BL10A9030 Laboratory Course in Electrical Engineering

Java Python BL10A9030 Laboratory Course in Electrical Engineering

Three Phase System

Laboratory Instructions

Topic featured in following courses:

Basics of Electric Engineering Electric Circuits

20.12.2022

1.   DESCRIPTION

In this assignment we study the basic properties of three phase electrical systems, such as line and phase voltages, the phase shift of voltage and current, asymmetry and wye/delta configured loads. The pre-lab task contains a personal quiz and group preparations for the actual laboratory measurements, including the design of the circuit diagrams and measure- ment sheets. In the laboratory we will make measurements for wye and delta configured loads and measure the currents in an asymmetric system. Finally, we will assess the results and compare how different configurations (wye/delta) affect the three-phase system, how asymmetric load affects the system and how the results differ from calculated ones.

The pre-lab task (both the quiz and the group task) needs to be completed and returned to Moodle before the laboratory session. The laboratory task takes place in room 6318. After the session, a short analysis paper is prepared.

1.1 Learning goals

After completing the laboratory assignment, the student is able to:

•   Explain and understand the concepts of line and phase voltages

•   Configure a delta and a wye connection

•   Explain how a delta and a wye configuration affect the currents and power ofa circuit

•   Use a wattmeter to measure three phase power

•   Explain the terms symmetrical and asymmetrical load

1.2 Grading

•   Pre-lab task

o Quiz 15 %

o Group laboratory work preparation 20 % (group grading)

•   Laboratory work: 30 % (group grading)

•   Analysis: 35 % (group grading)

Assessment is done using the assessment matrices posted on Moodle. The pre-lab quiz as- sessment is described in the quiz.

2.   PRE-LAB TASK

The pre-lab task consists of drawing circuit diagrams. For example, they can be made with ProfiCAD, or using a browser-based tool called diagrams.net (previously known as draw.io). Diagrams.net provides suitable stencils for components. They can be accessed by selecting More Shapes from the lower left corner, and then selecting Electrical. The circuit diagrams can be made with any tool you find suitable, as long as the finished diagrams are clear.

2.1    Three-phase power measurement in wye configuration

Design a circuit diagram with a three-phase voltage source, three-phase load resistor in wye configuration and power measurement from the circuit using three power meters (watt me- ters).

Design a circuit diagram for making the same measurement using only two power meters (line voltages and phase currents are measured, more information can be found by searching the internet for two wattmeter method. Check the tips in chapter 4.1.)

2.2    Three-phase power measurement in delta configuration

Design a circuit diagram with a three-phase voltage source, three-phase load resistor in delta configuration and power measurements for the circuit using three wattmeters.

2.3 Measurement sheet

Create measurement sheets for the measurements described in chap BL10A9030 Laboratory Course in Electrical Engineering ters 3.2-3.4.

3.   MEASUREMENTS

3.1 Required eqiupment

1 pc.    3-phase AC power source (SM1003)

3 pcs   Variable resistor 100 Ω npcs   Multimeter

3 pcs   Wattmeter Metrahit 29S

3.2    Three-phase power measurement in wye configuration

Build the circuit you designed in the pre-lab task (chapter 2.1). Adjust the three-phase load resistor to 100 Ω and the phase voltage of the three-phase supply to 60 V. Connect the neutral conductor to the neutral point and measure the current of the neutral conductor. Document the active power, voltage, current and power factor of each line and the current of the neutral connector to the measurement sheet. What is the power factor stated by the wattmeter?

Next, measure the three-phase power using only two wattmeters. What does the wattmeter state as the power factor now? Document the active power, current, voltage and power factor from the wattmeters to the measurement sheet.

3.3    Three-phase power measurement in delta configuration

Build the circuit you designed in the pre-lab task (chapter 2.2). Alter the circuit so that the load resistor is connected in delta configuration. The voltage source and the load resistor values are unchanged. Measure the three-phase power using three wattmeters. Document the active power, voltage, current and power factor of each line to the measurement sheet.

3.4 Asymmetric load

Connect three variable resistors in wye configuration and add the neutral conductor to the neutral point of the circuit. Add a current meter to each line and the neutral conductor. With a low phase voltage (approximately 15 V): Test what happens to the currents of the lines and the neutral conductor when there is an imbalance in the resistance of the load in each line. Start from an approximately symmetrical situation, and then alter the resistance values of the variable resistors. Be careful not to exceed the maximum rated current of each resis- tor!

Document the current for each phase, when they all have noticeably different loads. Next, remove the neutral conductor and document the current values again.

4.   ANALYSIS OF RESULTS

The analysis of the results consists of answering the questions presented in the assignment instruction document. Including, making possible calculations, presentation of results in an illustrative form. and verbal assessment (for example, observations or conclusions made from figures). Assess whether the results are reasonable. If some of the results are completely incorrect or inadequate, state this and try to find the reason for the anomaly.

4.1    Three-phase power in wye and delta configured loads

Calculate the total active power in measurement 3.2 when using three and two wattmeters, and the total active power in measurement 3.3. Compare your calculations to the measured values.

Tips:

-    Using three wattmeters, the three-phase power is obtained by adding together the power from each line

P = √3√3Uv Iv cos(φ) = √3UP Iv cos(φ) = 3Uv Iv cos(φ) = P1  + P2  + P3

-    Using two wattmeters, the 30 degree phase difference between the line voltage and the current has to betaken into account

P = UP Iv cos(φ − 30°) + UP Iv cos(φ + 30°) = P1  + P2

4.2 Asymmetric load

Present and analyze the results of the measurement in chapter 3.4. Calculate the current of the neutral conductor based on the phase currents and compare how the calculated value differs from the measured one