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Transcript

SUBJECTELECTICAL POWER SYSTEM TOPIC- A.C. DISTRIBUTION ENROLLMENT NUMBER NAME 130020109030 ANKIT PATEL 130020109031 DRUVIL PATEL 130020109032 JIGER PATEL 130020109033 JINAL PATEL 130020109034 NIKUNJ PATEL 130020109035 PARTH PATEL 130020109036 SURESH PATEL 130020109037 NIRAV PRAJAPATI TOPICA.C. DISTRIBUTION DISTRIBUTION SYSTEM The part of system by which electric power is distributed among various consumers for local use is known as distribution system. A low tension distribution system is shown in figure which comprises of feeder, distribution and service mains. (1)-Feeder- A line or conductor which connect the major sub-station to the distributor is known as feeder. -It is feed the electric power to the distributor. (2)-Distributor- A line or conductor to which various consumers are connected through service mains is known as distributor. -It is distribute electric power among various consumers, thus a number of tapping are taken from the distributor. (3) –Service mains-A line which connected the consumer to the distributor is known as a service mains. -It is designed as per the connected load of the consumers. TYPES OF DISTRIBUTION According to the nature of current (1) A.C distribution system (2) D.C distributor syestem - A.C distribution system is almost universally emloyed due to its several advantages over D.C. distribution system. A.C. DISTRIBUTION SYSTEM The A.C. distribution is classified into two types (1) primary distribution system (2) secondary distribution system (1)-Primary distribution system - In the substation voltage is stepped down to 11kv or 6.6kv and from here is transferred to different substation for distribution purpose and to the consumers. This system is known as high voltage or primary distribution system. - From the point of view of economy, primary distribution is carried out by 3-phase 3-wire system (2)-Secondary distribution system - At distribution substation voltage is step down to 400 volts. From these station, voltage is at low level i.e. 400 volts and 230 volts is distribution to feed the consumers. This is known as low voltage or secondary distribution system. - In this system, we use 3-phase 4-wire A.C. system for distribution purpose. CONNECTION SCHEMES OF DISTRIBUTION SYSTEM The following connection schemes of distribution system are generally employed: (1) Radial system (2) Ring main system (3) Interconnected system RADIAL SYSTEM 1.Radial Distribution system - only one/single path is connected between each Distribution and substation is called radial Distribution system. - Fault occurs either on feeder or a distributor, all the consumers connected to that distributor will get affected. - In India, 99% of distribution of power is by radial distribution system only. Advantages- Its initial cost is minimum - Simple in planning, design and operation. - Useful when the generation is at low voltage. - Station is located at the center of the load Disadvantages- - • Distributor nearer to the feeding end is heavily loaded. - The consumers at the far end of the feeder would be subjected to series voltage fluctuations with the variations in load. RING MAIN SYSTEM (2 ) Ring main system - Feeder covers the whole area of supply in the ring fashion and finally terminates at the substation from where it is started. - Closed loop form and looks like a ring. Advantages- Less conductor material is required as each part of the ring carries less current than in the radial system. - • Less voltage fluctuations. Disadvantage- It is difficult to design when compared to the designing of a radial system. INTERCONNECTED SYSTEM Interconnected system- -In this system, the feeder is energised by two or more than two generating station or sub station. Advantages-There is more flexibility. -Reliability is more. If fault occur on one section, supply can be continued by other route. -Good voltage regulation is achieved. -Size of substation is less compared to the radial system. METHOD OF SOLVING A.C. DISTRIBUTION PROBLEMS Two method is use for solving A.C Distribution problem(1) power factor referred to receiving end voltage (2) power factor referred to respective load voltages POWER FACTOR REFERRED TO RECEIVING END VOLTAGE Consider an a.c. distribution PQ with concentrated load of I1 andI2 tapped off at point R and Q respectively. Taking receiving end voltage as the reference vector, let the power factor of the loads tapped at R and Q be cos ∅1 and ∅2 respectively. Let the resistance and inductive reactance of the section PR and RQ be Rpr,Xpr and Rrq and Xrq respectively. Resistance- R Reactance- X Impedance of section PR is given by, 𝑍 𝑃𝑅 = 𝑅1 + 𝑗𝑋1. Impedance of section RQ is given by, 𝑍 𝑅𝑄 = 𝑅2 + 𝑗𝑋2 The load current at point R is 𝐼1, 𝐼1 = 𝐼1(cos ∅1 − 𝑗 sin ∅1) The load current at point Q is 𝐼2, 𝐼2 = 𝐼2(cos ∅2 − 𝑗 sin ∅2) Current in section RQ is nothing but 𝐼 𝑅𝑄 = 𝐼2 = 𝐼2(cos ∅2 − 𝑗 sin ∅2) Current in section PR is 𝐼 𝑃𝑅 = 𝐼1 + 𝐼2=𝐼1(cos ∅1 − 𝑗 sin ∅1)+𝐼2(cos ∅2 − 𝑗 sin ∅2) Voltage drop in section RQ, 𝑉𝑅𝑄 = 𝐼 𝑅𝑄 𝑍 𝑅𝑄 𝑉𝑅𝑄=[𝐼2(cos ∅2 − 𝑗 sin ∅2)] [ 𝑅2 + 𝑗𝑋2] Voltage drop in section PR , 𝑉𝑃𝑅 = 𝐼 𝑃𝑅 𝑍 𝑃𝑅 =[𝐼1(cos ∅1 − 𝑗 sin ∅1) + 𝐼2(cos ∅2 − 𝑗 sin ∅2)][𝑅1 + 𝑗𝑋1]. Sending end voltage 𝑉𝑃 = 𝑉𝑄 + 𝑉𝑅𝑄 + 𝑉𝑃𝑄 Sending end current 𝐼 𝑃 = 𝐼1 + 𝐼2 Phasor diagram POWER FACTOR REFERRED TO RESPECTIVE LOAD VOLTAGES When the power factors are to their respective load point voltage, the current I2 will lag behind the voltage Vb by an angle ∅2 whears current I1 will lag behind the voltage Vc by an angle ∅1. The phasor diagram under these conditions is shown in fig. Current in section RQ, 𝐼1 = 𝐼1(cos ∅1 − 𝑗 sin ∅1) Voltage drop in section RQ, 𝑉𝑅𝑄 = 𝐼1 𝑍 𝑅𝑄 𝑉𝑅𝑄=[𝐼1(cos ∅2− 𝑗 sin ∅2)]. Voltage at point R, VR=VQ+VRQ Current tapped at point c,I1 Current in section PR, Ipq= I1+I2= = 𝐼1(cos(∅2−α) − 𝑗 sin(∅2 − α))+ 𝐼1(cos ∅1 − 𝑗 sin ∅1) Voltage drop in section PR, VPR=IPR*ZPR Sending end voltage, VA=VR+VPR+VRQ Phasor diagram