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ElemeNts of electrical design TOPIC •LOAD ASSESSMENT •PERMISSIBLE VOLTAGE DROP •CONDUCTOR SIZE CALCULATION GUIDED BY : M.R.VASAVdA SR NO NAME 1. PAVAGADHI MEGHANA ENROLLMENT NO. 140233109007 2. SABALPARA NIKUNJ 140233109008 3. CHOPDE NILESH 140233109010 LOAD ASSESSMENT Basic Terms • Active power (useful or real power) Time average of instantaneous power when the average is taken over a complete cycle of an A/C waveform, expressed in Watt (W) For single phase, P = V I cos ø For balanced three-phase, P = √3 Vph-ph I cos ø • Apparent power For single phase, AP = V I For three phase, AP = √3 Vph-ph I • Reactive power In a direct current circuit, or in an alternating current circuit whose impedance is a pure resistance, the voltage and current are in phase, and the following formula holds: P= ErmsIrms where P is the power in watts, Erms is the rootmean-square (rms) voltage in volts, and Irms is the rms current in amperes. • Connected load Sum of all the loads connected to the electrical system, usually expressed in watts • Demand factor = Maximum demand / Connection load • Load factor ratio of the average demand to the maximum demand over a defined intervaI • In commercial buildings, between the hours 9:00 to 18:00 the load factor is usually close to unity • Power factor The ratio of the apparent power in a circuit (V.A)to the useful power (W) if the voltage and current are sinusoidal Power factor = kW/ Kv.A PERMISSIBLE VOLTAGE DROP • Maximum voltage drop from supply terminals to any point on the installation is not exceed the permissible limit viz.2% of the supply voltage plus one volt for light load wiring and 5% percent of declared supply voltage for power load wiring. • How Much Voltage Drop Is Acceptable? • The National Electrical Code (NEC) recommends that the combined voltage drop of the electrical system (branch circuit and feeders) not exceed 5% for optimum efficiency. This recommendation not only can improve safety but can insure proper equipment operation and power efficiency. the table shows below gives rating for single, twin or multi-core cable with VIR, PVC, polythene insulation including TRS, PVC lead or aluminium sheathed, run singly or in conduit, toughing, casing or in free air. The ratings are based on an ambient temperature of 30⁰C. Use multiplying factor of 1.13 for 25⁰C, 0.86 for 35⁰⁰C, 0.69 for 40⁰C and 0.47 for 45⁰C. If more than one cable is used, multiply the given current ratings by a factors of 0.8 for 2 cables, 0.7 for 3 cables and 0.65 for 4 cables. Voltage drop on ac cable is greater than dc due to inductance and capacitance but difference is vary small and need only be taken into account when we are dealing with heavy loads and long run. Current rating of cu and equivalent aluminium conductor/cable The maximum voltage drop values taken from Table For 230 VOLTS For 400 VOLTS CONDUCTOR SIZE CALCULATION • The following points must be considered while calculating the size of the conductors. 1. Current carrying capacity 2. Voltage drop 3. Minimum permissible size • Current carrying capacity the conductor or wire should be of size sufficient to carry the maximum circuit current continuously without overheating. • Voltage drop the voltage drop in a conductor or wire depends upon the current flowing through the conductor and resistance of the conductor. The resistance is inversely proportional to area, therefore the voltage drop will be less if the area of conductor is more. The permissible voltage drop in a lighting circuit is 2% of the supply voltage plus one volt. In case of industrial loads, the maximum voltage drop at the extreme end equipment should not be more than 5% of the declared supply voltage. • Minimum permissible size the minimum permissible size of conductor or wire should be as follow: The conductor used in domestic wiring should not be size less than 1/1.12 mm in copper or 1/1.40 mm in aluminum wire. The various sizes of copper and aluminium conductor with current ratings and voltage drops are given in table bellow 1,2&3. Current rating of copper conductor single core cable (VIR, PVC or polythene insulated including tough rubber, PVC or lead sheathed). Current rating of aluminium conductor single core cable (VIR, PVC or polythene insulated including tough rubber, PVC or lead sheathed). Current rating of aluminium conductor twin, three core or four core cables. (VIR, PVC or polythene insulated and sheathed with tough rubber, PVC or lead) Thank you