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# Power transmission(ppt)

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### Power transmission(ppt)

1. 1. POWER TRANSMISSION ENGR MUHAMMAD ZEESHAN
2. 2. PER UNT SYSTEM:- IN PER UNT SYSTEM WE DISCUSS  INTRODUCTION TO PER UNIT SYSTEM  FORMULAS FOR PER UNT SYSTEM  USES OF PER UNT SYSTEMS  ADVANTAGES OF PER UNIT SYSTEMS  DISADVANTAGES OF PER UNT SYSTEM
3. 3. PARAMETERS USED IN ELECTRICAL CIRCUIT:- VOLTAGES KV,MV CURRENTS A,KA IMPEDENCE OHM, K.OHMS POWER KW,KVA,MVA INTRODUCTION
4. 4. PER UNIT SYSTEM 4 In the per-unit system, the voltages, currents, powers, impedances, and other electrical quantities are expressed on a per-unit basis by the equations: Quantity per unit = Actual value Base value of quantity It is customary to select two base quantities to define a given per-unit system. The ones usually selected are voltage and power.
5. 5. We choose only voltages and power as a base value and base current, base impedance can b found as: Either base value given When base value is not given If base value is not given then largest value of the among the quantities is chosen as base. HOW TO CHOOSE A BASE VALUE?
6. 6. For each system parameter, per-unit value is equal to the actual value divided by a base value: Vpu = V / Vbase Ipu = I / Ibase Zpu = Z / Zbase Select rated values as base values, usually rated power in MVA and rated phase voltage in kV: Sbase = Srated = 3VlineIline Ebase = Ephase = Eline/ SQR(3) FORMULAS OF PER UNIT SYSTEM
7. 7. FORMULAS
8. 8. Per unit has relation with kva and Vl_l Per unit impedence α base kva Per unit impedence α 1/(base v) PER UNIT IMPEDENCE RELATION.
9. 9. CHANGE OF BASES.
10. 10. TO FIND EQUIVALENT IMPEDENCE OF BOTH SIDES OF TRANSFORMER.. TO FIND EQUIVALENT CKT OF INDUCTION MACHINE USES
11. 11.  Circuits are simplified.  Same ranges of voltages (EHV to distribution and utilization).  Per unit values are same for all machine regarding their size.(same p.u for both 100 MVA,1000MVA)  P.U reactance for both primary and secondary side remain same.  This method is ideal for eliminate ideal transformer in ckt  Sqrt (3) factor in the three phase circuit calculations is eliminated  P.u value remain same for both ‘Y’ and ‘∆’ connection of T/F.  Manufacturer specify values mostly in per unit.  P.U values are same for both single phase and three phase.  Multiplication of two per unit is also per unit. ADVANTAGES OF PER UNIT SYSTEM
12. 12. For transmission lines, value of impedence and admittance are same regardless of level of voltages(KVA,MVA) Equivalent circuits of the components are modified, making them somewhat more abstract. Sometimes phase shifts that are clearly presented in the unscaled circuits varnish in per-unit system DISADVANTAGES OF PER UNIT SYSTEMS
13. 13. QUESTIONS?