Power Quality Troubleshooting

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Published on January 5, 2008

Author: Natalya

Source: authorstream.com

7x24 Exchange:  7x24 Exchange Power Quality Troubleshooting Dallas, May 5th 2005 What is Power Quality ?:  What is Power Quality ? Power: “ The ability to do something “ Quality: “ The degree of excellence “ What is Power ?:  What is Power ? Major utility company had a faulty electrical switch and had to open the branch while under load. Note that one of the air switches, refused to disconnect immediately. Watch the result!!! How is your Power today? :  How is your Power today? Is it good? Is it bad? Is it getting better? Is it getting worse? Where is it getting worse? Why is it getting worse? Expensive Downtime:  Expensive Downtime Semiconductor Manufacturer $3,000,000+ per event Intel, Motorola, AMD Telecom Switch $50,000 per minute Bell, Sprint, MCI Data Center $20,000 to $1,000,000 per min EDS, Fidelity, American Express dot.com IBX centers Car Manufacturer $25,000+ per minute General Motors, Ford PQ Troubleshooting tools:  PQ Troubleshooting tools Voltage logger. Single phase. voltage Transient capture Sags, swells Hand held portable. Single phase power In-Rush current N-G bonding PQ Troubleshooting tools:  PQ Troubleshooting tools Power Quality. 3 phase. Voltage, current Transient capture Sags, swells, Harmonics Unbalance Power Quality. 3 phase power Cycle by Cycle Full Disclosure capture PQ Troubleshooting Philosophy:  PQ Troubleshooting Philosophy Start at the scene of the crime Examine the victim (the load) Take time to visually inspect What is the business cycle? Ask questions? PQ Troubleshooting: Bottom-up :  PQ Troubleshooting: Bottom-up Example: High harmonics everywhere Load location Problem location, most likely causes Monitoring issues PQ Troubleshooting: Getting Started:  PQ Troubleshooting: Getting Started Make a simplified “as-built” one-line Do a walk-around Interview witnesses Power Distribution System:  Power Distribution System 1. Branch circuit and service panel 3. Feeder loads 2. Distribution Transformer Receptacle Line to Neutral Voltage:  Receptacle Line to Neutral Voltage The Case of the Rural Transformer Failure:  The Case of the Rural Transformer Failure Scene of the crime: Rural area surrounded by farmland and open space Enigma: Utility transformer failure occurred in location where power quality problems are rare Risk: Loss of power Utility Electrical Engineer’s Notes:  Utility Electrical Engineer’s Notes Load: consists of 3 end-users What happened during the day of the transformer failure? Single Phase Measurements:  Single Phase Measurements Battery chargers are non-linear loads that generate harmonic currents Utility Electrical Engineer’s Notes:  Utility Electrical Engineer’s Notes Problem: All three end-users experienced peak loads at the same time (5 – 7pm) Residential peaks occur at dinnertime with use of TV sets, stoves, dishwashers, etc. Addition of the large battery charger load on the day of the golf tournament caused the transformer to overheat Utility Electrical Engineer’s Notes:  Utility Electrical Engineer’s Notes Solution: Golf club supervisor agreed to use careful load management Restrict number of chargers connected at one time Avoid use of chargers during peak times Takeaways:  Takeaways Transformers can overheat and fail if heavily loaded with harmonic currents Battery chargers are non-linear loads that generate harmonic currents Golf clubs and marinas are vulnerable to sudden large battery charger loads Timing was important in solving this case history …always ask for timing info Careful load management can usually avoid overloads Power Quality Troubleshooting: Service Panel:  Power Quality Troubleshooting: Service Panel Feeder Current :  Feeder Current Feeder Phase Balance:  Feeder Phase Balance How much current do you expect on the feeder neutral? ØA ØB ØC Neutral Current:  Neutral Current Neutral current 180 Hz waveform 40.57A 3rd harmonic 37.35A Fundamental 3.71A 3rd Harmonic:  3rd Harmonic The Case of the 5th Harmonic Resonance:  The Case of the 5th Harmonic Resonance Scene of the crime: A small city gets its water from a mountain lake 30 miles away A pumping system at the lake brings water through a pipeline that feeds the city’s water distribution system Enigma: Under generator power, the backwash filtering system suddenly shuts off Risk: Interruption of water supply to the city Water Plant Electrical Engineer’s Notes:  Water Plant Electrical Engineer’s Notes Diagram of the water plant: Utility: System has no problem when utility power is connected Generator: Backwash pump shuts off partway through the start sequence Water Plant Electrical Engineer’s Notes:  Water Plant Electrical Engineer’s Notes Generator: Why does the backwash pump shut off partway through the start sequence? Backwash pump shuts off partway through the start sequence due to a “stop signal” from the protection circuit Fluke 43B showed 5th harmonic distortion rising to 80% of the fundamental prior to the “stop signal” Distortion caused by high resonance current at the 5th harmonic flowing between the motor inductance and the PF correction caps Harmonic current flowing into the generator impedence caused enough voltage distortion to produce a stop signal Water Plant Electrical Engineer’s Notes:  Water Plant Electrical Engineer’s Notes Solution: Move the capacitors to the utility side of the transfer switch so that the capacitors are out of the circuit when the generator is operating Takeaways:  Takeaways System operation on generator power should be tested for all load combination Voltage distortion is usually higher when operating on a generator due to higher impedance of the generator Power factor correction caps can make the system resonant near the 5th harmonic Semiconductor soft start circuits are often not compatible with PF correction caps Common test equipment is not adequate for harmonic analysis. Voltage Severity ITIC :  Voltage Severity ITIC Voltage Severity ITIC:  Voltage Severity ITIC Selected Event:  Selected Event Why Worry About Sags?:  Why Worry About Sags? Voltage quality was monitored at the wall outlet at 112 North American locations from 1990-1994: Sags average 27.9 per month with an average sag amplitude of 99.3Vrms. The median sag duration is 260ms (4.3 cycles) Sags are the most prevalent event 10c-1s 2-10cycles 10s-1min >1min 1-10s 41% 22% 20% 6% 11% RMS Inrush Measurement:  RMS Inrush Measurement Half cycle rms value of the r.m.s. current measured over each half-period Inrush current begins when the half-cycle rms current rises above the inrush threshold, and ends when the half cycle rms current is equal to or below the inrush threshold minus a user-selected hysteresis value. The measurement should be the half cycle rms values. Each half-cycle interval is contiguous and non-overlapping. Inrush Current :  Inrush Current Transients:  Transients Causes of Transients: Utility transformer tap switching Capacitors switching on. Lightning Motors switching off (Elevators) Switch and relay contact “bounce” Effects of transients: Damage semiconductor junctions Couple into adjacent circuits because of high frequency (fast rise times) Corrupt data signals Protection: TVSS Transient Voltage Surge Suppressors Case Study: Re-active decision:  Case Study: Re-active decision Large European Wafer Plant 5,000 employees Serious failure condition No monitoring Costly downtime Installed equipment to prevent similar incident Case Study: Pro-active decision:  Case Study: Pro-active decision Major US bank Central HQ for ATM and On-Line customer transactions Failure of UPS system SCR misfiring Bank identified problem Corrective action in place New ways of thinking:  The old way: Did anything happen? What happened? What is the cause? The new way: What will happen next? When will it happen again? How can I prevent it? New ways of thinking Slide39:  BREADTH OF MEASUREMENTS DEPTH OF MEASUREMENTS FULL DISCLOSURE MONITORING Slide40:  BREADTH OF MEASUREMENTS Power Quality Power Consumption Harmonics Flicker Imbalance Ground loops Oscilloscopes Slide41:  DEPTH OF MEASUREMENTS Cycle by Cycle measurements: RMS, harmonics, THD, W, VA, VAR, PF, etc. Power Quality: No thresholds set limits after the fact use power tolerance curve use indices to track conditions Slide42:  PQ Index = 100 PQ Index = 0 Power Quality Index PQ Index = 0 PQ Index = 100 Slide43:  time Slide44:  1250 1000 750 500 250 0 1250 1000 750 500 250 0 Atlanta Power Quality Index Peak : 270 Mean : 55 7x24 Exchange :  7x24 Exchange Thank you for attending john.carroll@fluke.com

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