1. Advanced Protection Technologies
Surge Protection Overview
Prepared by: Lou Farquhar, PE, CEM, GBE
VP – APT Engineering Service
(800)
May 17-18, 2001
Introduction:
Lou Farquhar, P.E., C.E.M.
APT Engineering Sales Dept.

2. APT 26 Years Supplying Surge Protective Devices
ISO Quality Management System
ISO 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
PQ50 - Handout #1 in your binder.

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
What is a transient? By IEEE definition, a transient is at least two times the system’s RMS voltage. This contrast noise which is less than two times the system’s RMS voltage. A transient is a very short duration event (microseconds) and will be a significant overvoltage or impulse on the AC sine wave. A transient is a small fraction of a 360° sine wave.
Millionths of second 3 3

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%
Transients tend to be caused by lightning, utility operations or internal disturbances.
There are two predominant wave forms used to describe transients. One is a high-energy impulse, a rapid rise and fall. The other is a ring wave, which oscillates at high frequency as it dissipates.
IEEE has developed typical waveforms to describe these events, which will be discussed later.
In outdoor environment, this ratio probably reverses 4 4

5. 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
How do transients cause damage? Transients can cause data transfer glitches as "0's"are misinterpreted as "1's" in a digital data transmission. Bad data can and has shut down operations. The overall cost of any kind of disruption is staggering. Manpower is expensive as people stand around waiting for equipment to reset. Production is lost in batch runs. Many industries require a continuous production flow or else the product must be discarded.
Transients have a cumulative effect much like static discharges. One of the fundamental purposes of surge suppression is to limit voltages to microelectronic equipment such as IC chips. Chips are composed of layered silicon substrates that are permanently damaged when excessive voltage “punches-through” a silicon layer. This occurs at the micron level and is difficult to troubleshoot. The appropriate repair is to replace suspect components.
A rare but worst case transient scenario is substantial destruction. This is usually caused when a component fails due to a transient and an unusual chain of events leads to catastrophic failure. 5

6. 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
The Metal Oxide Varistor is the primary surge suppression component. MOVs are typically made of zinc oxide and are a solid-state semiconductor device. They are bi-directional and will control both positive and negative surges. MOVs come in many diameters and configurations. They are very common in automotive applications. 6

7. 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  0A
Above ‘threshold’ voltage: resistance approaches 0: I = high A
Current diverts through MOV as I = V/R (high V, low R)
Normal voltage
Overvoltage
V V
V V
I =
= 0.12A
I =
= 6000A
R 
R 
The Metal Oxide Varistor is the primary surge suppression component. MOVs are typically made of zinc oxide and are a solid-state semiconductor device. They are bi-directional and will control both positive and negative surges. MOVs come in many diameters and configurations. They are very common in automotive applications.
Trivial leakage current
Surge Current

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 -
MOV reaction times are less than 1/2 nanosecond… transients occur in the microsecond range of time.
MOVs sum like capacitors when installed in parallel. Resistance decreases like paralleled resistors.
Paralleling MOVs increases capacity, lowering impedance at the same time. + + -

9. SPD Operation Load 1 Load 2 Load 3
MOV/SPD Acts as a momentary ‘short circuit’ ‘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 and sends it away

10. ‘short circuit’ ≈ no overvoltage ≈ protected load
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 10

11. SPD Connector Leads Need short lead lengths!
NEC : “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  V to clamping voltage
No Sharp bends or kinks
No Wire Nuts!
Right Hand Rule – can cancel inductive effects by bundling, tie-wrapping conductors together

12. 2008 NEC Art 285 12 12

13. 2011 NEC Art 285 13 13

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.