The “Wave Breaking Factor” and it’s Vital Role in ... · PDF filewithin...
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© Copyright 2012 DEHN + SÖHNE
The “Wave Breaking Factor” and it’s Vital Role in Surge Protection Device
Coordination
Hans Slagter, DEHN + SOHNE
Earthing, Bonding & Surge Protection Conference, Auckland 2012
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Discussion topics
1. Introduction to IEC 61643, SPD product standards2. Comparing lightning current parameters between
IEC and AS/NZS 17683. Demonstrating difference between Imax and Iimp4. Lightning current distribution, 50%/50% Rule5. Defining minimum and maximum rating of SPDs6. Coordination of more than one SPD and
introduction the “Wave Breaking Factor”7. Conclusion
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Introduction to IEC 61643 series 98
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Introduction to IEC 61643 series 154
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There are basically 3 Different Classes of SPD
Spark-gap Type
Class I Type
Triggered Spark-Gap Type
Varistor Type
Introduction to IEC 61643-11 & 12
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There are basically 3 Different Classes of SPD
Spark-gap Type
Combined Class I + II Type
Triggered Spark-Gap Type
Varistor Type
Introduction to IEC 61643-11 & 12
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There are basically 3 Different Classes of SPD
Class II and III Type Varistor Type
Suppressor Diode Type
Introduction to IEC 61643-11 & 12
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IEC 61643-11 addresses safety and performance tests for surge protective devices (SPDs).
For the different Classes of SPD different impulse tests waveshapes are specified:
The Class I test is intended to simulate partial conducted lightning current impulses. SPDs subjected to Class I test methods are generally recommended for locations at points of high exposure, e.g., line entrances to buildings protected by lightning protection systems.
• SPDs tested to Class II or III test methods are subjected to impulses of shorter duration, induced surges.
Introduction to IEC 61643-11 & 12
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Nominal voltage of the supply system based
on IEC 60038
Voltage line to neutral derived from nominal
voltage a.c. or d.c. up to and including
Rated impulse voltage
Overvoltage category
Three phase Single phase
V I II III IV
120-240
50 330 500 800 1 500100 500 800 1 500 2 500150 800 1 500 2 500 4 000
230/400 277/480
300 1 500 2 500 4 000 6 000
400/690 600 2 500 4 000 6 000 8 000 1 000 1 000 4 000 6 000 8 000 12 000
IEC 60664-1, Ed 2: 2007
Table F.1 – Rated impulse voltage for equipment energized directlyfrom the low-voltage mains
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AS/NZS 1768:2007
In AS/NZS 1768:2007 Continuous reference is made to IEC
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SECTION 5 - PROTECTION OF PERSONS AND EQUIPMENT WITHIN BUILDINGS
5.1 SCOPE OF SECTION ............................................................................... 66
5.2 NEED FOR PROTECTION........................................................................ 66
5.3 MODES OF ENTRY OF LIGHTNING IMPULSES..................................... 66
5.4 GENERAL CONSIDERATIONS FOR PROTECTION............................... 69
5.5 PROTECTION OF PERSONS WITHIN BUILDINGS................................ 70
5.6 PROTECTION OF EQUIPMENT............................................................... 73
AS/NZS 1768:2007 Lightning protection
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Lightning Current Parameters
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Lightning Current Parameters –IEC & AS/NZS lightning protection standards
0 20 40 60 80 100 120 140 160 180 200 220
LPL IV
LPL III
LPL II
LPL I (<99%) 200 kA3 kA (>99%)
(<98%) 150 kA5 kA (>97%)
10 kA (>91%)
16 kA (>84%)
(<97%) 100 kA
(<97%) 100 kAIpeak/kA
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Maximum values of lightning parameters according to lightning protection levels – IEC 62305-1 Table 5
First Stroke Lightning protection level
Current parameters Symbol Unit I II III IV
Peak current I kA 200 150 100
Short stroke charge Qshort C 100 75 50
Specific energy W/R MJ/Ω 10 5.6 2.5
Time parameters T1 / T2 µs/µs. 10/350
IEC 62305-1 : 2010
NOTE: One of the possible test impulses which meet the above parameters is the 10/350 wave shape proposed in IEC 62350-1
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Section 5 Protection of persons and equipment within buildings : AS/NZS 1768:2007
5.6.3.7 Application of SPDs.
(c) Surge ratings – (iii)...........While table 5.1 gives a surge rating forSPDs in the case (Category C3) using the 8/20 s wave shape, it shouldbe acknowledged that the IEC standards make reference to a 10/350 swave shape for this use in this case, and the symbol given to the currentrating using this wave shape Iimp
It has been found that a factor of 10 may loosely be used to provide anindication of the equivalence between these two waveshapes for typicalSPD ratings. For example, an SPD withstanding a 100 kA 8/20 μsimpulse might be expected to withstand a 10 kA 10/350 μs impulse.
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Comparison between Iimp and Imax test currents
20 kA
40 kA
60 kA
80 kA
100 kA
I (kA)
200 µs 350 µs 600 µs 800 µs 1000 µst (µs)
20 µs
50 kA
12
110/350
40
28/20
40
Wave form µs
I kA
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Section 5 Protection of persons and equipment within buildings : AS/NZS 1768:20075.6.3.7 Application of SPDs.
(c) Surge ratings – iii) the lightning surge current to be handled by a point-of-entrySPD has traditionally been considered to come into the building via the serviceconductors.
However, another mechanism is now understood to exist. If lightning strikes the building LPS, or even the ground or an object nearby, a local EPR occurs. The incoming service conductors are typically referenced to a distant earth (such as the neutral conductor grounded at the secondary transformer some distance down the street, with the phase conductor also being referenced to that distant earth by virtue of the transformer winding).
The effect of the local EPR is that a proportion of the lightning current flows OUT through the point-of-entry SPDs on its way to reaching the distant earth. The surge current in the SPDs in this case is very large, being a significant proportion of the lightning current itself.
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Assumed Current Distribution of a Lightning Strike
telecommunication system
metal pipelines50% earth-termination system
external lightning protection system
PEB
100%
power supply system50%
Ref: IEC 61643-12
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Lightning Current Distribution LPL I
ServiceTransformer
25 kA per Line
External Lightning Protection
Building
200 kA
100 kA
100 kA
100 kA
25 kA each
Ref: IEC 61643-12
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Lightning Current Distribution LPL III or IV
ServiceTransformer
12.5 kA per Line
External Lightning Protection
Building
100 kA
50 kA
50 kA
50 kA
12.5 kA each
Ref: IEC 61643-12
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Minimum Requirements for SPDs in accordance with IEC Standards
For SPDs connectedbetween
Maximum RatingClass I Type SPD
Minimum RatingClass I Type SPD
Iimp Iimp
L-N 25.0 (10/350 ųs) 12.5 (10/350 ųs)
Single Phase N-PE 50.0 (10/350 ųs) 25.0 (10/350 ųs)
Three Phase N-PE 100.0 (10/350 ųs) 50.0 (10/350 ųs)
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Use of more than one set of SPDs in power supply systemsIEC 62305-4
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Coordination of more than one SPD and the need for „Wave
Breaking Factor“
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Section 5 Protection of persons and equipment within buildings : AS/NZS 1768:2007
5.6.3.7 Application of SPDs.
(d) Coordination Often the approach taken is to have the primary SPDhandle the bulk energy (surge current) and not be too concerned aboutthe Up value for that protector.
A secondary protector that will not need to handle such a high value ofsurge current, can be installed close to the equipment and can bechosen to have an acceptable Up value.
However, to achieve this result, careful coordination between the twodevices needs to be undertaken. This is quite a complex matter, and atotal examination of the issues is beyond the scope of this Standard.
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Coordination of more than one SPDDesign of Class I - ZnO varistor-based arresters
Typical products: Class 1 - ZnO varistor-based arresters
Company 2Company 2Company 1Company 1 Company 3Company 3
Class I - ZnO varistor-based arresters have one thing in common:
The actual protective element consists of a ZnO varistor or ZnOvaristors connected in parallel that were tested for lightning current carrying capacity (10/350 impulse currents)
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Iimp 12.5 kA (10/350)Uc 280 VUp < 1.3 kV
T1, T2
Iimp 12.5 kA (10/350)Uc 335 VUp < 1.2 kV
T1, T2
Iimp 12.5 kA (10/350)Uc 280 VUp < 1.5 kV
T1, T2, T3
Coordination of more than one SPDDesign of Class 1 - ZnO varistor-based arresters
Company 2Company 2Company 1Company 1 Company 3Company 3
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Impulse current and voltage protection level
Class 1 – ZnO varistor-based SPD: Equivalent circuit diagram: Measurement of the voltage protection level (acc. to IEC 61643-11)
SPD8/20 µsimpulse generator
Itotal
12.5 kA (8/20)
A
AISPD
VUSPD
Coordination of more than one SPDDesign of Class 1 – ZnO varistor-based arresters
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Impulse current and voltage protection level
t [µs]
Type 1 varistor-based SPD: Oscillograms - Measurement of the voltage protection level
0.0
2.0
4.0
6.0
8.0
10.0
i [kA]
100
300
500
700
900u [V]
5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0
12.0
impulse current
voltage across the SPD
Application conflict Spark Gap & Varistor Type SPDsTypical varistor type curve (8/20µs)
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Class 1 - ZnO varistor-based SPD:
Measurements in accordance with IEC 61643-11 were carried out for different products.
The specified impulse currents (12.5 kA 10/350) were discharged.
The specified voltage protection level values were adhered to.
Impulse current and voltage protection level
What about the coordination with downstream terminal devices or type 3 arresters?
According to the manufacturers, the arresters are classified as fully energy coordinated for terminal equipment T1/T2 or T1/T2/T3
Coordination of more than one SPDDesign of Class 1 - ZnO varistor-based arresters
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Energy coordination
Class I arrester
terminaldevice
?
Cable length max. 5m
Initial interferenceLightning impulse current 10/350 µs
230 / 400 V
Cable length > 5m
230 / 400 V
Class 3 arrester
Residual interference uncritical to terminal
deviceClass I+II arrester
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Why coordination with a S20K275?
Most Class 1 ZnO varistor-based arresters are T1, T2 or T1, T2, T3 classified. These arresters must be combinable with the downstream terminal devices or type 3 arresters.
20 mm ZnO varistors are typically used for protection levels within terminal devices and type 3 arresters.
In 230/400 V low-voltage systems these S20 ZnO varistorsare usually rated with 275 V.
Therefore S20K275 is typically used for terminal devices.
Coordination of a Class1 SPD with a ZnO varistor with a 20 mm disc (S20K275)
Coordination with the varistor of a terminal device
Typicalprotective circuit
in a terminal device
VaristorS 20 K 275
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SPD10/350 µsimpulse generator
Itotal
0.1... 1.0 x Iimp
1.25 kA … 12.5 kA (10/350)
A
AISPD
VUSPD
Coordination of a typical Class I varistor with the varistor of a terminal device:Equivalent circuit diagram for a minimum decoupling length
S20K275
Energy coordination of SPDs in accordance with EN 61643-12 Annex J: Coordination of SPDs and relevant test methods
Coordination of a Class 1 ZnO varistor with the varistor of a terminal device
Ivar
A
VUvar
≤ 0.5m
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ZnO varistor of the terminal device
ZnO varistor of the type 1 SPD
current measuring equipment
Coordination of a typical Class 1 varistor with the varistor of a terminal device:Test set-up for a minimum decoupling length
Coordination of a Class 1 ZnO varistor with the varistor of a terminal device
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Coordination of a Class 1 ZnO varistor with the varistor of a terminal device
High speed video for a minimum decoupling length
Load:1.0 x limp (12.5kA 10/350µs)
Result:Varistor of the terminal device exploded!
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SPD10/350 µsimpulse generator
Itotal
0.1... 1.0 x Iimp
1.25 kA … 12.5 kA (10/350)
A
AISPD
VUSPD
Repetition of the test with a decoupling length of 10 m
S20K275Energy coordination of SPDs in accordance with EN 61643-12
Coordination with the varistor of a terminal device
Coordination of a Class 1 varistor with the varistor of a terminal device
Ivar
A
VUvar
10 m
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Load:1.0 x limp (12.5kA 10/350µs)
High speed video for a decpoupling length of 10 m
Coordination of a Class 1 ZnO varistor with the varistor of a terminal device
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Load:1.0 x limp (12.5kA 10/350µs)
Result:
The varistor of the terminal device is totally destroyed even with a decoupling length of 10 m
High speed video for a decpoupling length of 10 m
Coordination of a Class 1 ZnO varistor with the varistor of a terminal device
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SPD10/350 µsimpulse generator
Itotal
0.1... 1.0 x Iimp
1.25 kA … 12.5 kA (10/350)
A
AISPD
VUSPD
S20K275Energy coordination of SPDs in accordance with EN 61643-12Annex J: Coordination of SPDs and relevant test methods
Coordination between Triggered Spark-gap and the ZnO varistor of the terminal device
Ivar
A
VUvar
0.5m / 10 m
Class 1 spark-gap-based SPD:Circuit diagram for minimum decoupling and a decoupling length of 10 m
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Strommessung
Class 1 spark-gap-based SPD
Coordination of a Class 1 spark gap with the varistor of a terminal device:Test-set up for a minimum decoupling length
Coordination between Triggered Spark-gap and the ZnO varistor of the terminal device
varistor of the terminal device
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Coordination of a Class 1 spark gap with the varistor of a terminal device:Test-set up for minimum decoupling and a decoupling length of 10 m
Coordination between Triggered Spark-gap and the ZnO varistor of the terminal device
Result:
No overload in case of a minimum decoupling length.
No overload in case of a decoupling length of 10 m.
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Class 1 varistor-based SPD Class 1 spark-gap-based SPD
Comparison of the coordination behaviour of a spark gap and a varistor
Current characteristics for a decoupling length of 10 mLoad: 0.1 x limp (1.25kA 10/350μs)
-0.25
0.00
0.25
0.50
0.75
1.00
1.25
1.50i [kA]
0.0 0.2 0.4 0.6 0.8 1.0 1.2t [ms]
current flowing through the type 1 SPD (spark gap)
current flowing through the varistor of the terminal device
total current
t [ms]
-0.25
0.00
0.25
0.50
0.75
1.00
1.25
1.50i [kA]
0.0 0.2 0.4 0.6 0.8 1.0 1.2
total current
current flowing through the varistor of the terminal device
current flowingthrough the type 1 SPD (varistor)
Redution of the impulse time
“wave breaker function“
Comparison of the coordination behaviour
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Class 1 varistor-based type arrester
Class 1 spark-gap-based type arrester
Impulse current characteristic Energy load in the varistor of the terminal device
Surge current is flowing through the varistor of the terminal device for almost the entire duration of the impulse current
Destructive energy overloadeven in case of low impulse current amplitudes
After the spark gap has triggered,hardly any current flows throughthe varistor of the terminal dev. “Reduction of the impulse
“time” / “wave breaker function“
Almost no energy load through the varistor of the terminal dev.even in case of the maximumspecified impulse current
Comparison of the coordination behaviour
Comparison of the coordination behaviour of a spark gap and a varistor
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i [kA]
t [ms]
Diagram of the wave breaker factor *Class 1 arrester limits the current-time area (Charge Q) of the 10/350µs impulse current Measurement of the impulse current characteristic at Iimp
A10/350 – AWB
A10/350Wave breaker factor =
New SPD parameter: Wave breaker factor
A10/350
AWB
AWB Wave breaker areaCurrent-time area of the current which is let through by the Class 1 arrester and which reaches the downstream protective element.
A10/350 Total current-time area of the 10/350 impulse current
* Wave breaker factor: Amount of energy absorbed by the SPD which is not affecting the downstream equipment
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Example DEHNventil: Load Iimp (12.5kA 10/350µs) minimum decoupling
0.0
2.0
4.0
6.0
8.0
10.0
12.0
i [kA]
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 t [ms]
current flowing through the varistor of the terminal device
total current
99.5 %
New SPD parameter: Wave breaker factor
A10/350 – AWB
A10/350Wave breaker factor =
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Example Class 1 varistor-based SPD: Load Iimp (1.25kA 10/350µs) decoupling length of 10 m
New SPD parameter: Wave breaker factor
-0.25
0.00
0.25
0.50
0.75
1.00
1.25
1.50i [kA]
0.0 0.2 0.4 0.6 0.8 1.0 1.2 t [ms]
total current
current flowing through the varistor of the terminal device
36 %
A10/350 – AWB
A10/350Wave breaker factor =
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Conclusion
There are basically 3 types of SPDs, Class I, II & III
Coordination between SPD is vital as most downstream terminal devices have some form of built-in surge protection, this has to be considered in the overall design!
Coordination between two sets of Voltage limiting type (Varistor) SPDs including those in downstream terminal devices is extremely difficult when considering long duration lightning impulse wave shape as a result of direct or nearby lightning strokes!
Coordination between SPDs for long and short duration lightning impulse wave shape should be carried out using Voltage Switching (Triggered Spark-gaps) type SPDs in conjunction with voltage limiting type SPDs.
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To ensure proper coordination between SPDs the “Wave Breaking Factor” must be established, the higher the factor the better the protective effect for downstream electrical and electronic equipment.
Conclusion
99.5 %
36 %
Class 1 varistor-based SPD
Spark-gap-based DEHNventil®
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There is a urgent need for Australia and New Zealand to adopt the IEC 61643 series as an SPD product standards in order to establish a systematic, cost effect approach to the implementation of Surge Protection
Conclusion
DEHN + SÖHNE
GMBH + CO.KG
HANS SLAGTERMarketing Executive
Australia
eMail: [email protected]