SN EN 60071-2 : 1997

1 General
    1.1 Scope
    1.2 Normative references
    1.3 List of symbols and definitions
2 Representative voltage stresses in service
    2.1 Origin and classification of voltage stresses
    2.2 Characteristics of overvoltage protective devices
    2.3 Representative voltages and overvoltages
3 Co-ordination withstand voltage
    3.1 Insulation strength characteristics
    3.2 Performance criterion
    3.3 Insulation co-ordination procedures
4 Required withstand voltage
    4.1 General remarks
    4.2 Atmospheric correction
    4.3 Safety factors
5 Standard withstand voltage and testing procedures
    5.1 General remarks
    5.2 Test conversion factors
    5.3 Determination of insulation withstand by type tests
6 Special considerations for overhead lines
    6.1 General remarks
    6.2 Insulation co-ordination for operating voltages
          and temporary overvoltages
    6.3 Insulation co-ordination for slow-front overvoltages
    6.4 Insulation co-ordination for lightning overvoltages
7 Special considerations for substations
    7.1 General remarks
    7.2 Insulation co-ordination for overvoltages
Tables
1 Recommended creepage distances
2 Test conversion factors for range I, to convert required
    switching impulses withstand voltages to short-
    duration power-frequency and lightning impulse
    withstand voltages
3 Test conversion factors for range II to convert required
    short-duration power-frequency withstand voltages to
    switching impulse withstand voltages
4 Selectivity of test procedures B and C of IEC 60-1
A.1 Correlation between standard lightning impulse withstand
    voltages and minimum air clearances
A.2 Correlation between standard switching impulse withstand
    voltages and minimum phase-to-earth air clearances
A.3 Correlation between standard switching impulse withstand
    voltages and minimum phase-to-phase air clearances
C.1 Breakdown voltage versus cumulative flashover
    probability - single insulation and 100 parallel
    insulations
F.1 Corona damping constant Kco
F.2 Factor A for various overhead lines
G.1 Typical gap factors K for switching impulse breakdown
    phase-to-earth
G.2 Gap factors for typical phase-to-phase geometries
H.1 Summary of minimum required withstand voltages obtained
    for example H.1.1
H.2 Summary of required withstand voltages obtained for
    example H.1.2
H.3 Values related to the insulation co-ordination
    procedure for example H.3
Figures
1 Range of 2% slow-front overvoltages at the receiving end
    due to line energization and re-energization
2 Ratio between the 2% values of slow-front overvoltages
    phase-to-phase and phase-to-earth
3 Diagram for surge arrester connection to the
    protected object
4 Distributive discharge probability of self-restoring
    insulation described on a linear scale
5 Disruptive discharge probability of self-restoring
    insulation described on a Gaussian scale
6 Evaluation of deterministic co-ordination factor Kcd
7 Evaluation of the risk of failure
8 Risk of failure of external insulation for slow-front
    overvoltages as a function of the statistical co-
    ordination factor Kcs
9 Dependence of exponent m on the co-ordination switching
    impulse withstand voltage
10 Probability P of an equipment to pass the test dependent
    on the difference K between the actual and the rated
    impulse withstand voltage
11 Example of a schematic substation layout used for the
    overvoltage stress location (see 7.1)
B.1 Earth-fault factor k on a base of Xo/X1 for R1/X1=0
B.2 Relationship between Ro/X1 for constant values of
    earth-fault factor k where R1 = 0
B.3 Relationship between Ro/X1 et Xo/X1 for constant values
    of earth-fault factor k where R1 - 0.5 X1
B.4 Relationship between Ro/X1 et Xo/X1 for constant values of
    earth-fault factor k where R1 = X1
B.5 Relationship between Ro/X1 et Xo/X1 for constant values
    of earth-fault k where R1 = X1
C.1 Conversion chart for the reduction of the withstand
    voltage due to phasing insulation configurations in
    parallel
D.1 Example for bivariate phase-to-phase overvoltage curves
    with constant probability density and tangents giving
    the relevant 2% values
D.2 Principle of the determination of the representative
    phase-to-phase overvoltage Upre
D.3 Schematic phase-phase-earth insulation configuration
D.4 Description of the 50% switching impulse flashover
    voltage of a phase-phase-earth insulation
D.5 Inclination angle of the phase-to-phase insulation
    characteristic in range b dependent on the ratio of
    the phase-phase-clearance D to the height Ht above earth
E.1 Distributed capacitances of the windings of a transformer
    and the equivalent circuit describing the windings
E.2 Values of factor J describing the effect of the
    winding connections rn the inductive surge transference
Annexes
A Clearances in air to assure a specified impulse withstand
    voltage installation
B Determination of temporary overvoltages due to earth
    faults
C Weibull probability distributions
D Determination of the representative slow-front over-
    voltage due to line energization and re-energization
E transferred overvoltages in transformers
F Lightning overvoltages
G Calculation of air gap breakdown strength from
    experimental data
H Examples of insulation co-ordination procedure
J Bibliography
ZA (normative) Normative references to international
    publications with their corresponding European
    publications

Consists of an application guide concerned with selecting insulation levels of equipment or installations for three-phase electrical systems. Gives guidelines for determining the rated withstand voltages for ranges 1 and II of IEC 71-1 and justifies association of these values with standardized highest voltages for equipment.