1、 TECHNICAL REPORT ATIS-0600013 Electromagnetic Compatibility (EMC) and Electrical Protection Environment ATIS is the leading technical planning and standards development organization committed to the rapid development of global, market-driven standards for the information, entertainment and communic
2、ations industry. More than 200 companies actively formulate standards in ATIS Committees, covering issues including: IPTV, Cloud Services, Energy Efficiency, IP-Based and Wireless Technologies, Quality of Service, Billing and Operational Support, Emergency Services, Architectural Platforms and Emerg
3、ing Networks. In addition, numerous Incubators, Focus and Exploratory Groups address evolving industry priorities including Smart Grid, Machine-to-Machine, Networked Car, IP Downloadable Security, Policy Management and Network Optimization. ATIS is the North American Organizational Partner for the 3
4、rd Generation Partnership Project (3GPP), a member and major U.S. contributor to the International Telecommunication Union (ITU) Radio and Telecommunications Sectors, and a member of the Inter-American Telecommunication Commission (CITEL). ATIS is accredited by the American National Standards Instit
5、ute (ANSI). For more information, please visit . Notice of Disclaimer 2/10, 10/160, 10/250, 10/560 and 10/1000. The IEEE C62.41 standard (formerly known as IEEE 587) has defined a 10/1000 waveform based on nominal and not limit values. However, such IEEE based 10/1000 generators are uncommon. 1.2/50
6、-8/20 Combination wave generator In 1966, a group of engineers set out to characterize the surge environment of low voltage AC power circuits. The outcome in 1980 was the IEEE 587 standard (now C62.41). It was this standard that created the 1.2/50-8/20 combination wave generator. Combination means t
7、hat the generator was formulated by combining the existing 1.2/50 voltage waveform, used for insulation testing, and the existing 8/20 current waveform, used for component testing. The research results set the generator to produce a 6 kV maximum (nominal) open-circuit 1.2/50 voltage and 3 kA short-c
8、ircuit 8/20 current. A2 ATIS-0600013 8The fictive impedance (peak open-circuit voltage divided by peak short-circuit current) of the 1.2/50-8/20 Combination wave generator is 2 . The 1.2/50-8/20 Combination wave generator is often used with external resistors to reduce or share currents to multiple
9、outputs. The prospective short circuit current is the defined by the voltage setting, the 2 fictive impedance and the external series resistance(s). The 1.2/50-8/20 Combination wave generator output waveshape is load dependent. Figure 4 shows the waveshape variation with external resistance. Externa
10、l Resistance - 0 5 10 15 20Time-s1.522.533.54567815202530354050110DurationRiseFigure 4 - The 1.2/50-8/20 Combination wave generator output waveshape variation with external resistance For specialized purposes, there are “1.2/50-8/20 Combination wave” generators with different output currents to the
11、original 3 kA value at a 6 kV setting. UL 1449 has one such special generator. At the 6 kV setting, the UL 1449 generator variant produces selectable short-circuit 8/20 currents of 125 A, 500 A and 750 A. The corresponding fictive impedances are 48 , 12 and 8 . The standard 1.2/50-8/20 Combination w
12、ave generator is not a substitute for the UL 1449 generator for UL 1449 testing as it cannot give the correct current waveshape. The 10/1000 waveform In 1955, Bell Telephone Laboratories standardized on a 10/600 waveshape for protection testing A3 The recommendations of a 1961 Bell Laboratories fiel
13、d study report resulted in the adoption of a 10/1000 waveshape A4 The chosen front time of 10 s was less than 99.5 % of the recorded values and the chosen decay time of 1000 s was greater than 95 % of the recorded values. The study covered five voice-grade trunk routes with a mixture of aerial and u
14、nderground cabling. However ATIS-0600013 9measurements made on modern, short distance DSL-capable lines show much faster front times, typically in the sub-microsecond region. A Canadian Bell-Northern Research 1968-1969 field study A5 studied three types of facility. The report suggested the followin
15、g waveforms, 1000 V, 10/1000 to cover 99.8 % of all paired and coaxial cable lightning surges and 2000 V, 4/200 to cover 99.8 % of all open wire circuit lightning surges. The report showed an inverse correlation existed between the surge voltage and decay for higher level surges. The 10/700 generato
16、r The “10/700” generator is circuit defined see Figure 5. The ITU-T “Blue Book” extraction of ITU-T K.17 (1988) Tests on power-fed repeaters using solid-state devices in order to check the arrangements for protection from external interference had two generator circuit variants; 10/700 and 100/700.
17、The different rise times, 10 s and 100 s, were obtained by changing value the of rise time controlling capacitor C2from 200 nF to 2 F. France favored a faster rise 0.5/700 generator using a C2value of 20 nF. The specification of the circuit-defined 10/700 generator output waveforms came later. The s
18、pecified values depend on what standards body did the determination. ANSI/TIA-968-A (formerly known as FCC Part 68) gives voltage waveshape values of 9 s (30%) rise time and a 720 s (20%) decay time. IEC 61000-4-5 gives voltage waveshape values of 10 s 30 % rise time and a 700 s 20 % decay time. The
19、 current waveshape values are dependent on the number of outputs used. Only one output is used for transverse or metallic testing and both outputs are used for longitudinal testing. The short circuit current waveshape of a single output is 5/320 and for two outputs shorted is 4/250. R4= 25 R3= 25 Vo
20、ut1R2= 15 S1R1= 50 C1= 20 F C2= 200 nFVout2CommonFigure 5 - The 10/700 generator circuit 10/160 and 10/560 waveforms These two waveforms are specific to TIA-968-A high level type A surge testing of the telecommunications port. The metallic (transverse) surge test uses a 10/560 waveform with a peak o
21、pen-circuit voltage not less than 800 V and the peak short-circuit current of not less than 100 A. The longitudinal surge test uses a 10/160 waveform with a peak open-circuit voltage not less than 1.5 kV and the peak short-circuit current of not less than 200 A. Withstand, type B, surge testing of t
22、he telecommunications port uses the 10/700 generator. 10/250 waveform ATIS-0600013 10This waveform was defined from field study failure returns on cables due to nearby lightning strikes. This waveform with a peak current of 600 A is found in locations such as customer premises and outside plant that
23、 are served by cables predominantly of less than 25 pairs and loops shorter than 1000 feet in length. This waveform with a peak of 2000 A is found on long unshielded cables at high-exposure lightning environments. 2/10 waveform The grounding wire inductive voltage caused by the flow of primary prote
24、ctor surge current is simulated by the 2/10 waveshape in GR-1089-CORE. A different 2/10 waveshape, in terms of tolerance, is defined in ANSI/TIA-968-A for AC mains port testing. 4.6 Ground Potential Rise (GPR) Differential GPR results in current flowing between grounded equipment through their conne
25、cting wires or cable shield if present. The current will be similar in waveshape to the lightning current, although truncation may occur as a result of side flashes. In high resistivity soils, lightning ionized paths can divert currents from AC transmission lines to ground resulting in AC ground cur
26、rents at the equipment location of several hundreds of amperes. Multi-point grounding of telecommunication equipment makes it susceptible to damage from changes in ground potential. Peak currents during a lightning event are typically 20-25 kA but can be as high as 200 kA. This large current flows i
27、nto earth causing a change in the ground potential due to the finite conductivity of the earth. Some of this current will flow on various electrical cables. The current on these cables will flow to earth in other buildings locations. This results in a common-mode current transient. 4.7 Lightning Wav
28、eshape Characteristics External telecommunication lines The major portion of lightning currents from external lines is diverted to ground by the operation of the primary protection. This diverted lightning current, di/dt, flowing in the primary ground connection inductance results in a voltage pulse
29、 that is characterized by the 2 x 10 waveshape. 5 Power Contact 5.1 General Telecommunications distribution cables are often run in the same area as primary power lines. In joint-use plant, the distribution cable support strand and the cable shield are generally bonded in many locations to the power
30、 neutral. In this configuration, the support strand, the lashing wire and the telecommunications cable may be subjected to large currents in the event of a power fault. These fault currents result in either power induction or power contact events in the distribution cable. The telecommunications pla
31、nt needs to be protected against these events. ATIS-0600013 11Ideally the requirements for power fault protection would be based on data from field trials. The telecom literature has information about power induction, but doesnt have much to say about power contact in the distribution cable, as a re
32、sult of power faults. The most widely quoted paper A6 found that an event recorder set to trigger at 50A was never activated. An extensive unpublished study in Australia recorded 81 power-frequency transients. All but one of these events had peak currents of 5 amps or less. The one exception had 11
33、amps peak current. These low levels of current were more likely due to power induction than power contact. Other trials have given similar results. So there is field data on which to base requirements for power induction. What is missing is data on high-current events, which could be used as a basis
34、 for setting power contact also called second-level, or safety requirements. The field trials cited above say nothing about the high-current region, other than that events in that region are rare. Since field trials extensive enough to find these rare events might take years, and would be expensive,
35、 they are unlikely to be performed. So for the purpose of setting second-level (or safety) power contact test limits in standards, field trials have not been, and probably will not be available. An alternative to using field trial data is to set test limits based on worst-case analysis. This is the
36、approach taken in GR-1089-CORE A7. This method analyzes events that could occur on the power grid, and then see how those events might impact the telecommunications system. Unlike the telecommunications network, events on the power grid have been reasonably well characterized. The incentive for this
37、 work was power quality issues raised by the power companys customers. These issues surfaced in the 70s, when precision processes tied to the power grid, such as semiconductor manufacturing, were becoming increasingly sensitive to voltage fluctuations, and momentary interruptions in power. One examp
38、le was consumers who began to complain about the frequency of the “12:00 flashing display” in various electronic devices with a clock. EPRI the research arm of the power industry similar to what Bell Labs was to the telecom industry undertook a long, large and very expensive survey of the power grid
39、 to see what conditions existed. 5.2 Power Lines under Fault conditions The key findings of the EPRI survey were summarized in a book written by persons involved in the study A8. The material in this book was developed through numerous power quality case studies. Chapter 3 of the book discusses powe
40、r interruptions. It begins by saying, “The most basic overcurrent protective element on the system is a fuse. Fuses are relatively inexpensive and maintenance-free. For those reasons, they are generally used in large numbers on most utility distribution systems to protect individual transformers and
41、 feeder branches (sometimes called laterals or lateral branches)” “Ideally, utility engineers would like to avoid blowing a fuse needlessly on transient faults because a line crew must be dispatched to change it. Line reclosers were designed specifically to help save fuses.” Lines protected by fuses
42、 are discussed in subclause 5.3.2. In the case of a line protected by a recloser, the authors say, “If the fault is temporary in nature, a reclosing operation on the breaker should be successful and the interruption will only be ATIS-0600013 12temporary. It will usually require about five or six cyc
43、les for the breaker to operate i.e. about 0.1 sec, during which time a voltage sag occurs. The breaker will remain open for a minimum of 20 cycles up to 2 to 5 s depending on utility reclosing practices” Then they observe that, “If the fault is still there when the recloser or breaker recloses, ther
44、e are two options: 1. Switch to a slow, or delayed, tripping characteristic. This is frequently the only option for substation circuit breakers; they operate only once on the instantaneous trip. This philosophy assumes that the fault is now permanent and switching to a delayed operation will give a
45、downline fuse time to operate and clear the fault by isolating the faulted section. 2. Try a second fast operation. This philosophy is used where experience has shown a significant percentage of transient faults need two chances to clear while saving the fuses. Some line constructions and voltage le
46、vels have a greater likelihood that a lightning-induced arc may reignite and need a second chance to clear. Also, a certain percentage of tree faults will burn free if given a second shot.” The authors also observe that, “It is generally fruitless to automatically reclose in distribution systems tha
47、t are predominantly underground distribution (UD) cable unless there is a significant portion that is overhead and exposed to trees or lightning.” ATIS-0600013 13Table 2 - Table 2 (Telcordia Technologies A9)Operating time as a function of fault current Fault Current (kA) Trip # Overcurrent Trip Time
48、 (s) GE 100 A Recloser Kearny 100 A Recloser WE 100 A Recloser IEEE 321 Std 100 A Recloser Kyle 140 A Recloser Kyle 140 A Recloser1 1 0.05 0.04 0.055 0.05 0.06 0.06 2 0.05 0.04 0.18 0.4 0.06 0.06 3 0.45 0.24 0.18 0.4 0.45 1 4 0.45 0.24 0.18 0.4 0.45 1 Summation of Trip Times 1 0.56 0.595 1.25 1.02 2
49、.12 0.5 1 0.07 0.06 0.11 0.09 0.1 0.1 2 0.07 0.06 0.65 1 0.1 0.1 3 1.3 0.5 0.65 1 1.2 3 4 1.3 0.5 0.65 1 1.2 3 Summation of Trip Times 2.74 1.12 2.06 3.09 2.6 6.2 Reclosers trip when an overcurrent occurs for a predetermined time The recloser then waits a user programmable preset time before reclosing to re-energize the circuit. This process repeats up to a maximum of four times after which, if the fault persists, the recloser will trip and lockout. There are other views on reclosers. Telcordia A9 notes that before t
