ENGINEERING ARTICLES

Introduction Synchronous generators and motors share many theoretical and operational similarities, making it essential to understand their common aspects. These machines are pivotal in industrial applications, particularly in the oil and gas sector, where their reliability and efficiency are critical. Theory of Operation Both synchronous generators and motors operate based on the same fundamental principles. The primary difference lies in the direction of the stator current and the flow of power. In a generator, mechanical energy is converted into electrical energy, while in a motor, electrical energy is converted into mechanical energy. The rotor in these machines can be of either cylindrical or salient pole design, with synchronous motors typically featuring salient pole rotors due to their design advantages in various applications. Construction Similarities The construction of generators and motors with equivalent power ratings is quite similar, especially in their stator and rotor...

A wound-rotor motor (Slip Ring Motor) is a type of induction motor where the rotor windings are connected through slip rings to external resistances. Adjusting the resistance allows control of the speed/torque characteristic of the motor. Wound-rotor motors can be started with low inrush current, by inserting high resistance into the rotor circuit; as the motor accelerates, the resistance can be decreased. Squirrel Cage Motors have a heavy winding made up of solid bars, usually aluminum or copper, joined by rings at the ends of the rotor. When one considers only the bars and rings as a whole, they are much like an animal's rotating exercise cage, hence the name. PROPERTY SQUIRREL CAGE MOTOR SLIP RING MOTOR Rotor Construction Bars are used in rotor. Squirrel cage motor is very simple, rugged and long lasting. No slip rings and brushes Winding wire is to be used. Wound rotor required attention. Slip ring and brushes are needed also need freq...

1) KNOW THE LOAD CHARACTERISTICS For line-operated motors, loads fall into three general categories: constant torque, torque that changes abruptly, and torque that change gradually over time. Bulk material conveyors, extruders, positive displacement pumps, and compressors without air unloaders run at relatively steady levels of torque. Sizing a motor for these applications is simple once the torque (or horsepower) for the application is known. Load demands by elevators, compactors, punch presses, saws, and batch conveyors change abruptly from low to high in a short time, often in a fraction of a second. The most critical consideration for selecting a motor in these cases is to choose one whose speed-torque curve exceeds the load torque curve. Loads from centrifugal pumps, fans, blowers, compressors with unloaders, and similar equipment tend to be variable over time. In choosing a motor for these conditions, consider the highest continuous load point, which typically occurs a...

MOTOR A motor is an extended version of a transformer. Here we can introduce the analogy between a transformer and a motor that is a motor is like a transformer with a moving secondary. The primary that is not moving is called stator and the secondary that is moving is called rotor. The type of motor that is used worldwide with a greater percentage is the three phase induction motor. The principle is somewhat like a transformer. If we place three coil at 120 degree physical alignment and also apply three phase ac supply which is also with 120 degree electrical phase relation, then the resultant flux, that is created from the vectorial space summation of the three phase fluxes, will rotate at the frequency of the supply voltage. Here the magnitude of the flux is same throughout the rotation. Now this revolving flux will cut the rotor and there will be an induced voltage across the rotor as well. As the rotor is short circuited there will be a flow of current through the short cir...

(1) By using a starting motor. This motor is directly coupled to the motor. It may be an induction motor which can run on a synchronous speed closer to the synchronous speed of the main motor. (2) Starting as an induction motor. This is the most usual method in which the motor is provided with a special damper winding on rotor poles. The stator is switched on to supply either directly or by star delta/reduced voltage starting. When the rotor reaches more than 95% of the synchronous speed, the dc circuit breaker for field excitation is switched on and the field current is gradually increased. The rotor pulls into synchronism (A) Pull-in torque. It is the maximum constant load torque under which the motor will pull into synchronism at the rated rotor supply voltage and rated frequency, when the rated field current is applied (B) Nominal pull in torque. It is the value of pull in torque at 95 percent of, the synchronous speed with the rated voltage and frequency applied to th...