66 substation operation and maintenance pdf free download transformers, each with a capacity of 150 MVA. This substation is constructed using steel lattice structures to support strain bus wires and apparatus.
Between the generating station and consumer, electric power may flow through several substations at different voltage levels. Substations may be owned and operated by an electrical utility, or may be owned by a large industrial or commercial customer. As central generation stations became larger, smaller generating plants were converted to distribution stations, receiving their energy supply from a larger plant instead of using their own generators. Substations may be described by their voltage class, their applications within the power system, the method used to insulate most connections, and by the style and materials of the structures used.
The simplest case is where all transmission lines have the same voltage. In such cases, substation contains high-voltage switches that allow lines to be connected or isolated for fault clearance or maintenance. Transmission substations can range from simple to complex. A warning notice can be clearly seen on the “front door”. Disguises for substations are common in many cities.
It is uneconomical to directly connect electricity consumers to the main transmission network, unless they use large amounts of power, so the distribution station reduces voltage to a level suitable for local distribution. The input for a distribution substation is typically at least two transmission or sub-transmission lines. Input voltage may be, for example, 115 kV, or whatever is common in the area. The output is a number of feeders. Distribution voltages are typically medium voltage, between 2. 4 kV and 33 kV, depending on the size of the area served and the practices of the local utility.
In addition to transforming voltage, distribution substations also isolate faults in either the transmission or distribution systems. The downtown areas of large cities feature complicated distribution substations, with high-voltage switching, and switching and backup systems on the low-voltage side. More typical distribution substations have a switch, one transformer, and minimal facilities on the low-voltage side. Usually for economy of construction the collector system operates around 35 kV, and the collector substation steps up voltage to a transmission voltage for the grid. In some special cases a collector substation can also contain an HVDC converter station. Collector substations also exist where multiple thermal or hydroelectric power plants of comparable output power are in proximity. If no transformers are required for increasing the voltage to transmission level, the substation is a switching station.
These stations contain power electronic devices to change the frequency of current, or else convert from alternating to direct current or the reverse. A switching station is a substation without transformers and operating only at a single voltage level. Switching stations are sometimes used as collector and distribution stations. Sometimes they are used for switching the current to back-up lines or for parallelizing circuits in case of failure. In this case the generators from the power station supply their power into the yard onto the Generator Bus on one side of the yard, and the transmission lines take their power from a Feeder Bus on the other side of the yard. Switching events may be planned or unplanned. A transmission line or other component may need to be de-energized for maintenance or for new construction, for example, adding or removing a transmission line or a transformer.
To maintain reliability of supply, companies aim at keeping the system up and running while performing maintenance. All work to be performed, from routine testing to adding entirely new substations, should be done while keeping the whole system running. Former high-voltage substation in Stuttgart, Germany, now 110kV switching station. The 220kV level is eliminated for grid simplification. The function of the switching station is to isolate the faulty portion of the system in the shortest possible time.