A Distribution substation is a substation which Transfer Electrical power from transmission system to the distribution system.
Elements of Distribution Substation
The various elements of distribution substation are:
- Distribution Transformer
- Lighting Arrester
- Gang operated switch
- Drop out Fuse
- DT Meter
- Low tension distribution box
- Silica gel Breather
- Arcing horns
Distribution Transformer is a main component of Distribution Substation. Distribution Transformer is an electrical transformer which convert high-voltage electricity to lower voltage levels acceptable for use in homes and business. A distribution transformer’s function is to step down the voltage to level accepted by the consumers. Generally, Distribution transformers are 11/0.433 KV i.e. they step down 11KV voltage to 433 V. The Capacity of these transformers vary, the standard capacity of distribution transformers is 25KVA, 63KVA, 100KVA, 250KVA etc.
In the distribution Substation the distribution transformers generally are mounted on 9m long two steel tubular poles with separation between the poles should 8 feet and the height of transformer from ground should also be 8 feet.
Lightning Arrester is the device used to provide protection against travelling waves by diverting the abnormal high voltages to ground without affecting the continuity of the supply. It is connected between line and earth i.e. in parallel with equipment to be protected.
Gang operated switch
The gang operated switch is also called Air break switch. They are called Gang Operated as they are operated in a Gang, all three switches together, using a single mechanism. They are also called air-break switches as they use air as the breaking medium or G.O.D.(Gang operated Disconnector) switch.. The air acts as a dielectric medium for the air-break switch. The air break switch is operated manually when their handle is placed on a ground level. These switches do not have any load-breaking capacity. They can only be operated when the transformer is on no-load and only the small magnetizing current flows through them. A substation must be disconnected from the load it is feed and only then can these switches located on the incoming lines of the substation be disconnected
Drop-out Fuses are protection devices that protect networks and equipment from current surges and overloads. An overcurrent will melt the fuse element in the carrier disconnecting the line or equipment. They also provide network isolation points when manually operated with a hot stick.
The dropout (swing out) fuse is an expulsion type and its main function is to protect Transformers on rural distribution network. It is also particularly useful for inaccessible Sub-stations where indication of fusing is of advantage
On blowing of fuse element, the fuse carrier hangs down vertically from the bottom contact. This is advantageous locating the fault as hanging fuse carrier is noticeable from distance and this save times which otherwise would be taken in investigation.
Lift out the fuse carrier by means of the insulated operating rod, rewire the fuse element and swing it up the carrier and thus remake the circuit.
Earthing of transformer is an important aspect of Distribution Transformer installation. For the distribution Transformer it is necessary to have three earthing electrodes, one for Lighting arrester, second for transformer neutral and third for transformer body and structure.
These three earth electrodes are connected to each other to form earth bus at one feet below the ground. The earth resistance of these interconnected electrodes should not exceed 5 ohms
DT Meter or Energy Meter
The Energy Meter is micro-controlled based metering device with class of accuracy 0.5S and inbuilt GPRS/GSM Modem that simultaneously carries out real-time calculation of parameters, manages memory, Display, RTC & Automatic/remote Communication with Head End Server.
Low tension distribution box
Low tension distribution box is electrical distribution board that receives power from Distribution transformer. and distributes the same to various Consumers. The LTDB contains different MCCBs to prevent the Distribution Transformer and circuits serving the consumers against overloading of Transformer and provide protection against the short circuits
Silica Gel Breather
Silica gel breather is cylindrical type container fitted to conservator tank through pipe line, filled with silica gel crystals used for absorbing any moister present in the air during the breathing action of transformer due to expansion and contraction of transformer oil in the transformer. When the Silica gel breather is first installed, the crystals have a blue tint, and after a period of operation, the colour of the tinted crystals gradually changes to pink, this is an indication that the silica gel is becoming saturated and losing its absorbent properties. When there is a preponderance of pink crystals the silica gel should be changed or reactivated.
Arcing horns are an inexpensive form of over voltage protection. They are employed mainly as lightning protection. Their function is to prevent damage to equipment that would be caused by high levels of voltage by providing an independent path for that voltage to earth. Furthermore, they must allow the equipment to resume normal operation once the high voltage event is dissipated.