CYMCAP, Cable Ampacity Calculation
The CYMCAP software is dedicated to the calculation of ampacity and temperature rise calculations for power cable installations. It addresses steadystate and transient thermal cable rating as per the analytical techniques described by NeherMcGrath and the IEC 287© and IEC 853© International standards. The accuracy of our software provides increased confidence when upgrading power cable installations and designing new ones; maximizing the benefits from the considerable capital investment associated with them. It also helps increase system reliability and support the proper utilization of the installed equipment.
Program Features
The CYMCAP software is dedicated to performing ampacity and temperature rise calculations for power cable installations. Determining the maximum current power cables can sustain without deterioration of any of their electrical properties is important for the design of electrical installations. It was developed jointly by Ontario Hydro (Hydro One), McMaster University and CYME International, under the auspices of the Canadian Electricity Association.
The fieldtested accuracy of the CYMCAP software provides increased confidence when upgrading existing power cable installations and designing new ones, thus maximizing the benefits from the considerable capital investment associated with them.
Analytical Capabilities
 Iterative techniques based on NeherMcGrath and IEC60287© methods
 Full compliance with North American practice and support all pertinent IEC standards IEC 60287©, IEC 60228©, IEC 601042©, IEC 60853©, etc.
 Detailed graphical representation of virtually any type of power cable. This facility can be used to modify existing cables and enrich the cable library with new ones. This includes singlecore, threecore, belted, pipetype, submarine, sheathed, and armored cables
 Different cable installation conditions such as directly buried, thermal backfill, underground ducts or duct banks
 Pipetype cables directly buried or in a thermal backfill
 Independent libraries and databases for cables, ductbanks, load curves, heat sources and installations
 Modeling of cables in air on riser poles, groups of cables in air, moisture migration, nearby heat sources and heat sinks, etc.
 Different cable types within one installation
 Nonisothermal earth surface modeling
 Cyclic loading patterns as per IEC60853©
 Multiple cables per phase with proper modeling of the sheath mutual inductances which greatly influence circulating current losses and thus derates the ampacity of cables
 All bonding arrangements for flat and triangular formations are supported with explicit modeling of minor section lengths, unequal cable spacing, etc
Transient Analysis
The program supports a Transient Thermal Analysis Option which includes the following:
 Ampacity given time and temperature
 Temperature analysis given time and ampacity
 Time to reach a given temperature, given the ampacity
 Ampacity and temperature analysis as a function of time
 Userdefined load profiles per circuit
 Multiple cables per installation
 Circuits can be loaded simultaneously or one at a time
CYMCAP Additional Modules
Installations
The CYMCAP Additional Modules offer extended capabilities to the CYMCAP software, allowing modeling more installations, particularly nonstandard installations. This includes the modeling of installations with multiple ductbanks and backfills of different thermal resistivity each; the calculation of the ampacity and temperature of cables in unventilated tunnels; the rating of cables in both filled and unfilled troughs; and the rating of cables in one or more nonmagnetic casings.
Analyses
The CYMCAP Additional Modules allow performing several analyses of interest for cables installations like evaluating the magnetic flux density at any point on or above the ground of an underground cable installation, determining the positive and zero sequence impedances and admittances for all the cables present in an installation, performing shortcircuit cable ratings, determining the optimal placement of several circuits within a ductbank given specified constraints and calculating the ampacity of two circuits crossing each other.
Multiple Duct Banks and Backfills
The Multiple Duct Banks and Backfills module (MDB) is the addon module designed to determine the steadystate ampacity of cables installed in several neighboring duct banks and/or backfills with different thermal resistivity. The module presents a unique solution combining standard and nonstandard calculation methods. The module computes the values of T4 (the external to the cable thermal resistance) using the finite element method and then the ampacity (or operating temperature) of the cable installation is obtained using the IEC standardized solution method.
The following capabilities can be highlighted:
 Modeling up to eleven rectangular areas with different thermal resistivity
 Modeling up to three duct banks in a single installation
 Modeling one heat source or heat sink in the installation
 Computation of the steadystate ampacity or temperature
 Transient analysis, cyclic loading and emergency ratings are supported
 Computation of the thermal rating of cables in filled troughs
Cables in Tunnels
The optional Cables in Tunnels module allows the user to determine steadystate temperature and ampacity, cyclic loading, emergency rating and transient analysis for cables installed in unventilated tunnels. Note that only equally loaded cables having the same type and loading are considered. This addon module supports a large variety of cable arrangements for single core (flat formations or trefoils) and threecore cables. Major features are:
 Modeling of a large variety of installation methods: laying on the floor; hanging from supports clamped on a wall; in laddertype racks; or in cable trays
 Cables and groups of cables can be singlecore or threecore. Singlecore cables can be arranged in flat formations (vertically or horizontally) or in trefoil
 Computation of the steadystate ampacity or temperature. Cyclic loading using daily, weekly and yearly load factors. Computation of emergency ratings
Cables in Troughs
The thermal rating of cables installed in unfilled or in filled troughs is determined using the CYMCAP/UNF and the CYMCAP/MDB modules respectively.
A trough (or a trench) is understood in these modules as a long shallow rectangularshaped excavation, where the walls, bottom and cover are made of concrete. The cables can be installed on the floor, hanging from supports on the walls or racks. The trough can be filled with a material with good thermal properties or it can be left unfilled (air filled). The heat transfer mechanism is different for filled and unfilled troughs and therefore they are treated independently.
Unfilled Troughs
Originally, the only option to rate unfilled trough installations was the IEC standard. In this approach the cables rating is calculated as for cables in free air, but the temperature inside the trough is computed according to the IEC Standard 6028721©. The module has been improved significantly and includes three options besides the IEC standard to model a given trough installation: Slaninka Method 1, Slaninka Method 2 and AndersCoates Method.
With the IEC standard, thermal resistivities of the soil and the trough’s cover are ignored. With the Slaninka Method 1, the thermal resistivity of the trough’s cover is considered. The Slaninka Method 2 considers both the thermal resistivities of the cover and the soil surrounding the trough. With the AndersCoates method, in addition to the thermal resistivities of the soil and the cover, the wind velocity above the trough is taken into account. In all options the user can choose whether the trough is exposed to sun radiation or it is shaded. The approaches are all based on field research by independent parties and published in scientific journals.
Filled Troughs
Filled troughs are treated in the CYMCAP/MDB module as multiple backfills. Cables in filled troughs are rated in the CYMCAP software using:
 Finite elements method to compute the externaltothecable thermal resistance T_{4}
 IEC Standards procedures to perform efficiently ampacity calculations
Besides, the module offers many possibilities according to the known input data:
 Computes the temperature and steadystate unequally loaded ampacity as customary
 Facilities to move the troughs down and model asymmetrical troughs
 Considers cyclic loading through the use of load factors
Multiple Casings
The Multiple Casings module (MCAS) is the optional addon module that allows the user to determine the steadystate unequally loaded ampacity and/or temperature rating of cables installed in one or more nonmagnetic casings. A casing is understood in the CYMCAP software as a large nonmagnetic conduit filled with air, inside which cables in ducts and cables not in ducts can be installed. Casings can be immersed in water, placed on the sea bed or buried underground. No other filling material than air is considered in the casing(s) or in the duct(s).
The module features many modeling facilities among which the following capabilities can be highlighted:
 Different burial environments are allowed: water or underground
 Modeling of any number of casings in parallel in the same installation
 Modeling of any number of ducts inside one or more casings at the same time
 Capable of modeling any number of circuits inside a casing and a duct
 Circuits in ducts and in casings can be multiple cables per phase
 Several materials are available to model ducts and casings, including nonmagnetic metallic materials (PVC, Polyethylene, Earthenware, nonmagnetic metal, etc.)
 Sizes of ducts and casings are not limited
Duct Bank Optimizer Module
The Duct Bank Optimizer is an addon module that allows the user to determine the optimal placement of several circuits within a duct bank. More specifically, the module can recommend various circuit dispositions within a duct bank so that:
 The duct bank overall ampacity, i.e. the sum of the ampacities for all circuits, is maximized
 The duct bank overall ampacity, i.e. the sum of the ampacities for all circuits, is minimized
 The ampacity of any given circuit is maximized
 The ampacity of any given circuit is minimized
For a 3 by 4 duct bank with three trefoils and one threephase circuit (one phase per conduit), there are up to 665,280 possible combinations. The elaborated mathematical algorithm of the module prevents the repetitive calculation of equivalent cases, therefore the solution is obtained very efficiently. The condition illustrated on the right hand side of the illustration shows the cable locations for maximum ampacity.
Magnetic Fields
The Magnetic Fields Module (EMF) is an optional addon module to the CYMCAP software. Although this module is not directly related to cable thermal rating, it offers convenience to the CYMCAP users. After a steadystate ampacity or temperature simulation, the module computes the magnetic flux density at any point on or above the ground of an underground cable installation. The output is a plot (or a table) of magnetic flux density versus position. Modeling features include:
 Infinitelength thinwire twodimensional approach
 Consideration of timevarying currents producing an elliptically polarized rotating magnetic vector
 The currents in a threephase circuit can be unbalanced (in magnitude and phase)
 All media is assumed homogenous, isotropic and linear
 The induced currents are neglected
Cable Impedance Calculation
The Cable Impedances Calculation addon module (ZMat) determines the electrical parameters for cables necessary for performing network studies at the power frequency (50/60 Hz). The calculation of impedances is performed after a steadystate ampacity or temperature simulation has been successfully completed. The final results of the module are the positive and zero sequence impedances and admittances for all the cables present in the installation.
All impedance and admittance matrices are displayed in the report: starting from the primitive matrices per section per metallic component, the bonding matrices, then the phase and circuit matrices and finally the resulting symmetrical components matrices. The following features are supported:
 Computation of the sequence impedances for all the cables present in an installation
 Computation of the sequence admittances for all cables present in an installation
 Multiple cables per phase are supported
 One or more neutrals can be represented and are taken into account in the calculations
 Resistivity of the soil can be changed
CYMCAP/SCR, ShortCircuit Cable Rating
The ShortCircuit Cable Rating (SCR) addon module is dedicated to the rating of cables for shortcircuit currents. The implemented method is based on the IEC Standard 949© (1988) “Calculation of thermally permissible shortcircuit currents, taking into account nonadiabatic heating effects”. The CYMCAP program computes both adiabatic and nonadiabatic ratings. The module offers two possibilities according to the known input data:
 Compute the maximum shortcircuit current that a cable component can carry given the shortcircuit time together with the initial and final temperatures
 Compute the final temperature that a given cable component will reach for a specified shortcircuit current, initial temperature, and time interval.
Shortcircuit ratings can be computed for all metallic layers supported in CYMCAP:
 Conductor
 Sheath
 Sheath Reinforcement
 Concentric Neutral / Skid Wires
 Armour
Circuits Crossing
The Circuits Crossing (Xing) module is the optional addon module that allows the user to determine the steadystate ampacity of two circuits crossing each other.
When two circuits cross each other, each of them behaves as a heat source for the other one. The amount of generated heat, the vertical distance between the crossing circuits and the crossing angle are the main parameters that influence the crossing rating. In the absence of crossing calculations, the general practice is to use the conservative result where the circuits are assumed to be parallel. When the circuits are parallel, the thermal interaction is maximum. It goes to a minimum when they cross each other at a right angle. The conservative approach unnecessarily derates both circuits. By using the Circuit Crossing module, one can achieve ratings up to 20% higher than the conservative ampacities that are obtained based on the parallel installation scenario. Modeling features include:
 Modeling of two circuits crossings each other in the same installation
 Circuits crossing directly buried underground, in buried ducts and in buried pipes underground
 • Rating approach as per the IEC standard 6028733©
