Engineering and Construction
paraphrasing all the papers and editing
To complete this laboratory you need to determine the phase sequence of a three phase source.
Phase sequence is usually indicated on bus bars by a colour code of some kind, or it may be found by using phase sequence indicator, commercially available. In the absence of such a decide, the phase sequence can be found by connecting in star two equal resistor and a capacitor to the three terminals of the power source as shown in Figure 2-1. The voltage across the two resistors will be found to be unequal and the phase sequence is in the order, (high voltage)-(low voltage)-(capacitor). For example, if the voltages across the resistors are 20 V and 80 V as shown in figure 2-1, the phase sequence is B-A-C. The voltages succeed each other in the sequence B-A-C-B-A-C; hence the sequence B-A-C is the same as the sequence A-C-B or the sequence C-B-A.
1) Using the resistive load, capacitive load and AC voltmeter the circuit was connected correctly.
2) Voltage of E1 and E2 was measured and they are 365.4 vac and 96.15 vac respectively.
3) The phase sequence was determined and this is 1-2-3.
4) When the phase was according to the direction the power supply was connected.
5) While we connected the phase sequence was connected then we also connected the power supply and the sequence was 4-5-6.
6) Voltmeter was connected through the three terminal 1-4,2-5and 3-6. The voltage according to the sequence is E1-4= 10.29 vac, E2-5= 9.527 vac, E3-6= 9.937vac.
7) When we put the power supply clock wise we get metering close to zeros and anticlockwise we get the voltage close to voltage 171.6vac, 171.8vac, 171.8vac.
REAL POWER & REACTIVE POWER
To complete this laboratory you should be able to interpret the meaning of positive, negative, real & reactive power. Also, observe the flow of real and reactive power in three phase circuits.
In three phases, three wire Ac circuits two wattmeters are needed to measure the real power while three phase, four wire circuits require three. These meters may be combined into a single wattmeter of special construction, which greatly simplifies the problem of adding the reading of two or three wattmeters to obtain the total three phase power. A typical three phase wattmeter has three inputs terminals and outputs too.
In addition, the three phase alternating circuits may involve many types of circuit’s and devices, but the flow of active and reactive power can always be determined by introducing wattmeter and varmeter.
1) Using the load of 1200? the circuit was connected according to the figure.
2) The inductive load was replaced in the place of resistive load. And the value was recorded.
3) And the procedure was repeated by twice.
4) The real power was affected when the capacitive load was switched off.
5) The real power was affected when the resistive load was switched off.
6) We were agreed that whatever we used for all intents and purposes the capacitive load supplying most of the reactive power required by the inductive load.
7) The motor absorb both real and reactive power.
8) We get the following results. pic
9) We have calculated the apparent power by using formula s=E1/v3
To conclude, the only way to be sure that the connections are identical for various receptacles is to measure the voltage between similarly marked terminals. And if the voltage is zero in all cases, then the phase sequence and the connections are identical. In the end, Wattmeters and varmeters are connected on either side of an electrical circuit or device, and we can determine the real and the reactive power which produces or absorbs.
POWER FLOW & VOLTAGE REGULATION OF SIMPLE TRANSMISSION LINE
To complete this laboratory, we need to observe the flow of real and reactive power in a three-phase transmission line with known passive loads. Also, voltage regulation at receiver as a function of the type of load.
The resistance, inductance and capacitance of a transmission line are uniformly distributed over its length, the magnetic field around the conductors existing side by side with the electric field created by the potential difference between them. We can picture a transmission line as being made up of thousands of elementary resistors, inductors and capacitors.
In high frequency work this is precisely the circuit required to explain the behaviour of a transmission line .Fortunately, at low frequencies of 50Hzor 60Hz.we can simplify most lines so that they comprise one inductance. one resistance.
The inductance L is equal to the sum of the inductances and the same is true for the resistance R,The capacitance C is equal to one half the sum of capacitance. And the inductance C can be replaced by their equivlent reactance Xl & Xc.
In the end, Very high voltage lines which run for many kilometres have appreciable capacitive and inductive reactance.
1) We was connected the wattmeter in series to the variable three phase 415 v and we got the following result. P1= 15w , Q1= 80 var ; P2= 10w, Q2= 80var.
2) Using the variable voltage ac source the circuit was connected and the impedence was set of the transmission line to 400?. The load was connected to the inductive load of 1200?.
3) We the line of an open circuit the voltage was adjusted of the source so that the line to line voltage is E1= 350V.
4) Three phase inductive load was connected with 1200?.
5) Three phase resistative load was connected with 1200?.
6) Three phase capacitative load was connected with 1200?.
7) The circuit was short circuited and the readings were recorded.
8) The real and reactive power was recorded through the transmission line.
9) The voltage regulation was calculated through the transmission line by the formula %regulation =(Eo-El)*100/Eo
Where Eo is the open circuit voltage and El is the voltage under the load. The recorded value is as following.
PHASE ANGLE & VOLTAGE DROP BETWEEN SENDER & RECIVER
To complete this laboratory you need to cover, the receiver and voltage. And observe the phase angle between the voltage at the sending and the receiving and of the transmission line. Also, the line voltage drop when the sending & receiving 7 voltages have the same magnitude.
The capacitors should deliver reactive power equal to that consumed by the inductive load. This produces a parallel resonance effect in which reactive power required by the inductance is in effect supplied by the capacitance and none is furnished by the transmission line. So, the reactive power which the capacitors must supply to regulate the voltage, isn’t easy to calculate. Our purpose of this experiment is to determine the reactive power by trial & error. And adjusting the capacitors until the receiver end voltage is equal to sender & voltage.in the end, loads which draw both real and reactive power, the capacitors must be tailored to compensate first, For the inductive components of the load and second, for the resistive component.
1) The impedance was set at 200?. The voltmeter was connected according to the figure. The circuit was connected in three phase variable voltage supply.
2) By using the three phase voltage load E1 was adjusted to 350 v and we kept that constant. We increased the resistive loading steps. And calculated the values.
3) Then we connected the three phase balanced capacitive load in parallel with the resistive load. We repeated the step by two times. And tried adjusted the value close to 350 v.
4) In this experiment we observed significant voltage drop along transmission line even when the voltages E1 and E2 at the sender and receiver ends are equal in magnitude. pic
5) We used the results of procedure step 4 we calculated the voltage , current , real power and reactive power per phase .
We reduced all voltages and powers to a per phase basis, assumed a star connection. Since E1 and E2 are line to line voltages the corresponding line to line neutral voltages are 0.577 (1v3) times the line to line voltages.
Real power Q2 is smaller than P1 because of the line I^2R loss line transmission line.
We measured the current directly but measurement of the real and reactive power and knowledge of the voltages was sufficient to enable us to calculate everything about the line.
PARAMETERs WHICH AFFECT REAL & REACTIVE POWER FLOW
To complete this laboratory, we need to observe reactive power flow when sender & receiver voltage are different, but in phase. Also, Observe real power flow when sender & receiver voltages are equal. But, Out of phase.
Transmission lines are designed and built to deliver electric power. Power flows from the generator to the load but, In complex interconnected systems, The sender and receiver ends may become reversed. Power in such a line may flow in either direction depending upon the system load conditions which of course vary throughout the day. The character of the load also, changes from hour to hour, both as to KVA loading and as to power factor.
When the voltages at the sender & receiver ends are in phase, but unequal reactive power will flow. The direction of flow is always from the higher voltage to the lower. Moreover, the real power can only flow over a line if the sender and receiver voltages are out of phase. the direction of power flow is from leading to the lagging voltage and again, it should be noted that this rule applies only to transmission lines which are principally reactive.
1) The three phase transmission was connected between terminal 4,5,6 of two consoles, one of which is designated as station A and the other. And section B was connected three phase wattmeter at the other end as well as phase meter as shown in figure.
2) With the transmission line switch was open then we adjusted the line to line voltages to that E1 & E2 were both equal to 370 V & the phase angle was zero between terminal 4-5of station A and terminal 4-5 of station B.
3) With making any changes we measured the phase angle terminal between 4-5 of section A & terminal 5-4 of section B. And that was leading .
4) The phase angle between terminal 4-5 of section A and terminal 5-4 at section B the angle was legging.
5) We then measured all phase angle between two section.
6) We closed the three phase transmission line switch E1=E2=370V and the impedance=200? P1= -0.9w ; P2=-0.8w; Q1=90 var; Q2=-0.8var.
7) We raised the voltage to 415 V and observed the power P1=-10w ; P2=-12w; Q1=90 var; Q2= -65var.
8) Then we reduced the section voltage to 350 V and observe power follow P1=-4w ; P2=-5w; Q1= -30 var; Q2=-35var.
9) The voltage was varied of both section A &B and we checked the truth of the statement of the reactive power statement that always flows from the higher voltage to the lower voltage.
10) We changed the terminal settings got the following data. Table
11) The phase shift was same for all three phases and that all voltages are balanced.
12) The three phase connection was changed and the settings was 400? transmission line between secondary terminals 4,5,6. We got following data
13) Using only one console we set up the experiment as figure 6-15 where E1 = 415 V and using a star connected resistive load of 1200 ? per phase 200 ? transmission line.
14) We repeated procedure 13 as inductive load of 1200 ?/ phase.
15) We repeated the step 13 again as capacitive load of 1200?/ phase.
16) We got the following values.
The experiment was carried out by 5 group members. There was high voltage presents and we had be careful while we operating the experiment and every time we changed the settings we turned off the power supply the we carried out our experiment. We did the following procedure as our experiment sender and receiver voltage was unequal but in phase; sender and receiver voltages was equal but out of phase; sender and receiver was unequal but out of phase.
PARALLEL LINES TRANSFORMERS & POWER HANDLING CAPACITY
To complete this laboratory, we need to cover the real power Vs Phase angle curve of a transmission line. Use of transformers to increase the power handling capacity of a line.also, transmission lines in parallel.
The real power which could be delivered by a transmission line depends upon the voltages at the sender and receiver ends and the phase angle between them. The real power P of a three-phase line is given by the equation. Formula
In addition, Sender & receiver voltages are held constant. The power delivered will be dependent on the phase angle. This relationship between the power P and the angle.
In the end, we should note that any phase can exist between Zero and 360 Degree or, which is the same thing, between 0 and 180 Degree lagging and 0 and 180 Degree leading, if the power Vs phase angle curve is extended to cover all possible angles then we obtain this curve.
1) On figure 7.7 stations A and B were linked by a transmission line having a certain reactance X . from the value of the line to line voltages we determine the reactive power and the direction the flow.
2) We referred the procedure step 1 we calculate the maximum power.
3) Two parallel transmission lines operating at a three phase line to line voltage of 120 KV each had line reactance of 60 ?, if the total power would differed is 84 MW we could calculated the phase angle between the sender and receiver voltages.
4) Using two independent power supplies and three phase regulating autotransformer we set the line reactance to 600 ? and we measured the real power flow when the phase shift is +15 ?. E1 =419V; E2 = 415.9V; P1 =-75W; P2 =-80 W. Q1 =19 var; Q2=0 var.
5) Now at sections A and sections B we had been introduced set up and set down transformer s connected in delta star and star delta respectively. And we got the following values. E1 =627.0V; E2 = 648.3V; P1 =226W; P2 =-249W. Q1 =-29 var; Q2=-185var.
The experiment we had done there was high voltage connection ie had to be care then we could successfully finished our lab experiment. The experiment was carried out by 5 group members. There was high voltage presents and we had be careful while we operating the experiment and every time we changed the settings we turned off the power supply the we carried out our experiment.
Please refer to the Lab Manual Handbook, Phase sequence LAB one and parameters which effect real and reactive power flow LAB two. And this is provided by unit ENS3206 resource, under Assessment session upon ECU Blackboard website.
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