The negative effects of voltage unbalance on the performance of three-phase induction motors include: higher losses, higher temperature rise of the machine, reduction in efficiency and a reduction in developed torque .
What happens if the induction motor runs on unbalanced voltage?
A small amount of voltage unbalance may increase the current an excessive amount. The effect on the motor can be severe and the motor may overheat to the point of burnout. The voltages should be evenly balanced as closely as can be read on the usually available commercial voltmeter.
What are the effects of unbalance voltage?
Voltage unbalance at the motor terminals causes high current unbalance, which can be 6 to 10 times as large as the voltage unbalance. Unbalanced currents lead to torque pulsation, increased vibration and mechanical stress, increased losses, and motor overheating.
What is the impact of negative sequence voltages on induction motors?
Performance of these induction motors is affected by the unbalance in bus voltage caused by negative sequence currents, which produces an air gap flux rotating opposite to the direction of rotor thereby heats up the rotor and generates a breaking torque.
What is the effect of operation with unbalanced rotor impedances of three-phase induction motor?
Unbalanced Rotor Impedance Operation causes unbalance in rotor currents. The unbalanced rotor currents can be resolved into positive and negative sequence components. Positive sequence rotor currents produce driving torque in the same way as in a motor with balanced rotor resistances.
What causes voltage imbalance?
Unbalanced voltages usually occur because of variations in the load. When the load on one or more of the phases is different than the other(s), unbalanced voltages will appear. This can be due to different impedances, or type and value of loading on each phase.
What is plugging in induction motor?
Plugging is the method of inducing negative torque in the rotor of an induction motor to rapidly bring its speed of rotation to zero. This is done by reversing the supply connection at the stator terminals.
How do you fix voltage imbalance?
Redistributing and reconnecting single-phase loads can reduce voltage unbalance caused by excessively unequal load distribution among phases. The most prevalent culprits among heavy, single-phase loads are lighting equipment and occasionally welders.
What is voltage unbalance factor?
voltage unbalance factor, u. defined as the ratio of the modulus of the negative-sequence to the positive-sequence components of the voltage at fundamental frequency, expressed as a percentage. (%) NOTE 1 Phase-to-phase voltages may also be used instead of line to neutral voltages.
Why is motor current unbalanced?
Current unbalance can be due to the motor or the supply line. … If the high current and low current readings follow the same line leads, the supply is the cause of the problem. If the high and low readings follow the motor leads, the motor is the source of the problem.
What causes negative sequence current?
Causes and Effects of Negative Sequence Components
Unbalanced loads in the system. Unbalanced system faults (line to ground faults, two phase faults, triple line to ground faults, double line to ground faults) Open phases (open circuit faults)
What is unbalanced condition?
Answer: Phase unbalance of a three-phase system exists when one or more of the line-to-line voltages in a three-phase system are mismatched. … The unbalanced voltages cause unbalanced current in the motor windings; unbalanced currents mean an increase of current to at least one winding raising that winding temperature.
Which of the following motor is preferred for traction work?
Explanation: DC motors are used for traction as, according to the characteristics of DC motors speed is inversely proportional to torque and square of armature current as well, if linear magnetization is concerned. Thus, DC motors are perfectly suitable for traction.
What is regenerative braking in induction motor?
Regenerative Braking of Induction Motor
When the speed of the motor is more than the synchronous speed, relative speed between the motor conductors and air gap rotating field reverses, as a result the phase angle because greater than 90o and the power flow reverse and thus regenerative braking takes place.
What are the drawbacks associated with the operation of induction motor with unbalanced rotor impedance?
If the motor is started with one rotor phase opened or with rotor impedances greatly unbalanced, it will accelerate to half speed and operate stably as a motor or generator. … Disadvantages of half speed operation are the low power factor, low pull-out torque, the subfrequency line currents, and motor vibrations.
How does a synchronous motor develop torque?
The torque of a synchronous motor is produced by the phase difference between the rotating magnetic field and the rotor. The torque is low when there is a small phase difference between the rotating rotor and the rotating magnetic field. … The torque will reach a maximum when this phase difference approaches 90 degrees.