It is a usual follow to indicate the varied components (e.g. electrical device, fuse, isolator, instrument transformers, etc.) of a sub-station by their graphic symbols within the affiliation schemes. Symbols of the necessary instrumentation in sub-station square measure given below :
Equipment in a Transfer Sub-Station:
The instrumentation needed for an electrical device sub-station depends upon the kind of sub-station, service demand and therefore the degree of protection desired. However, in general, an electrical device sub-station has the subsequent main instrumentation :
1.Bus-bars. once a variety of lines operative at an equivalent voltage have to be compelled to be directly connected electrically, bus-bars area unit used because of the common electrical part. Bus-bars area unit copper or metallic element bars (generally of rectangular x-section) and operate at a constant voltage. The incoming and outgoing lines in a very sub-station area unit connected to the bus-bars. the foremost unremarkably used bus-bar arrangements in sub-stations area unit :
(i) Single bus-bar arrangement
(ii) Single bus-bar system with division
(iii) Double bus-bar arrangement
A detailed discussion on these bus-bar arrangements has already been created. However, their sensible applications in sub-stations area unit mentioned.
2. Insulators. The insulators serve 2 functions. They support the conductors (or bus-bars) and confine this to the conductors. the foremost unremarkably used material for the manufacture of insulators is ceramic ware. There area unit many styles of insulators (e.g. pin type, suspension kind, post stuff, etc.) and their use within the sub-station can depend on the service demand. for instance, post stuff is employed for bus-bars. Post stuff consists of a ceramic ware body, forged iron cap, and flanged forged iron base. the opening within the cap is rib in order that bus-bars are often directly fast to the cap.
3. uninflected switches. In sub-stations, it’s usually desired to disconnect an area of the system for general maintenance and repairs. this is often accomplished by Associate in Nursing uninflected switch or isolator. Associate in Nursing isolator is basically a knife switch and is intended to open a circuit beneath no load. In different words, isolator switches area unit operated only the lines during which they’re connected carry no current.
4. breaker. A breaker is an associate instrumentality which may open or shut a circuit underneath traditional furthermore as fault conditions. it’s thus designed that it is often operated manually (or by remote control) underneath traditional conditions and mechanically underneath fault conditions. For the latter operation, a relay circuit is employed with a breaker. Generally, bulk oil circuit breakers area unit used for voltages up to 66kV whereas for top (>66 kV) voltages, low oil circuit breakers area unit used.
5. Power Transformers. an influence electrical device is employed during a sub-station to change of magnitude or diminution the voltage. Except at the ability station, all the following sub-stations use diminution transformers to step by step cut back the voltage of the electrical provide and at last deliver it at utilization voltage.
6. Instrument transformers. The lines in sub-stations operate at high voltages and carry current of thousands of amperes. The activity instruments and protecting devices area unit designed for low voltages (generally a hundred and ten V) and currents (about five A). Therefore, they’ll not work satisfactorily if mounted directly on the ability lines. This issue is overcome by putting in instrument transformers on the ability lines.
7. Metering and Indicating Instruments. There area unit many metering and indicating instruments (e.g. ammeters, voltmeters, energy meters, etc.) put in during a sub-station to take care of look into the circuit quantities. The instrument transformers area unit invariably used with them for satisfactory operation.
8. Miscellaneous instrumentality. additionally to higher than, there could also be following instrumentality during a sub-station :
(ii) carrier-current equipment
(iii) sub-station auxiliary supplies
Bus-Bar Arrangements in Sub-Stations:
Bus-bars ar the vital elements during a sub-station. There are many bus-bar arrangements that may be utilized in a sub-station. the selection of a selected arrangement depends upon varied factors like system voltage, the position of sub-station, degree of responsibleness, cost, etc. the subsequent ar the vital bus-bar arrangements utilized in sub-stations :
Single bus-bar system:
Because the name suggests, it consists of one bus-bar and every one the incoming and outgoing lines are connected to that. The chief benefits of this sort of arrangement ar low initial value, less maintenance, and easy operation.
The only bus-bar system with partition:
During this arrangement, the only bus-bar is split into sections and cargo is equally distributed on all the sections. Any 2 sections of the conductor are connected by a breaker and isolators. 2 principal benefits are claimed for this arrangement. Firstly, if a fault happens on any section of the bus, that section will be isolated while not poignant the provision from different sections.
Secondly, repairs and maintenance of any section of the conductor will be dole out by de-energizing that section solely, eliminating the likelihood of complete termination. This arrangement is employed for voltages up to thirty-three kilovolt.
Duplicate bus-bar system:
This method consists of 2 bus-bars, a “main” bus-bar, and a “spare” bus-bar. every bus-bar has the capability to require up the complete sub-station load. The incoming and outgoing lines will be connected to either bus-bar with the assistance of a bus-bar mechanical device that consists of a breaker and isolators. Ordinarily, the incoming and outgoing lines stay connected to the most bus-bar. However, just in case of repair of main bus-bar or fault occurring thereon, the continuity of providing to the circuit will be maintained by transferring it to the spare bus-bar.
Key Diagram of 66/11 kV Sub-Station:
- There square measure 2 sixty six kilovolt incoming lines marked ‘incoming 1’ and ‘incoming 2’ connected to the bus-bars. Such a meeting of 2 incoming lines is termed a double circuit. every incoming line is capable of activity the rated sub-station load. each these lines will be loaded at the same time to share the sub-station load or anybody line will be known as upon to satisfy the complete load.
- The sub-station includes a duplicate bus-bar system; one ‘main bus-bar’ and also the alternative spare conductor. The incoming lines will be connected to either bus-bar with the assistance of a bus-coupler that consists of an electrical fuse and isolators. The advantage of the double bus-bar system is that if repair is to be carried on one bus-bar, the availability needn’t be interrupted because the entire load will be transferred to the opposite bus.
- There’s a meeting within the sub-station by that constant sixty-six-kilovolt double circuit provide goes out i.e. sixty-six kilovolts double circuit provide is passing through the sub-station. The outgoing sixty-six kilovolts double circuit line will be created to act as the associate incoming line.
- There’s additionally a meeting to step down the incoming sixty-six kilovolt provide to eleven kilovolts by 2 units of 3-phase electrical devices; every transformer activity to a separate bus-bar. Generally, one electrical device provides the complete sub-station load whereas the opposite electrical device acts as a standby unit. If the necessity arises, each the transformers will be known as upon to share the sub-station load. The eleven-kilovolt outgoing lines feed to the distribution sub-stations placed close to shoppers localities.
- Each incoming and outgoing lines square measure connected through circuit breakers having isolators on their either finish. Whenever a repair is to be carried over the road towers, the road is initial changed and so earthed.
- The potential transformers (P.T.) and current transformers (C.T.) and appropriately placed for providing to metering and indicating instruments and relay circuits (not shown within the figure). The P.T. is connected right to the purpose wherever the road is terminated. The CTs square measure connected at the terminals of every electrical fuse.
- The lightning arresters square measure connected close to the electrical device terminals (on H.T. side) to pro- text them from lightning strokes.
- There square measure alternative auxiliary parts within the sub-station like capacitance bank for power issue improvement, earth connections, native provide connections, d.c. provide connections etc. However, these are omitted within the key diagram for the sake of simplicity.
Key Diagram of 11kv /400 V Indoor Sub-Station:
- The 3-phase, 3-wire eleven kV line is abroach and delivered to the gang in operation switch put in close to the sub-station. The G.O. switch consists of isolators connected in every part of the 3-phase line.
- From the G.O. switch, the eleven kV line is delivered to the indoor sub-station as underground cable. it’s fed to the H.T. facet of the electrical device (11 kV/400 V) via the eleven kV O.C.B. The electrical device steps down the voltage to four hundred V, 3-phase, 4-wire.
- The secondary of the electrical device provides to the bus-bars via the most O.C.B. From the bus-bars, 400 V, 3-phase, 4-wire provide is given to the varied shoppers via four hundred V O.C.B. The voltage between any 2 parts is four hundred V and between any phase and neutral, it’s 230 V.
- The CTs area unit placed at appropriate places within the sub-station circuit and provide for the metering and indicating instruments and relay circuits.