Situation today Specification of Insulators Mechanical
Electrical Guidance
Ultimate failing load Cantilever load Etc.
Testing
IEC 60071 Ins. Co-ord.
LIWL (kV) SIWL (kV) Wet a.c. (kV)
IEC 60060 Test methods
IEC 60815 Polluted ins.
Creepage(mm)
IEC 60507 Pollution tests
Suggestion Functional specification of Insulators Mechanical
Electrical Guidance
Ultimate failing load Cantilever load Etc.
Testing
IEC 60071 Ins. Co-ord.
LIWL (kV) SIWL (kV) Wet a.c. (kV)
IEC 60060 Test methods
IEC 60815 Polluted ins.
PSWL (Severity, kV)
IEC 60507 Pollution tests
Simplified statistical approach (Based on IEC 60071) 1
2
0,8
1,5
0,6
1
0,4
0,5
0,2
0
0 0
0,05
0,1
0,15 2
Pollution Severity (ESDD:mg/cm )
0,2
Probability (p.u.)
Probability density
2,5
Simplified statistical approach
1 0,5
0,8 0,6 0,4 0,2
0
0 0
0,05
0,1
0,15
0,2
0,25
Pollution Severity (ESDD:mg/cm2)
0,3
Probability (p.u.)
1,5
1
Required withstand severity
2
Statistical severity
Probability density
2,5
Co-ordination withstand severity
(Based on IEC 60071)
Selection of laboratory test severity (Based on IEC 60071) Determine Statistical severity γs2
1. •
2.
Severity having a 2% probability of being exceeded
Determine statistical co-ordination factor Kcs •
Correct for pollution measurements on different profile
•
Correct for pollution measurements on un-energised units (for both d.c. and a.c.)
•
Correct for not enough pollution measurements
Determine co-ordination withstand severity γcw
3. •
γcw = Kcs * γs2
Determine required withstand severity γrw
4. •
Correct for limited number of tests
•
Correct for testing only one insulator
•
γrw = γcw /(1-nc)1/α (Values for variables provided in tables)
Simplified statistical approach
1,5 1 0,5
1/(1-nc)1/α
0,8 0,6 0,4 0,2
0
0 0
0,05
0,1
0,15
0,2
0,25
Pollution Severity (ESDD:mg/cm2)
0,3
Probability (p.u.)
2
1
Required withstand severity
Kcs Statistical severity
Probability density
2,5
Co-ordination withstand severity
(Based on IEC 60071)
What made this approach possible (Milestones since 1986)
• IEC publications since IEC 60815 (1986) • Standardised laboratory test methods AC: IEC 60507 (1991); DC: IEC 61245 (1993) • Simplified statistical procedure IEC 60071(1996)
• A function describing the statistical strength in terms of pollution severity was derived
Why is this approach necessary • Same functional approach for all electrical parameters • Specify stress, qualify with a withstand test
• Simplified specification procedure for users • Functional approach can lead to cost reductions • It encourage technical innovations • More competition amongst suppliers
• Opportunities to apply emerging technologies
Why is this approach necessary • Creepage distance is not the sole parameter • Cigré review • More so for polymeric insulators
• Difficult to give guidance for creepage • Required creepage distance function of Material / Shed profile / Energisation / Type of environment / Pollution severity
• Utilise benefit of performing ESDD measurements • Input for selection of withstand test severity
Cigré TF 33.13.01 Insulator Application Guidelines
2.
FLOWCHART FOR THE SELECTION AND DIMENSIONING PROCESS
Basic data Application
PROJECT Objective
System parameters Environment
Definition of task
Constraints Possible solutions Insulator characteristics
Material considerations
Profile considerations
Maintenance considerations
Life time considerations
Service Experience Qualification method
Acceptable performance?
Performance monitoring & inspections
Pollution test method
Field trial site
Pollution test Severity
Field trial duration
Insulation specification (Function)
Insulation specification (Design) Qualified insulators
Laboratory tests Test certificates Field trials
Qualification of insulators
Cost/Risk?
Approved Insulator
3
20/4/01
