Articles: High Voltage Cable Design

New methods address IEC 60287 limitations for soil drying calculations. Considers multiple circuits, load factor, and backfill installations for accurate power cable ampacity.

Explore the factors affecting cable ampacity in trays, including thermal and electromagnetic effects. Learn calculation methods and best practices for safe power cable installations.

Based on extensive field experience, this article recommends the best materials for cable trays for use in offshore facilities such as offshore wind, solar, and oil rigs.

It’s difficult to decide on the thermal resistivity of soil or backfill to use for cable rating studies. The typical thermal resistivities of common native soils and engineered materials used as backfills for buried cables are provided in tables.

The widely accepted maximum operating temperature of XLPE insulated power cables under “normal use” conditions is 90 ˚C. During emergencies, the temperature of a buried cable may be permitted to exceed this temperature. The duration considered for such emergencies ranges from 10 minutes up to 15 days. In many countries, XLPE-insulated cables are allowed to operate up to 100-105 ˚C for short durations.

We performed ampacity calculations for hundreds of industrial and utility power cables from Southwire. The assumptions used for modelling in the software are explained. The calculated ampacities were all within 3 % of the values given in ICEA and NEC standards.

The standard HV cable rating calculation methods do not cover all real-world situations. This article proposes a new method of finding the current rating for 10 cables touching in the air.

Explains the effects of the installation conditions and the bonding arrangement on the current rating of high voltage power cables.

The AC resistance of a cable conductor is always larger than the DC resistance. The primary reasons are ‘skin effect’ and ‘proximity effect’. Equations and example calculations are provided in this article.

Accurate high voltage cable current ratings achieved – ELEK Cable HV software matches CIGRE TB 880 and performs IEC 60287 compliant calculations.

Explains the fundamentals of oil-filled cables current rating calculations to IEC 60287 and provides and example calculation for a 400 kV single core cable.

Sheath bonding is one of the most important design aspects for high-voltage cable power transmission. Solidly, single-point, and cross-bonded systems are explained.

Crossing multiple cables or heat sources at a crossing angle causes a current rating reduction, calculated using IEC Standard 60287.

New 13 kV power circuits will be installed in an unfilled trough with ventilated covers. These new circuits will cross with existing buried 400 kV cables at approximately 90 degrees with a continuous current rating requirement of 1136 MVA (1640 A) per phase for all seasons.

Most power cables have a design life of between 20 to 30 years. If the cables are not fully loaded, they are expected to last beyond their design life. The insulation is the weakest part of a cable. Montsinger’s Rule states: Insulation life is halved by a temperature increase of 8 to 10 ˚C. An example calculation using the Arrhenius equation is provided.

This article explains how to calculate the current rating of cables in J-tubes. Typically J-tubes are the thermal bottleneck of submarine power cable routes.

The calculation of submarine cable current ratings is different from land cables due to their complex construction and installation conditions.

A new calculation method based on FEM and IEC 60287 for current rating of HV cables in soils with multiple different thermal resistivities is explained with an example calculation. Modelling the different soil thermal resistivity zones (multiple backfills) is important for obtaining accurate cable current ratings.

The methods for calculating the current rating of multiple cables installed in ventilated tunnels are explained with example calculations. Overall tunnel length and air velocity inside the tunnel have a significant impact on cable current ratings.

The calculation of current ratings for groups of (multiple) cable circuits require the quantification of the mutual heating component between the groups of circuits. This example is for multiple groups of circuits in air on the same cable ladder. This article will discuss the IEC 60287 approach.

A report investigated 6214 cable failures over a 14 year period. The main causes were insulation breakdown, excavation, joints or switchgear failure. The results may surprise you.

Charging current in power cables is 10-20 times larger than for overhead lines. The maximum length of cable circuits is determined by their capacitance. This report provides equations and shows how critical cable length depends on voltage level, cable size and frequency.

The effects on the current rating of cables buried in soils with different thermal resistivities are examined with software using the finite element technique.

The definition of emergency rating is the permissible short-term rating of a cable already loaded and at a steady-state, considering the thermal capacitances and the thermal resistances of an installed cable system. The definition of cyclic rating is the maximum current of a cable when the load is varied in a sequence of steps that are repeated cyclically. The cyclic rating differs for different sequences and different cycle periods. Both emergency and cyclic ratings deal with time-varying loads

This article explains why dynamic ratings are important when dealing with long AC cables for wind farms. An example calculation of a dynamic rating which uses the measured load profile is given.

Waveform cables are commonly used in the UK for low-voltage power networks. The term waveform refers to the way the neutral/earth wires are laid around the cores/bedding. Using this configuration enables the neutral/earth wires to be opened so a connection can be made to the conductors anywhere along its length.

This article analyses the magnetic fields produced by electrical power cables installed in various configurations under varying conditions in the context of a health and safety-related issue. A software program has been used for calculating the results based on the Biot-Savart law. Techniques for the mitigation of magnetic fields are also presented.

We have benchmarked our Cable HV Software current rating results for 110 kV cables against the well-known software CYMCAP. We have shown the results are virtually identical (under 1.5 % difference).

The current rating of bare conductors is affected by the conductor temperature, weather parameters, heat losses due to convection and radiation, the solar heat gain and conductor resistance, the calculation of which is governed by a steady-state and a non-steady-state heat balance equation.