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13 Per unit in 1-phase systems

# 13 Per unit in 1-phase systems - Lecture 11 Per unit in 1...

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Lecture 11 Per unit in 1 φ systems Each device is assigned 2 base (or rated) values, V B and S B , the base voltage in Volts and the base power in VA. The voltage in pu is pu B V V V = and the power is pu pu B P jQ Pj Q S + += The bases for the impedance and current are , BB SV IZ VI == . Form the 2 base quantities we define other base quantities so as to maintain KVL, KCL and Ohm’s laws invariant. Ohm’s Law. VZ I = or I YV = B p up u pu B B B B Z Z Z I I Z I VV Z V Z I = = = For KVL, _ 00 k kk p u loop loop loop B V V ∆= =∆ = ∑∑ Similarly for KCL, _ p u node node II =→ = For the power formulae the same thing applies. cos cos cos cos B B B B pu pu pu pu S V P VI V PV I SS V I V I φ φφ = =

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Similarly, 2 _ sin pu transmitted pu pu V P X δ = Where δ is in radians. Conversion from one pu base to another. Suppose you are given two devices with impedance Y 1 and Y 2 . Figure 1 - Change of base Y 1 is known in pu on a base V B1 and S B1 , Y 2 is known in pu on a base V B2 and S B2 . Since Y 1 and Y 2
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13 Per unit in 1-phase systems - Lecture 11 Per unit in 1...

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