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Cable Sizing Calculations

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Siddhartha mudgal

This document discusses cable sizing calculations and techniques. It explains that proper cable sizing is important to ensure efficient, safe and economic transmission of electrical energy without interruptions or exceeding the cable's limits. The document outlines the common steps for cable sizing: 1) gathering data on the cable, load and installation conditions, 2) determining the minimum size based on current capacity, voltage drop, temperature rise and fault impedance, and 3) selecting the optimally sized cable. Several examples are provided to illustrate implementing the cable selection process. Risks of improper sizing like voltage drops, overheating and shorter lifespan are also summarized.

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CABLE SIZING CALCULATIONS BY SIDDHARTHA MUDGAL ELECTRICAL ENGINEERING DEPARTMENT MEERUT INSTITUTE OF ENGINEERING AND TECHNOLOGY, MEERUT,UTTAR PRADESH Dr. APJ ABDUL KALAM TECHNICAL UNIVERSITY(AKTU) (Formerly known as UPTU)
What is Cable Sizing ? The determination of conductor's parameters to get efficient, safe and economic operation of transmission. Importance of Cable Sizing The proper sizing of an electrical cable(Which is bearing load) is important to ensure that the cable can: • Operate without any interruptions. • Withstand the full load currents. • Bear the voltage as well as transients . • Minimize the initial capital investment. • Provide effective and efficient transmission of electrical energy.
Major Solution providers for conductors in INDIA:- • Havells India Ltd. • Polycab Wires Pvt. Ltd. • Sterlite Technologies Ltd. • Finolex Cables Ltd. • Diamond Power Infrastructure Ltd.
Techniqes of Cable Sizing:- • Cable sizing methods do differ across international standards (e.g. IEC, NEC, BS, etc) and some standards emphasise certain things over others. However the general principles underlying any cable sizing calculation do not change. As per IEC As per NEC
Common STEPS:- • STEP 1:- Gathering the data about the cable, it's installation conditions and the load which it needs to be supply. • STEP 2:- Determine the minimum cable size based on the following:- i)Current Carrying Capacity. ii)Voltage Drop. iii)Short circuit Temprature rise. iv)Earth fault loop impedance. • STEP 3:- Selection of the cable which have highest sizing based on the above parameters
What we look for in STEP-1 ? A)LOAD:- • Type of load which is to be supplied. • Maximum current required by the load. • Voltage capacity of the system. • Expected power factor of the system. • Distance of load from the source. B)CONTRUCTION OF CABLE:- • CONDUCTOR MATERIAL:- Normally copper or aluminium. • CONDCTOR TYPE:- Stranded or solid. • CONDCUTOR SURFACE COATING:- Plain (no coating), tinned, silver or Ni. • INSULATION TYPE:- PVC, XLPE, EPR. • TYPE OF CORE:- Single core or multicore.
c)INSTALLATION CONDITIONS:- • Installation medium:- i)eg. Underground or overhead, soil thermal resistivity for underground cables, etc. • Arrangement:- i)For underground cables whether it is placed directly or in a conduit, for overhead wires whether it is installed supported by the walls, on the cable towers etc. ii)Depth of laying iii)Bunching of cables, spacing b/w them. • Atmospheric Temprature:- i)Ambient of soil temprature. ii)Soil thermal resistivity, in the case of undergrond cables.
What we look for in STEP-2 ? A)Current carrying capacity:- The current plays a vital role while deciding the sizing for a cable due to following factors:- i)Copper lossess. ii)Thermal capacity of cable iii)Reactive power. iv)Insulation,bedding,armour and other components of cable Thus depending upon these parameters we find out the minimum possible and feasible size for the cable.
i)Base current ratings:- Cable manufactuers maintains a table for base current rating for different type of cables. These ratings are taken out in base environmental conditions and ths these ratings are relevant for base installation conditions. ii)Installed Current Rating:- Whenever there is difference b/w the base conditions and actual instllation conditions, then the derating factor is used in order to find out the actual installed crrent ratings.
i) In ground Installation (Direct Burial) C =Cs * Cg * Cd *Ct Where, Cs = Rating factor for variation in ground temperature Cg= Rating factor for Group of cables Cd= Rating factor for Depth of laying Ct=Rating for thermal resistivity ii) Above Ground Installation C = Ca * Cg Where, Ca= Rating factor for variation in ambient air temperature Cg= Rating factor for Grouping cables Then installation current rating is obtained as:- I(new) = I(base) * C
B)VOLTAGE DROP:- Current flow through the cable – the higher the current flow, the higher the voltage drop. Impedance of the conductor – the larger the impedance, the higher the voltage drop. As, For a three phase system:- For a single phase system:- For a DC system:- 1000 )sincos(3 3 LXRI V cc     1000 )sincos(2 1 LXRI V cc     1000 2 LIR V c dc 
C)SHORT CIRCUIT TEMPRATRUE RISE:- During a short circuit, a high amount of current can flow through a cable for a short time. This surge in current flow causes a temperature rise within the cable. k ti A 2  k ti A 2  Minimum Cable Size Due to Short Circuit Temperature Rise:- The temperature rise constant is calculated based on the material properties of the conductor and the initial and final conductor temperatures          i if k   5.234 1ln226          i if k   228 1ln148 (for copper conductors) (for aluminum conductors)
D)EARTH FAULT LOOP IMPEDANCE:- EARTH FAULT LOOP IMPEDANCE Zs = Zc + Ze Where Zs is the earth fault loop impedance (Ω) Zc is the impedance of the active conductor (Ω) Ze is the impedance of the earth conductor (Ω)           22 1000 ececs XXRR L Z
Implementation examples of Cable Selection process EXAMPLE 1 EXAMPLE 2  Electrical Details:- Electrical Load of 80KW, Distance between Source and Load is 200 Meter, System Voltage 415V Three Phase, Power Factor is 0.8,Permissible Voltage drop is 5%, Demand Factor is 1,  Cable Laying Detail:- Cable is directly buried in Ground in trench at the depth of 1 meter. Ground Temperature is approximate 35 Deg. No of Cable per Trench is 1. No of Run of Cable is 1 Run.  Soil Details:- Thermal Resistivity of Soil is not known. Nature of Soil is Damp Soil
Risk and Impact of Wrong Sizing • High voltage drops, which increases reactive power. • Sudden increase in cable temprature. • Damage of cable components, such as armour, bed sheath, insulation etc. • Damage of protective components. • Poor power factor. • Non continuous supply. • Shorter Life span of cables. • Increase in maintainance cost of the system.
Conclusion Efficient, safe and economic operation of transmission can be obtained by proper sizing and selection of cables References Wikipedia, https://wiki.openelectrical.org/index.php?title=Cable_Sizing_Calculation Electrical Engineering Portal, https://electrical-engineering-portal.com/an-example-how-to-calculate-voltage-drop-and-size-of-electrical- cable My Electrical Engineering https://myelectrical.com Elements Of Power System,by U.A.BAKSHI
Thank You

More Related Content

Cable Sizing Calculations

  • 1. CABLE SIZING CALCULATIONS BY SIDDHARTHA MUDGAL ELECTRICAL ENGINEERING DEPARTMENT MEERUT INSTITUTE OF ENGINEERING AND TECHNOLOGY, MEERUT,UTTAR PRADESH Dr. APJ ABDUL KALAM TECHNICAL UNIVERSITY(AKTU) (Formerly known as UPTU)
  • 2. What is Cable Sizing ? The determination of conductor's parameters to get efficient, safe and economic operation of transmission. Importance of Cable Sizing The proper sizing of an electrical cable(Which is bearing load) is important to ensure that the cable can: • Operate without any interruptions. • Withstand the full load currents. • Bear the voltage as well as transients . • Minimize the initial capital investment. • Provide effective and efficient transmission of electrical energy.
  • 3. Major Solution providers for conductors in INDIA:- • Havells India Ltd. • Polycab Wires Pvt. Ltd. • Sterlite Technologies Ltd. • Finolex Cables Ltd. • Diamond Power Infrastructure Ltd.
  • 4. Techniqes of Cable Sizing:- • Cable sizing methods do differ across international standards (e.g. IEC, NEC, BS, etc) and some standards emphasise certain things over others. However the general principles underlying any cable sizing calculation do not change. As per IEC As per NEC
  • 5. Common STEPS:- • STEP 1:- Gathering the data about the cable, it's installation conditions and the load which it needs to be supply. • STEP 2:- Determine the minimum cable size based on the following:- i)Current Carrying Capacity. ii)Voltage Drop. iii)Short circuit Temprature rise. iv)Earth fault loop impedance. • STEP 3:- Selection of the cable which have highest sizing based on the above parameters
  • 6. What we look for in STEP-1 ? A)LOAD:- • Type of load which is to be supplied. • Maximum current required by the load. • Voltage capacity of the system. • Expected power factor of the system. • Distance of load from the source. B)CONTRUCTION OF CABLE:- • CONDUCTOR MATERIAL:- Normally copper or aluminium. • CONDCTOR TYPE:- Stranded or solid. • CONDCUTOR SURFACE COATING:- Plain (no coating), tinned, silver or Ni. • INSULATION TYPE:- PVC, XLPE, EPR. • TYPE OF CORE:- Single core or multicore.
  • 7. c)INSTALLATION CONDITIONS:- • Installation medium:- i)eg. Underground or overhead, soil thermal resistivity for underground cables, etc. • Arrangement:- i)For underground cables whether it is placed directly or in a conduit, for overhead wires whether it is installed supported by the walls, on the cable towers etc. ii)Depth of laying iii)Bunching of cables, spacing b/w them. • Atmospheric Temprature:- i)Ambient of soil temprature. ii)Soil thermal resistivity, in the case of undergrond cables.
  • 8. What we look for in STEP-2 ? A)Current carrying capacity:- The current plays a vital role while deciding the sizing for a cable due to following factors:- i)Copper lossess. ii)Thermal capacity of cable iii)Reactive power. iv)Insulation,bedding,armour and other components of cable Thus depending upon these parameters we find out the minimum possible and feasible size for the cable.
  • 9. i)Base current ratings:- Cable manufactuers maintains a table for base current rating for different type of cables. These ratings are taken out in base environmental conditions and ths these ratings are relevant for base installation conditions. ii)Installed Current Rating:- Whenever there is difference b/w the base conditions and actual instllation conditions, then the derating factor is used in order to find out the actual installed crrent ratings.
  • 10. i) In ground Installation (Direct Burial) C =Cs * Cg * Cd *Ct Where, Cs = Rating factor for variation in ground temperature Cg= Rating factor for Group of cables Cd= Rating factor for Depth of laying Ct=Rating for thermal resistivity ii) Above Ground Installation C = Ca * Cg Where, Ca= Rating factor for variation in ambient air temperature Cg= Rating factor for Grouping cables Then installation current rating is obtained as:- I(new) = I(base) * C
  • 11. B)VOLTAGE DROP:- Current flow through the cable – the higher the current flow, the higher the voltage drop. Impedance of the conductor – the larger the impedance, the higher the voltage drop. As, For a three phase system:- For a single phase system:- For a DC system:- 1000 )sincos(3 3 LXRI V cc     1000 )sincos(2 1 LXRI V cc     1000 2 LIR V c dc 
  • 12. C)SHORT CIRCUIT TEMPRATRUE RISE:- During a short circuit, a high amount of current can flow through a cable for a short time. This surge in current flow causes a temperature rise within the cable. k ti A 2  k ti A 2  Minimum Cable Size Due to Short Circuit Temperature Rise:- The temperature rise constant is calculated based on the material properties of the conductor and the initial and final conductor temperatures          i if k   5.234 1ln226          i if k   228 1ln148 (for copper conductors) (for aluminum conductors)
  • 13. D)EARTH FAULT LOOP IMPEDANCE:- EARTH FAULT LOOP IMPEDANCE Zs = Zc + Ze Where Zs is the earth fault loop impedance (Ω) Zc is the impedance of the active conductor (Ω) Ze is the impedance of the earth conductor (Ω)           22 1000 ececs XXRR L Z
  • 14. Implementation examples of Cable Selection process EXAMPLE 1 EXAMPLE 2  Electrical Details:- Electrical Load of 80KW, Distance between Source and Load is 200 Meter, System Voltage 415V Three Phase, Power Factor is 0.8,Permissible Voltage drop is 5%, Demand Factor is 1,  Cable Laying Detail:- Cable is directly buried in Ground in trench at the depth of 1 meter. Ground Temperature is approximate 35 Deg. No of Cable per Trench is 1. No of Run of Cable is 1 Run.  Soil Details:- Thermal Resistivity of Soil is not known. Nature of Soil is Damp Soil
  • 15. Risk and Impact of Wrong Sizing • High voltage drops, which increases reactive power. • Sudden increase in cable temprature. • Damage of cable components, such as armour, bed sheath, insulation etc. • Damage of protective components. • Poor power factor. • Non continuous supply. • Shorter Life span of cables. • Increase in maintainance cost of the system.
  • 16. Conclusion Efficient, safe and economic operation of transmission can be obtained by proper sizing and selection of cables References Wikipedia, https://wiki.openelectrical.org/index.php?title=Cable_Sizing_Calculation Electrical Engineering Portal, https://electrical-engineering-portal.com/an-example-how-to-calculate-voltage-drop-and-size-of-electrical- cable My Electrical Engineering https://myelectrical.com Elements Of Power System,by U.A.BAKSHI