Engineering Calculation for Power System Analysis

Engineering Calculation for Power System Analysis Page of 178 CONTENTS Modules Pages Load Flow Calculation 3-16 Short Circuit Analysis 17-47 Case1-ANSI/IEEE Method Case2-IEC Method Motor Starting Analysis 48-66 Transient Stability Analysis 67-96 Case1-Single Machine System Case2-Multi Machine System Relay Co-ordination 97-107 Harmonic Analysis 108-125 Ground Grid Analysis 126-141 Optimal Capacitor Placement 142-151 Arc Flash Analysis 152-164 10 Underground Raceway System 166-183 Page of 178 LOAD FLOW ANALYSIS Page of 178 INTRODUCTION: Load flow solution analysis is essential for designing a new power system and planning of the existing one for increased load demand, which determine the steady state operating condition to calculate,  Voltage Profile - its magnitude in kV or % of nominal kV  Current flow throughout the System  MVA and /or MW plus Mvar power flows throughout each branch of the (i.e transformer, cables, line or series reactor etc) electrical system  Voltage drop and Power factor  Branch Losses i.e MW & Mvar losses on each branch Page of 178 Input data required for LFA: Sl.no Component Bus Power Grid Syn Generator Transformer Motor Syn Motor Static Load Lump Load Cable Transmission Line 10 MOV Protective Devices 11 Capacitor 12 Impedance Required input Nominal kv Voltage rating, MVA sc, X/R ratio Swing (slack) – %v and del Voltage Control (PV) – MW, Mvar limits Mvar Control (PQ) -MW, Mvar and Var limits PF Control-MW and PF Py kV, Sec kV, MVA, %Z Positive sequence Impedance, %Tap, Tolerance and LTC settings Status- Continuous , Intermittent or Spare Rating-HP and kV Status- Continuous , Intermittent or Spare Rating-HP and kV Status- Continuous , Intermittent or Spare Rating-kV, MW, Mvar and PF Status- Continuous , Intermittent or Spare Ratings- kV, MW, Mvar and PF Load Type-Motor Load or Static load Length in ft/m/mile/km Cable Type- Size, Insulation, kV and #/Cable Impedance/conductor-Positive sequence Length in ft/m/mile/km Parameter-Phase conductor Impedance per phase-positive sequence Rating-HP, kV and rated Torque Circuit Breakers-Rated kV Fuses-Rated kV Switches-Rated kV and amps Contactors- Rated kV and amps 1) Status- Continuous , Intermittent or Spare 2) Rating-kV, Max kV, Mvar Bank and No of Banks 1) Rating-Amps and kV 2) Impedance- Positive sequence Z and X/R Page of 178 STEP by STEP Procedure for Load Flow Analysis Step 1: Build the Single Line Diagram Page of 178 Step 2: Input Parameters/data for LFA Power Grid:Nominal kV kAsc X/R = 11kV = 40 kA = 14 Assume it is the base kV=11 Cable:Cable sizes and types are selected from the software library Insulation = XLPE kV = 15 Conductor type= CU #/Cable = 3/c Size = 300mm2 Length = 0.836 km Transformer:Primary kV = 11 Secondary kV = 0.433 MVA = 10 %Z and X/R = Typical Value Z Tolerance = If %Z 10 tolerance is 7.5 ( thumb rule) Tap = If needed (To improve the bus voltage) Lump Load:MW =4 Mvar =3 %PF = 80 Load Type = 100% Motor Load & 0% Static Load Step 3: Data needed for Hand Calculation Power Grid:X/R MVAsc = 14 = 762.102 Cable:R X Transformer:Z% X/R = 0.0801 Ω/km = 0.1273 Ω/km = 6.75 = 15.5 Page of 178 Step 4: ETAP WITH HAND CALCULATION To find Voltage Drop(Vd) Formula: %Voltage drop= Delta V*100 - eq1 To find Delta V: Delta V= (√ (Vr+ (RP+XQ/Vr) ^2+ (XP-RQ/Vr) ^2))-Vr - eq2 Where: Vr = Receiving end voltage R = Resistance of the cable/transmission in p.u P = Real Power in MW Q = Reactive Power in Mvar X = Reactance of the cable in p.u S= Apparent power in p.u We know that, Base MVA = 100 MVA Base kV = 11 kV Nominal kV = 11 kV Load PF = 0.8 R Ω/km = 0.0801 Ω X Ω/km = 0.12736 Ω Length = 0.836 km Assume Vr = p.u To find Z base: Zbase = BasekV^2/Base MVA = 11^2 / 100 Page of 178 Z base = 1.21 R = R*length / Zbase = 0.0801*0.836 / 1.21 R = 0.0554 X = X*length / Zbase = 0.12726*0.836 / 1.21 X = 0.0879 To Find P, Q and S: We know MW and Mvar of Lump load, a To find MVA =√ (MW^2+Mvar^2) = √ (4^2+3^2) MVA=5.033 P = MW/Base MVA = / 100 P=0.040 Q = Mvar/Base MVA = / 100 Q=0.030 S = MVA/Base MVA =5.033 / 100 S=0.0503 The following tabular columns are the results in p.u: R 0.055 X 0.088 P 0.040 Q 0.030 S 0.0503 Page of 178 To find % voltage drop: eq 2=> Delta V= (√ (Vr+ (RP+XQ/Vr) ^2+ (XP-RQ/Vr) ^2))-Vr Consider Vs=1 p.u Assume Vr = p.u Substitute the above calculated values from the table in the eq2 Delta V= (√ (1+ (0.055*0.040+0.088*0.030/1) ^2+ (0.088*0.040-0.055*0.030) ^2))-1 Delta V = 0.005 Note Vs ≠Vr so we are finding the new Vr new Vr new=Vr -Delta V -eq3 = 1- 0.005 Vr new=0.995 To find Voltage drop: eq 1=> Voltage drop= Delta V*100 = 0.005*100 Voltage drop (Vd) = 0.5 Page 10 of 178 STEP 8: Comparision Table: Hand Calculation ETAP Calculation Difference Incident Energy 17.25 Cal/cm2 17.31 Cal/cm2 0.06 Cal/cm2 Arcing Current 3.5 kA 3.557 kA 0.05 kA Flash Boundary 5.68 ft 5.71 ft 0.03 ft Page 164 of 178 UNDERGROUND RACEWAY SYSTEM ANALYSIS Page 165 of 178 INTRODUCTION: Cable derating analysis is an important part of power system design and analysis When you are designing a new system, this determines the proper size of cables to carry the specified loads When performing an analysis of an existing system, it examines cable temperatures and determines their ampacities ETAP provides five types of calculations for cable derating analysis, namely, steady-state temperature calculation, uniform-ampacity cable ampacity calculation, uniform-temperature cable ampacity calculation, cable sizing, and transient temperature calculation The steadystate temperature calculation is based on the IEC 60287 or the NEC accepted Neher-McGrath method The cable ampacity calculation and cable sizing are based on the NEC accepted NeherMcGrath method only The transient temperature calculation is based on a dynamic thermal circuit model All of these calculations can handle multi-raceway systems and consider the effect of heat generated by neighboring cables and external heat sources Underground Raceway System GUI: The UGS presentation is conceptually a cross-section of desired raceways, conduits/locations, cables, and heat sources, which are in the same vicinity which was as shown in the below Fig The UGS presentation allows you to graphically arrange raceways, conduits, cables, and external heat sources to represent cable routing and to provide a physical environment to conduct cable ampacity derating studies Each UGS presentation is a different cross-section of the underground system This is a different concept than the multi-presentation of the one-line diagram, where all presentations have the same elements Page 166 of 178 Fig You can create as many UGS presentations as you wish There is no limit on the number of raceways and heat sources that can be created/added in one presentation In UGS, each presentation acts independently If you add a raceway to a UGS presentation, this raceway will not be shown in the other UGS presentations However, raceways from any UGS presentation can be added to the other UGS presentations as existing raceways Also, if you delete a raceway from a UGS presentation into the Dumpster, this raceway can be added to other UGS presentations as an existing raceway Page 167 of 178 Cable Derating Calculation Methods: ETAP provides five types of cable derating calculations, namely, steady-state temperature calculation, uniform-ampacity ampacity calculation, uniform-temperature ampacity calculation, cable sizing, and transient temperature calculation In the calculations, all conductors from the same cable branch are presumed to equally share the total line current They can be located in the same conduit/location or different conduits/locations in the same raceway Note: The cables located in different conduits/locations in general will not have the same temperature, even though they carry the same load current However, if they are located in the same conduit/location, the calculated temperature will be the same The raceway system can contain several raceways and external heat sources The calculation considers the mutual heat effect of cables in the same raceway as well as in different raceways It also considers the heat effect from external heat sources Steady-State Temperature Calculation: The Steady-State Cable Temperature calculation determines the temperature of all the cable conductors involved in the raceway system under a specified loading condition The calculation is based on the IEC 60287 standard or the NEC accepted Neher-McGrath approach, which employs a thermal circuit model to represent heat flow situations It is assumed that the cables have been carrying the specified load long enough that the heat flow has reached its steady-state and no more changes of temperature will occur throughout the raceway system The cable temperature calculated is dependent on raceway system configuration, cable loading, and the location of each particular cable Page 168 of 178 Cable Ampacity Calculations: The Cable Ampacity calculation determines the maximum allowable load current that the cables in a raceway system can carry under the specified system conditions and the cable conductor temperature limit ETAP provides two approaches to ampacity calculation: Uniform-Ampacity calculation and Uniform-Temperature calculation Both approaches employ the NEC accepted Neher-McGrath method to calculate cable temperature, but they differ in the criteria used to determine the maximum allowable load current Uniform-Ampacity (UA) Ampacity Calculation This approach is based on the equal loading criterion for ampacity calculation It determines the maximum allowable load currents when all the cables in the system are equally loaded to the same percentage of their base loading The base load is obtained from the Cable Library for the appropriate system configuration type, such as duct bank or directly buried raceways The calculation involves an iterative process of cable temperature calculation and load adjusting, as listed below Determine an initial loading level based on the base ampacity from the Cable Library and using cable derating factors for the given configuration Calculate cable temperature as in the steady-state temperature calculation described above Check cable temperature values against the cable temperature limit If the temperature of the hottest cable is within close range of the temperature limit, the solution has been reached If not, adjust the cable loading uniformly at the same percentage, either increasing or decreasing the loading in order to make the highest cable temperature come closer to the temperature limit Then go to back to step to recalculate cable temperature If the Update Currents from Ampacity Calc option is checked in the study case, the cable allowable current is updated by the calculated ampacity Page 169 of 178 Uniform-Temperature (UT) Ampacity Calculation This approach is based on the equal temperature criterion for ampacity calculation It determines the maximum allowable load currents when all the cables in the system have their temperature within a small range of the temperature limit Since all the conductors in a cable branch are assumed to equally share the load current, in the case where these conductors are not located in the same conduit/location, they may not have the same temperature When this situation occurs, the temperature of the hottest conductor in this cable branch will be used to represent this cable branch The calculation involves an iterative process, which adjusts cable loading current in each iteration so that the cable temperature approaches the temperature limit The load adjustment in each step is determined based on the gradient of cable temperature change and therefore offers fast convergence to the solution The following steps are involved in the calculation: Determine an initial loading level based on the base ampacity from the Cable Library and using cable derating factors for the given configuration Calculate cable temperature as in the steady-state temperature calculation described above Check cable temperature values against the cable temperature limit If the temperature values of all the cables are within close range of temperature limit, the solution has been reached If not, determine the load change required for the cable temperature to approach the temperature limit based on the gradient of cable temperature change Update the cable loading and go back to step to recalculate cable temperature If the Update Currents from the Ampacity Calculation option is checked in the study case, the cable allowable current will be updated by the calculated ampacity If for any of the cables the Fixed Current option from the Loading page of the Cable Editor is checked then Uniform Temperature calculations cannot be conducted In this situation ETAP stops the calculations and provide an error message informing the user that UGS contains a cable with fixed ampacity Page 170 of 178 Cable Sizing – UGS: The Cable Sizing calculation determines the minimum size for each cable that will carry the specified load current without violating the cable temperature limit The cables considered as candidates for cable sizing are the ones that are flagged as available cables in the Cable Library of the same cable type, that is, they have the same voltage, insulation, conductor type, etc., as the cable to be sized The calculation is an iterative process involving repetitively adjusting the cable size and calculating cable temperature The cable temperature calculation is done in the same way as the steady-state temperature calculation described above If there are no available alternative sizes for a cable, the cable will be considered not changeable If a solution is reached, calculation results will be reported in the output report and the cables involved in the study will be changed to the new sizes if the Update Size option is checked in the study case Cable Derating Required Data: Underground Raceway System Data The data for the underground raceway system can be entered from the Underground System editor The minimum requirement for underground system data includes soil type, soil thermal resistivity, and ambient temperature Raceway Data Two types of raceways are supported in the current version of ETAP: Duct Bank Raceway and Direct Buried Raceway Raceway data can be entered from the Raceway page of the Raceway editor The minimum requirement for raceway data includes raceway dimension, raceway fill type, and its thermal resistivity You can run studies with raceways that contain no cables However, you cannot run studies if the raceway contains unassigned cables (cables that are assigned to a raceway but are not located in a specific conduit or location) Page 171 of 178 Conduit/Location Data The data for conduit/location can be entered into the Location page of the Raceway editor A conduit/location can be empty (contain no cables) Conduit A conduit can only be placed in a duct bank raceway The minimum requirements for conduit data include location, type, outside diameter, and thickness Location A location is a specified space in a direct buried raceway in which cables are placed Location can only be assigned to a direct buried raceway The only requirement for location data is its location Cable Data Cable data is entered into several pages of the Cable editor a) Data from the Info Page The cable type data must be available before performing any cable derating calculation You can select cable type from the Cable Library by clicking on the Library button Other data that are needed for cable derating calculations and that can be entered into the Info page include the cable size and the number of conductors per phase Special attention should be given to the Link to Library box When this box is checked, the cable derating calculation will extract the cable physical data directly from the Cable Library; otherwise it will use the data from the Physical page of the Cable editor b). Physical Page  This page is designed especially for entering parameters employed in cable derating calculations These parameters describing the physical aspect of a cable are required to Page 172 of 178 calculate cable electrical resistance, thermal resistance of different layers, dielectric losses, etc c). Loading Page  The data entered in this page describe the loading condition of a cable The Transient Load Profile data is used for transient temperature calculation The Operating Load or the first current value in the Transient Load Profile list are used, depending on the selection in the Cable Derating Study Case, as the initial or steady-state load current in the transient temperature calculation, steady-state temperature calculation, and cable sizing The Load Factor is used in all types of cable derating calculations to represent cyclic load conditions The Projection Multiplication Factor is used to modify cable loading in the transient temperature calculation, steady-state temperature calculation, and cable sizing, if the corresponding option is checked in the Cable Derating Study Case The Sheath/Armor Current is specified as a percentage of the load current It represents the situation where the sheath/armor is intentionally utilized to carry part of the load current In all other situations, sheath/armor current should be set to zero The Sheath/Armor Current is considered by the Neher-McGrath method only d). Ampacity Page  The Application Multiplication Factor is used to modify cable loading in the transient temperature calculation, steady-state temperature calculation, and cable sizing, if the corresponding option is checked in the Cable Derating Study Case External Heat Source Data The external heat source data required for cable derating calculations include the location of the external heat source, its outside diameter, and its temperature Page 173 of 178 STEP 1: Create an single line diagram with some cables Page 174 of 178 STEP 2: Enter the cable input dates as per the data sheet given below Cable Datas for 300mm2: Basic Datas: Cable Length : 1.5 km Resistance : 0.079 Ω / km Reactance : 0.1 Ω / km Cable Data Sheet Fig Page 175 of 178 Physical Dimensions:Rdc : 60.1 µΩ Cable OD : 10.8 cm Conductor OD : 2.37 cm Insulation Tickness : mm Sheath tension : 4.4 mm Jacket tension : 4.5 mm Cable weight : 18710 kg/km Max cable tension : 7.2 kg/ mm2 Max SW pressure : 355 kg/m Loading:Operating Load/current (we can get this by running load flow analysis) a Cable : 87.8 Amps b Cable : 267.3 Amps c Loading current for sizing: Select operating current UGS Load factor : 100% STEP 3: Create the Underground raceway system Fig Page 176 of 178 Procedure to create the UG raceway system Select the New direct buried or Duct bank raceway from the right side toolbar (see fig 2) and place in the design location window In this case select direct buried with required size Double click on the raceway and enter the fill type and fill RHO ( Termal resistance of fill material) in C-cm/Watt Here in this case it’s Sandy dry and 90 respectively Select and place the new conduit inside the receway with required size in this case the size of the conduit is 13cm After that click on the existing cable from the menu and place inside the conduit Goto Cable derating study case by selecting the edit study case and select the required informations Here in this case the method of calcualtion is Neher-McGrath method Run the UG Raceway System one by one see (fig 3) Steady-state temperature, UG Ampacity calcualtion, UT Ampacity calc, cable sizing and Transient temeperature calculation STEP 4: Run the Underground raceway system Fig Page 177 of 178 STEP 5: Output Report Manager Note:- From the above summary report shows that the required size of the cable for the system is 35mm2 and 95mm2 with respect to the load current The derating current or Ampacity of the cable is 87.8 and 267.30 amps for cable1 and cable respectively Page 178 of 178 ... Standard for Metal Enclosed Low-Voltage Power Circuit Breaker Switchgear IEEE Std 399 IEEE Std 141 1990 & 1997 1986, 1993, 2002 Power System Analysis – the Brown Book Electric Power Distribution for. .. 166-183 Page of 178 LOAD FLOW ANALYSIS Page of 178 INTRODUCTION: Load flow solution analysis is essential for designing a new power system and planning of the existing one for increased load demand,... Load Flow Calculation 3-16 Short Circuit Analysis 17-47 Case1-ANSI/IEEE Method Case2-IEC Method Motor Starting Analysis 48-66 Transient Stability Analysis 67-96 Case1-Single Machine System Case2-Multi