ENGINEERING ARTICLES

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...

Transformers reduce the voltage of the electricity supplied by the utility to a level suitable for use by the electric equipment. Since all of the electricity used by a company passes through a transformer, even a small efficiency improvement will result in significant electricity savings. High-efficiency transformers are now available that can reduce total electricity use by approximately 1 percent. Reduced electricity use provides cost savings for a company. Two types of energy losses occur in transformers: load and no-load losses. Load losses: result from resistance in the copper or aluminum windings. Load losses (also called winding losses) vary with the square of the electrical current (or load) flowing through the windings. At low loads (e.g. under 30 percent loading), core losses account for the majority of losses, but as the load increases, winding losses quickly dominate and account for 50 to 90 percent of transformer losses at full load. Winding losses can be reduce...

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...

To perform the economical analysis of transformer, it is necessary to calculate its life cycle cost, sometimes called total cost of ownership, over the life span of transformer or, in other words, the capitalized cost of the transformer. All these terms mean the same – in one formula, costs of purchasing, operating and maintaining the transformer need to be compared taking into account the time value of money. The concept of the ‘time value of money’ is that a sum of money received today has a higher value – because it is available to be exploited – than a similar sum of money received at some future date. In practice, some simplification can be made. While each transformer will have its own purchase price and loss factors, other costs, such as installation, maintenance and decommissioning will be similar for similar technologies and can be eliminated from the calculation. Only when different technologies are compared e.g. air cooled dry type transformers with oil cooled transfor...

TRANSFORMER A transformer is an extended version of an inductor. The flux that is created inside the inductor is used here to induce voltages at other coil, which is termed as secondary coil. If the rate of change of flux can induce voltage across the primary coil, from which it is created, then it is also possible to induce voltage across secondary coil, provided that we can pull the flux to flow through the other coil. The rate of change of flux will induce voltage as many turn we use. If the turn is double the turn in primary then the voltage will also be double. If we increase the number of secondary coils, then voltage will be induced in all the secondary coils according to the number of turns present in each secondary coil. We can increase or decrease the secondary voltage level according to our requirement. If the secondary voltage is increased then it is called step up transformer and for the decreasing case it is called step down transformer. Each secondary voltage will...

TCSC is used to decrease or increase overall effective series transmission impedance from sending end to the receiving end so as to control the transmission of power and the current in the reactor can be controlled from zero to maximum by the method of firing delay angle. Closure of the thyristor valve is delayed w.r.t. peak of the applied voltage in each half cycle thus duration of the current conduction interval is controlled. Figure1: Operation of thyristor with various firing and conduction angles. There are three modes of operation of TCSC depending upon the firing angle of the pulses fed to the thyristor. 1) Thyristor blocked mode 2) Thyristor bypassed mode 3) Vernier operating mode 1) THYRISTOR BLOCKED OPERATING MODE: When the thyristor valve is not triggered and the TCSC is operating in blocking mode. In this mode, the TCSC performs like a fixed series capacitor. 2) THYRISTOR BYPASS OPERATING MODE: In bypass mode the thyrist...