What is feeder in transmission and distribution?
Transmission and distribution feeders are generally installed above the distribution lines of wooden poles, or buried underground or in complete sets of cables, to transport electrical energy from the substation to the entire service area. The feeder runs at the primary distribution voltage. The primary distribution voltage used throughout North America is 12.47kV, and 4.2~34.5kV is widely used in other regions. In the world, there are many primary distribution voltages as low as 1.1kV or as high as 66kV. Many power distribution systems use several primary voltages. For example 23.9kV. 13.8kV and 4.16kv.
According to the wire size, the rated voltage level and the use of the service load by the public facilities, the main feeder distributes the voltage from 2MV.A to more than 30MV.A. Europe and the United States are slightly different in the wiring of the main feeder or medium voltage feeder. The most commonly used in European systems is to establish a ring configuration, while the United States usually establishes a tree configuration-the feeder is repeatedly divided into smaller branches as the feeder extends from the substation to the user. In such a combination, all feeders of the power system form the main feeder system. Normally, a substation has 2-12 feeders-the purpose of the substation is to reduce the voltage. Some substations have only one feeder. There is a substation that extends up to 84 feeders (Com-monwealth Edison Northwest Substation on the edge of downtown Chicago).
The main three-phase trunk line of the feeder of power transmission and distribution is called the main trunk line or main circuit, which can be branched or switched to several branches or alternative main lines. The terminals of these main branches are normally open contacts, and the feeder intersects with other feeders at the normally open contacts-pointing to a normally open switch that serves as an emergency connection of the two feeders. In addition, each feeder line will be divided into several switchable elements by a normally closed switch. In an emergency, these parts can be re-switched to isolate the damaged section, and bypass the faulty equipment to deliver power to the user, otherwise the user can only wait for repairs to restore the power supply.
According to the definition, a power transmission and distribution feeder is composed of all the primary voltage levels between the substation and the normally open contacts (switches). Any part of the switchable distribution line-three-phase, two-phase or single-phase-is regarded as part of the main feeder. The main trunk line and the switchable part are usually established by three-phase, using the largest size distribution wire (usually 500~600MCM wire, but the wire above 1000MCM is not commonly used. In special circumstances, a feeder line has been designed and built. 2000MCM wire), and adjusted for reasons other than the maximum capacity (such as emergency switch). The excess capacity of other feeders is due to the need to provide backup for other feeders in emergency situations.
Worldwide, most of the feeders for power transmission and distribution are overhead lines, using wooden poles, wooden poles or column insulators. Only in dense urban areas, or in the case of high aesthetic requirements, higher cost underground projects can be used. In this case, the main feeder line is built from the insulated cable, which passes through a concrete pipe buried in the ground in advance. The cost of underground feeders is 3-10 times that of overhead lines.
However, in many cases, even if the system is built overhead, the first few hundred yards of the overhead main feeder are buried underground. This section of the underground is used as a feeder outlet. Especially in large-scale substations, the underground connection is determined by actual demand, reliability and aesthetics.
In large substations, 10 to 12 three-phase overhead feeders extend out of the substation means that 40-48 lines are erected in the middle of the substation site, and each feeder needs to be properly spaced for electrical insulation, safety and maintenance. In large-capacity substations with tight locations, there is simply not enough overhead space to erect so many feeders. Even if there is, the line does not look beautiful, and the most important thing is the potential unreliability-if a damaged wire is dropped in an inappropriate location, a lot of power transmission capacity may be lost.
The solution to this problem is to use an underground feeder to connect. Usually, underground feeders are connected with buried pipeline cables containing hundreds of yards. The pipeline cables lead the feeders to the poles, and the feeders on the poles are above the ground and connected to the overhead lines. Usually, the initial underground feeder capacity determines the maximum capacity of the entire feeder-the capacity of the underground cable is the limiting factor for feeder transmission.
The above is the feeder for power transmission and distribution.
Basics of Transmission and Distribution Network,You can learn more about power transmission and distribution.