SUBSTATION SAFETY

There are numerous laws, rules, codes, etc. governing safety requirements; of the most important beingIEEE Standard C2-2012. 2012 National Electrical SafetyCode(NESC)

Rule no. 1 (clearance)Enough clearancefrom energized parts should be provided to avoid accidentalcontact with them. If that cant be met, live parts should be guarded or enclosed.

Rule no. 2 (minimum height)Aminimum height from the groundto any ungrounded part of an electricalinstallation should be 8-6, so a person staying on the ground cant touch asubstation element or its part which may become energized accidentally. Forexample, the bottom of a post insulator supporting an energized bus does notnormally have any potential.However, ifbus flashover to the ground overinsulator occurs, touching the bottom of the insulator may become unsafe. Thatswhy an8-6 distancefrom the bottom of insulator to the ground should beprovided.

Rule no. 3 (illumination)There should be sufficient illumination for personnel to clearly see theirsurroundings and perform any work safely. Required illumination levels arespecified inNESC [1].

Rule no. 4 (passageways)Allpassageways and stairsshould be wide enough for personnel to navigate themsafely, adequate railing should be provided, and floor openings should have guardrails.

Rule no. 5 (evacuation routes)Exits should beclearly markedand evacuation routes should befree fromobstructions. Depending on the function of the building (for example, controlhouse), it may require several exits to avoid personnel being trapped duringequipment fault, fire, etc.

Rule no. 6 (grounding, as always)All substation metallic structures, fences, and equipment tanks should beconnected to a station ground gridwhich should be designed to ensure that stepand touch potential values are lower than the ones stipulated in the applicablestandards.

InstallationDry-type transformers should be installed over foundations that areproperly leveledandcapable to withstand their weight.When a transformer is fitted with wheels, make sure the equipment will be equally supported on its base points in order to assure its stability and to prevent any deformation.When installing the transformer, the following factors should be carefully taken in account:1.There should be aminimum spacing of 0,5 mbetween one transformer and another, and between the transformer and any adjacent wall in order to facilitate the access forinspection and ventilation, depending, however, on the project dimensions and the voltages;2.The room where the transformer will be installedshould be well ventilatedas to assure proper natural ventilation, since this is an essential parameter for a proper performance of a dry transformer.In this regard, it is important that the air inlets are located at the front part of the transformer near the bottom and the air outlets are located at the back part of the transformer, with near the top openings large enough to allow for a circulation of approx.2,5 cubic meters of air per minute/kW of loss. (See the example calculation below).Proper ventilation in the transformer roomwill grant theexpected useful lifeand stable operation either on continuous regime or under momentaryoverloads.Figure 1 - Natural transformer ventilation

As normally the natural ventilation is not sufficient, fans can be installed toincrease the air flow i n the room according toFigure 2or, preferably, adopt therefrigeration o f the room where the transformer will operate .Danger!If the transformer room is going to be air conditioned,make sure theconditioned air will not be directly blown on the transformer, otherwise watercondensation can be built on it and can result in the transformer s burning.Figure 2 - Forced transformer Room Ventilation

To calculate the approximate size of the openings or the airflow necessary in theroom the following expressions cab be used, considering adifference of 15C betweenthe inlet air and the outlet air.

where:Pt= total transformer losses sinked at 115C [kW]S= lower opening surface [m2]S= upper opening surface [m2]H= distance measured between the middle of the height of the transformer andthe middle of the upper opening for air outlet [m]V= cooling air volume[m3/min]Example: Installation of two 2.000 kVA dry-type transformers Typical total lossesPT for 2 MVA dry-type transformer at 115C =27kW Distance Hbetween the middle of the transformer height and the middle of theair upper outlet opening:1,5m

From the calculated area we know that the installation of forced ventilation in the roomwill be necessary.The minimum flow of the fans will be:

This exampledoes not consider the presence of a protection cabinet, wich would be putin questi on in the case of a proper room for thetransformer installation.

The selection of investment-related re protection can be done based on company policies and standards, insurance engineering recommendations, industry practices, specic codes and standards (IEEE 977 and NFPA 850), or by risk-based economic analysis.Oil-Filled Equipment in Substation IEEE 980-1994 (R2001)

IEEE 979, Guide for Substation Fire Protection; Factory Mutual Data Sheets; NFPA 851, Recommended Practice for Fire Protection for Electric Generating Plants and Current Converter Stations [2]; and CIGRE TF 14.01.04, Report on Fire Aspects of HVDC Valves and Valve Halls [3] provide guidance on other types of fire hazards and fire protection.