ECE421‐IntroductiontoPowerSystems

Lab01‐PowerSystemStructure,TransmissionLines,PowerFlow

andSupervision

1. Objective

Introduce electrical power system structure; Become familiar with the Analog Model Power System (AMPS); Show SCADA system running; System behavior with variation in transmission line impedance; Compare practical results with theoretical calculations and different line models.

2. Introduction

2.1. PowerSystemStructure

Nowadays, electrical energy is fundamental in our society both in our personal activities (electronic devices, heating, cooling and so on) and industry (manufacturing of some products requires a big amount of energy). Therefore, when energy is missed, it usually causes big losses. For example, when a manufacturing process is interrupted, it may imply losses in all products which were being produced.

The electrical energy is produced from a different energy source (coal, oil, natural gas, nuclear, hydro, wind, solar, etc), which is converted through the electrical machines. After generated, this energy needs to go up to the load, where it is consumed. The load is usually far from the power plants and in order to transfer the energy between them, transmission lines are used. The transmission system often has high voltage level. Finally, most part of the loads are in low voltage level, in distribution systems. Generation, Transmission and Distribution systems, further transformers, CTs, PTs, substations and some others compose the Power System. The Figure 1 shows a simple diagram with the basic power system structure.

Figure 1 ‐ Basic structure of Electrical Power System.

2.2. SupervisoryControlandPhasorMeasurementUnit(PMU)

In each sector of this system, we have a lots of devices monitoring all operation. Measures, sensors, CTs, PTs, relays and electronic devices are used to get data all the time from different places and units. These information are transferred through various communications types, protocols and channels existing in the Power System. All of these can be concentrated and send to computers in an operation center, for example. There, people will be able to deal with these data according to their needs.

SCADA

One common example of this process of gathering data and sending to computers (servers), is the SCADA (Supervisory Control and Data Acquisition). This system is very popular in industrial systems and also it is used in electrical power system. Through it, engineers can supervise voltages, currents, breakers status (opened/closed), power flow as well as they can control breakers, relay's outputs, excitation or speed of machines, depending on the application. How a SCADA system works is not important to this experiment.

HMI

The computer screen is where all information is exhibited to the users through an HMI (Human Machine Interface), which is a software able to show all the data. Usually, an HMI has a nice interface which makes it easier to the users to understand what is going on. Besides, the HMI usually provides buttons to carry out remote control about any controllable variable on the system. Figure 2 shows an example of a SCADA HMI applied in electrical grid and Figure 3 shows a SCADA application in industry.

Figure 2 ‐ HMI of a SCADA Applied in Power Grid.

Figure 3 ‐ HMI of a SCADA applied in Industry.

3. AnalogModelPowerSystem(AMPS)

The AMPS is located in the room G‐10 of the Buchanan Engineering Building. This analog power system contains six buses which can be connected in different ways in order to get various networks depending on desired application.

The lab represents a real power system in small scale. You can find there a system with: six buses, four transmission lines, an infinite bus (Avista), a synchronous machine, loads, breakers, relays, logic processors, CTs, PTs, meters, communication cables, Ethernet switch, routers, server, SCADA and some other things.

Further AMPS specifications can be found in the Chapter 1 of the "Draft Users Manual for Analog Model Power Systems (AMPS)" [2].

4. EquipmentandLab.Methods‐beforestartup

Loads

Two different kinds of loads will be used in these tests and both are going to be Y connection.

Resistive Load: Light bulbs of 100W per phase + Resistor bank with all resistors in series (around 77.3 Ω each phase);

Inductive Load: Resistive load + Inductor bank with all reactances in series (around 6.3234+j69.7948 Ω each phase, pf = 0.09);

TABLE 1 shows the impedance values:

TABLE 1 ‐ IMPEDANCE VALUES

Light Bulbs Resistive Bank (Ω) Inductor Bank (Ω)

100 W per phase

16.4 1.469 + j16.216

15.2 1.215 + j13.460

15.6 1.392 + j15.419

15.5 1.371 + j15.177

14.6 1.049 + j11.611

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.

Figure 4 ‐ Resistor Bank.

Figure 5 ‐ Light Bulbs.

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 6. 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 6 ‐ SEL 734 Meters (PMUs)

ServerandHMI

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 voltages and currents are 100 times higher than the real one.

SystemNetwork

a) The experiment will be done with an infinite bus feeding a load by two parallel transmission lines as seen in Figure 7;

Figure 7 ‐ 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 8 ‐ Breaker and Jumper Cables on AMPS.

c) The line impedances should be always equal to each other. Initially, let's use 100% percent of Lines 1 and 2, and completely by‐pass Lines 3 and 4. It is done to reduce errors, as explained in [2];

d) Certify that both source impedances are in tap 10 (100%).

StartUp

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." 10[2]. Do not energize the system yet.

5. Lab.Methods‐afterstartup

5.1. ResistiveLoadTest

a) Set up all resistances on resistor bank in series and insert it at Bus R, as well as the light bulbs;

Note: Now, the initial condition test is 100% of top and bottom lines with resistive load.

Note: The load bulbs can draw more power than their nominal power since their resistive load is not accurate.

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;

d) Record (print screen) all those screens;

e) Now, open all breakers and turn the system off (OFF bottom);

f) Reduce the line impedance to 70% (0.7 + j7.0 Ω) always using line one and line two;

g) Repeat steps b) up to f);

h) Now, reduce the line impedance to 30 % (0.3 + j3.0 Ω) and repeat steps b) up to f);

i) After that, turn off the system and go to heavy load test.

5.2. InductiveLoadTest

a) Put line impedances back to 100% and set up all inductances of the bank in series. After that, insert the inductor bank 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;

d) Record (print screen) all those screens;

e) Now, open all breakers and turn the system off (OFF button);

j) Reduce the line impedance to 70% (0.7 + j7.0 Ω) always using line one and line two;

k) Repeat steps b) up to f);

l) Now, reduce the line impedance to 30 % (0.3 + j3.0 Ω) and repeat steps b) up to f);

m) After finished, turn off the AMPS.

6. PostLab

In order to get a theoretical comparative to this lab, calculate in MathCAD everything what will be done. Create a variable transmission line impedance vector (10% step) and calculate to Avista bus, Bus S and Bus R (load bus): voltages and currents, real and reactive power, losses and power factor.

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 16. .

7. Report

a) In G10 Lab we have, in smaller scale, all structures present in a real Power System. Describe the Power System lab with a real one. Write all you have learned about how the lab work (AMPS, Communications, server and so on);

b) 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;

c) 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;

d) For resistive load, show the results and write about the questions bellow:

What are the effects of line impedance variation in real and reactive power flow, voltages and currents (take care about unbalances) and power factors (calculate them, specially the system power factor);

Calculate real and reactive power losses in the line. What do you conclude with the results?

e) Repeat item 6.b) for the heavy loads;

f) Reflect about obtained results to only resistive load and resistive and inductive loads. Write your conclusions.

8. 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.