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- 1. POWER TRANSMISSION ENGR MUHAMMAD ZEESHAN
- 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. PARAMETERS USED IN ELECTRICAL CIRCUIT:- VOLTAGES KV,MV CURRENTS A,KA IMPEDENCE OHM, K.OHMS POWER KW,KVA,MVA INTRODUCTION
- 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. 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. 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. FORMULAS
- 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. CHANGE OF BASES.
- 10. TO FIND EQUIVALENT IMPEDENCE OF BOTH SIDES OF TRANSFORMER.. TO FIND EQUIVALENT CKT OF INDUCTION MACHINE USES
- 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. 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. QUESTIONS?

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