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Transcript
Mike Hopkins, Thermo Keytek TR41.7-02-11-010 Comments on PN-03-3283RV2 TR41.7-02-11-006 Working Draft 00 – Initial Distribution Telecommunications Telephone Terminal Equipment Environmental Considerations My area of expertise is in the lightning and ESD areas, so I’ll restrict my comments to sections 4.3.3 and 4.3.5, plus Annex C. Section 4.3.3 As a general comment, I found it confusing to figure out which generator is used where. In some cases, as seen in the table that follows, it isn’t clear to me which generator is required for testing. Some generators seem to have a 4 ohm effective source impedance that doesn’t fit with any of the other generators specified. 4.3.3.1 say that test shall be conducted per IEC 1000-4-5 (now IEC 61000-4-5) where practicable, but several other generators are specified for the telecom line tests. This paragraph needs to be modified to make it clear that generators specified in other standards are also used – FCC Part 68 and Bellcore GR 1089 from what I can see. Figure 2 provides basic schematics for the 1.2/50 – 8/20us Power Line Surge Generator and the 10/700us Telephone line Surge Generator. I’m assuming these were included because they are available (from IEC 61000-45) and others not included since they are not so available. Rather than raise the question, I strongly suggest removing all generator schematics and specify the unit stimulus instead as follows: General Waveform definitions according to IEC 60060-1 Front time = 1.67 x T, +/- 30% Time to half-value = T2 20 %. Mike Hopkins, Thermo Keytek TR41.7-02-11-010 Front time = 1,25 x T ; 20 % Time to half-value = T2 20 %. Virtually all surge and lightning standards use this criteria: IEC, FCC, ANSI, ITU and Bellcore. Because the discharge network of any generator consists of a charged capacitor and a (primarily) resistive wave forming network, the maximum energy that you can get out of the charged capacitor is 1/2 of the energy that is stored -- and that ONLY into a matched load. In other words, it's like power (since energy is the integration of power with respect to time): in a matched load, you can deliver half the power --hence, half the energy. The implication here is that the stored energy has little bearing on the energy delivered into a real, complex load. Mike Hopkins, Thermo Keytek TR41.7-02-11-010 Generator specifications: Lightning Generator specifications Peak Power Line Generator G, Open-circuit voltage P1, P2 and P3 Short-circuit current Front time Duration 6kV 1.2us 50us 3kA 8us 20us Telecom Wave M1 Open-circuit voltage Short-circuit current* 1kV 25A 10us 5us 700us 320us Telecom Wave M2 Open-circuit voltage 800V 10us 560us Short-circuit current Open-circuit voltage Short-circuit current Open-circuit voltage Short-circuit current 100A 1kV 100A Unclear which generator to use Unclear which generator to use 10us 10us 10us 560us 1000us 1000us Open-circuit voltage Unclear which generator to use Short-circuit current Open-circuit voltage Short-circuit current Open-circuit voltage Short-circuit current Unclear which generator to use 1kV 10us 1000us 100A 10us 1000us 1.5kV 2us 10us 100A unspecified** Open-circuit voltage Unclear which gen to use Short-circuit current Unclear which gen to use Telecom Wave M3 Telecom Wave L1 Telecom Wave L2*** Telecom Wave L3 Telecom Wave I1 Telecom Wave T1, T2 *FCC specifies this to be 5us x 320us; IEC specifies it as 4us x 300us; ITU is not clear; 5us x 320us is closer to the actual waveform from most generators. **The current waveshape is not specified in FCC Part 68 ***Figure 3 of the draft shows a Power Line generator. I'm assuming this was a mistake Mike Hopkins, Thermo Keytek TR41.7-02-11-010 Figure 3 In two places, additional 3 ohm resistors are shown. There are no commercial generators available that I’m aware of that incorporate such resistors and I don’t see any rational for using them. Personally, I believe it would be a mistake to require the user to find and wire these resistors into his test circuit. First of all, they need to be rated for the surge voltages and currents expected, and secondly, it could pose a danger to an operator performing tests (for example, and improperly rated resistor could explode!). Not to mention, sourcing such resistors could be challenging. Annex C1 – No problem. Annex C2 Line 760 and 761 – change 10ms and 1000ms to 10us and 1000us respectively. Annex C4 Lines 814 and 815 – change ms to us Line 814 – who says induction voltages are usually less than 1000 volts and of the 10/1000us type? Line 815 ANSI/IEEE C62.41 (currently being revised) shows that voltages to 6kV can be expected on the low voltage mains entering a building, and is widely used as a design specification by U.S. industry. Additionally, ANSI also shows that most voltage waves seen inside a structure will be ringing waveforms and not likely to be the 1.2us x 50us variety. Suggest lines 814 and 815 be replaced with the following: “Surges induced into telecom cables due to a nearby lightning strike are likely to be elongated, or smeared, due to the high degree of coupling between individual lines in the cable and the relatively high inductance of such cable to the lightning current. Surges induced or injected onto the AC mains are likely to be of higher peak amplitudes and shorter durations. Peak voltages on telecom cables are generally limited to around 1kV by primary arrestors at the service entrance; however, such primary arrestors rarely exist across the AC mains at the service entrance.” Line 818 – 1000V is the limit ONLY if primary arrestors are in place – see ITU-K series documents: they go up to 6kV for unprotected lines; Australian telecom goes to 7kV. C5. Needs considerable revision. Suggest the following: “Peak available current and current waveshape are very important for CPE that use voltage and current limiting. A typical surge protective element will initially appear to be a high impedance, but rapidly drop to a very low impedance once the operating voltage of the protective device is reached. For a varistor, the impedance is dependant on the amplitude of the applied surge current. For high current surges, a MOV will have a clamping impedance of a few 10ths of an ohm; from a lower current surge generator, the impedance may be as high as a few ohms. The duration of the surge current waveform will be effected very little by the low impedance of an MOV or other clamping device, and during a test, will be very close to the specified short-circuit current waveshape from the generator (any impedance would tend to make the duration slightly longer than specified, but for most surge tests this would be on the order of a few percent at most). Where crowbar type protective devices are used, the impedance of the device when it is conducting will be very low and is unlikely to affect the surge current waveform at all. Lines 830 through 833 can remain as is. Line 854 – change ms to us. C7 Change ms to us throughout – many places…. C7 FCC rules Mike Hopkins, Thermo Keytek TR41.7-02-11-010 The energy calculations don’t’ seem right. Unless I’m missing something, the integral of the voltage over time has no relation to the stored or delivered energy unless you also have the load impedance defined. Then you can calculate the energy by integrating the power over time, from 0 to infinity. ∫(V2 e –2t/RC)/R dt : Calculate the integral at ∞ minus the integral at t=0 and you’ll get the stored energy. Of course, you can calculate the stored energy without knowing the load impedance, but then you need to know the value of the energy storage capacitor: j = ½ CV2. Line 871 – the short-circuit current is actually about 5 x 320us. ANSI C62.45 The reference may be incorrect --- IEEE WG 3.6.4 wrote IEEE 587 as a guide for surges on the low voltage distribution system. This is now ANSI/IEEE C62.41. ANSI C62.45 is intended to be a guide for those writing surge test standards based on the work done in C62.41. The defined waveshapes are historical – the 1.2/50us voltage waveform was widely used for testing high impedance circuits for lightning surges; the 8/20us waveform was established as a waveshape for testing low impedance circuits. With the advent of surge arrestors and the need to surge test electronic products where the impedance of the EUT was either unknown or changes over time (a protector operating, for example), it became necessary to define both the open-circuit voltage and short-circuit current from a single generator. It turned out that it was possible to design a generator to produce these two historical waveforms – 1.2/50us voltage when observed into a high impedance; 8/20us current when observed into a low impedance. A source impedance of 2 ohms was considered to be representative of an induced surge current coming down a drop line into a building. Line 887-888 The peak voltage specified in ANSI/IEEE C62.41 (and also C62.45) is 6kV for BOTH categories A and B. IEC 1000-4-5 – Now IEC 61000-4-5 CCITT is no longer – these standards are now all ITU-T K series standards. Lines 895 through 897 need to be changed. Suggest the following: “The open circuit voltage is specified at the output terminals of the generator.” References to the necessity to have a higher charge voltage on the capacitor for some standards is certainly irrelevant in this paragraph. IEC 61000-4-5 makes no mention of this. The reference actually comes from some CCITT standards and an Australian standard the specify the charge voltage on the capacitor. My guess is this is a holdover from times when it was easier to measure the voltage on the energy storage capacitor than it was to measure the peak open circuit voltage. In any case, this is not done today – no modern surge generator comes with a port that allows the user to access the energy storage capacitor. An additional problem with this is that the relationship between the necessary charge voltage on the capacitor and the peak output voltage is different for different waveforms and different generator designs – even though CCITT attempts to dictate the circuit design, subtle differences in components can lead to variations in the output voltage. Section C9 I2T (Is this I2T?) is used throughout – don’t know the relevance of this with regard to the tests being performed or the voltage waveforms – It’s a current issue and related to the exponential current discharge through a protective device, so I think there are some terms missing.