Hello learners, having gone through the self learning modules on cabling concepts for cable trenches covering the bay trenches, and the main trenches and road crossings. We will now go through the details of the cable trenches for their typical 33 by 11 KV substation which is partly outdoor and partly indoor. The inputs for the cable routing are furnished by the electrical department to the civil department. The actual cable translated for construction is prepared on the civil foundation layouts so that fouling if any with the tower or the equipment foundations can be noticed and rule rooted. It also helps in planning to provide the cable decks with pipes at road crossings if applicable. In this particular substation, it may please be noted from the above layout that there is no road closing involved for the cable trenches. EMV power cables are necessary in this project As 11 kV switchgear is of indoor type Cables used or 11 kV earth, aluminum conductor, xlp insulated, armored and PVC outer sheets of the following sizes. 10 MVA transformer one to 11 kV switchgear incomer one, clearance of single core 630 square mm cable in trefoil formation will be used. 10 MVA transformer two, to the incomer two, clearance of single core 630 square mm cable into file formation will be used. Now 11 kV switchgear, outgoing line feeders, there are six feeders out there so three court, 300 square mm cable will be used for each feeder. 11 KV switchgear to the capacitor banks, one and two, three core 300 square mm cable will be used. 11 kV switchgear to auxiliary transformer three core 300 square cable, you could absorb the bay trench wide section one, one which is the transformer bay trench between two transformers base, this is the Section one, one bay trench for the transformer base. These are the clearance of single core cables in the trefoil formation, clearance of single core 630 square mm cables in the foil formation from each transformer is taken through this particular range. And later at the bottom most territory of the EMV cables so totally as sixth sense of single core 630 square mm cable. The LV power and control cables from the transformer marshaling boxes, of these 10 MVA transformers, the control panels and the RTC panels are laid in pipes and taken through this transaction, one, one. And further to the control building through train sections six, six, and seven, seven, two pipes are provided, one for LV power cable and one for control cable. 11 kV outgoing cables to the line feeders on the capacitor banks, for two outgoing feeders behind the 11 kV switchgear building where the two pole structures are placed, 11 kV cables can be taken through the pipes behind the switchgear building. For 11 kV outgoing feeders, three, four, and five, 11 kV cables can be taken through strength section, three, three, and then through the pipes to the pole structures. Section three, three, of the cable trench this is the cable, three quart 300 mm square cable three cables for the three feeders. For the 11 kV outgoing line six, and the capacitor banks 11 kV cables can be taken through train section four, four, and then through their pipes to the two pole structures. So the cables will go through like this through this trench below the building, it goes to the capacitor banks and then to this particular two pole structure for the line six. Section two, two, is the equipment trends for current transformers, potential transformers, circuit breakers and transformers marshaling boxes. Section if you see, this is the cable trench section two, two, this is further equipment trenches for CTs, PTs, marshaling box and circuit breaker. So cable from the equipments assured in the details A, B, C, and D, in the plan from various pipes enter into these trench sections, one, one and two, two. We will see detail A, detail is shown in the plan for 33 kV CTs in the transformer base, this is 33kV CTs, one pipe 100 dia, PVC pipes for cable from CT junction box. To the control panel for meeting and protection is shown, totally six cables from the two transformer based CTs will enter into section one, one, three cables from here and three cables from here will enter into section one, one, this is detail A for the CT cabling. There is a CT junction box here, this is their trench section we are seeing the cable will be going in the pipe, 100 dia pipe. Similarly for the Line Bay 33 kV CTs, one paper of 100 dia is provided from the CT junction box to the control panel for meeting and production, totally two cables from line bay CTs will enter into section two, two. Detail B shown for the 33 kV circuit breakers in the transformer base showing two numbers of 100 dia PVC pipes from circuit breaker mechanism cubicle to the control panel. One pipe will be used for LV power cables and the second pipe will be used for control cables for trip coil one, trip coil two secures, closing secures, indication, annunciation secures, inter trip, etcetera. This is detail B is shown, this is a circuit breaker mechanism cubicle, these are the two pipes shown here, this is the cable trench section. Similarly for the line based circuit breaker, two numbers of 100 dia PVC pipes are again provided and enter into the trench section, two, two. Detail C is shown in the plan for the 33 kV PTs in the line bay, one paper of 100 dia is being provided for cable from PT junction box to the control panel for metering. Only one cable from the line bay PT will enter into bay trench section two, two, four metering, this is the 38C, 432kV PT, PT junction boxes here, so this is the cable which is going and enter into section two, two. So section six, six, and section seven, seven, they are the main trenches leading to the control building housing the one kV switchgears and protection and control panels. So this is trench section six, six, trench section seven, seven, they will have three tires, one for control cable, one for LV power cable, and one for EMV cable. The top tire is used for the control cable, while the bottom tire is used for the 11 kV cables, the middle tire is used for the anti power cables. No cables or envisaged for isolators as they are operated manually and also from local, so proper coordination has to be ensured that circuit breaker is open before the operation of the associated isolators in the line bay and the transformer base. Separate PVC pipes shall be used for LV power cables and control cables wherever it is necessary. EMV power, LV power and control cables are laid in separate tires, inside the cable trenches filling has to be insured. EMS angles are supported at every 1000 intervals along the horizontal run inside these trenches for cable laying, the cables are laid directly on these angles, there are no separate cable trays and envisaged. The cabling philosophy can be absorbed with this, the control cable on the top tire, the LV power cables on the middle tire, and the MV power cables on the bottom to provide a better bending radius, cable trenches are of RCC type of construction. Distance between the top of the covers lab to the faster tire, similarly the distance between the two tires, distance between the bottom most tire to the bottom of the trench all have been indicated. The top of the trench is kept at about 300 mm above the finished ground level, the gravel is kept at about 100 mm or 150 mm above the finished ground level so the top of the trench slab is maintained at about 150 to 200 mm above that gravel level. The earthing conductor, which is shown as E in section, it shall be ran all along the route inside the cable trenches in all the sections, and inter connected to the earthing conductor at intervals of 50 meters so they can see conductor E at almost all the sections. The detail D Is shown for the Transformer marshaling boxes for which two numbers of 100 dia pipes are used. One pipe is used for the control cables to marshaling box, to the control panel for alarm and trip functions. Associated with transformer for book holds really, alarm and trip oil temperature alarm and trip binding temperature, allotment, trip, minimum oil level alarm, etcetera. One pipe will be used for the LV power cables and pushing city cables from marshaling box to control panel, it's also used as a power cable.
