Advanced Protection Technologies

Surge Protection Overview

Prepared by: Lou Farquhar, PE, CEM, GBE

VP – APT Engineering Service

(800) 237-4567

Copyright APT 2012 2

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 standards

committees

Copyright APT 2012 3

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 2012 4

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%• Externally generated surges: ≈30%

In outdoor environment, this ratio probably reverses

Copyright APT 2012

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 2012

MOV - Metal Oxide Varistor• Varistor - variable resistor• Semiconductor; generally zinc oxide• Connects parallel to load (not series)• Thickness determines clamping voltage• Diameter determines current capacity

MOV symbol

Copyright APT 2012 7

MOV - Metal Oxide Varistor

Normal voltage Overvoltage

I =V 120V

R 109= 0.12A I =

V 6000VR 1

= 6000A

• MOV seeks to equalize overvoltage• Voltage sensitive conductor: V = IR & I = V/R• At ‘low’ voltages: very high impedance, 109: I 0A• Above ‘threshold’ voltage: resistance approaches 0: I = high A

– Current diverts through MOV as I = V/R (high V, low R)

Trivial leakage current Surge Current

Copyright APT 2012 8

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, I2R 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 2012 9

SPD Operation

MOV/SPD Acts as a momentary ‘short circuit’ ‘short circuit’ ≈ no overvoltage ≈ protected load

Load 1

Load 2

Load 3

Layman’s Terms: Visualize an ‘electronic guillotine’ that chops the head off a surge and sends it away

After the surge, MOV/SPD automatically resets itself to high impedance state drawing no current

Copyright APT 2012 10

SPD Operation

Load 1

Load 2

Load 3

MOV/SPD Acts as a momentary ‘short circuit’, then resets itself after the surge

‘short circuit’ ≈ no overvoltage ≈ protected load

Copyright APT 2012 11

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 - 170V to clamping voltage

• No Sharp bends or kinks• No Wire Nuts!• Right Hand Rule – can cancel inductive effects by

bundling, tie-wrapping conductors together

Copyright APT 2012 12

2008 NEC Art 285

Copyright APT 2012 13

2011 NEC Art 285

Copyright APT 2012 14

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.