Your question: How can a synchronous motor be made to have a leading power factor?

Once the synchronous motor is synchronized, the field poles on the rotor are in line with the rotating magnetic poles of the stator. … To increase the line voltage, the motor will supply ac magnetizing current to all “magnets” on the system to increase their magnetic flux. This is leading power factor.

How can a synchronous be employed for power factor correction?

The power factor of a synchronous motor is changed with a change in the excitation. When the excitation of the motor is increased, the power factor changes from lagging to unity and then to a leading power factor.

Can power factor of a synchronous motor be controlled?

This error signal is evaluated by FLC to obtain a control signal for the synchronous motor excitation circuit since the power factor of a synchronous motor can be controlled and held at a desired value by adjusting the excitation current. … Therefore, operating power factor of T&D systems must be corrected.

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Under what condition does a synchronous motor take a leading current?

Synchronous motor takes leading current when it is overexcited or under excited.

How do you find the power factor of a synchronous motor?

Synchronous machine power factor and angle

  1. Speed can be calculated by: n=120⋅fP , where f is frequency (60 Hz) and P are poles (8) … and we get the result 900 rpm.
  2. Power factor can be calculated by: PF=cos(PA), where PF is power factor, PA is power factor angle (is that the same as power angle?)

What is the power factor of a synchronous motor?

Synchronous motors are designed to operate at unity (1.0) power factor or 0.8 leading power factor. By varying the DC excitation of the motor, the power factor of the motor can be varied widely. Overexcited synchronous motors operate at leading power factor and provide reactive kVAR-like capacitors.

What is synchronous speed?

: a definite speed for an alternating-current machine that is dependent on the frequency of the supply circuit because the rotating member passes one pair of poles for each alternation of the alternating current.

What is the main disadvantage of synchronous motors?

Disadvantages or Demerits:

Synchronous motors requires dc excitation which must be supplied from external sources. Synchronous motors are inherently not self starting motors and needs some arrangement for its starting and synchronizing. The cost per kW output is generally higher than that of induction motors.

What is the power factor of induction motor?

The power factor of induction motors varies with load, typically from around 0.85 or 0.90 at full load to as low as about 0.20 at no-load. At no load, an induction motor draws a large magnetizing current and a small active component to meet the no-load losses.

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Why synchronous motors are not self starting?

Above a certain size, synchronous motors are not self-starting motors. This property is due to the inertia of the rotor; it cannot instantly follow the rotation of the magnetic field of the stator. … Once the rotor nears the synchronous speed, the field winding is excited, and the motor pulls into synchronization.

What is excitation EMF?

The process of generating a magnetic field by means of an electric current is called excitation. Field coils yield the most flexible form of magnetic flux regulation and de-regulation, but at the expense of a flow of electric current.

What does XD and XQ mean?

Xd- Direct-axis Synchronous Reactance the ratio of fundamental A.C. armature Voltage to A.C. armature current produced by the direct-axis flux. Xq- Quadrature-axis Synchronous Reactance the ratio of fundamental A.C. armature Voltage to A.C. armature current produced by the quadrature-axis flux.

What will happen if a synchronous motor is under Excited?

From the above discussion, it is concluded that if the synchronous motor is under-excited, it has a lagging power factor. As the excitation is increased, the power factor improves till it becomes unity at normal excitation.

How do you know if a motor is synchronous?


The rotor can be tested with an ohmmeter for an open winding or a grounded winding. To test the rotor for an open winding, connect one of the ohmmeter leads to each of the slip rings on the rotor shaft, Figure 17–5.

What is synchronous speed and it’s formula?

The synchronous speed of an AC motor is determined by the frequency of the source and the number of poles. The RPM is calculated by multiplying the frequency times 60 and dividing by the number of pairs of poles. … Actual speed of the induction motor will be less than the synchronous speed.

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How does excitation effect Power Factor?

A change in the excitation, thus, affects only the power factor of its output. … This reduces the terminal voltage slightly, so let the excitation of the first alternator be increased so as to bring the terminal voltage back to its original value.