IEC 60287-3-2-2012 pdf free download – Electric cables – Calculation of the current rating – Part 3-2: Sections on operating conditions – Economic optimization of power cable size.
This part of lEC 60287 sets out a method for the selection of a cable size taking into accountthe initial investments and the future costs of energy losses during the anticipated operationallife of the cable.
Matters such as maintenance,energy losses in forced cooling systems and time of dayenergy costs have not been included in this standard.
Two examples of the application of the method to hypothetical supply systems are given inAnnex A.
2Normative references
The following documents, in whole or in part, are normatively referenced in this document andare indispensable for its application.For dated references, only the edition cited applies. Forundated references,the latest edition of the referenced document(including anyamendments) applies.
IEC 60228,Conductors of insulated cables
IEC 60287-1-1，Electric cables – Calculation of the current rating – Part 1-1: Current ratingequations (100 % load factor) and calculation of losses – General
IEC 60287-2-1，Electric cables – Calculation of the current rating – Part 2-1: Thermalresistance – Calculation of thermal resistance
IEC 60853 (all parts),Calculation of the cyclic and emergency current rating of cables
3 symbols
The symbols used in this standard and the quantities which they represent are given in thefollowing list:
a annual increase in I max %
A L constant component of cost per unit length related to laying conditions, etc. cu/m
A S variable component of cost per unit length related to conductor size cu/(m·mm 2 )
b annual increase in P, not covered by inflation %
B auxiliary quantity defined by Formula (1 6) –
c annual increase in loss load factor %
C capacitance per core F/m
CI installed cost of the length of cable being considered cu
CI(S) installed cost of a cable as a function of its cross-sectional area cu
CI 1 installed cost of the next smaller standard size of conductor cu
CI 2 installed cost of the next larger standard size of conductor cu
CJ present value of the cost of joule losses during N years cu
CT total cost of a system cu
D demand charge each year cu/(W·year)
4 Calculation of total costs The total cost of installing and operating a cable during its anticipated operational life, expressed in present values, is calculated as follows. Note that all financial quantities are expressed in arbitrary currency units, (cu).
The total cost = CT = CI + CJ (cu) (1 )
where
CI is the cost of the installed length of cable, in cu;
CJ is the equivalent cost at the date the installation was purchased, i.e. the present value, of the joule losses during an anticipated operational life of N years, in cu.
Evaluation of CJ
The total cost due to the losses is composed of two parts: a) the energy charge, and b) the charge for the additional supply capacity to provide the losses.
a) Cost due to energy charge
Energy loss during the first year = (I 2 max × R L × L × N p × N c )T (W × h)
where
I max
is the maximum load on the cable during the first year, in A;
L is the length of cable, in m;
R L cable a.c. resistance per unit length, including the effect of λ 1 and λ 2 , R L = R(1+ λ 1 + λ 2 ).IEC 60287-3-2 pdf download.