Welcome to this module on cable routing layouts. This module describes concept of cable routing layouts, typical indoor and outdoor cable routing layout in 33kV outdoor substation. You have already seen the different types of cable installation methods. Now, let us see how the cable routing has been applied for the 33kV outdoor substation. Need for cable routing layout. In outdoor substation, all equipment are installed as per equipment layout plan and section. The control building has to be located at an optimal location. The control building typically houses 11 kV switchgear, AC and DC auxiliary system, control and relay panels, telecom panels, battery and battery charges, etc. These equipment and systems are interconnected by means of cables. Cables are routed in a predefined path so that the interconnecting cables are of optimal length. During maintenance, cables are required to be identified and traceable with minimal effort. In the 33 kV substation, typically following cables are used: MV power cables, about 1.1 kV week up to 33 kV, low voltage power cables, 1.1 kV grade, control cables, 1.1 kV grade, and signal cables, 250 volt grade. Methods for estimation of number of cables. The number of cables depends on : type of busbar configuration, total number of bays, line bays, transformer bays, bus section bays, etc. Total number of bays, in turn, decides the total number of equipment like circuit breakers, isolators, CTs, PTs, transformers, etc. Power distribution arrangement, control, protection, and interlocking schemes. Cables required for interconnecting various equipment are listed in cable schedules: brief specification, conductor cross section, route length, routing, and identification numbering are also provided for each cable in the cable schedule. Cable schedules are separately prepared for power and control cables. The block diagram indicates the interconnection cables between the field equipment and control building. This block diagram is decided at the initial stage of the project based on which cable schedule is prepared. Depending upon the quantum of power and control cables involved, the dimensions of the cable trench section is decided. For example, consider current transformer from the R phase of the line CT in the switchyard, two runs of 5 core 2.5 square mm cables are to be run to the current transformer junction box. Note that both are located in the switchyard itself. Now, from the CT junction box to the CRP in control room building, again two runs of 5 core 2.5 square mm control cable run through switchyard cable trenches to CRP of control room. Similar set of cables run for the Y phase and B phase of the line CT, and for all three phases of the line PT also. In the control room building, cables from CRP to ACDB or the DCDB will be routed through trays. Similarly, for the circuit breaker situated in the switchyard, cables from ACDB and CRP in the control room building are laid in a common trench up to VCB. The same philosophy can be extended to other equipment also. The figure shows the various legends and symbols used to identify the main and bay trenches in the control room. Field routing in PVC duct for individual equipment. Branch trenches B1, B2, and B3 connection to the conduit. Road crossing using PVC duct or concrete hume pipes. Main trench from control building. Figure shows the predetermined trench routing of a 33KV substation. A trench can be a simple body trench or a concrete trench. In this example, we will see about the concrete trench. A trench shall always be routed through the shortest path to the control building from the switch yard equipment in order to optimize the length of the cables laid. Bay trench is normally provided, common for two or three adjacent base referred to B1, B2, B3 branch. The number of cables laid in the trench is determined through cable schedules as already seen. All the cables will be running in the [inaudible] branch of the trench as shown in the figure, which is considered as main trench. RCC hume pipes or concrete encased duct banks are provided at road crossing locations. More details on road crossing aspects are covered in a module on civil works. Cable trays can be installed inside concrete trenches and in the cable cellar. In such cases, the LV power cables and control cables shall be laid on separate tracks. The LV power cables and control cables can be installed on top or bottom rack depending on individual practice considering other factors like bending radius, heat dissipation, etc. The LV way power cables up to 25 sqmm maybe installed in two layers. The LV power cables more than 25 sqmm should be installed in a single layer based on utility practices. Cables from equipment to bay trenches shall be laid in uPVC or GI pipes. Separate pipes for the LV power cables and control cables shall be considered. Sizing of these pipes shall be based on 40 percent fill criteria. The screen shows the layout for the indoor cable trench inside the control room. Let us cut through the control room across section A, A and see how the cable trenches looks like in the sectional view. The same philosophy of outdoor trench sizing shall be followed for indoor trench. Let us cut through the control room across section 1,1 and see how the cable trench looks like in the sectional view. All cable trench openings behind the panels and unused cutouts or trenches shall be covered with the MS checkered plates to prevent any falling incidents. Trenches in the control room shall be provided with perforated or ladder type trace. The HV power cable shall be taken through the bottom most cable tray. This philosophy to be adopted for trays below panels to get more cable bending radius for power cables. Here is a quick recap of what you have learned this far. In an outdoor substation, equipment are installed as per equipment layout, plan, and section. Cables are routed in a predefined path so that the interconnecting cables are all optimal length. During maintenance, cables are required to be identified and traceable with minimal effort. Number of cables in a substitution depends on the busbar configuration, number of base, number of equipment, and power distribution arrangement, control, protection and interlocking schemes. A cable schedule comprises, cable size, length of the cable, cable construction, cable deck, feeder description, and routing of the cable. Trenches are routed through the shortest path to the control building to optimize the length of cables laid. For two or three adjacent base, a common bay trench is normally provided. Cables from equipment to bay trenches shall be laid in uPVC or GI pipes. Cables crossing roads are installed in RCC hume pipes or concrete encased duct banks. Separate pipes should be considered for the LV power cables and control cables. Pipe size shall be based on 40 percent fill criteria. HV power cable shall be taken as the bottom most cable tray. All cable trench openings behind the switch gear panels and unused cutout or trenches shall covered with the MS checkered plates.
