The “Wave Breaking Factor” and it’s Vital Role in ... · PDF filewithin...

© 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


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


Introduction to IEC 61643 series 98


Introduction to IEC 61643 series 154


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



Spark-gap Type

Combined Class I + II Type

Triggered Spark-Gap Type

Varistor Type




Class II and III Type Varistor Type

Suppressor Diode Type



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.



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


AS/NZS 1768:2007

In AS/NZS 1768:2007 Continuous reference is made to IEC


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


Lightning Current Parameters


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


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


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.


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


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.


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


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


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


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)


Use of more than one set of SPDs in power supply systemsIEC 62305-4


Coordination of more than one SPD and the need for „Wave

Breaking Factor“


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.


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)


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


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



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)


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.


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


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


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



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


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




High speed video for a minimum decoupling length

Load:1.0 x limp (12.5kA 10/350µs)

Result:Varistor of the terminal device exploded!



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


Load:1.0 x limp (12.5kA 10/350µs)

High speed video for a decpoupling length of 10 m



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




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


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


varistor of the terminal device


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


Result:

No overload in case of a minimum decoupling length.

No overload in case of a decoupling length of 10 m.


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 flowingthrough the type 1 SPD (varistor)

Redution of the impulse time

“wave breaker function“

Comparison of the coordination behaviour


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


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


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]


total current

99.5 %


A10/350 – AWB



Example Class 1 varistor-based SPD: Load Iimp (1.25kA 10/350µs) decoupling length of 10 m


-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


36 %

A10/350 – AWB



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.


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®


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]

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