Electronics Review Vol 23 No. 3 - ST Electronics

P R O J E C T S...continued from page 11to route the PSD cable trunking toaccommodate these interferences. Veryoften, it may not be feasible to install thecable trunking in the linear fashion inall stations below the platform edge. Atypical and proven method of installationof half-height PSD and running of cablesis shown in figure 3.Sometimes, it may be difficult tofind space to house the new PSCC.One of the existing rooms may haveto be refurbished or retrofitted toaccommodate the new PSCC. Thisnew equipment room should beproperly air-conditioned and securedwith fire protection system suitablefor electronics equipment. A typicalPSCC will be about 1,200mm (width) x400mm (depth) x 2,000mm (height) insize, and could weigh anywhere between300kg to 600kg with all the necessaryequipment. PSD system providers mayhave to undertake the role of installingthe environment control system andfire protection system for the new PSDequipment room. These additionalsystems need to be integrated withthe existing control system and evenwith the operation control centre formonitoring purposes. If there is noseparate room available, the PSCCcan also be installed at the platformheadwall.All these design changes, structuralassessments and materials to be usedSTATION PLATFORM 车 站 月 台Concrete Platform 月 台 混 凝 土Cement Screen Layer 水 泥 层250mm THKBrickwall砖 墙250 ~40475x75x6 THK SHSPED Column Post端 门 立 柱200 Edge Distance边 缘 距 离4 Nos. M16Grade 8.8Bolts 螺 铨Concrete Baseslab 混 凝 土 基 座Figure 2: Reinforcement of platform edge图 2: 月 台 边 缘 加 固 方 法for the modification works must beperformed by qualified personnel, andwill require approval from relevantbuilding construction authoritiesbefore any modification to the stationstructures can be carried outGrounding and Touch VoltagePSD systems are typically connected tothe return rails of the track to maintainequal-potential with the train so that thealighting passengers will not experiencean electric shock when they touch thePSD panels. In order for a PSD systemto be connected to the return rails of thetrack, they need to be isolated from thestation earth.When MRT stations are being built, theplatform edges are usually isolated fromthe station earth by means of insulatingmembranes about two metres in lengthfrom the platform edge. However, overa period of time, weathering takes placeand these membranes will wear off,causing the insulation to be reducedto below the acceptable value. Theminimum safe value of platform floorto-electrical-earthresistance over a300mm x 300mm area at 250V DC is10,000ohm and 35,000ohm under dampand dry conditions respectively. If theresistance is below the acceptable value,the platform floor must be re-tiled withinsulating tiles, which should have aninsulation value of minimum 0.3MΩ.75x75x6 THK SHSat 2m C/C6mm THKStiffener Plate 加 劲 助 板TRACK200 轨 道125min90 + 1165PSD Platform TrunkingPSD 月 台 线 槽1 - 100mm x 150mm and1 - 75mm x 75mmFigure 3: Installation of Half Height PSDsystem and the cables图 3: 半 高 式 PSD 系 统 的 安 装 及 布 线Alternatively, electrical insulationcoating of PSD facade can also preventtouch voltage (figure 4).Power Supply and UninterruptedPower Supply System InterfacesElectric motors are the prime movers ofPSD system. They consume significantamount of energy since the motors arealways powered up even when the doorsare closed and in the standby mode.The power consumption is relativelyhigh when the doors start opening andclosing (figure 5).The PSD system must be connected touninterruptible power supply (UPS) toensure that passengers can disembarksafely in case of power failure. Inmost cases, the existing UPS and thebattery back-up systems will not besufficient to support additional powerrequirements of the PSD system. Thismeans the existing UPS system needsto be upgraded. As MRT operators willnot want disruptions to the station’spower supply, installing additional UPSand batteries to the existing powersupply system requires detailed andcareful planning. To verify the actualincreased capacity of the UPS system,the following steps need to be carriedout systematically:• Survey and measurement ofexisting UPS load;• Design calculation anddetermination of additional UPS andbattery capacity;• Perform factory acceptance test ofnew UPS and batteries;12 ELECTRONICS REVIEW