase substation transformer capacity Add a substation transformer Higher transmission voltage service Add a transmission line Express feeders (isolation from other load) Dedicated transformers (more isolation) 4/23/2008 Pollution-Resilent Electric Power System 12 6

7 Benefits of Sectionalizing Better interruption indices More RMS variations (they were interruptions before) No inherent impact on harmonics, flicker, or transients 4/23/2008 Pollution-Resilent Electric Power System 13 Permanent Fault Effect of Sectionalizing SARFI SAIFI SARFI SARFI SAIFI Temporary Fault SARFI MAIFI SARFI SARFI MAIFI 4/23/2008 Pollution-Resilent Electric Power System 14 7

8 Impact of Distributed Resources The effect is mixed, and benefits may accrue primarily to the DG owner Good Impacts: Higher source strength? Depends on interconnection Backup source may reduce long-term interruption indices Bad Impacts: Higher ground fault voltages on healthy phases May produce more flicker or harmonics 4/23/2008 Pollution-Resilent Electric Power System 15 DG Effect on Overcurrent Protection No Fuse Saving Loss of Sensitivity Sympathetic Tripping 4/23/2008 Pollution-Resilent Electric Power System 16 8

9 DG Impact on Reclosing Reclose Interval DG Must Disconnect Here DG has to disconnect early in the reclose interval, may lengthen to 2 5 seconds Dead time changes from instantaneous to momentary category of IEEE /23/2008 Pollution-Resilent Electric Power System 17 Reducing the Event Rate Helps both interruptions and RMS variations Upgraded lightning protection Arresters Overhead shield wires, with better grounding More insulation Vegetation management 4/23/2008 Pollution-Resilent Electric Power System 18 9

10 Other Measures Capacitor switching surge reduction Synchronous or zero-voltage control Preinsertion resistors Power electronic devices to reduce flicker or harmonics (STATCOM, DVAR, etc.) Passive harmonic filters PWM converters don t inject low-order harmonic currents 4/23/2008 Pollution-Resilent Electric Power System 19 Capacitor Switches Mitigation None 20-Ω Resistor Standard Inductor Enhanced-Duty Ind. Peak [p.u.] % >= 1.7 p.u /23/2008 Pollution-Resilent Electric Power System 20 10

11 2 No Mitigation g 1 Voltage (V pu) Time (ms) 4/23/2008 Pollution-Resilent Electric Power System 21 Pre-insertion Resistor Voltage (V pu) Time (ms) 4/23/2008 Pollution-Resilent Electric Power System 22 11

12 2 Pre-insertion Inductor y 1 Voltage (V pu) Time (ms) 4/23/2008 Pollution-Resilent Electric Power System 23 Why Do We Need PQ Simulation? Measurements take a long time Measurements are after the fact Simulation can be a virtual laboratory 4/23/2008 Pollution-Resilent Electric Power System 24 12

13 Stochastic Fault Application Rate (0.1 / mile / yr) Other Variables: Phases Involved Permanent? (20%) Resistance? (5 Ω) Each type makes a weighted contribution to MAIFI and SARFI 4/23/2008 Pollution-Resilent Electric Power System 25 Fault Analysis Flowchart Coil Pickup Contact Time dial Trip and Reset Times 100 Seconds Multiples of Pickup (M) 4/23/2008 Pollution-Resilent Electric Power System 26 13

14 Stochastic Load Variations 600 Power Time [s] Peak = MW 2% Level = MW 5% Level = MW Frequency Power [MW] % 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 4/23/2008 Pollution-Resilent Electric Power System 27 How Accurate Can This Be? Overcurrent device models are very good Utilities used these for decades They have been essential to protect life and property Voltage and current calculations are very good Utilities used these for decades They have been essential for equipment specification The greatest uncertainty lies in the number, types, and locations of faults, or the variation of harmonic and flicker injections Utilities do gather some statistics Benchmark over time with PQ measurements 4/23/2008 Pollution-Resilent Electric Power System 28 14

15 Conclusion You can t manage something unless you measure it Software tools need to produce figure-ofmerit outputs (SARFI, MAIFI, P ST, THD 95 ) How to assign value to the indices? EPRI software tools: PQ Planner (not used much) DSS (going open source!!) 4/23/2008 Pollution-Resilent Electric Power System 29 15