INVESTIGATION OF THREE PHASE SYSTEM

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Elfreda Hensley
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1 EXPEIMENT 4 INVESTIGATION OF THEE PHASE SYSTEM. Purpose of the exercise. a) To be familiar with certain methods of the measurements of the average power in the three phases three and four-wire balanced and unbalanced configurations. b) To learn some methods of calculation of the three phases system and construction on of phasor diagrams.. Preparation. Before starting work in the laboratory student ought: a) to be familiar with the course of the exercise, b) supplement the theoretical knowledge with the help of test questions. 3. Performance of the exercise All measurements are done in a schematic as per diagram shown in Fig.. Note Please be extremely careful when performing the experiment. HIGH VOLTAGES AE PESENT. All the changes of the connection must be done when the supply is disconnected. Before switching on, it is necessary to find out the phase sequence of the three-phase secondary winding of the supplying transformer, by using the phase sequence-measuring instrument. Next connect the circuit as per diagram. 3.. Investigation of a three wire balanced system. Performing of the exercise: - Measurement of phase and line voltages, currents and voltage. - Measurement of the average power using different methods Measurement. In order to obtain three phase three wire balanced system (A,B,C) is necessary to see switches and change over switches in the following position: Table Switching element W Position closed open The measurement of the average power can be obtained by two different methods: a) In two wattmeters connection set the switch P in position (-) and P3 in position (-3). The average power is equal the sum of P w + Pw wattmeter readings. b) By measurement of the power in one phase by wattmeter W (P position (-), the end of the voltage coil is connected to the centre point of the load; see the dotted line). The system average power is equal 3P w = P. '

2 All the measurement results of currents and voltages should be stated in Table : Table V V V 3 A A 3 A P w P w P ' w V V V A A A W W W 3... esults. It is necessary to calculate currents distributions in the system, load phase voltage and average power. Compare the calculated and the measured results and tabulate them in Table 3; Table 3 V 3 A A A 3 V Meas. Cal. Meas. Cal. Meas. Cal. Meas. Cal. Meas. P + P w w P Meas. P ' 3 w Cal. V V V A A A A A A W W W 3.. Investigation of three-wire system with the break in phases S. It is necessary to measure voltage circuit., currents, phase voltages and averages power of the 3... esults. Connection of the switches in the system as per Table 4: Table 4 Switching element Position P - P 3-3 W (OPEN) (OPEN) Current, voltage and power measurements should be set in Table 5: Table 5 Meas. Cal. V V V 3 A A A 3 w P w V V V A A A W W P

3 3.. esults In the report calculate currents distribution, phase voltages, voltage and the average power of the circuit taking into consideration the load parameters and the line voltage ( indication). The results should be tabulated in the Table 5. Construct also the phasor diagram. 3.3 Investigation of three-phase system with the phase C short-circuited. V It is necessary to measure voltage system., currents, phase voltages and the average power of the Positions of switches as per Table 6: Table 6 Switching element Position P - P 3-3 W (CLOSED) (CLOSED) The results should be allocated in Table 7: Table 7 Meas. Cal. V V V 3 A A A 3 w P w V V V A A A W W P In the report calculate currents distribution, phase voltages, voltage and the average power, taking into consideration load parameters and the line voltage ( indication). Allocate results in Table 7. Construct the phasor diagram of the system. V 4. Control questions. a) Describe different methods of calculations of three phase systems and construction of phasor diagrams for different load. b) Describe and substantiate the average power measurement methods, used in the experiment. Give the conditions of their application.

4 C A W S T 0 w A B C V A 3 P 3 P3 w C B A B B C A 3 B C V 3 w V Fig.

THREE PHASE SYSTEMS Part 1

ERT105: ELECTRCAL TECHNOLOGY CHAPTER 3 THREE PHASE SYSTEMS Part 1 1 Objectives Become familiar with the operation of a three phase generator and the magnitude and phase relationship. Be able to calculate