ECE 421 Introduction to Power Systems. Lab 02 Power System Feeding Different Loads

Transcription

1 Fall 201 Lab 02 ECE 421 Introduction to Power Systems Lab 02 Power System Feeding Different Loads 1. Objective Analyzing system behavior feeding different types of loads and impacts of load variations; Importance of capacitors banks; Comparing differences in each of them to different transmission line models to different loads. 2. Introduction 2.1. Undervoltage and Compensation The electric power system's main goal is to supply power with quality, without interruptions and as cheap as possible to all customers. These customers represent loads, which are not constant, varying a lot over one day, of over one year, for example. Of course, load variation has total impact in power system behavior and sometimes solutions are required to keep it working out properly. Figure 1 shows a load variation in one day when we have a heating system and when we do not (what points out an example of season variation). Figure 1 Load Variation in a Day in Different Seasons. A common operation is switching reactors and capacitors according to the system's needs. If we have a heavy load after a transmission line, it might cause an undervoltage in the system. Then, capacitors should enter on that system region in order to keep voltage in a permitted level. The 1

2 opposite is also true. Under light loads the system is capacitive and it might cause overvoltage. It requires reactors to decrease the voltage level. This kind of compensation provides a better voltage profile and power factor, besides also provides a proper reactive power balance (generation and consuming) [1]. When compensation does not exist, it will impact in the power quality supplied to costumers. Undervoltages cause inefficient operation of electrical devices and might reduce their operation life, while overvoltages can damage and burn those devices. The ideal system would operate at unity power factor, however it is not possible and we should seek for operation conditions as close as possible of this point, since it brings economics and technical benefits. 3. Equipment and Lab. Methods before start up Loads Figure 2 Example of a Bank and Numbers Tags. Three different kinds of loads will be used in these tests and all of them are going to be in Y connected in parallel. Resistive Bank and Light bulbs: Light bulbs of 100W each (300W 3 phase load) will be constant AND Resistor bank varying from (series) until it is only. Inductive Bank and Light bulbs: Light bulbs of 100W each (300W 3 phase load) will be constant AND Inductor bank varying from all in series ( ), up to only rest. Capacitor Bank and Light bulbs: Light bulbs of 100W each (300W 3 phase load) will be constant AND Inductor bank varying from all in series ( ), up to only rest. 2

3 TABLE 1 shows the impedance values: TABLE 1 IMPEDANCE VALUES Light Bulbs Resistive Bank (Ω) Inductor Bank (Ω) Capacitor Bank (Ω) j j W per phase (where V = 208V LL ) j j j j j j j j The inductor bank power factor is 0.09 and let's consider all reactances with exactly equal relation X/R. All of them should be connected in phase neutral voltage. Resistor bank needs to have its neutral of each phase shorted by cables. How these loads will be used is going to be explained after. 3

4 Fall 201 Lab 02 Figure 3 Resistor Bank. Figure 4 Light Bulbs. 4

5 Meters The meters used will be SEL 734, located in the rack in G 10 laboratory. There are six SEL 734s and they are allocated as we see in Figure 5. These SEL 734s are also called PMUs since they are operating by transferring data in synchronized time. They have tags saying where they are connected. In SEL devices, it is possible to access them and see the specific data through an HMI. In order to visualize a phasor diagram, we are going to access SEL 734 at Line 2. To establish communication, we need a computer, an Ethernet cable connected in the lab's hub and AcSELerator QuickSet software. Figure 5 SEL 734 Meters (PMUs) Server and HMI One of the computers in G 10 Laboratory will work as the system's server. There you will be able to find the SCADA HMI where all the data will be shown. After you open the HMI, look all tags, their contents and information. The tags "One Line" and "Real Time Data" are the most important. Note: All power values are in real scale while voltage and currents are 100 times higher than the real one. System Network a) The experiment will be done with an infinite bus feeding a load by two parallel transmission lines as seen in Figure 6; 5

6 Figure 6 System Network used in this Lab. Note: 52 AC Circuit Breaker by ANSI/IEEE Standard Device Numbers. b) To certify that the system is correctly connected, check/make the following connections using jumpers cables: [J1 J2], [J5 J26], [J27 J29], [J30 J31], [J32 J33], [J34 J36], [J38 J22], [J20 J18], [J15 J17], [J13 J14], [J11 J12], [J8 J10]; DO NOT connect [J23 24]. Figure 7 Breaker and Jumper Cables on AMPS. c) In this lab the line impedance will not change. This way, keep Line 1 and Line 2 impedance always at 100% percent; d) Certify that both source impedances are in tap 10 (100%). 6

7 Start Up The energization must be done by the lab instructor or with his agreement. "To start up the AMPS, first remove the padlock and turn on the main breaker located on the south wall. Flip on the Fault Matrix and DC Power Supply switch located on panel number 2F on the left side of AMPS." 9[2]. Do not energize the system yet. 4. Lab. Methods after start up 5.1. Resistor Bank + Light Bulbs Test a) Set up to in series in the resistor bank and insert it at Bus R; b) Connect the light bulbs at Bus R; c) Press the START button on AMPS and close all breakers (red lights on); d) Check the Power Flow in One Line tag of the HMI, voltages, currents and their angles in Real Time Data tag and also in the Phasor Diagram from SEL 734 Human Interface. Also observe the light bulbs; e) Record (print screen) all those screens; f) Now, open both breakers at right hand side in order to isolate Bus R. This way we are able to disconnect/connect loads in that bus without risks); g) Reduce the bank's resistance pulling next switch to left side and putting the switch above on middle position; h) Repeat steps c) up to f) up to rest only ; i) After that, open all breakers and turn off the system and go to the next test Inductor Bank + Light Bulbs Test a) Disconnect the resistor bank from the system. Set up all inductances of the bank in series and connect them at Bus R; b) Press the START button on AMPS and close all breakers (red lights on); c) Check the Power Flow in One Line tag of the HMI, voltages, currents and their angles in Real Time Data tag and also in the Phasor Diagram from SEL 734 Human Interface. Also observe the light bulbs; 7

8 d) Record (print screen) all those screens; e) Now, open both breakers at right hand side in order to isolate Bus R. This way we are able to disconnect/connect loads in that bus without risks); f) Reduce the bank's inductance pulling next switch to left side and putting the switch above on middle position; g) Repeat steps b) up to f) up to rest only ; h) After that, open all breakers and turn off the system and go to the next test Light Bulbs + Resistor Bank + Capacitive Bank (Capacitive Compensation) Test a) Disconnect the inductor bank from the system. Insert the capacitor bank and resistor bank. Set up all capacitances and resistances of each bank in series and connect them at Bus R. The Capacitors and resistors must be switched equally (1 to 1, 2 to 2, and so on). If it does not happen light bulbs can be burned; b) Press the START button on AMPS and close all breakers (red lights on); c) Check the Power Flow in One Line tag of the HMI, voltages, currents and their angles in Real Time Data tag and also in the Phasor Diagram from SEL 734 Human Interface. Also observe the light bulbs. Try to compare the difference between conditions with capacitors and without; d) Record (print screen) all those screens; e) Now, open both breakers at right hand side in order to isolate Bus R. This way we are able to disconnect/connect loads in that bus without risks; f) Reduce the banks' resistance and capacitance pulling next switch to left side and putting the switch above on middle position; g) Repeat steps b) up to f) up to rest only and ; After that, open all breakers and turn off the system. 5. Post Lab In order to get a theoretical comparative to this lab, calculate in MathCAD everything what was done. Create a variable load vector and calculate to Avista bus, Bus S and Bus R (load bus): voltages and currents, real and reactive power, losses and power factor. 8

9 Do it to different transmission lines models: series impedance and Pi Circuit. More about transmission lines models can be found in [3]. Plot all calculations to get a easier visualization. Tip: To each step of line impedance we have 0.1+j1 ohm. The line capacitive effect is created by real capacitors of 0.47 (to phase ground and phase phase is the same value). When calculating the equivalent transmission line you should use Report a) Transfer all data to a MathCAD spreadsheet or similar, where you will be able to deal with those information. Calculate measures which were not present on HMI and you feel they are important; b) Compare your MathCAD calculations and plots with the results gotten in lab. Compare also results from pi model and series impedance models of transmission Lines. Use graphs to get a better visualization. Plot together real power at Avista bus measured from: HMI and also from your calculations. Then, compare if they are similar. Do the same to reactive power, voltage and current; c) Analyze and write your conclusions about each kind of load, losses variations, real and reactive power behavior, power factor and any other point you judge is important; d) Why do the light bulbs change their performance depending on the load. How to deal with this problem? What kind of concern should we have when dealing with compensation. 7. References [1] D. P. Kothari, I. J. Nagrath; Modern Power System Analysis, Mc Graw Hill, 2008; [2] Draft Users Manual for Analog Model Power Systems (AMPS); [3] J. Ducan Glover, M. S. Sarma, T. J. Overbye; Power System Analysis and Design Fifth Edition. [4] SEL University IA 309, Synchrophasor Measurement & Application; [5] J. V. Espinoza, A. Guzmán, F. Calero, M. V. Mynam, E. Palma, SEL; Wide Area Measurement and Control Scheme Maintains Central America's Power System Stability. 9