REPRESENTATION OF POWER SYSTEM COMPONENTS

TON DUC THANG UNIVERSITY FACULTY OF ELECTRICAL AND ELECTRONICS ENGINEERING 401069 GENERATION AND TRANSPORT OF ELECTRICAL ENERGY CHAPTER 3: REPRESENTATION OF POWER SYSTEM COMPONENTS Huynh Van Van, PhD CHAPTER 3: REPRESENTATION OF POWER SYSTEM COMPONENTS 3.1 Representation of transmission line 3.2 Representation of generator 3.3 Representation of transformer 3.4 Representation of load 3.5 Base unit system 3.6 Per unit system 12/21/21 401069-Chapter 3: Representation of power system components OBJECTIVES  Understand about components of transmission lines which is corresponding to length and voltage of lines  Represent the model of generator, load  Calculate problems regarding base unit system  Calculate problems regarding per unit system 12/21/21 401069-Chapter 3: Representation of power system components 3 3.1 REPRESENTATION OF TRANSMISSION LINE 3.1.1 Short length transmission lines  Its length is less than 100 km  There are only two parameters in the short length transmission line, resistance and reactance  The complex component consisting of the two parameter is called impedance, Z=R + jX 12/21/21 401069-Chapter 3: Representation of power system components 4 3.1 REPRESENTATION OF TRANSMISSION LINE A Two port network The voltage and current at the sending-end are calculated as the following expression   12/21/21 = 401069-Chapter 3: Representation of power system components 5 3.1 REPRESENTATION OF TRANSMISSION LINE ABCD line constant in the equation is obtained by:   =1 ==R+jX= =0 =1 Consequently, the sending-end voltage and current are rewritten as below   =(1) + =() +(1) 12/21/21 401069-Chapter 3: Representation of power system components 6 3.1 REPRESENTATION OF TRANSMISSION LINE7 3.1.2 Medium length transmission lines  Its length is in the range of 100-250 km  When the length is from 200-250 km, the transmission line can be represented as either medium or long length models  The model of medium length transmission line is either Pi or T both of them are equivalent 12/21/21 401069-Chapter 3: Representation of power system components 7 3.1 REPRESENTATION OF TRANSMISSION LINE Nominal-Pi-representation  Impedance of the line is located in the middle  The shunt admittance is divided into two identical parts, one located in the sending-end and one located in the receiving-end 12/21/21 401069-Chapter 3: Representation of power system components 8 3.1 REPRESENTATION OF TRANSMISSION LINE  ABCD line constant for the Pi model is obtained by:   =1+ = =+ =1+ The voltage and current at the sending-end are calculated as the following expression   12/21/21 = 401069-Chapter 3: Representation of power system components 9 3.1 REPRESENTATION OF TRANSMISSION LINE Nominal-T-representation  Shunt admittance of the line is located in the middle  Impedance is divided into two identical parts, one located in receiving half and one located in the sending half 12/21/21 401069-Chapter 3: Representation of power system components  10 3.3 REPRESENTATION OF TRANSFORMER  Reactance of winding is calculated by    Reactance of windings and are obtained by the same equation 12/21/21 401069-Chapter 3: Representation of power system components  20 3.3 REPRESENTATION OF TRANSFORMER  Resistance of each winding is dependent on the capacity of each winding Case 1: high voltage winding/medium voltage winding/low winding=100%/100%/100%   === = 12/21/21 401069-Chapter 3: Representation of power system components  21 voltage 3.3 REPRESENTATION OF TRANSFORMER Case 2: high voltage winding/medium voltage winding/low voltage winding=100%/100%/67%   === = = 12/21/21 401069-Chapter 3: Representation of power system components  22 3.3 REPRESENTATION OF TRANSFORMER Case 3: high voltage winding/medium voltage winding/low voltage winding=100%/67%/67%   = = 12/21/21 401069-Chapter 3: Representation of power system components  23 3.3 REPRESENTATION OF TRANSFORMER 3.3.3 Autotransformer  The symbol (Fig.a) and circuit diagram (Fig.b) of a three-winding transformer Fig.a 12/21/21 Fig.b 401069-Chapter 3: Representation of power system components  24 3.3 REPRESENTATION OF TRANSFORMER  The benefit parameter and resistance of each winding:   =1- 12/21/21 401069-Chapter 3: Representation of power system components  25 3.3 REPRESENTATION OF TRANSFORMER  The reactance of each winding:   =0 12/21/21 401069-Chapter 3: Representation of power system components  26 3.4 REPRESENTATION OF LOAD  Load bus is represented as the following symbol  In solving problems regarding voltage, current, power, the load is represented as a impedance or two types of power: jX + R SLoad=P+jQ 12/21/21 401069-Chapter 3: Representation of power system components  27 3.4 REPRESENTATION OF LOAD  There are three types of Load:  Resistive load: P=S, Q=0, power factor=1  Inductive load: P>0, Q>0, power factor 0, Q