Advanced Protection Technologies Surge Protection Overview Prepared by: Lou Farquhar, PE, CEM, GBE VP – APT Engineering Service (800) 237 -4567
APT • 26 Years Supplying Surge Protective Devices • ISO 9001 -2008 Quality Management System • ISO 17025 evaluation by UL • Power Quality Assurance magazine – PQ 50 Company • Frost & Sullivan ranked APT – Leading Supplier of Three Phase Devices • Market Engineering Customer Focus Awards • Members of UL, IEEE, NEMA Copyright APT standards committees 2
What Is a Surge/Transient? • High amplitude, short duration overvoltage • Can be positive or negative polarity Tidbit: Transient: > two times system’s RMS voltage Noise: < two times system’s RMS voltage Transient Overvoltage – Can be thousands of volts Millionths of second Copyright APT 3
What Causes Surges/Transients? • Lightning • Switching: – Load Switching – utility & customer • Motors, Large Loads, Faults, Fuse Operation – Source Switching • Smart Grid, Gensets, PV, Wind Turbine • Internally generated surges: ≈70% In outdoor • Externally generatedenvironment, surges: this ratio probably reverses Copyright APT 4
Effects of Transient Voltages? • Microelectronics Intolerant to Surges • Disruption – Lockups, Downtime & Interruption costs – Computing glitches and errors • Degradation – Microelectronics – Slow & continuous damage to motor insulation • Destruction – Failed microelectronics, ballasts, motors, controllers, etc. Maybe analogous to: - ‘Water hammer’ in a plumbing system - ‘Rust’ to microelectronics Copyright APT
MOV - Metal Oxide Varistor • • • Varistor - variable resistor Semiconductor; generally zinc oxide Connects parallel to load (not series) Thickness determines clamping voltage MOV Diameter determines current capacity symbol Copyright APT
MOV - Metal Oxide Varistor • • MOV seeks to equalize overvoltage Voltage sensitive conductor: V = IR & I = V/R At ‘low’ voltages: very high impedance, 109 : I 0 A Above ‘threshold’ voltage: resistance approaches 0 : I = high A – Current diverts through MOV as I = V/R (high V, low Normal Overvolta R) voltage I= V R 120 V = 0. 12 A 9 10 Trivial leakage current Copyright APT ge 6000 V V I= = 6000 A R 1 Surge Current 7
MOV - Metal Oxide Varistor • Overvoltage diverts through MOV as current • Voltage is “clamped” or “equalized” as energy is transferred to other side of MOV(s) • MOV does not ‘absorb’ surge, however, I 2 R heat is retained • Bidirectional – Operates same for positive or negative surges • Creates a momentary low impedance (acting like short-circuit) to pass transient energy to earth; analogous to water heater pressure relief valve - + Copyright APT + - 8
SPD Operation Load 1 Load 2 Load 3 MOV/SPD Acts as a momentary ‘short circuit’ ≈ no overvoltage ≈ protected load After the surge, MOV/SPD automatically resets itself to high impedance state drawing no current Layman’s Terms: Visualize an ‘electronic guillotine’ that chops the head off a surge Copyright APT and sends it away 9
SPD Operation Load 1 Load 2 Load 3 MOV/SPD Acts as a momentary ‘short circuit’, then resets itself after the surge Copyright APT ‘short circuit’ ≈ no overvoltage ≈ protected 10
SPD Connector Leads • Need short lead lengths! • NEC 285. 12: “The conductors used to connect the SPD (surge arrester or TVSS) to the line or bus and to ground shall not be any longer than necessary and shall avoid unnecessary bends” • Industry typically states: Each foot of conductor adds 100 - 170 V to clamping voltage • No Sharp bends or kinks • No Wire Nuts! • Right Hand Rule – cancel inductive effects by bundling, tie-wrapping conductors together Copyright APT 11
2008 NEC Art 285 Copyright APT 12
2011 NEC Art 285 Copyright APT 13
APT Here to Help: (800) 237 -4567 • • Specification Assistance Training Sounding Board for issues Competitive crosses or analysis General Help On-Line webinar services Forensic Testing & Analysis of failed SPDs • Etc. Copyright APT 14
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