Download TR41.7-02-11-010-LightningSurgeCommentsOnTIA-571

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.