36-WG11/Renardières/78 22/06/01 Minutes of the sixth meeting of Working Group 11 of TC36 (Revision of IEC 60815) Held at EdF Renardières on 25th and 26th April 2001.
Present: Clive Lumb – Project Leader Chris Engelbrecht (guest) Kuniaki Kondo (replacing Rick Suzuki) Franco Marinoni Richard Martin Sven Nord Wolfgang Petrusch Frank Schmuck Eric Spangenberg Don Swift Jacek Wankowicz Dong Wu 1. Opening of the meeting Eric Spangenberg welcomed the experts to France and to the EdF Renardières complex. The Project Leader thanked him on behalf of the WG. 2. Approval of the agenda The agenda (36-WG11/Renard /60) was approved. 3. Apologies for absence, Apologies for absence were received from • • • •
Gustav Goedel Allan Hurst – Allan is much better and back at work Rick Suzuki (replaced by K Kondo) Wallace Vosloo
4. Membership Chris Engelbrecht was present as a guest, it was suggested that he become a full member. He will contact the Swedish National Committee so that the official nomination can be made – he will probably request corresponding member status. Prof. Zheng Jianchao has not shown much sign of life. CL to write to him asking if he wishes to continue as corresponding member. 5. Approval of the minutes of the 5th meeting held in Stockholm (36-WG11/Stockholm/61) No comments were received.
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36-WG11/Renardières/78 22/06/01 6. Submitted document numbering The web site was updated with the documents submitted at the meeting as follows. 36-WG11/Renardières/70
C. Engelbrecht
Statistical method for qualification
36-WG11/Renardières/71
CIGRE TF33.13.01
Revised flow chart
36-WG11/Renardières/72
K. Kondo
Performance of contaminated bushings of UHV line
36-WG11/Renardières/73
R. Suzuki
Comments on low solubility salts
36-WG11/Renardières/74
C. Engelbrecht
Presentation of Statistical method for qualification
36-WG11/Renardières/75
K. Kondo
Flashover on contaminated insulators of different diameters
36-WG11/Renardières/76
R. Suzuki
Effect of NSDD/ESDD on pollution withstand curve
7. Report on the activity of CIGRE TF 33.13.01 (DAS) DAS reported that a statistical method for qualification was being studied by the TF and that he was pleased that Chris Engelbrecht had been invited/able to come to the meeting to explain the method in more detail. The application guide is focussed on helping utility engineers to choose an insulator, now with the Engelbrecht method they have a means to evaluate this choice. DAS indicated that the work was being done bearing in mind a "normal" approach to insulator selection, which is to use IEC60815 > CIGRE Application Guide > CIGRE 158 Review in that order according to the degree of resources and knowledge available. The first complete draft is expected for the end of October 2001 (meeting in Padua) with the final version 6 available months later. The customary question on whether the WG should meet before or after the next TF33.13.01 meeting was tabled. It was suggested that again the WG meet after TF 33.13.01. (See point 13) 8. Presentation by Chris Engelbrecht on statistical link between site severity and test criteria – Documents 70 & 71 CE presented the method which, briefly, consists in measuring site severity with standard insulators, determining mean and standard deviation of the pollution level, applying factors and coefficients to specify the parameters for an artificial pollution withstand test on the chosen insulation. The withstand test guarantees a low risk of flashover in service and is fast and easy to perform compared with a U50 determination test. CE to supply copies of his PowerPoint presentation to those who request it (Including CL who has managed to delete it from his laptop).
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36-WG11/Renardières/78 22/06/01 The following points arose in the ensuing discussion: FS
Cost of insulators is minimal compared to total line cost, must avoid forcing materials to the limit for unsound economic reasons.
DW
Method is very interesting, but we do not have finalised standard lab tests for DC, composite etc. Still believe that creepage is not totally irrelevant.
SN
Case of large porcelains – who will pay for the tests ?
DW
What does the test prove ?
JW
Conclusions are drawn from existing information – there is not enough information for extreme conditions, neither on how to test nor on test/field conditions. Hence utilities must rely on experience and over-designing.
CE
The method has been critically assessed, it now remains to convince the utilities.
SN
Reminder that testing costs are very important nowadays and that optimisation requires testing.
After this discussion, the Project Leader had the impression that the method was of interest to the working group and that it could be taken on board as part of Approach B in the draft. 9. Discussion of tabled documents 9.1. Martin 58 - Axial voltage distribution This document is pertinent to §9.2.3 Hollow Insulators. The conclusion is that we can expect lower flashover values if axial voltage distribution is not linear. JW reminded that this effect can be important even in high pollution if the deposit is non-uniform. It was decided to integrate the document into §11 of the draft. The effect of altitude also to be inserted in §11. CL to do the insertion. RM to check the resulting text. 9.2. Schmuck 68 – Influence of diameter FS
suggested keeping the existing factors. It was agreed that this was possible for a.c.
FS
said that better performance was found with composites with respect to similar diameter porcelain long-rods.
??
Does the diameter effect apply to hydrophilic, hydrophobic surfaces or both ? It was agreed that it applies when surfaces are hydrophilic.
WP
It would seem that the factor is double for d.c.
The discussion that followed was enlarged to include other factors and to decide whether the factors were general or specific to an application or type of insulator. Additionally it was reconfirmed that insulator dimensions should start from a basic specific creepage distance (line to ground!) which would then be modified by the factors. RM agreed to summarise this discussion. This is reproduced below:
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36-WG11/Renardières/78 22/06/01 mm/kV (max.Φ-G)
65
53 54 42 44 34 35
28
VL Very light
L Light
M Medium
H High
VH Very high
Recommended min. specific leakage for AC, ceramic standard reference disk Recommended min. specific leakage for DC, ceramic standard reference disk. Figure x – Basic specific creepage distance as a function of site severity For the sake of filling in, the numbers for DC, the AC values have been increased by 20%. Formerly, the multiplication was by approx. 2, to take into account the Φ-Φ versus Φ-G, and an added value for the DC attraction effect. Once the minimum specific leakage has been established, we proceed with the application of K factors to establish the final proposed leakage using as a base the specific leakage values for the chosen site severity for AC application (red numbers)There would be a similar table for DC (using blue numbers). « K » Factors
Cap & Pin
Long rod
Profile (flat,fog,standard wetting orientation… Diameter Material Glass Porcelain Sil. grease Cleaning, natural washing Presence of low solubility salts. Altitude Accumulation AC DC
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Bushing (Hollow core)
Composite -hydrophilic -hydrophobic
36-WG11/Renardières/78 22/06/01 Note on diameter factors The values started with the original IEC 815 recommendations 1---------------for < 300 mm average diameter 1.1-------------for > 300 mm, < 500 mm 1.2------------for > 500 mm, < 700 or 750 mm. There was a proposal for k= 0.9 for small diameters (approx. 115 mm). More discussions are needed on that subject, WP saying there were no difference between small diameter long rod and string insulators. NGK document shows that k = 1 starts at 115 mm. Special case for “Marine” site contamination. This type of site severity was introduced as a special case, where sea coast storms can occur and bring wetted salt solutions on the insulators. The measurements after the fact of ESDD would not give a proper evaluation of the site severity. It was also noted that typically in this case NSDD was not significant if present at all. For this particular type of site, the document would strongly suggest measurements be made with reference standard disk. With a given AC voltage source, the surface currents would be measured and recorded with frequency, duration and period of time ( months, year ..) to be determined. The terms I max or I highest were discussed. From the values obtained ( most probably I max ), it would be possible, with available data obtained with past salt fog tests to translate into a severity in terms of g/l. ( task taken by WP and CE) The function box (I max - SES) would not be included into the document.
VL Very light
L
M
Light
Medium
5
14
H
VH
High
48
Very high
80
1xx
Figure y – Correspondence of Site Equivalent Salinity (SES) with site pollution severity It was decided not to combine the SES chart with the ESDD-NSDD site severity chart. The readers of the document would easily make the false correspondence between SES and ESDD (NSDD being close to nil). 9.3. Swift 69 - Arid areas It was agreed that the first paragraph should be used in the description of the flashover process, the 2nd paragraph in any discussion of specific environments. DAS said that there might be more data available after the next TF meeting CL to integrate, DAS to check the result. -5-
36-WG11/Renardières/78 22/06/01 9.4. Kondo 72 - Performance of contaminated bushings of UHV line RM indicated that the information had already been taken on board. 9.5. Suzuki 73 - Comments on low solubility salts This document shows that for low solubility salts it is possible to apply corrections to determine the effective ESDD. WP
This phenomenon appears if there is insufficient wetting, this means: Must wait a limited time when measuring ESDD, Gypsum can be a problem in heavy/prolonged rain.
CE
Suggest we play it safe and do not correct.
This was agreed. 10. Discussion of document 67 – 2nd draft, including documents 62-66 (see also annotated draft 36-WG11/Renard/77) 3. Definitions Some definitions were removed. Tasks on CE , CL , SN , KK , RM , FS shown in doc 77. 5.
Pollution types and flashover mechanism
Needs slimming down DW , refer to "rapid" event rather than instantaneous. Need pollution definitions for pollution deposited before wetting occurs and for pollution deposited as wetting occurs. 6.
Parameters and approaches..
ALL to study and comment on Figure 1. 7.
Pollution severity
DAS & CL to find appropriate terms. CE – paragraph on risks with slow dissolving salts under heavy wetting. WP & CE to look into conductivity/salt fog on-site measuring principle and figures. WP to supply figure 2A (ESDD/NSDD for standard long-rod). RM to take on board the are covered by the tests in document Suzuki 76 in Figure 2. CE to look into DSL points along the abscissa of figure 2. At this point we ran out of time... 11. Examination of other outstanding documents (time permitting) All the tabled documents had been reviewed and/or integrated into the draft. 12. Task list, timetables etc. The tasks are shown above LIKE THIS ; a few further tasks can be found in document 77. Additionally, ALL of the members are asked to continue study of the current draft in preparation for the next meeting. Also, CL to start work on the outline of parts II & III. The projected meeting plan, along with prospective readiness dates for various drafts is reproduced hereafter. The main target dates being :
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36-WG11/Renardières/78 22/06/01 Part 1 – CD April 2002, Part 2 – DC/CD April 2002 Part 3 – DC October 2002 (Next TC 36 meeting in Beijing)
Part I
Part II
Part III
Now
% Time of meeting spent on each Part April 2001 EdF
60 %
30 %
10 %
Oct 2001 Milan
40 %
40 %
20 %
April 2002 ???
30 %
50 %
20 %
Oct 2002 Beijing ?
Study comments 30%
40 %
30 %
13. Date and place of the next meeting Franco Marinoni invited the WG to meet in Milan on October 29th, 30th and 31st where it is intended to have a full 2 ½ day meeting. 14. Close of the meeting The project leader thanked the members for their hard work and Eric Spangenberg and EdF for their hospitality. He then declared the meeting closed
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