Production of Rotating Magnetic Field

Production of rotating magnetic field is only possible when on 3 phase stat or winding application of 3 phase voltage is done appropriately. This on transformer action in rotor winding induces e.m.f which is stated to be in working condition. Working e.m.f is the given term for rotor induced e.m.f. due to a certain fact. This e.m.f. is the reason which makes a current flow through conductors. These conductors have armature windings. This in combination with revolving flux density wave produces a resultant in the form of torque. So, all these details give away the fact that for the appropriate operation of induction motor, the key aspect is its revolving field.

It can be clearly seen when there is a visible displacement in 3 phase windings. Its angular displacement in time, on measurement, is seen to be 120°. This displacement is fed by 3 phase current. This as an outcome produces resultant magnetic flux which in space rotates. The result of this movement is similar to actual magnetic poles which rotate mechanically.

If we consider a phase diagram of 3 phase winding and stat or structure, we will find the distribution of each phase in a normal pattern. In fact, its angular difference will also be more than 60°. This distribution degree is expressed in electrical term. In order to represent the total structure in a simpler way, a single coil is used.

The complete phase winding (I) is depicted by coil “I-I.”This winding showcases its flux axis which is directed in the vertical section. It can be clearly seen in the diagram provided below. This representation of phase winding expresses the fact that whenever current is carried through this phase structures, then flux field production directly pointed along downward side or vertically upside.

This complete representation or statement is verified with the help of right hand flux rule. In the same way, when this flux axis is displaced from its phase (I), then its calculated electrical degree displacement is 120°. This flux axis represents a phase which is denoted by ‘m’. Now again, when another calculation is made from the phase ‘m’ with that of phase ‘n,’ its electrical degree displacement also stands to be 120°. Both ‘m’ and ‘n’ depicts each phases’ beginning terminals and is known as unprimed letters.

This provided graph highlighted below showcases 3 phase current. It is considered that these current flows through the 3 phases respectively. Those 3 phases are – ‘n,’‘m,’ and ‘I.’On going through this graph, these currents are found to be time displaced. This displacement is highlighted by 120 electrical degrees.

Direction and magnitude of resultant flux compatible to t1 (time instant)

If we again consider the above graphical figure, we will find the position of the current in the phase I. On close consideration it is found to be atthe maximum positive value at I. But in case of the other phases, i.e., ‘n’ and ‘m’,the value of current becomes one half of the maximum value.

Now in the above figures depicting rotating magnetic fields,the assumption in the arbitrary level states that the current is in a positive state in the provided phase. The flow of current into paper is in accordance to unprimed conductors. So at the first figure of rotating magnetic field where the time is depicted by t₁, utilization of cross is for conductor ‘I, ’ and in this case, i₁ is positive.

In this figure, you will find that I is represented by a dot. These depiction states return connection. On using the right hand rule, we can see it following that same phase I. This on utilization gives out the outcome as a flux contribution which is directly focused downwards on the vertical side. After the resultant is seen, we can see the value of current is at its maximum position because this contribution’s magnitude is also high.

Therefore, the equation, in this case, will show,

Φ_max = Φ_l

In this case, Φ_maxrepresents maximum flux per pole in phase I.

And Φ_lrepresents sinusoidal distribution.

In order to study sinusoidal flux field, it is necessary that we understand about phase I. This is because the latter one produces the former one with the help of amplitude. This amplitude is positioned in the axis of phase I.

This is clearly highlighted in this above figure.

In order to find out the direction and magnitude of field contribution at a certain phase and at a certain time (here at time t₁ and at phase m), the first aspect is to pinpoint the fact whether the current is in positive phase or in the negative phase. As per the diagram, the current is seen to be negative in consideration to phase ‘m’. So, it is necessary that the conductor who stands in the initial position is assigned with certain signs like dots and crosses to determine few aspects.

In order to assign in an appropriate way, the whole ‘m’ is depicted with a cross, whereas the beginning phased of that ‘m’ is portrayed with the help of a dot. In this case, phase contribution regarding instantaneous flux is directed downward which is along the phase magnitude ‘m’ and its flux axis.

Here the value of flux is seen to be one half of maximum value. This is due to the value of current which is again one half of the total maximum value. This specific reason also leads to the same outcome in phase ‘n’.

Now, coming back to this figure below that depicts the association of the time t1, it is clear that resultant flux per pole has a magnitude whose value is one half of its maximum value in a certain single phase. The direction of this resultant flux is directed at downward side.

The graph that is represented above has the same outcome as the image showcased above. But its result is because it follows necessary terms which are insinuated by sinusoidal flux waves instead of flux vectors.

Those vectors involve:

Direction and magnitude of resultant flux concurring with time instant t3

In the above diagram, the value of current in phase I is zero. This results in zero flux contribution. In phase ‘m’ when value of current is measured then it comes to stand as equal and positive in consideration to its total value.

The value in case of phase ‘n’ is seen to be negative but with similar current magnitude to phase ‘m.’When both the phases ‘n’ and ‘m’ are combined with each other, its outcome is seen as a resultant flux which at time t₁willhave similar magnitude.

Now, according to the above diagram, we can see 90 electrical degrees elapse in the time results. This calculation is based on magnetic flux field’s rotation in that 90 electrical degrees.

At time instant t₅

After the prior time elapses, its value becomes equal to 90 additional electrical degrees. This addition results in a situation which finally produces an outcome highlighted in this diagram.

Characteristics

When 3 phases current’s proper application moves via a balanced 3 phase winding, this collaboration produces rotating magnetic field. This displays 2 important characteristics:

1. It has a constant speed
2. It has constant amplitude

In case of consistence speed, 3 phases current follows the aspect regarding resultant flux, which transverses in space via 2π electrical radians. And for all variation of 2π electrical radians, it depictsthe time for phase currents.

Therefore, when mechanical degrees and electrical degrees are same for 2 pole machines, every variational cycle regarding current gives out a complete revolution in case of flux field. This relationship can be stated as fixed. This is completely dependent on number of poles upon which this 3 phase winding is allotted and definitely on the current’s frequency.

Now in specific scenarios,the design of windings is mainly based on 4 poles to produce a singler evolution regarding the flux field.It requires the help of cycles of variation which is in consideration to current. This in finality leads to an equational formation revolving around p pole machine. Its relationship is depicted by,

In the first equation, the symbol N_sis known as synchronous speed. Its unit is relayed by r.p.m. It is a known factor that every synchronous machine has the tendency to run at their respective and specific synchronous speed.

If again this first equation is taken into close consideration, it can be clearly seen that the speed of rotation has a comparative connection to phase windings which carry time varying currents. As per this equation, a certain scenario can be seen in the passing state that we can see that the winding itself starts revolving. And while revolving, the speed of its rotation of that certain field becomes parallel to its inertial force. The value in both the cases on calculation comes to be entirely different when the measurement is in the prospect of winding.

Links of Previous Main Topic:-

• Current Electricity Basic Concepts
• Introduction to Alternating Current
• Introduction Three Phase A C Circuits
• Magnetic Field
• General Aspects
• General Aspects Polyphase Induction Motors
• Classification of A C Motors

Links of Next Electrical Engineering Topics:-

• Theory of Operation of an Induction Motor
• Slip
• Frequency of Rotor Current
• Rotor E M F and Rotor Current
• Torque and Power
• Effect of Change in Supply Voltage on Starting Torque
• Effect of Change in Supply Voltage on Torque and Slip
• Torque Slip and Torque Speed Curves
• Operating Characteristics 3 Phase Squirrel Cage Induction Motor
• Shows a Wound Rotor Induction Motor with Controller Rheostat
• Power Stages in an Induction Motor
• Induction Motor as Transformer
• Equivalent Circuit of an Induction Motor
• Starting of Induction Motors
• Factors Governing Performance of Induction Motors
• Effects of Operating Conditions
• Ratings of 3 Phase Induction Motors
• Squirrel Cage Motors Advantages Disadvantages and Applications
• Wound Rotor or Slip Ring Induction Motors Advantages Disadvantages and Applications
• Comparison of a Squirrel Cage and a Slip Ring or Phase Wound
• Comparison Induction Synchronous Motors
• Highlights in Polyphase Induction Motors
• Single Phase Motors
• Characteristics of D C Generators
• Measuring Instruments
• Power Supply System