CALCULATION OF THE CYCLIC AND EMERGENCY CURRENT RATING OF CABLES - PART 2: CYCLIC RATING OF CABLES GREATER THAN 18/30 (36) KV AND EMERGENCY RATINGS FOR CABLES OF ALL VOLTAGES
International Electrotechnical Committee
Foreword
Preface
Section One - Background
Clause
1. Introduction and scope
1.1 General
1.2 Inclusion of cable thermal capacitance
1.3 Conditions where thermal capacitance can
be neglected
1.4 Guide to clauses applicable to particular
types of cable
1.4.1 Transient calculation and emergency rating
1.4.2 Cyclic rating
2. Symbols
3. Layout of this standard
Section Two - Transient Temperature Response
4. Transient temperature response to a step function of
current
4.1 General aspects
4.1.1 Background
4.1.2 Criteria for the attainment factor to be
unity
4.1.3 Representation of the cable
4.1.4 Criteria for selecting the thermal circuit
4.2 Calculation of partial transients for long
durations (>1/3T Q) and cyclic rating
4.2.1 Representation of the dielectric
4.2.2 Representation of the cable
4.2.3 Calculation of cable partial transient
4.2.4 Calculation of cable environment partial
transient
4.3 Calculation of partial transients for short
duration (<1/3T Q)
4.3.1 Representation of the dielectric
(single and 3-core cables)
4.3.2 Representation of the cable
4.3.3 Calculation of cable partial transient
4.3.4 Calculation of cable environment partial
transient
4.4 Calculation of the complete temperature transient
4.4.1 Transient temperature response
4.4.2 Correction to transient temperature
response for variation in conductor losses
with temperature (emergency ratings only)
4.4.3 Transient temperature response caused by
sudden application of voltage (transient
due to dielectric loss)
Section Three - Cyclic Ratings
5. Computation of the cyclic rating factor (M)
5.1 General
5.2 Calculation of cyclic rating factor (including
cable thermal capacitance)
5.2.1 Any load cycle of known shape
5.2.2 Flat top load cycle
5.2.3 Load cycle of unknown shape but with a
known loss-load (mu)
6. Calculation of loss-load factor (mu)
7. Calculation of OR(i)/OR(x)
7.1 Single isolated 3-core cable
7.2 Single isolated circuit
7.3 Group of "N" cables with equal losses; cables or
ducts not touching
7.4 Group of circuits, each of three single-core identical
touching cables or ducts, all cables having equal losses
Section Four - Emergency Ratings
8. Calculation of emergency ratings
8.1 Thermally isolated circuits
8.2 Groups of circuits
8.3 Correction to transient temperature response to take
account of variation in conductor losses with temperature
9. Bibliography
Appendix A - Reduction of a multiple thermal circuit to
one having two sections
Appendix B - Transient average temperature variation
through dielectric or through oil filling in pipes
Appendix C - Method for dealing with different soil
resistivities, thermal diffusivities and depths of
laying
Appendix D - Diffusivity of soil
Appendix E - Physical constants of materials
Appendix F - Examples
Gives manual methods for calculating cyclic rating factors for cables whose internal thermal capacitance cannot be neglected; in general this applies to cables for voltages greater than 18/30 (36) kV. It also gives a method for calculating the emergency rating for cables of any voltage.
| Document Type | Standard |
| Status | Current |
| Publisher | International Electrotechnical Committee |
| Committee | TC 20 |
