Transmission|& Training Module-II Distribution SubstationRecap of Module-I BUU:TS / DS Following areas were covered in module-I + Type of substations + Busbar switching scheme + Content of substation a 2 ent ae By art ep oi Inpue to wl eed + Layout engineering —< aa y‘ 1g) 9 NS moe ob Avardanion?, + Design & Engineering tools + Business development strategy + Important referencesContents of Module -Il BUU:TS / DS + Frequently Asked Questions (FAQ) on substation engineering covering the following — Busbar material — Earthing — Auxiliary system = Cable engineering = Illumination — Structural engineering — Civil engineering — Installation activity + Competitors and our positioning + More on sales/marketing analysisFAQ : Busbar Material BUU:TS / DS What are the types of Busbar? + Rigid bus comprising of AL tube + Strung bus comprising of ACSR /AAA conductor What are the types of support? + Bus post insulator for rigid bus + String Insulator for strung busFAQ : Busbar Material BUU:TS /DS How busbar sizing is done? + Busbar sizing is done to check withstand ability of — Thermal Stress — Mechanical Stress — Deflection What are the input parameters? * Continuos current + Short circuit current & duration + Ambient temperature * Wind load on the conductor + Cantilever strength / Ultimate ten: + Minimum clearance + Span of the conductor strength of the supportFAQ : Busbar Material BUU:TS /DS Thermal Stress: + Flow of current causes thermal stress. + Temperature rise is checked for — Normal load current — Fault current. Note: Sizing based on governing criteria + Steady state temperature depends on — Radiation heat loss — Convective heat loss — Solar heat gain by the conductorFAQ : Busbar Material BUU:TS /DS Mechanical Stress + Mechanical stress on the busbar material is due to Dynamic force — Electrodynamic force during short circuit condition —. Wind force Static force — Static conductor tension — Self weight + Adequacy of busbar material is decided when it’s bending stress / tensile stress are within the limiting value.FAQ : Busbar Material BUU:TS /DS Deflection + Deflection of busbar happens At Dynamic condition — Due to’combination of electromagnetic force & Wind force At Static condition — Due to self weight and sag + Check for deflection in case of rigid busbat which decides the limiting value + In case of strung busbar it is minimum electrical clearance decides the ing value.Purpose of Grounding system BUU-TS / DS Two main design goals to be achieved by any substation ground system under normal as well as fault condition + to provide means to dissipate electric current in to the earth h out exceer g Operating and Equipment li + to Assure that a person ii the vicinity of the grounded facility is not exposed to the danger of electric shock. ah FATerms and Definitions BUU:TS / DS Ground Electrode : A Conductor imbedded in the earth and used for collecting ground current from or dissipating current in the earth. Ground Grid : A closely spaced horizontal and vertical bare conductor that are connected to each other at junction point and often placed in shallow depths. Grounding System : Comprises all interconnected grounding facilities in a specific area.BUU:TS/ DS Basic of Grounding system DesignDesign Philosophy BUU:TS / DS First step is to calculate the tolerable touch and step values based on IEEE 80 guidelines, which ensures the safety of person working in the substation =>Calculate attainable step and touch voltages based on preliminary design of grounding mat. Attainable value in the individual meshes should be less then the tolerable values. = The attainable step and touch potentials depend on fault current, earth resistivity and grounding mat configuration.Design Procedure BUU:TS / DS Brace fivng [reese 20] Attainable step and Touch voltage « p, Ig, DIEEE80 based grounding system design ur Se * Simple method based on empirical equations. + Gives only approximate peak attainable touch and step voltage. + Limited to Square, Rectangular, T or L configuration of the substation. + Uniform spacing of conductors. * No need of sophisticated computers.Limitation of IEEE80 design BUL:TS /DS * Uniform spacing of conductors. * Not possible to analyze the grid performance in Multi layer soil. + Not possible to consider the effect of the long Electrodes. + Not possible to consider the effect of the non energized component. + Inefficient design + Leakage current current density is non uBUU:TS / DS How to analyze the ground grid performance ?How to analyze the ground grid performance ? BUU:TS / DS | >From the safety point of view, touch and step voltages must be investigated over the entire grid area. Conventional analysis ( IEEE80) can calculate touch and step voltages only at the corner mesh where the voltages are likely to be highest. >The most vulnerable part of the substation from the safety point of view is the fence because potential gradient are high near the periphery of the grid. Person standing outside the substation touching the fence should be safe. Touch and step voltages should be investigated over the entire periphery for safety point of view.How to analyze the ground grid performance ? BUU:TS /DS l Cont... =>Pipe lines buried in the ground may carry the transfer potential during the fault on the substation, this has to be investigated in the vicinity of the substation. >In some cases, the substation grid is connected with the other auxiliary grounding mat. This is usual practice in power/industrial plants. For this type of study we have to investigate safety aspects at all the points in both the grids as well as the interconnecting grids. Ab Bi FADHow to analyze the ground g performance ? BUU:TS / DS. 1 >In conventional analysis with the irregular configuration of substation analysis for the equivalent rectangular area is performed then the analysis of the rectangular area is superimposed on to the actual area. | With improved knowledge and computational ete facility, we can go to micro level analysis and | improve the relial The step and touch voltages can be investigated at ty from safety point of view. I the point in the substation. Location of the highest step and touch voltages are also very important to design the efficient and safe Grounding grid.FAQ : Earthing specific to HV substation BUU:TS / DS Why Earthing? Earthing system is a key element of electrical system. It is critical to ensure personnel safety as well as to provide protection for equipment and to minimise interruption of service. Guideline? Earthing is carried out based on IEEE-80, 1S:3043 and also by finite element method. Input required? — Fault current & Duration — Ground current and fault clearing time Soil resistivity — Area of the switchyardFAQ : Earthing specific to HV substation BUU:TS/ DS Soil Resistivity Measurement + Resistivity test should be made to determine any important variation of ity with the depth of soil. in the site. The wenner's four pin methods is the most commonly used technique. Four probes are di (A) apart, driven to the depth (B). The voltage between the two inner electrodes is then measured and divided by the current between the two en in to the earth along the straight line, at equal distance outer electrodes to give a value of mutual resistance R. Then, _ 4TIAR Oe 2A A It eo VA?+4B?) VA?+B? Ab FADFAQ : Earthing specific to HV substation BUU:TS / DS Soil Resistivity Measurement Where, p= Resistivity of soil in Q-m R= resistance in ohms resulting from dividing the voltage between the potential probes by the current flowing between the current electrodes. A=Distance between adjacent electrodes. B=Depth of electrodes in meter.FAQ : Earthing specific to HV substation BUU:TS / DS Soil Resistivity Measurement + IfB is small’compared to A, as is the case of probes penetrating the ground a short distance only, the above equation can be reduced to p=4TIAR + The current tends to flow near the surface for small probe spacing, whereas more of the current penetrates deeper soils for large spacing Thus the resistivity measured for a given probe spacing A represents the apparent resistivity of a soil to a depth of A. + The above derivat n for the soil measurement is based on the assumption that the soil resistivity is uniform. Uniform soil resistivity means, soil resistivity remains constant both laterally and with depth to infinity.FAQ : Earthing specific to HV substation BUU:TS / DS Earthing Design + Following aspects are checked while designing earthing system — Adequacy of earthing conductor cross section — Grid size of the earthing conductor — Step potential and Touch potential Cross section of earthing conductor is to be sufficient to withstand the short circuit current. Also while selecting the size corrosion allowance is taken into consideration. In the switchyard earthing conductors are laid forming a mesh. Usually the grid spacing is uniform. But non-uniform grid spacing also can be adopted by calculation earthing through finite element method.FAQ : Earthing specific to HV substation BUU:TS / DS Step Potential Step Potential is the voltage difference between a person cause by the dissipation gradient of a fault entering the earth. Typically, ‘one meter from a fault entry point voltage reduced by 50%. (e.g. a 1000A fault entering through ground impedance of 5 ohms. will create voltage of 5000V. At a distance of less than one meter away a fatal potential of 2500V will exist). Earthmat installed in that area wil make the voltage gradient uniform and less than the safety li With PROTECTION 's feet ft NAL Ey eal NIM POTENTIAL ON ONE STEPFAQ : Earthing specific to HV substation BUU:TS / DS. Touch Potential \7= witHouT PROTECTION Touch Potential is similar to step potential except that the part of the fault current passes through the person's hand and body if he/she touches any structure which is carrying fault current. Touch potential is eliminated by connecting structure to the Earthmat so that least ee POTENTIAL ON TOUCHING resistance path for fault current is +FAQ : Earthing specific to HV substation BUU:TS / DS What are the critical issues for earthing design? Earthing design becomes critical when. + Soil resistivity is high in rocky areas ( > 150 ohm-m ) + High value of fault current and fault duration + Switchyard area is too small + Tolerable values of touch potential & step potentialFAQ : Lightning Protection for HV substation 8UU:Ts/ps What is D.S.L.P.? lee 62308, UNA Lem, Bie bein aan, eetcons bem Direct Stroke Lightning Protection (D.S.L.P) for outdoor air insulated substation is a very important aspect. Design of the D.S.L-P. is probabilistic approach which ensures minimum probability of lightning. How achieved? It can be achieved by providing — Lightning Mast — Shield Wire — Combination of above twoEAC! Lightning Protection fon HE substation BUU:TS / DS What are the methods for D.S.L.P. design? + As per "High Voltage Engineering" by Razevig with help of LM + As per 1S:2309 whicl + As per electro-geometry method by using combin wire also using LM and spikesFAQ: AC Auxiliary System BUU:TS /DS. What is AC auxiliary system? System that provides auxiliary AC to + Equipments ighting + HVAC system + Firefighting What are the configuration normally followed? One Incomer and required outgoing feeders Two Incomer with Sectionalized switchboard Dedicated LT Transformer/s Duplication of source to have redundancy Separate PCC (Power Control Center) and ACDB (AC Distribution Board) Diesel Generator as emergency source of powerFAQ: AC Auxiliary System BUU:TS /DS This a typical AC system block single {i} 415V MAIN SWDB-41A line diagram. This comprises of two separate incoming enERGeN ov source and DG LIGHTING as backup power supply. CHARGERFAQ: AC Auxiliary System BUU:TS /DS How feeders requirements are being engineered? The following requires AC supply: + Isolator motor operating mechanism + Circuit Breaker compressor / spring charging mechanism + OnLoad Tap Changer(OLTC) and Transformer cooling (Fan power supply) + Space heater, Lamp, Power socket for: CB switch cubicle, RTCC, Indoor Switchgear, Control & Relay panel, Bay MK, Junction box, Isolator drive box etc. + Switchyard lighting * Control room lighting + Transformer oi + Battery Charger + Air Cont + Storm water drainage pump tration ioning/Ventilation systemFAQ : AC Auxiliary System BUU:TS /DS What else to decide a feeder? The following aspects are to be considered. + Load current. + Type of duty (continuous, intermittent) + Amount of overloading to be considered. + Spare feeder requirement (e.g. 10% spare are considered as good engineering practice unless specified). Typical Incomer for PCC is Air Circuit Breaker (ACB) with electrical tripping form OIC & E/F protective release or from built-in release + Typical outgoing feeders are with Switch Fuse Units (SFU). gle phase distribution are usually through SFU or MCB. + However Molded Case Circuit Breakers (MCCB) are provided for outgoing feeders as specification requirement by the customer.FAQ:DC Auxiliary, System BUU:TS /DS ble DC source for control & protection circuit of substation equipment. DC system backed up by Battery erisures higher level of security over AC auxiliary system What are DC loads in a substation? * Protection & interlocks * Switchgear control ¢ Remote control & indication Annunciation system ¢ Control & instrumentation © Power line carrier ( PLCC ) * Emergency DC Lighting * Electric clocks * Commu ation systems * Data acquisition & logging systemFAQ : DC Auxiliary System BUU:TS /DS What are the type of Battery? Lead Acid Battery + Tubular battery comprises of tubular positive plates where tubes of terylene hold the active material with lead antimony spines. + Plante positive plates are solid cast plates of 99.99 purity lead. Negative plates are pasted grid made of lead. + Maintenance free battery comprises of flat pasted positive and negative plates made of lead calcium alloy tightly pressing against each other with glass wool mat in between. Ni-Cad Battery + Ni-Cad cell consists of nickel in the positive plate and cadmium in the negative plate. Electrolyte is potassium hydroxide in deionised water.FAQ : DC Auxiliary System Which type of Battery you need? Tubular Battery + Battery is simple construction + Life is 10 years. + Most Economical Maintenance Free + Does not require any topping up of water + Less hazardous and no special room required + Needs control environment at 27°C | * Cost is 2 times of Tubular battery Plante Battery + 40% better performance + Longer Life (20 years) + Almost 2.5-3 times Costlier than Tubular battery Ni-Cd Battery + Longer life span (25 years) + More stable & reliable performance + Less hazardous and corrosion free * Cost is 4 times of tubular battery BUU:TS / DSFAQ : DC Auxiliary System BUU:TS /DS What you need to size the Battery? Ampere Hour Capacity of battery is decided from the loading pattem or duty cycle over a discharge period of the battery. Following load are calculated * Continuous Load * Emergency Load * First & Last minutes Instantaneous LoadFAQ: DC Auxiliary System BUU:TS /DS What you need to size the Battery Contd... + Instantaneous or Momentary Load — Circuit Breaker Trip / Close, Protective Relays + Continuous Load — Annunciation system, DC supervision, Indication Lamps, Au: Relays, Semaphores + Emergency Loads — Emergency lightingFAQ : DC Auxiliary System BUU:TS / DS What is the Battery Charger? + Battery Charger is to — Charge the battery when battery gets discharged (Boost Charging) — Keep / maintain the battery charge (Float Charging) — Cater station continuous DC load during normal condition What are the Battery & Charger configuration? + One float charger and one boost charger * One float charger and one float-cum-boost charger + Two identical float-cum-boost chargers each capable of performing both duties + Three charger combination (2 main & 1 standby)FAQ: DC Auxiliary System BUU:TS /DS What does a battery charger contains? — AC unit comprising of rectifier transformer and AC switching unit — Rectifier unit (uncontrolled / half controlled / full controlled) — Control circuit for rectifier, current controller, monitoring & annunciation system — DC changeover with contactor, dropper diode or tap cell arrangement wand DCDB Transformer & ‘SFU/MCB Rectifier Control Ckt. DC Changeover Ckt. & DCDBFAQ : Cable Engineering What is cable engineering? * Cable engineering for substation is done to achieve — Reliable performance of the system — Optimized solution — Easy access and identification BUU:TS / DS = Optimal efforts during erection/ commissioning/ maintenance What are the areas of cable engineering? + Power Cable — LT Power Cable — HT Power Cable — Ynrur dx catia amenity caleutanten + Control CableFAQ : Cable Engineering BUU:TS / DS What is in cable engineering? + Power cable engineering - si ing of cross section and number of run of cable based on + Load current + Short circuit current + Fault clearance time + Voltage drop in cable + De-rating factors — Selection of insulation (especially for HT cable) + HT cable insulation based on the type of system i.e. Unearthed or effectively Earthed system + Specific care to be taken where impedance earthing is done but system behavior is near to Unearthed system — Cable routing, numbering, grouping and type of laying Ab PADFAQ : Cable Engineering BUU:TS / DS What is in cable engineering (contd.)? + Control cable engineering — Sizing of cross section and number of cores + Type of signals control cable to carry — Voltage (PT, CVT) — Current (CT) — DC Circuit (Closing, Tripping, Indication) — AC Circuit (DC supervision, operating mechanism ckt.) — Potential free contact circuit (Indication, Annunciation, logic ckt.) + Voltage drop due to longer cable route length — Grouping of signals for deciding the number of cores — Cable routing and marking and crossing — Cable and core numberingFAQ : Illumination BUU:TS /DS About + Illumination for substation is an important requirement for making operation possible at night. + Scope of — Outdoor Switchyard — Control Room building — Auxiliary building — Street Lighting (service road within the switchyard) jlumination? lu tion for typical substation are: ighting system for substation are considered as: - Normal AC to cater lighting requirement during normal operating condition — Emergency lighting on failure of normal AC lighting source + DC emergency for illuminating strategic locations + Lighting from DG system for bigger substations Ab i PAuFAQ : Illumination BUU:TS / DS How much illumination level required for substation? + Lighting shall provide enough light depending on nature of work to be carried out. Operational lighting as per 1S:3646 part-lll.FAQ : Illumination What are the typical luminaries used in substation? + Luminaries for outdoor switchyard: — High Pressure Sodium Vapour (HPSV) luminaries with various combination of rating with high beam & narrow beam used to achieve desired illumination BUU:TS / DS — Ratings usually considered * 2X400W HPSV, 1X400W HPSV for switchyard and outdoor equipment + 2X250W HPSV, 1X250W HPSV for switchyard and outdoor equipment + 1X150W HPSV for street lighting — High Pressure Mercury Vapour / Halogen luminaries are also taken if they specifically required by customer Bb Bi FADFAQ : Illumination BUU:TS / DS What are the typical luminaries used in substation? + Luminaries for control roo! Indoor illumination is achieved by various types of luminaries according to the requirement and utility of various rooms Room with CP/RP, office, conference room with air conditioning and false ceiling are provided with recessed mounted 2X36W fluorescent lamp with mirror optic reflector. For LT room, DG, Store etc. where no false ceiling or AC provided, industrial type 2x36W fluorescent lamp is used. For cable cellar bulk head or industrial type 2x36W fluorescent lamp is used as per specification Battery room is provided with corrosion proof indust fluorescent lamp. For DC emergency bulk head incandescent lamps are used. I type 2X36W fk BP ED PADDFAQ : Illumination BUU:TS /DS How illumination designed? + Input requirement — Lux level to be achieved at what height — Size of the area for outdoor and dimension of the room. — Type of interior color in case of room + Design Calculation — Lighting design calculation are normally carried out by the manufacturer with their in-house software. — Calculation provides point by point illumination level by which total area jumination can be analysed. Ab Gi PADFAQ : Structural Engineering BUU:TS/DS Input for structural engineering? + Drawings — Plan & Section Layout — Equipment drawings, Operating box / Junction box details + Customers specification — Minimum thickness of the member — Factor of safety — Type of structure ( Lattice / Pipe) + Loading information — Conductor tension (static and short circuit) — Wind pressure on structure, conductor, insulator — Equipment loading data — Weight of conductor, insulator string, hardwareFAQ: Structural Engineering BUU:TS / DS Column & Beam loading details? + Horizontal Loading — T: Conductor Tension — SWT: Shield wire tension — Wind load * Parallel to Beam + Perpendicular to Beam + Vertical Loading — Insulator String — Conductor — Deviation component — Self weight of + Beam * ColumnFAQ : Structural Engineering BUU:TS /DS Equipment loading details? + Horizontal Loading — Electrodynamic force of busbar — Wind load * on equipment * on busbar + on structure body + Vertical Loading — Weight of busbar — Self weight of equipmentFAQ : Civil Engineering BUU:TS /DS Input for Ci * Loading data Tower foundation loading Equipment foundation loading — Foundation load data for + Transformers * Reactors + NGR — Cable trench length & sections — Weights of cable in trenchesFAQ : Civil Engineering BUU:TS / DS Input for Civil Engineering? + Control room details — Equipment Layout — Cable trench or Cable cellar details — Equipment mounting & inserts details — Pipe inserts and opening for cables — Cable rack and inserts details ight fittings layout and air conditioning ducting layout — Erection / maintenance openingFAQ : Civil Engineering BUU:TS / DS Input for Civil Engineering? + Input from customer Technical specification with + Type of foundation + Factors of safety + Finishing schedules Soil investigation report Water Table Land contour map for levels Finish Ground Level (FGL) Out fall point for surface drainage discharge Type of roads and it’s construction specificationInstallation Activities BUU:TS / DS Installation activities for substation can be divided into following groups: Civil Activity (outdoor and control room) Structural erection (column, beam, equipment support structure) Equipment erection (indoor and outdoor) g and termination Erection of auxiliary system (HVAC, Fire-fighting, Illumination etc.) Pre-commissioning testing (indi test) Commissioning (energization) Punch list / defect list finalisation lual equipment / system e.g. sta Final commissioning certification (from customer) Handing over / taking over certification (from customer) Winding up Ab Bi PAuInstallation Activities BUU:TS /DS Following activities are also important for completion of site stallation work: + Site leveling and land development + Material checking and inspection + Monitoring & control of sub-contractor agency + Measurement and invoicing + Electrical Inspectorate approval / clearance + Material reconciliation + As-built marking on document / drawings + SafetyBUU:TS / DS. Control Panel AL tube weldingfh GD iD PADDED Brain Power: