CYMCAP-SCR the Short Circuit Cable Rating (SCR) add-on module to CYMCAP is dedicated to the rating of cables for short circuit currents.

The implemented method is described in the IEC Standard 949 (1988) "Calculation of thermally permissible short-circuit currents, taking into account non-adiabatic heating effects". CYMCAP computes both adiabatic and non-adiabatic ratings.

CYMCAP-SCR offers two possibilities according to the known input data:

• Compute the maximum short-circuit current that a cable component can carry given the short circuit time together with the initial and final temperatures.
• Compute the final temperature that a given cable component will reach for a specified short circuit current and initial temperature.

The short circuit rating can be computed for up to the five metallic layers in the CYMCAP model:

• Conductor
• Sheath
• Sheath Reinforcement
• Concentric Neutral / Skid Wires
• Armour

 

CYMCAP-MDB the Multiple Duct Banks module is the extension to CYMCAP designed to determine the steady state 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 non-standard calculation methods.

The module computes the values of T4 (the external to the cable thermal resistance) using finite elements and then the ampacity (or operating temperature) of the cable system is obtained using the IEC standardized solution method.

CYMCAP-MDB features many modeling facilities. 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 sink in the installation.
• Computation of the steady state ampacity or temperature.

 

CYMCAP-OPT the duct bank optimizer is an add-on module to CYMCAP that allows the user to determine the optimal placement of several circuits within a duct bank. More specifically, the module can recommend the various circuit disposition within the duct bank in order 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 three-phase circuit (one phase per conduit), there are over 110,000 possible combinations.

CYMCAP elaborated mathematical algorithm prevents the repetitive calculation of equivalent cases, therefore the solution is obtained very efficiently. The condition illustrated on the right hand side, below, shows the cable locations for maximum ampacity.

 

CYMCAP-EMF the Magnetic Fields Module (EMF) is an optional add-on that can be connected to CYMCAP. Although this module is not directly related to cable thermal rating, it offers convenience to the CYMCAP users. After an ampacity or a temperature steady state 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:

• Infinite-length thin-wire two-dimensional approach.
• Consideration of time-varying currents producing an elliptically polarized rotating magnetic vector.
• The currents in a three-phase circuit can be unbalanced (in magnitude and phase).
• All media is assumed homogenous, isotropic and linear.
• The induced currents are neglected.

 

CYMCAP-CIT the optional Cables in Tunnels Module allows the user to determine the temperature, steady state, cyclic and transient ampacity of cables installed in unventilated tunnels. Note that only equally loaded cables having the same type and loading are considered.

This add-on module supports a large variety of cable arrangements for single core (flat formations or trefoils) and three-core cables. The cables can be laid down on a floor, hanging from supports clamped on a wall, installed in ladder racks or in cable trays.

Major features are:

• Modeling of a large variety of installation methods: laying on a floor; hanging from a wall; in ladder-type racks; or in cable trays.
• Cables and groups of cables can be single-core or three-core. Single-core cables can be arranged in flat formations (vertically or horizontally) or in trefoil.
• Computation of the steady state ampacity or temperature. Cyclic loading using daily, weekly and yearly load factors. Computation of emergency ratings.

 

The Multiple Casings module (MCAS) is an optional add-on to CYMCAP that allows the user to determine the steady state unequally loaded ampacity and/or temperature rating of cables installed in one or more non-magnetic casings. A casing is understood in CYMCAP as a large non-magnetic 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).

CYMCAP/ MCAS 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 non-magnetic metallic materials (PVC, Polyethylene, Earthenware, non-magnetic metal, etc.)
• Sizes of ducts and casings are not limited.

 

The Cables Impedance calculation module (ZMat) is the optional add-on to CYMCAP that determines the electrical parameters for cables necessary for performing network studies at the power frequency (50/60 Hz). The estimation of parameters is performed after an ampacity or temperature steady state simulation has been successfully completed. The final results of ZMat are the positive and zero sequence impedances and admittances for all the cables present in an installation.

All impedance and admittance matrices are displayed in the report: starting from the primitive matrices per section per metallic component, the transposed matrixes (if they exist), then the reduced to phase conductor matrices and finally the resulting symmetrical components matrices.

• Computation of the sequence impedances for all the cables present in an installation.
• Model 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.

 

The Cable Crossing (Xing) module is the optional add-on to CYMCAP that allows the user to determine the steady state ampacity of circuits crossing each other.

When two circuits cross each other, each 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 important 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 Cables Crossing module, one can achieve ratings up to 20% higher than the conservative ampacities that are obtained based on the parallel installation scenario.

• Capable of modeling two circuits crossings each other in the same installation.
• Cable crossing is supported in directly buried underground, buried ducts and buried pipes underground.
• Rating approach follows the IEC standard 60287-3-3.

 

Numerous underground transmission projects are emerging worldwide. Each project requires a substantial investment of time and money in a market where shortfalls and blackouts are not acceptable anymore.

Nowadays, it is a universal practice to use Distributed Temperature Sensing (DTS) systems based on fiber optic technology to monitor the cables temperature all over the run.

To supplement this technology, we introduces its CYMCAP/RTTR Dynamic or Real Time Temperature cable Rating system to extend the monitoring functionality and predict/forecast the behavior of the installation under emergency situations.

CYMCAP/RTTR is designed to provide both steady state and transient thermal analysis. It is based on the IEC Standards 60287 and/or 60853 or finite elements. This function allows the user to be ready, by looking into the future, when an emergency situation arises.

RTTR Operating Modes

The Real-time Temperature Rating based on CYMCAP has two modes of operation:

• Estimating the conductor temperature from the fiber measured temperature.
• Performing emergency ratings with the transient engine.

CYMCAP-RTTR Modeling Capabilities

Virtually every cable construction available in the market can be modeled with CYMCAP: one-core, three-core, sheathed cables, concentric neutrals, armored cables, screens, shields, beddings, servings, jackets, etc. The following installation types can be modeled: duct banks, backfills, directly buried, buried ducts, buried pipes, cables in air (including groups of cables and riser poles) and cables in tunnels. Unique to CYMCAP is its ability to model several materials with different thermal resistivities, for example: stratified soil layers, multiple duct banks and multiple backfills.

Emergency Rating

CYMCAP/RTTR provides the following information useful to the cable operator:

• Given the operating temperature and the applied (over) load, the RTTR software predicts the temperature of the cable in the future.
• Given the operating temperature and the applied (over) load, the RTTR gives the time that it will take to the cable to reach a specified emergency temperature.
• Given the operating temperature and a time frame for an over load, the RTTR computes the maximum current that the circuit can carry to reach certain emergency temperature.

Computational Procedures

When there are available real-time measurements of both the temperature at the cable surface and the current, CYMCAP/RTTR uses the IEC Standards 60853 to conveniently compute the temperature of the core conductor. When only the temperature at the location of the fiber is available, the temperature of the core can be estimated from the IEC Standards 60287.

Transients Calculations

Cable operating temperature very much depends on the load shape applied to the cable. In other words, the temperature of a cable depends on the intensity of the current and its time variations. Therefore, cables have different ratings, i.e. steady state, cyclic, emergency and short circuit. Since cables installations have thermal inertia, it takes time to heat up the cable and its surroundings. A typical response to a step overload of 100% lasting 12 hours is shown in the figure below. One can appreciate that the temperature of the cable follows in an exponential way the changes in current.

 

 

 

 

 

There are many underground (UG) transmission/distribution systems in operation forlonger than 50 years (a few even longer than 100 years). Utilities are facing the need to provide reliable service with an aging cable infrastructure. UG system planners and operators currently do not know if (which, where, when and for how long) cables have exceeded, at some point in time, their operating or emergency temperature.

CYMCAP-CHOTE the Cable Historical Operating Temperature Estimator (CHOTE) is a software application that offers an innovative way to evaluate the temperature at which underground cable systems have operated during their in-service life.

CYMCAP-CHOTE provides important information to transmission and distribution engineers. It allows identifying, qualifying and quantifying the following important conditions:

• The cables and cable installations that have been exposed to thermal damage. Say which cables have exceeded their normal and/or emergency temperatures during their in-service life.
• For how long and for how much the applied over-temperatures compare with the original design characteristics.

Cable engineers can take advantage of the above information to plan additions and/or substitutions in and informed manner. By using CYMCAP-CHOTE an engineer knows for how long each cable has exceeded a desired certain target temperature. As a consequence, there is valuable information to estimate the remaining life of a cable, which can be used to manage efficiently capital investments in cable installations. For example, an investment to substitute a cable can be postponed, or planned to do it “just in time”, with greater certainty thanks to the information that CYMCAP-CHOTE offers.

Transient Calculation

Cable operating temperature very much depends on the load shape applied to the cable. In other words, the temperature of a cable depends on the intensity of the current and its time variations.

Therefore, cables have different ratings, i.e. steady state, cyclic, emergency and short circuit. Since cables installations have thermal inertia, it takes time to heat up the cable and its surroundings. A typical response to a step overload of 100% lasting 12 hours is shown in the figure below. One can appreciate that the temperature of the cable follows in an exponential way the changes in current.

Application Highlights

Using transient simulations, CYMCAP-CHOTE processes archived loading information usually available through the SCADA/PI systems on an hourly (or 15 minutes) resolution. Thus, the input to the temperature estimator is the current of all cables on a particular installation. CYMCAP-CHOTE is capable of automatically analyzing all the thermal sections of a system. This may include transmission and even the entire distribution system (manhole-to-manhole). The temperature estimator can process achieved information for any length of time. Currently 10 years of historical data are being used.

The output of CYMCAP-CHOTE is a list of cable sections that have exceeded the (definable) normal and/or emergency target temperatures. CYMCAP-CHOTE produces a global ranking report. The cables that exceed their target (normal/emergency) temperatures for the longest time are given the first place in the report. The output displays not only where, but also when the hot spots have occurred.

CYMCAP-CHOTE is capable of indicating the location of the cables that have exceeded a target, either normal or emergency, temperature. It will give the thermal section (manhole-to-manhole), the feeder name, the dates, times and for how long certain temperature was exceeded. Additionally, the application shows graphically the location of the cable with problems in the duct bank and even allows re-creating the condition that produced the temperature problem.

CYMCAP-CHOTE can perform what-if scenarios to study the impact of addition of new cables. This facility can also be used to determine the remaining ampacity of one or more of the cables installed in a given duct bank.