The Wave Breaking Factor and it s Vital Role in Surge Protection Device Coordination. Hans Slagter, DEHN + SOHNE

Transcription

1 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 standards 2. Comparing lightning current parameters between IEC and AS/NZS Demonstrating difference between I max and I imp 4. Lightning current distribution, 50%/50% Rule 5. Defining minimum and maximum rating of SPDs 6. Coordination of more than one SPD and introduction the Wave Breaking Factor 7. Conclusion

2 Introduction to IEC series 98 Introduction to IEC series 154

3 Introduction to IEC & 12 There are basically 3 Different Classes of SPD Class I Type Spark-gap Type Triggered Spark-Gap Type Varistor Type Introduction to IEC & 12 There are basically 3 Different Classes of SPD Combined Class I + II Type Spark-gap Type Triggered Spark-Gap Type Varistor Type

4 Introduction to IEC & 12 There are basically 3 Different Classes of SPD Class II and III Type Varistor Type Suppressor Diode Type Introduction to IEC & 12 IEC 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.

5 Table F.1 Rated impulse voltage for equipment energized directly from the low-voltage mains IEC , Ed 2: 2007 Nominal voltage of the supply system based on IEC Three phase Single phase Voltage line to neutral derived from nominal voltage a.c. or d.c. up to and including Rated impulse voltage Overvoltage category V I II III IV / / / AS/NZS 1768:2007 In AS/NZS 1768:2007 Continuous reference is made to IEC

6 AS/NZS 1768:2007 Lightning protection SECTION 5 - PROTECTION OF PERSONS AND EQUIPMENT WITHIN BUILDINGS 5.1 SCOPE OF SECTION NEED FOR PROTECTION MODES OF ENTRY OF LIGHTNING IMPULSES GENERAL CONSIDERATIONS FOR PROTECTION PROTECTION OF PERSONS WITHIN BUILDINGS PROTECTION OF EQUIPMENT Lightning Current Parameters

7 Lightning Current Parameters IEC & AS/NZS lightning protection standards LPL I 3 ka (>99%) (<99%) 200 ka LPL II 5 ka (>97%) (<98%) 150 ka LPL III 10 ka (>91%) (<97%) 100 ka LPL IV 16 ka (>84%) (<97%) 100 ka I peak /ka Maximum values of lightning parameters according to lightning protection levels IEC Table 5 IEC : 2010 First Stroke Lightning protection level Current parameters Symbol Unit I II III IV Peak current I ka Short stroke charge Q short C Specific energy W/R MJ/Ω Time parameters T 1 / T 2 µs/µs. 10/350 NOTE: One of the possible test impulses which meet the above parameters is the 10/350 wave shape proposed in IEC

8 Section 5 Protection of persons and equipment within buildings : AS/NZS 1768: Application of SPDs. (c) Surge ratings (iii)...while table 5.1 gives a surge rating for SPDs in the case (Category C3) using the 8/20 s waveshape,it should be acknowledged that the IEC standards make reference to a 10/350 s waveshapeforthisuseinthiscase,and the symbol given to the current rating using this wave shape I imp It has been found that a factor of 10 may loosely be used to provide an indication of the equivalence between these two waveshapes for typical SPD ratings. For example, an SPD withstanding a 100 ka 8/20 μs impulse might be expected to withstand a 10 ka 10/350 μs impulse. Comparison between I imp and I max test currents 100 ka Wave form µs 1 10/ /20 80 ka IkA I (ka) 60 ka 50 ka 40 ka 20 ka µs 200 µs 350 µs 600 µs 800 µs 1000 µs t (µs)

9 Section 5 Protection of persons and equipment within buildings : AS/NZS 1768: Application of SPDs. (c) Surge ratings iii) the lightning surge current to be handled by a point-of-entry SPD has traditionally been considered to come into the building via the service conductors. 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 100% telecommunication system 50% power supply system metal pipelines Ref: IEC % PEB external lightning protection system earth-termination system

10 Lightning Current Distribution LPL I Service Transformer Building External Lightning Protection 200 ka 100 ka 25 ka per Line 25 ka each 100 ka Ref: IEC ka Lightning Current Distribution LPL III or IV Service Transformer Building External Lightning Protection 100 ka 50 ka 12.5 ka per Line 12.5 ka each 50 ka Ref: IEC ka

11 Minimum Requirements for SPDs in accordance with IEC Standards For SPDs connected between Maximum Rating Class I Type SPD I imp Minimum Rating Class I Type SPD I imp 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 (10/350 ųs) 50.0 (10/350 ųs) Use of more than one set of SPDs in power supply systems IEC

12 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: Application of SPDs. (d) Coordination Often the approach taken is to have the primary SPD handle the bulk energy (surge current) and not be too concerned about the U p value for that protector. A secondary protector that will not need to handle such a high value of surge current, can be installed close to the equipment and can be chosen to have an acceptable U p value. However, to achieve this result, careful coordination between the two devices needs to be undertaken. This is quite a complex matter, and a total examination of the issues is beyond the scope of this Standard.

13 Coordination of more than one SPD Design of Class I - ZnO varistor-based arresters Typical products: Class 1 - ZnO varistor-based arresters Company 1 Company 2 Company 3 Class I - ZnO varistor-based arresters have one thing in common: The actual protective element consists of a ZnO varistor or ZnO varistors connected in parallel that were tested for lightning current carrying capacity (10/350 impulse currents) Coordination of more than one SPD Design of Class 1 - ZnO varistor-based arresters Company 1 Company 2 Company 3 I imp 12.5 ka (10/350) U c 280 V < 1.3 kv U p T1, T2 I imp 12.5 ka (10/350) U c 335 V < 1.2 kv U p T1, T2 I imp 12.5 ka (10/350) U c 280 V < 1.5 kv U p T1, T2, T3

14 Coordination of more than one SPD Design of Class 1 ZnO varistor-based arresters Impulse current and voltage protection level 12.5 ka (8/20) 8/20 µs impulse generator SPD V USPD A I total A I SPD Class 1 ZnO varistor-based SPD: Equivalent circuit diagram: Measurement of the voltage protection level (acc. to IEC ) Application conflict Spark Gap & Varistor Type SPDs Typical varistor type curve (8/20µs) Impulse current and voltage protection level i [ka] u [V] voltage across the SPD impulse current 100 t [µs] Type 1 varistor-based SPD: Oscillograms - Measurement of the voltage protection level

15 Coordination of more than one SPD Design of Class 1 - ZnO varistor-based arresters Impulse current and voltage protection level Class 1 - ZnO varistor-based SPD: Measurements in accordance with IEC 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 Energy coordination Initial interference Lightning impulse current 10/350 µs Class I+II arrester Residual interference uncritical to terminal device 230 / 400 V 230 / 400 V Cable length max. 5m Cable length > 5m terminal device? Class I arrester Class 3 arrester

16 Coordination with the varistor of a terminal device Coordination of a Class1 SPD with a ZnO varistor with a 20 mm disc (S20K275) 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 varistors are usually rated with 275 V. Therefore S20K275 is typically used for terminal devices. Typical protective circuit in a terminal device Varistor S 20 K 275 Coordination of a Class 1 ZnO varistor with the varistor of a terminal device x I imp 1.25 ka 12.5 ka (10/350) 0.5m 10/350 µs impulse generator SPD V USPD V Uvar Energy coordination of SPDs in accordance with EN Annex J: Coordination of SPDs and relevant test methods A I total A I SPD A I var S20K275 Coordination of a typical Class I varistor with the varistor of a terminal device: Equivalent circuit diagram for a minimum decoupling length

17 Coordination of a Class 1 ZnO varistor with the varistor of a terminal device ZnO varistor of the type 1 SPD ZnO varistor of the terminal device 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 Load: 1.0 x limp (12.5kA 10/350µs) Result: Varistor of the terminal device exploded! High speed video for a minimum decoupling length

18 Coordination with the varistor of a terminal device Coordination of a Class 1 varistor with the varistor of a terminal device x I imp 1.25 ka 12.5 ka (10/350) 10 m 10/350 µs impulse generator SPD V USPD V Uvar Energy coordination of SPDs in accordance with EN A I total A I SPD A I var S20K275 Repetition of the test with a decoupling length of 10 m Coordination of a Class 1 ZnO varistor with the varistor of a terminal device Load: 1.0 x l imp (12.5kA 10/350µs) High speed video for a decpoupling length of 10 m

19 Coordination of a Class 1 ZnO varistor with the varistor of a terminal device High speed video for a decpoupling length of 10 m Load: 1.0 x l imp (12.5kA 10/350µs) Result: The varistor of the terminal device is totally destroyed even with a decoupling length of 10 m Coordination between Triggered Spark-gap and the ZnO varistor of the terminal device x I imp 1.25 ka 12.5 ka (10/350) 0.5m / 10 m 10/350 µs impulse generator SPD V USPD V Uvar Energy coordination of SPDs in accordance with EN Annex J: Coordination of SPDs and relevant test methods A I total A I SPD A I var S20K275 Class 1 spark-gap-based SPD: Circuit diagram for minimum decoupling and a decoupling length of 10 m

20 Coordination between Triggered Spark-gap and the ZnO varistor of the terminal device Class 1 spark-gapbased SPD varistor of the terminal device Coordination of a Class 1 spark gap with the varistor of a terminal device: Strommessung Test-set up for a minimum decoupling length 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. 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

21 Comparison of the coordination behaviour Comparison of the coordination behaviour of a spark gap and a varistor Class 1 varistor-based SPD Class 1 spark-gap-based SPD i [ka] total current current flowing through the varistor of the terminal device i [ka] total current Redution of the impulse time wave breaker function current flowing through the type 1 SPD (spark gap) current flowing through the type 1 SPD (varistor) t [ms] current flowing through the varistor of the terminal device t [ms] Current characteristics for a decoupling length of 10 m Load: 0.1 x l imp (1.25kA 10/350μs) Comparison of the coordination behaviour Comparison of the coordination behaviour of a spark gap and a varistor Class 1 varistorbased type arrester Impulse current characteristic Surge current is flowing through the varistor of the terminal device for almost the entire duration of the impulse current Energy load in the varistor of the terminal device Destructive energy overload even in case of low impulse current amplitudes Class 1 spark-gapbased type arrester After the spark gap has triggered, hardly any current flows through the 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 maximum specified impulse current

22 New SPD parameter: Wave breaker factor 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 I imp * Wave breaker factor: Amount of energy absorbed by the SPD which is not affecting the downstream equipment i [ka] Wave breaker factor = A 10/350 A WB A 10/350 A 10/350 A WB Wave breaker area Current-time area of the current which is let through by the Class 1 arrester and which reaches the downstream protective element. A WB t [ms] A 10/350 Total current-time area of the 10/350 impulse current New SPD parameter: Wave breaker factor Example DEHNventil: Load I imp (12.5kA 10/350µs) minimum decoupling i [ka] total current Wave breaker factor = A 10/350 A WB A 10/ % current flowing through the varistor of the terminal device t [ms]

23 New SPD parameter: Wave breaker factor Example Class 1 varistor-based SPD: decoupling length of 10 m Load I imp (1.25kA 10/350µs) i [ka] total current A 10/350 A WB Wave breaker factor = A 10/ % current flowing through the varistor of the terminal device t [ms] 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.

24 Conclusion 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. Spark-gap-based DEHNventil 99.5 % Class 1 varistor-based SPD 36 % Conclusion There is a urgent need for Australia and New Zealand to adopt the IEC series as an SPD product standards in order to establish a systematic, cost effect approach to the implementation of Surge Protection HANS SLAGTER Marketing Executive Australia DEHN + SÖHNE GMBH + CO.KG Hans.Slagter@dehn.com.au