Task 1 Any two lines is the voltage measured in a three-phase circuit is called a line voltage. Phase voltage is the voltage measured across a single component in a three-phase source or load. The voltage measured across a single component in a three-phase or load is called a phase voltage. Line current is the current through any one line between a three-phase source and load . phase current is the current through any one component comprising a three-phase ac system consist of three voltage sources that supply power to loads connected to the supply lines, which can be connected to either delta (”) or star (Y) configuration In three-phase system, the voltage differs in phase 120°, and their frequency and amplitude are equal.
If the three-phase loads are balanced the analysis of such a circuit can be simplified on a per-phase basis. This follows from the relationships that the per-phase real power and reactive power are one-third of the total real power and reactive power, respectively.
Star connection In star connection, there are 4 wire, 1 wire is neutral wire and 3 wires are phase which is taken from the star point. Star connection is would be more partial for far distance power Transmission because it will be having the neutral point. For this we will need to come to the idea of a balanced and unbalanced current in power system.When equal current will run through all the 3 phases, that’s when it is named a balanced current then when the current isn’t equal in any of the phase then it’s called an unbalanced current.
For example, whilst balanced condition there wouldn’t be no current passing through the neutral line or passing through the three-phase circuit, neutral is having a important role. It will take the unbalanced current through to the ground and protect the transformer. The star connection is shown below: Delta connection.For the delta conception, there are 3 wires on its own there is no neutral terminal taken. usually delta connection is more liked for small distance because of the issue of unbalanced current in the circuit. The figure is shown below for delta connection. In the load station, ground can be used as neutral path if required. In the delta connection, the line voltage is same with that of phase voltage and the line current is €3 times of phases current. It is shown as expression Eline = Ephase and Iline = €3IphaseBut the power is unconventional, of the circuit arrangement of the 3 phase system. The net power that is within the circuit will be the same in both the star and the delta connection. The power in 3 phase circuit is calculated by using the equation below.Ptotal = 3 x Ephase x Iphone x PF Since there are three phases, so the multiple of 3 is made in the normal power equation and the PF is power factor. Power factor is a very important factor in three phase system and sometimes due to certain error, it is corrected by using capacitor.Task 2 I have done an experiment and during the experiment we worked in groups to check the power. If you wish to change the direction of the motor, then you must change the colored wires around.Below is a table of my experiment in the Star motor and this was done two tables. Analyser 1 Analyser 2 Vine 116.6v 116.4vIL(current) 0.86A 0.84APF +0.284 -0.704Apparent power 100.7VA 98.75VAReal power -28.79W +69.57WWhen switched off, the direction changed to anticlockwise then we swapped black and grey. After that the motor was Turing clockwise The table below shows the two results of delta. Analyser 1 Analysers 2 Vline 116.3V 115.6VIL (current) 3.96A 4.04APF +0.269 -0.700Apparent power 454.2VA 460.08.VAReal power -122.24W -322.7W The two tables above show the results of both-delta and star connection and judging from my experiment I can see that the voltages line for both delta and star is about the same. However, the current (IL) for delta is 5 times the amount in star. Also, for the apparent power delta is 4 times larger. This could mean that delta is slightly better depending on application.Task 3The 3 phase induction motors are the very frequently used electrical motor. Almost up to 80% of the mechanical power that is being used by industries is provided by 3 phase induction motor this is because of its easy and rugged construction, cheapness, brilliant operating characteristics, missing of commutator and fantastic speed regulation. In three phases induction motor the power is transferred from stator to rotor winding through induction. The induction motor is also called as called asynchronous motor as its runs at any other speed other than the synchronous speed Like every other electrical motor induction motor has 2 parts which are called rotor and stator.Stator is a stationary part of induction motor. A stator winding is placed in the stator of induction motor and the 3-phase supply that is given to it.Rotor of the three-phase induction motor are further classified as Squirrel cage rotor, Slip ring rotor and wound rotor or phase wound rotor.Depending upon the type of rotor construction used the three-phase induction motor are used for specific things and are classified into classified:Squirrel cage induction motor Slip ring induction motor or wound induction motor or phase wound induction motor The construction of stator for both the kinds of three phase induction motor remains the same.The other parts, which are required to complete the induction motor, are: Shaft for transmitting the torque to the load. This shaft is made up of steel. Bearing for supporting the rotating shaft One of the problems with electrical motor is the production of heat during its rotation. In order to overcome this problem, we need fan for cooling. For receiving external electrical connection terminal box is needed there is a small distance between rotor and stator which usually varies from 0.4mm to 4mm. Such a distance is a called a air gap.The pictures below shoe the basic construction of a motor.
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