LAB2 – ONE-LINE DIAGRAMS EE461 Power Systems Colorado State UniversityLab 2 – One-Line Diagrams PURPOSE: The purpose of this lab is to introduce the one-line diagram, also known as the Slider file in PSS/E. This lab will introduce the following aspects: ¾ Introduction to a one-line diagram ¾ Explanation of the Slider (*.SLD) file ¾ Using the Slider file to create a one-line diagram To properly perform this lab, start PSS/E and open the sample.sav file. Refer to Lab 1 on how to do this. Introduction to one-line diagrams A one-line diagram is a simplified graphical representation of a three phase power system, used extensively in power flow studies. In power engineering, one can make the assumption that the three phases of a system are balanced and can therefore be examined as a single phase. The assumption can be made because what happens on one of the three balanced phases, theoretically, will happen to all three phases. This makes the evaluation of the system much less complicated without losing any information. Per unit voltage used extensively in one-line diagrams to further simplify the process. The main components of a one-line (or single line) diagram are; Buses, Branches, Loads, Machines, 2 Winding Transformers, Switched Shunts, Reactor and Capacitor Banks. An explanation of these components will now be given: Buses Buses are represented as a dot, circle or a thick line. The bus name (EAST500) and number (202) are given, as well as the voltage measured on the line (510.5kV and 1.021V in per unit). The final characteristic given is the angle (-26.1 degrees). The voltage is indicated by the color of the bus. In this example, red indicates 500kV. Branches Branches are represented as a thin line. The real power P, as shown on the branch above, flows from 478MW to -473MW and the reactive power Q, flows from 89.9MVA flow to -229.4MVA. In other words, the power flows from the positive number to the negative number, and the number on top is the real power while the number on the bottom is the reactive power. The voltage is indicated by the color of the branch. In this example, red indicates 500kV. - 1 -Lab 2 – One-Line Diagrams Loads Loads are represented as a triangle with the ID number located inside the triangle. The real power, PLOAD, is denoted by the number on top (250MW), and the reactive power, QLOAD, is denoted by the number on bottom (100Mvar). The voltage is indicated by the color of the load. In this example, black indicates 230kV. Machines Machines are represented as a circle with the ID number located inside the circle. The real power, PGEN, is denoted by the number on top (321.0MW), and the reactive power, QGEN, is denoted by the number on bottom (142.3RMVAR). The “R” indicates this machine is in voltage regulation mode, and it is controlling a specific bus to a voltage set point which requires it to generate 142.3MVAR. The voltage is indicated by the color of the machine. In this example, red indicates 500kV. Two Winding Transformers Two winding transformers are represented as two separate windings with a gap separating them. The arrow pointing in at the connection reflects the primary side of the transformer. In this example, the primary voltage (1.0000 in per unit voltage) is given on the primary side of the transformer and the secondary voltage (1.0000 in per unit voltage), is given on the secondary side of the transformer. The voltage is indicated by the color of the transformer and is dictated by the primary side voltage. In this example, purple indicates 21.6kV. Switched Shunts or Switched shunts are represented as either a capacitor or an inductor at the end of a line. The “SW” shown on top (or on the left if the shunt is shown vertical) indicates that this unit is a switched shunt compensator. If you see these symbols with a number in place of the “SW”, that particular device is a permanently installed reactor or capacitor bank (see below). The number on bottom (or on the right if the shunt is shown vertical) indicates the initial reactive charge admittance, BINIT (253.8MVAR or -599.6MVAR). The voltage is indicated by the color of the shunt. In this example, red indicates 500kV. - 2 -Lab 2 – One-Line Diagrams Reactor Bank Reactor banks are represented as an inductor at the end of a line. The number on top (or on the left if the reactor is shown vertical) indicates the real charge admittance, GSHUNT, of the line (3.6MW). If you see a “SW” instead of a number, you are looking at a switched shunt compensator (see above). The number on bottom (or on the right if the reactor is shown vertical) indicates the reactive charge admittance, BSHUNT, of the line (490.0MVAR). The voltage is indicated by the color of the reactor. In this example, red indicates 500kV. Capacitor Bank Capacitor banks are represented as a capacitor at the end of a line. The number on top (or on the left if the capacitor is shown vertical) indicates the real charge admittance, GSHUNT, of the line (0.0MW). If you see a “SW” instead of a number, you are looking at a switched shunt compensator (see above). The number on bottom (or on the right if the capacitor is shown vertical) indicates the reactive charge admittance, BSHUNT, of the line (-1080.0MVAR). The voltage is indicated by the color of the capacitor. The Slider File As described in the previous lab, the Slider (*.SLD) file is a file that contains the one-line diagram. As can be see from the figure above, the one-line diagram can get pretty - 3 -Lab 2 – One-Line Diagrams complicated. To simplify matters, all the physical data related to each element shown in the one-line diagram is linked to the data file (*.SAV). This way, a simple thin line represents all of the data located in the branch tab. All of this data is interconnected and linked so as to perform power flow analyses. Once a one-line diagram is created, it can be saved as a Slider (*.SLD) file. The Slider file can be amended and updated as necessary, as long as the amendments and updates correspond with the *.SAV file, since the two files are intertwined. Another advantage of the Slider file is that one can view the power flow and the operating levels of a branch. This allows a Power Engineer to quickly see potential trouble spots in a power system and correct them before problems occur. The process of performing a power flow analysis is the main objective of