CLASSIFICATION OF CABLES USED IN SUBSTATION BASIC INFORMATION



No single cable characteristic should be emphasized to the serious detriment of others. A balance of cable characteristics, as well as good installation, design, and construction practices, is necessary to provide a reliable cable system.

Service conditions
a) Cables should be suitable for all environmental conditions that occur in the areas where they are installed.

b) Cable operating temperatures in substations are normally based on 40 °C ambient air or 20 °C ambient earth.

Special considerations should be given to cable installed in areas where ambient temperatures differ from these values.

c) Cables may be direct buried, installed in duct banks, conduits, and trenches below grade, or in cable trays, conduits, and wireways above ground. Cable should be suitable for operation in wet and dry locations.

High-voltage power cables are designed to supply power to substation utilization devices, other substations, or customer systems rated higher than 1000 V.

NOTE — Oil-filled and gas-insulated cables are excluded from this definition.

Low-voltage power cables are designed to supply power to utilization devices of the substation auxiliary systems rated 1000 V or less.

Control cables are applied at relatively low current levels or used for intermittent operation to change the operating status of a utilization device of the substation auxiliary system.

NOTE — leads from current and voltage transformers are considered control cables since in most cases they are used in relay protection circuits. However, when current transformer leads are in a primary voltage area exceeding 600 volts they should be protected as required by the NESC, Rule 150.

As used in this document, instrumentation cables consist of cables for Supervisory Controls and Data Acquisition (SCADA) systems or event recorders, and thermocouple and resistance temperature detector cables.

Instrumentation cables are used for transmitting variable current or voltage signals (analog) or transmitting coded information (digital).

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