CONSTRUCTION OF WATERPROOF UNDERGROUND SUBSTATIONS M.V. / L.V.

Transcription

1 23 rd Internatinal Cnference n Electricity Distributin Lyn, June 2015 CONSTRUCTION OF WATERPROOF UNDERGROUND SUBSTATIONS M.V. / L.V. Ernest VIDAL Edenr S.A. Argentina evidal@edenr.cm Miguel PULICE Edenr S.A. - Argentina mpulice@edenr.cm ABSTRACT Due t an increase f rainfall caused by climate change, the City f Buens Aires had been suffering frm intense flding. This directly effects undergrund substatins, and causes prblems in mid and lw vltage installatins, which affects end custmers. Fr this reasn, EDENOR S.A. (Empresa Distribuidra y Cmercializadra Nrte SA) had t launch a campaign t find a practical yet ecnmical way t make the undergrund vaults waterprf in rder t prevent prblems in the future. The campaign resulted in the replacement f the vault grilled-ventilatins at sidewalk level fr thers with high clumns (chimney) and minimum envirnmental impact, as well as the replacement f cnventinal manhle cvers, and transfrmer entry cvers fr waterprf nes. Its success imprved the quality f service, csts f peratin, and reduced utages resulting in a better Cmpany s image. INTRODUCTION In many cases during heavy rain (mre than 70 mm/hr), the water cming in thrugh the grilled-ventilatins placed at sidewalk level, and sme mre water cming in thrugh the manhles and transfrmer entry, flded the undergrund substatins. In rder t make them waterprf, many different alternatives were analyzed. Because f its lw cst, free maintenance, and minimal envirnmental impact, the slutin adpted was t deply clumn-style natural ventilatins n the sidewalk, and t replace the traditinal manhle cvers and transfrmer entry cvers fr waterprf nes. PROPOSED ALTERNATIVES: 1) Ventilatins with sidewalls and elevated grills n sidewalks. 2) Frced/natural ventilatins with hydraulic clsings. 3) Submergible electrical equipment. 4) Natural ventilatin with raised clumns n the sidewalk. ADOPTED SYSTEM: NATURAL VENTILATION WITH RAISED COLUMNS ON THE SIDEWALK Advantages: It keeps the existing equipment in place making it a relatively inexpensive slutin It ensures in mst cases the right natural ventilatin, even when facing different atmspheric and service cnditins. The manhle cvers require minimum maintenance, and the chimneys reduce the frequency f cleaning. Plan f wrk and executin Fr the implementatin f the plan, the fllwing cnsideratins were taken int accunt: - Areas prne t fld - Lcatin f the undergrund substatins - Undergrund substatins that were flded at least nce. - Structural characteristics f the undergrund substatins (dimensins, air flw, etc). This system was already applied t 294 substatins s far. The scheme f substatins with grids at the sidewalk level can be seen in figure n 1 CIRED /5

2 23 rd Internatinal Cnference n Electricity Distributin Lyn, June 2015 ESQUEMA DE CENTRO DE TRANSFORMACION ORIGINAL Scheme f Original Substatin Figure N 1 A preliminary plan fr each transfrmatin center was develped, which established the minimum structural changes that needed t be dne in rder t make them waterprf: Place the air duct nt higher than 0,3m abve the chamber s grund level t ensure a cnvective flw. Structural mdificatin f the vault fr the air ducts taking int cnsideratin the lcatin f the ventilatin grill, and defining the new psitin f the ventilatin clumns t avid garage entrances, frnts f business stres, sidewalk crners, etc. Demlitin f internal walls that may bstruct the airflw thrugh the entrance ventilatin, the transfrmer and the exit ventilatin. ESQUEMA DE CENTRO DE TRANSFORMACION ESTANQUIZADO Scheme f waterprf Substatin Figure N 2 CIRED /5

3 23 rd Internatinal Cnference n Electricity Distributin Lyn, June 2015 Cnstructive Characteristics The tasks were perfrmed by adjusting ventilatins (ducts) and cvers as described belw, taking n average abut 5 days, and withut the need f cutting pwer. Ducts The sectin f the duct is 0.6 m x 0.4 m which in mst cases prvided the necessary ventilatin withut the need f fans. The material used is a fiberglass PRFV reinfrced plastic, which meets the fllwing requirements: Waterprf Reduced thermal cnductivity Self- extinguishable Dielectric Shck resistant Lw envirnmental degradatin (UV radiatin resistance) Resistant t cntact with cncrete It allws the mdular cupling Once inside the substatin, the duct was installed by cnnecting the PRFV panels tgether, gluing them with a silicn sealer, and then clamping it t the walls r ceilings. On the utside f the chamber the ducts were wrapped with a small cncrete structure at grund level, which served as a mechanical prtectin as well as a secnd layer f water insulatin. The ducts had t be cnnected t the substatin as clse as pssible t the sidewalk level in rder t reduce the influence f hydraulic pressure due t grund water raise r leaks in sidewalk water installatins. As last, these external ventilatins were painted accrding t gvernment regulatins. Manhle/Transfrmer cvers They re made f steel sheet and its thickness is: a- In the sidewalk 3,2 mm b- In the rad 7,9 mm The cver has a nn-slippery surface, and it was placed fixing a weather strip n the bttm all alng its perimeter. Fr persnnel entrance a hatchway with a rubber weather strip was placed n the cver. Its perfect leveling was accmplished by a spring suspended system, which allws a crrect settling f the hatchway n the cver. The cver was treated t imprve its water resistance, and then it was placed n a cast irn frame (existing), which guarantees the system s impermeableness. The fit between the frame and cver was made frm inside the enclsure with turnbuckles ensuring the waterprfness. Thermal Cnsideratins Frm a thermdynamic pint f view, the area (frm nw n defined as System) behaves accrding t: 1) In permanent regime as an pen circulating system where the amunt f air that enters the system is the same than the ne that cmes ut, ensuring this way a mass flw. 2) In the transitry as an pen system in a nnpermanent regime - when the amunt f mass that cmes ut is nt the same as the ne that cmes in r vice versa. That means that the amunt f mass that frms the system varies during the transitry regime. Even if the mass amunt desn t vary, its cnditin varies. If we cnsider the system in a transitry regime, it will behave as an pen system in a nn-permanent regime. That means that at the mment where it is ut f balance (situatin where it starts t vary the amunt f heat Qexchanged between the system and the envirnment, whether it is due t a variatin in the transfrmer s charge, r due t the envirnmental cnditins, fr example temperature/ pressure/ humidity, etc.), it will behave accrding t the first principle f thermdynamic fr pen systems in a nn-permanent regime. Therefre appealing t the balance f energy we culd say: In an pen system in a nn-permanent regime, the energy that is added by the mass that is incrprated int the system, plus the net heat added t it, is equal t the energy that is taken by the mass that exits the system, the net wrk dne by the system, and the variatin f its ttal energy. On the ther hand, nce the permanent regime is reached reached the system will behave as an pen circulating system. Taking int cnsideratin that in mst f the technical applicatins, the variatin f ptential energy f the fluid may be dismissed (since fr representing a kilcalrie a height difference f 427 m wuld be necessary), as well as the variatin f kinetic energy, resulting in the fllwing expressin: Q - Lc= m (h2 h1) CIRED /5

4 23 rd Internatinal Cnference n Electricity Distributin Lyn, June 2015 Q = Amunt f Heat Lc = Wrk m = mass f air h2 = air enthalpy at the exit f the system h1 = air enthalpy at the entrance f the system If we cnsider fr the waterprf substatin, that the variables f the first term are maintained practically cnstant, and if we suppse that the air mass decreases as a cnsequence f the impermeabilizatin, it results that the term (h2 h1) Enthalpy differences h is increased, which implies an increase in the air temperature at the exit f the system. The vault s aptitude fr supplying the required ventilatin in a natural way (nt frced) is determined by the fllwing parameters: a) Transfrmer s pwer b) Electrmechanical equipment assciated t the substatin c) Charge s cnditin d) Structural characteristics f the vault e) Rm temperature The general equatin fr the air flw f the area will be: Pv F= (2) Where:.Cp. F= Ventilatin Air flw Pv= Pwer f lsses = Air density (cnstant) Cp= Specific heat f the air (cnstant) = Difference f air temperature between exit and entrance. Cnsidering the cnstants, the equatin culd be expressed as: Pv F= K0 (3) 1 K0 = (4).Cp K0= 2774 m3.k/kwh Fr ur analysis we will dismiss frm the cnstant the altitude crrectin factr, and we will nly cnsider the crrectin factr by temperature, suppsing the air is an ideal gas. If we take a pretty unfavrable cnditin such as fr example a rm temperature f 35 C it results that the cnstant K0 will be affected by this cnditin accrding t: T 308 Kt35 = = = 1,128 (5) T0 273 Thermal tests The experimental verificatin required fr measurements t be taken. T d s, the fllwing instrumentatin was used: - Temperature sensrs - Current transducer 0/800 A Fr the measurement, the sensrs were placed in the fllwing way: 1) One temperature sensr 2 meters high, facing the lw vltage panel (vault s temperature). 2) One temperature sensr at the extreme tp f the transfrmer radiatr (radiatr temperature). 3) A current transducer placed n the phase T f the transfrmer that was being measured. CIRED /5

5 23 rd Internatinal Cnference n Electricity Distributin Lyn, June 2015 Figure N 3 Frm figure 3 we see that: a) The maximum temperature that the transfrmer reached was 30 C, which is far frm its critical temperature. b) The temperature in the vault des nt fllw the ne f the transfrmer in a lineal way. It des it with certain inertia. c) The difference between the temperature in the vault and the transfrmer temperature was less than 10 C. CONCLUSIONS 1) The adpted slutin maintains the existing electrmechanical equipment, which ensures in mst cases, the right natural ventilatin, even when facing different atmspheric and service cnditin. 2) It has allwed the cntinuity f pwer distributin when facing adverse weather cnditins, which imprved the quality f service, and the Cmpany s image. 3) Operatinal and maintenance expenses were reduced. REFERENCES [1] Technical Thermdynamics 1984 Carls A. García- Editrial Alianza, Buens Aires, Argentina. [2] Switchgear Manual ABB. [3] Thermic studies n Stagnant Substatins I.yD; Buens Aires, Argentina CIRED /5