2/9/2016
Why..? Power Protection Systems
Surge Protection Systems
for Low Voltage and Low Power
Systems
(Part 2)
Nihal Kularatna
The University of Waikato
Hamilton
New Zealand
• Electronic Systems are more vulnerable to power line
disturbances
• Because they contain
• High energy power semiconductors
• Low-power sensitive chips
• adverse weather
• equipment malfunction
• vehicles running into poles
• Internal –(controllable at an extra cost)
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switching heavy loads
poor wiring
overloaded circuits
inadequate grounding
230 V / 50 Hz
110 V / 60 Hz
Electronic Systems
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Computers
Laboratory Instruments
CAD/CAM Systems
Modern Medical Equipments
Telecommunication Systems etc.
Power Line Disturbances
• External (unavoidable)
Commercial Power
Electronic Grade Power
• Protective devices are available to obtain
“Electronic Grade Power” from “Utility Grade
Power”
• Two types of power protection equipments
• Power Enhancement Equipments
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Transient voltage surge suppressors (TVSS)
Voltage regulators
Isolation transformers
Line conditioners
• Power Synthesis Equipments
• Resultant disasters
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scheduling conflicts
lost orders
lost production
accounting problems and many
more ……
• Standby generators
• Uninterruptible power supplies (UPS)
*** Most of the equipments other than computers can
also benefit from disturbance free electricity
2/9/2016
Transient Voltage Surge Suppressors
• Every user of electricity is
affected
• Effects of transients
• Unexplained data losses in
computer systems
• Scrambled data on computers
• Excessive lighting replacements
• Excessive motor insulation
deterioration
• and much more …….
Transient Voltage Surge Suppressors
• Transient energy
• The approximated energy absorbed by the suppression
element
t
E   Vc I p dt
0
• Where
Figure 1: A typical lightning
current waveform
• Transient activities due to
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E = Energy
Vc = Clamping voltage
Ip = peak pulse current
t = impulse duration
• External sources
• TVS protection devices
• Lightning
• High power switching at substation
levels
• Switching in nearby industrial
complexes
• Metal oxide varistors (MOVs)
• Gas discharge arrestors (commonly known as gas tubes)
• Solid state devices
• TVS Diodes
• TVS Thyristors
• Internal sources
• Turning on a motor
• Light on and off
Figure 2: Transients generated
by turning off a fluorescent light
Statistical Nature Of the Surges
Electro Static Discharge and Human Body Model Testing
•Rate of occurrences of surges vary over a wide limit
•Prediction is pretty difficult and could be very
inaccurate
•What is observed could be
•Driving voltage
•Voltage limited by the spark gap clearance in
the distribution system
•Sparkgap clearance
•in outdoor systems could be usually 10kV
(some times 20kV)
•In door TVSS systems can be typically 6kV or
even less
•Low exposure
•Geographical areas with low lightning activity
•Low load switching
•Medium Exposure
•Geographical areas with high lightning
activity
•High exposure
Source: IEEE 587-1987
•Real system supplied with long overhead lines
2/9/2016
Transient Voltage Surge Suppressors
Transient Voltage Surge Suppressors-Ideal and Characteristics Versus Real World
Devices
 Comparison of TVSS Devices
Suppression
element
Advantages
Disadvantages
Expected life
Gas tube
•Very high current
handling capability
•Low capacitance
•High insulation
resistance
Very high firing voltage
Finite life cycle
Slow response times
Non restoring under DC
•limited
MOV
•High current handling
capability
•Broad current spectrum
•Broad voltage spectrum
•Gradually degradation
•High clamping voltage
•High capacitance
TVS diodes
•Low clamping voltage
•Does not degrade
•Broad voltage spectrum
•Extremely fast response
time
•Limited surge current
rating
•High capacitance for
low voltage types
•Long limited
TVS thyristors
•Does not degrade
•Fast response time
•High current handling
capability
•Non restoring under DC
•Narrow voltage range
•Turn-off delay time
•long
•Degrades
Source: Beneden, V.B., Varistors, Ideal Solution to surge
protection, PET Magazine, May 2003
Table 1: Comparison of TVSS Devices
Metal Oxide Varistor Behaviour
Electrical Characteristics and Equivalent Circuit Model of MOVs
Source credit: Littlefuse application note 9767
Source credit: Littlefuse application note 9767
2/9/2016
Data Sheet Parameters
Speed of MOV operation – A typical example
Practical MOVs from Littlefuse
Source credit: Littlefuse application note 9767
Typical Varistor Data
2/9/2016
Transient Voltage Surge Suppressors
• TVS Device protection levels
• Practical surge protection circuits
• Primary protection
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For outdoor environment power lines and data lines
Service entry
AC distribution panels
Transient currents range: tens to hundreds of kilo amperes
• Secondary protection
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Equipment inputs (including power from long branch circuits)
Internal data lines
PBX
Wall sockets
Lines with a significant distance from the equipment (already have
primary protection)
• Transient voltages: several kilo volts
• Transient current: several hundred to several thousand amperes
• Board level protection
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Transient Voltage Surge Suppressors
• Basic circuit of a multi-stage surge suppressor using MOVs,
power zeners, and series inductors for power line surges
• Figure 3:a
• Telecom line protection using gas discharge tube, MOVs, and
zener diodes
• Figure 3:b
• Line driver/receiver protection
• Figure 3:c
• General IC protection
Internal to the equipment
For protection against residual transient from earlier stages of protection
System generated transients
Electro static discharge (ESD)
Transient voltages: tens to several thousand volts
Transient current: tens of amperes
Transient Voltage Surge Suppressors
• Figure 3:d
Transient Voltage Surge Suppressors
• Electrostatic discharge and circuit protection
• Different kinds of TVSS circuits
• Various standards for testing the ESD capabilities of
semiconductor products
• Human Body Model using the MIL-STD-883, Method 3015.7
• Machine Model using EIAJIC121
• Human Body Model using the IEC 1000-4-2 standard
(a)
(c)
(b)
(d)
• Each standard relates to the nature of ESD generated within a
system and
• The potential for damage to the IC
• Testing for ESD immunity is more broadly defined to include a
device, equipment or system
• Both direct contact and air discharge methods used
• Severity level ranging up to 8 kV and 15 kV
Figure 3: Comparison of TVSS solutions
2/9/2016
Transient Voltage Surge Suppressors
• ESD testing methods and waveforms
Transient Voltage Surge Suppressors
• Transient Protection Standards
• Standards committees
• ANSI, IEEE, IEC
• European or IEC transient standards include
• IEC 1000-4-2 for electro static discharge (ESD)
• IEC 1000-4-4 for electrical fast transients (EFT)
• IEC 1000-4-5 for electrical transients (Testing and
measurement techniques- Section 5: Surge immunity test-199502)
Figure 4: IEC 1000 - 4 - 2 testing
• US transient standards include
• ANSI/IEEE C62.41-1991 for power line transients
• FCC part 68 for telecommunication lines
• UL 1449, and various military standards
Useful Standards- C62-XX series from IEEE/ANSI
2/9/2016
IEC Standards Family