Medium Voltage Cable Accessories – Best Practice Guide
Published 12 Jan 2020
uploaded by Chris Dodds - Thorne & Derrick Sales | Marketing Manager
This series of Blogs have been written by MV Cable Accessory Manufacturers to help promote ‘best practice’ in the installation of their products including joints, terminations and connectors for medium voltage power cable systems.
It is principally for MV cable installers but hopefully will be instructive for all involved in the construction and operation of medium voltage (MV) cable networks. Cable networks cannot be built without jointing cables together and terminating them to substation electrical equipment (switchgear/transformers) or overhead lines.
The long-term reliability of the MV cable network therefore depends critically on both the cable and the MV cable accessories installed on it.
A fundamental difference between cables and accessories is that cables are made in factories under closely controlled conditions, whereas cable accessories have to be installed on site by competent cable jointers from a kit of components.
This puts a heavy responsibility on the MV cable accessory installer to do an accurate and skilled job, frequently under unfavourable conditions. It is an unfortunate fact that cable network faults are often located at accessory positions, and in the majority of cases the cause of the fault is inaccurate or poor quality installation by the jointer.
The articles listed below highlight the more important aspects of the installation of MV cable accessories from the point of view of their effect on system reliability. The writers of this document hope that it will be found both useful and interesting, and that it will contribute to the increasing reliability of medium voltage networks.
- Cables | MV Paper Insulated v MV Polymeric Insulated Cables
- The Installation Site | MV Cable Joints & Cable Terminations
- First Steps | MV Joints, Jointers & Initial Considerations
- Cable Preparation | Jointing & Terminating Aspects of MV Cable Preparation
- Conductor Connectors | Crimp v Mechanical Connectors with Joints & Terminations
- Earth Bonding | Joints & Terminations & Overheating Prevention
- MV Cable Accessory Technologies | Heat Shrink, Cold Shrink & Push-on
- MV Cables & Causes of MV Cable Failures
- MV Cables | Electric Field & Stress Control
Defining MV | Medium Voltage
‘Medium voltage’ (MV) in this document means power-frequency system voltages from Um = 7,2 kV to Um = 42 kV where Um is the ‘highest system voltage’ for which the cable and their accessories are designed.
Within this range, the common rated voltages of European networks are 10kV and 11kV (Um = 12 kV); 20kV and 22kV (Um = 24kV); 30kV and 33kV (Um = 36kV).
International technical specifications (CENELEC and IEC) refer to values of Um rather than country-specific rated voltages.
This series of articles refers both to modern polymeric insulated cables (XLPE) and to historic paper insulated cables (PILC).
Though the PILC cables are now rarely installed in Europe they are common in existing utility networks and there is a continuing need to connect and joint new polymeric cables to them via ‘transition joints’.
MV cable accessories mentioned in this series of Blogs are of the following types:
• Cable Joints for connecting cables of the same design (straight joints) or different design (transition joints), connecting a branch cable to a main cable (branch joint) or insulating a cable end (stop end)
• Cable Terminations making permanent connections between cable and electrical equipment or overhead line
• Screened Separable Connectors for terminating cable to equipment via standardised equipment bushings
The most common MV accessory technologies in use today are heat-shrink, cold-shrink and ‘push-on’ systems, all based on polymeric materials with specific characteristics according to their function in the accessory. Conductor connectors are compression (crimp cable lugs) or bolted (mechanical shearbolt) designs. These technologies, and the important aspects of their installation, will be addressed in the following Blogs.
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