The document discusses AC power distribution systems. It begins by explaining how AC systems became predominant over DC due to the development of transformers, which allow easy changing of voltage levels. The distribution system consists of primary circuits operating at higher voltages that deliver power to secondary circuits through distribution transformers. AC distribution calculations consider resistance, inductance, and capacitance, while voltages and currents are handled vectorially rather than arithmetically as in DC. There are two main methods discussed for solving AC distribution problems - considering power factor referred to receiving end voltages or power factor referred to respective load voltages.

1. AC DISTRUBUTION SYSTEM
ELECTRICAL POWER SYSTEM
PREET PATEL (151310109032)
Electrical Engineering Department

2. ELECTRICAL POWER SYSTEM
The distribution system isa part of the powersystem, existing between distribution sub-
stations and the consumers.
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3. INTRODUCTION
In the beginning of electrical age, electricity was generated, transmitted and distributed as direct current. The principal
disadvantage of D.C. system was that voltage level could not readily be changed, except by the use of rotating
machinery, which in most cases was too expensive.
With the development of transformer by George Westinghouse, A.C. system has become so predominant as to make
D.C. system practically extinct in most parts of the world. The present day large power system has been possible only
due to the adoption of A.C. system.
Now-a-days, electrical energy is generated, transmitted and distributed in the form of alternating current as an
economical proposition. The electrical energy produced at the power station is transmitted at very high voltages by 3-
phase, 3-wire system to step-down sub-stations for distribution.
The distribution system consists of two parts viz. primary distribution and secondary distribution. The primary
distribution circuit is 3-phase, 3-wire and operates at voltages (33kV or 66kV or 11 kV) somewhat higher than general
utilization levels. It delivers power to the secondary distribution circuit through distribution transformers.
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4. REQUIREMENTS OF GOOD DISTRIBUTION SYSTEMS
• Continuity in the powersupply must be ensured.
• Voltage must not vary more than the prescribed limits.(∓5%).
• Efficiency of line must be high aspossible.
• Safefrom consumerpoint of view.
• Layout shouldnot effectthe appearance of locality.
• Line shouldnot be overloaded.
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5. DISTRIBUTION
SYSTEM
DC
DISTRIBUTION
SYSTEM
GENERAL
DISTRIBUTION
SYSTEM
DC THREE WIRE
SYSTEM
AC
DISTRIBUTION
SYSTEM
RING MAIN
DISTRIBUTION
RADIAL
DISTRIBUTION
SYSTEM
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6. A.C. DISTRIBUTION CALCULATIONS
A.C. distribution calculations differ from those of DC distribution in the following respects :
1. In case of DC system, the voltage drop is due to resistance alone. However, in AC system, the
voltage drops are due to the combined effects of resistance, inductance and capacitance.
2. In a DC system, additions and subtractions of currents or voltages are done arithmetically but in
case of AC system, these operations are done vectorially.
3. In an AC system, power factor (P.F) has to be taken into account. Loads tapped off form the
distributor are generally at different power factors.
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7. METHODS OF SOLVING A.C DISTRIBUTIONPROBLEM
Power factor referred to receiving end voltages
Power factor referred to respective load voltages
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8. Case:
Resistance R , reactance X
Impedanceof sectionPR is given by, 𝑍 𝑃𝑅 = 𝑅1 + 𝑗𝑋1
Impedanceof section RQ is given by, 𝑍 𝑅𝑄 = 𝑅2 + 𝑗𝑋2.
The load current at point R is 𝐼1, 𝐼1 = 𝐼1 (cos ∅1 − jsin ∅1 )
The load current at point Q is 𝐼2 , 𝐼2 = 𝐼2(cos ∅2 − jsin ∅2 )
Current in sectionRQ is nothing but 𝐼𝑅𝑄 = 𝐼2 = 𝐼2(cos ∅2 − 𝑗 sin ∅2)
Current in section PR is 𝐼PR = 𝐼1 + 𝐼2 = 𝐼`1(cos ∅1 − 𝑗 sin ∅1)+ 𝐼2(cos ∅2 − 𝑗 sin ∅2)
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9. POWER FACTOR REFERRED TO RECEIVING END VOLTAGES
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10. Voltage drop in section RQ, 𝑉RQ = 𝐼RQ ZRQ
𝑉RQ=[𝐼2(cos ∅2 − j sin ∅2)].[ R2 + j𝑋2]
Voltage drop in section PR , 𝑉PR = 𝐼PR ZPR
=[𝐼1(cos ∅1 − j sin ∅1) + 𝐼2(cos ∅2 − j sin ∅2)][𝑅1 + j𝑋1]
Sending end voltage 𝑉P = 𝑉Q + 𝑉RQ + 𝑉PQ
Sending end current 𝐼P = 𝐼1 + 𝐼2
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11. POWER FACTOR REFERRED TO RESPECTIVE LOAD VOLTAGES
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12. POWER FACTOR REFERRED TO RESPECTIVE LOAD VOLTAGES
Voltage drop in section RQ is given, 𝑉RQ = 𝐼2 ZRQ
𝑉RQ=[𝐼2(cos ∅2 − j sin ∅2)] [ R2 + j𝑋2]
𝑉R = 𝑉Q+drop of voltage in section RQ=𝑉R angle of α.
𝐼1 = 𝐼1(cos ∅1 − j sin∅1) w.r.t voltage 𝑉R
𝐼1 = 𝐼1(cos(∅1−α) − j sin(∅1 − α)) w.r.t voltage 𝑉Q
𝐼PR = 𝐼1 + 𝐼2
= 𝐼1[cos(∅1−α) − j sin(∅1 − α)] +𝐼2[cos ∅2 − j sin ∅2]
𝑉RQ=𝐼1[cos(∅1−α) − j sin(∅1 − α)] +𝐼2[cos ∅2 − j sin∅2] [𝑅1 + j𝑋1]
Sending end voltage 𝑉P, 𝑉P = 𝑉Q + 𝑉RQ + 𝑉PR
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13. Advantages of AC Distribution System
• Cheaper transformation between voltages
• Easy to switch off
• Less equipment needed
• More economical in general
• Rotating field
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14. THANK YOU
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