Hello learners, the basic engineering documents associated with any substation are, Single Line Diagram, which we call shortly as SLD, Layout Plan and Sections, Engineering Calculations such as sizing of bus bar conductors, lightning protection coverage, sag tension calculations etcetera. The above basic documents provide inputs to civil engineering for their deliverables. Other engineering documents are based on the above documents for further detailed engineering. Single line diagram has already been covered in detail in one of the earlier modules. We will discuss the layout plan and sections of a typical 33 bar 11 KV substation, comprising of 200% 10 MVA transformers, and the associated electrical clearance requirements, which are to be considered, while preparing the layouts. 33 KV part of the layout is a conventional outdoor substation layout with a single busbar arrangement without any bus sectional izer. It comprises of one incomer line bay and two outgoing transformer base. There is no need of a bus sectionalizer since the incomer is only one. The transformers are of 200% each of 10 MBA rating, each transformer is capable of delivering the complete load requirements of the associated downstream loads at 11 KV and other oxiscillay loads, associated with the substation. 33 KV side lightning arrester are rated at 30 KV, Station Class duty gap list type arrestors. For incomer line bay, surge arrester is mounted on top of the beam, and for transformer base it is mounted on a separate structure. 33 KV line side PT, which is mounted below the gantry is oil immersed type with one secondary winding for metering applications. Protection winding is not required as there is no distance protection requirement. Since the incomer is only one, there is no need for a separate bus PT also. The only consideration to be kept in mind is that the load burden on the PT shall be considered with all connected load requirements for meters, recorders of all base of 33 KV. 33 KV line PT is mounted below the incomer gantry on supporting structures. The 33 KV line side isolator is of horizontal double break type, manually operated and locally for both main drive and earth switch. One common drive separate for main and earth drives is sufficient to operate all the three poles. All other isolators in line bay and transformer base are only manually operated without any Earth switch. No remote operation from control room has been envisaged for all isolators. They are all operated locally. Operator shall ensure that associated CB is open before the operation of the isolators. 33 KV in Commerce City is of oil immersed type provided with two secondary cores one for metering and the other core for over current and earth fault protection. 33 KV transformer bay cities are of oil immersed type provided with three secondary cores one for metering, second core for over current and earth fall protection and the third core for differential protection of the transformers. 33 KV circuit breakers for incomers and transformer base, are of vacuum circuit breaker type, three pole mechanically gang operated. Individual poll operation has not been envisaged, spring charged mechanism is commonly used for operations. Power transformers are oil immersed type with natural cooling, ONAN, Oil, natural, air natural, vector type DYN 11 and provided with on load tap changer mechanism OLTC. Range of steps are normally decided based on the voltage variations at 33 KV. 11 KV switchgear is of indoor type panel construction comprising of draw out type vacuum circuit breakers VCBS. 11 KV Indoor switchgear is a single busbar scheme with two transformer fed incomer base, bus sectionalizer, six outgoing line feeders, three on each sections A and B. Two capacitor bank feeders one on each section A and B. For improvement of power factor, one station transformer bay, since the 11 KV system is solidly earth at the transformer neutral, 11 KV earth cables are laid between the transformer and the associated 11 KV incomer for cable terminations. The outgoing 11 KV feeder panels are three in each section A and three in section B with VCB type, draw out type construction. 11 KV earth cables are considered to be terminated at two pole structures for outgoing line feeders. The two pole structures are provided with outdoor type 11 KV double brake isolator with Earth switch and surge arrester for each of these six lines. Capacitor banks are fed from each of Section A and Section B. Circuit breakers for capacitor banks shall be suitable for capacitors, switching duty applications. Outdoor mounted capacitor bank panels are provided to improve the power factor of the system. One feeder has been envisaged for feeding 200 KVA, 11 bar, 0.433 KV station transformer oil immersed type. Since the load is only 100 KV, a gang operated air break switch, withdraw out type fuse has been envisaged adjacent to the transformer for protection and isolation. Cable from switchgear panel will be terminated at two pole structure, which houses LA ,AB switch and drop out fuse. >> Continued in next part.
