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how does the current flow in a three phase circuit when neutral is not connected?
A balanced three-phase 4-wire circuit - one with equal currents in all three live wires - has zero current flowing in the 4th wire, the neutral. Therefore the neutral wire can be removed, leaving just the three live wires.
Instantaneously, the sum of the three currents is always zero in a balanced three-phase circuit. As an example, when the current reaches its peak in one wire, say 10 amps, the current in the other two wires is one half, 5 amps, in the opposite direction. Therefore the two wires take the return current for the first wire. This state of affairs happens continuously at every instant in the AC cycle, so three lives wires are all that is needed.
Wiki User
∙ 9y ago
Wiki User
∙ 14y agoYou do not need a neutral in a three phase circuit if you are delta connected. You only need the neutral if you are wye connected. In delta connection, current flows from one leg to the next. Assuming the three legs are called A, B, and C, each phase would be the connection of AB, BC, and CA.
Wiki User
∙ 9y agoAs usual you need to know the voltage and the kVA. For a balanced load, find the line-to-neutral voltage, which is the nominal voltage between lines divided by sqrt(3).
Each line supplies one-third of the kVA, so the current in each line is equal to the kVA times 1000 divided by the line-to-neutral voltage.
As an example, 50 kVA on a 208 v three-phase supply would have a line current of 50/3x1000/120 or 139 amps.
Another Answer
For a balanced load, star (wye) or delta, the equation for power is:
Power = 1.732 x line voltage x line current x power factor
Simply manipulate the equation to make the line current the subject of the equation.
Finding the line current for an unbalanced load is a great deal more complicated.
<<>> The current can also be sampled in each of the three lines using current Transformers.
Wiki User
∙ 11y agoThe neutral in a three wire single phase circuit carries the unbalanced load current. Measure the load current in L1, then measure the load current in L2. Subtract the smallest current number from the largest current number and you will have the current number that the neutral is carrying.
Wiki User
∙ 11y agoThe phase windings of a three-phase motor constitute a 'balanced load', which means they each draw identical currents. If the phase windings are star (wye) connected, then the phasor-sum of the three phase currents will be zero, making the need for a neutral redundant.
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Why neutral not conect in 3phase motor?
A 3 phase motor does not require a neutral conductor because the impedances that make up the stator coils are of equal magnitude and it is what is known as a balanced 3 phase load. If the loads of a wye connected 3 phase system were unbalanced, i.e. the load currents in each of the 3 phases are different, then the unbalanced currents would require a return path to the service transformer via a neutral conductor. The neutral conductor is the transformer centre tap and is usually earthed locally. ANOTHER ANSWER The impedance of each phase winding of a three phase motor is identical (we call it a 'balanced load'). For a star (wye) connected motor, the phasor sum of three identical phase currents is zero, so no current will flow through a neutral, so a neutral isn't required. For a delta-connected motor, there is no provision for a neutral.
What are the advantages of three phase induction motors over the other motors?
A Single phase induction motor includes a main winding, an auxiliary winding, a run capacitor, & a subsidiary star device. The auxiliary winding is configured such that the number of turns of the aauxiliary winding through which a current flows, varies according to the operating mode of motor. When the motor starts, the number of turns of the auxiliary winding through which a current flows is reduced there by increasing the start efficiency of the motor. when the motor runs in normal mode, the number of turns of auxiliary winding through which a current flows is increasing there by increasing the operations efficiency of motor
What is an ac motor?
An AC motor is an electric motor that runs on alternating current, like household electricity, as opposed to a DC motor that runs on direct current from a battery. Most AC motors work from the mains supply, which has a frequency of 50Hz in the UK and 60Hz in the USA. Other types are available that work like stepper motors and need a specialist supply to run them.
How star delta helping motor from overheat?
star delta motors start as a Y for 3 phase so the windings that normally see 480 volts see 277V a relay switches to delta then it runs as a normal delta motor the reduces the starting current by about 60% for 3 phase
How do you connect bulb in 3 phase power?
by using star connectionAnswerIt depends on the type of three-phase supply. If it's a three-wire system, then you can connect the lamp between any pair of line conductors. If it's a four-wire system, then you can connect the lamp either between any pair of line conductors or between any one line conductor and the neutral conductor. Of course, the voltage rating of the lamp must match the line-to-line voltage or the line-to-neutral voltage.
Why neutral not conect in 3phase motor?
A 3 phase motor does not require a neutral conductor because the impedances that make up the stator coils are of equal magnitude and it is what is known as a balanced 3 phase load. If the loads of a wye connected 3 phase system were unbalanced, i.e. the load currents in each of the 3 phases are different, then the unbalanced currents would require a return path to the service transformer via a neutral conductor. The neutral conductor is the transformer centre tap and is usually earthed locally. ANOTHER ANSWER The impedance of each phase winding of a three phase motor is identical (we call it a 'balanced load'). For a star (wye) connected motor, the phasor sum of three identical phase currents is zero, so no current will flow through a neutral, so a neutral isn't required. For a delta-connected motor, there is no provision for a neutral.
Why you use three phase electricity?
Three phase is used mostly with electric motors! Greater power with less current and more economical also. Motor runs cooler and starts quickly with improved starting torque.
How can you make a car that runs 6 feet without electricity?
Just put it in neutral on a hill. But what good is a car that only runs 6 feet?
What are the advantages of three phase induction motors over the other motors?
A Single phase induction motor includes a main winding, an auxiliary winding, a run capacitor, & a subsidiary star device. The auxiliary winding is configured such that the number of turns of the aauxiliary winding through which a current flows, varies according to the operating mode of motor. When the motor starts, the number of turns of the auxiliary winding through which a current flows is reduced there by increasing the start efficiency of the motor. when the motor runs in normal mode, the number of turns of auxiliary winding through which a current flows is increasing there by increasing the operations efficiency of motor
Why single phase induction motor always runs below the synchronous speed?
For exactly the same reason as three-phase motors always run below synchronous speed. If they were to run at synchronous speed then no voltage and, therefore, no rotor current will be induced into the rotor to drive it.
What runs but cannot?
Motors, watches, refrigerator
What is an ac motor?
An AC motor is an electric motor that runs on alternating current, like household electricity, as opposed to a DC motor that runs on direct current from a battery. Most AC motors work from the mains supply, which has a frequency of 50Hz in the UK and 60Hz in the USA. Other types are available that work like stepper motors and need a specialist supply to run them.
How star delta helping motor from overheat?
star delta motors start as a Y for 3 phase so the windings that normally see 480 volts see 277V a relay switches to delta then it runs as a normal delta motor the reduces the starting current by about 60% for 3 phase
What runs but cannot walk?
Motors, watches, refrigerator
How do you connect bulb in 3 phase power?
by using star connectionAnswerIt depends on the type of three-phase supply. If it's a three-wire system, then you can connect the lamp between any pair of line conductors. If it's a four-wire system, then you can connect the lamp either between any pair of line conductors or between any one line conductor and the neutral conductor. Of course, the voltage rating of the lamp must match the line-to-line voltage or the line-to-neutral voltage.
How does single phase induction motor varies from 3 phase induction motor?
All induction motors require a rotating magnetic field in order to drive their rotors. Unlike a three-phase motor, a single-phase induction motor does not have a naturally-rotating magnetic field set up in the air gap between the stator and rotor and, so, this rotating magnetic field must be artificially created by stator windings that are roughly 90 degrees out of phase with each other. In most cases, this is done by inserting a capacitor in what is termed its 'auxiliary winding'.
What are advantages of three phase ac and a single phase ac?
In a typical 3 phase system you have multiple voltages and configurations that can be used in either single phase or 3 phase, depending on how the circuit is designed. A single phase system is just single phase. You can have multiple voltages but it is always single phase.For example, in a typical 277/480v 3 phase system you can power 277v single phase lighting or equipment, 480v single phase lighting or equipment (which uses 2 legs of the 3 phase system but operates like any other single phase circuit), or 480v 3 phase motors.When comparing motors, a 3 phase motor will be substantially smaller than a single phase motor of the same horsepower. You can also reverse a 3 phase motor by switching any 2 leads. A single phase AC motor runs in one direction regardless of how the leads are connected.AnswerFor a given load, a three-phase transmission system requires less volume of copper in terms of conductor size, compared to single phase, so it is more economical to use three-phase.
