POLYTECHNIC UNIVERSITY OF THE PHILIPPINES College of Engineering Department of Mechanical Engineering Sta. Mesa, Manila MEEN 40023 DC AND AC MACHINERY Terms and Definitions on DC and AC Machinery Erica Jane Lomibao 2020-05611-MN-0 BSME 3-2 Prof. Armingol Morales Course Instructor October 12, 2023 MACHINERY PRINCIPLES Almost all practical motors and generators convert energy from one form to another through the action of a magnetic field. Generator -Electric machine turns a mechanical energy into electric energy, a form of a dynamic machine. Motor - Electric machine turns an electric energy into mechanical energy, a form of a dynamic machine. Newton’s Law -Newton’s law for objects moving in a straight line gives a relationship between the force applied to the object and the acceleration experience by the object as the result of force applied to it. J (Nm) Where is torque, J is moment of inertia, and is angular acceleration. Rotation Motion -Almost all electric machines rotate about an axis, called the shaft of the machines. Angular position, - is the angle at which it is oriented, measured from some arbitrary reference point. Its measurement units are in radians (rad) or in degrees. Angular Velocity, - Defined as the velocity at which the measured point is moving. d/dt (rad/s) Where is angular position/angular distance traversed by the rotating body, t is time taken for the rotating body to traverse the specified distance, . Angular acceleration, - is defined as the rate of change in angular velocity with respect to time. d/dt (rad/s2) Torque, Torque is known as a rotational force applied to a rotating body giving angular acceleration, a.k.a. ‘twisting force’. Product of force applied to the object and the smallest distance between the line of action of the force and the object’s axis of rotation. Greater the torque, more rapid the angular velocity changes. = F * r sin Magnetic fields Magnetic fields are the fundamental mechanism by which energy is converted from one form to another in motors, generators, and transformers. Ampere’s Law It is the basic law governing the production of a magnetic field by a current. Where H is the magnetic field intensity produced by the current Inet and dl is a differential element of length along the path of integration. H is measured in Ampere-turns per meter. Hdl Inet Magnetics Circuits The flow of magnetic flux induced in the ferromagnetic core can be made analogous to an electrical circuit hence the name magnetic circuit. TRANSFORMERS A transformer is a device that converts ac electric energy at one voltage level to ac electric energy at another voltage level. Transformers as a static machine operate on the same principle with generators and motors, the difference is just in the action of a magnetic field to accomplish the change in voltage level. Types of transformers There are different types of transformers and may vary depending on its core, voltage conversion, purpose, windings, insulation used, and on the number of phases. Core: Core type transformer A core type transformer has two cylinders and two horizontal bars forming the frame. The magnetic core is a square form with a common magnetic circuit. Shell type transformer Shell type transformer has a center cylinder and two outer cylinders. Both the HV and LV coils of it are located on a center column. Berry type transformer Berry type transformer: Magnetic circuit looks like a wheel. The metal shell is tightly fixed and filled with oil inside. Voltage conversion: Step-up transformer The step-up transformer helps the voltage increase on the output side because the number of turns on the secondary is always more than the number of turns on the primary. A high voltage is developed on the secondary side of the transformer. Step-down transformer A step-down voltage transformer reduces the output voltage. In other words, it converts high voltage, low current power into low voltage, high current power. Purpose: Power transformer Power transformers are mainly used in the transmission networks of higher voltages. The power transformer is designed for maximum efficiency of 100% and is larger than the distribution transformer. Distribution transformer A distribution transformer, also known as a consumption transformer, is responsible for switching from a low medium voltage source to the voltage used for home appliances and industrial equipment. Isolation transformer Isolation transformers are transformers with the primary and secondary winding independently of each other, and there is only a magnetic flux relationship between them. This type is composed of the primary and secondary windings linked only through a magnetic field. Instrument transformer They are generally known as an isolation transformer. Instrument transformer is an electrical device used to transform current as well as a voltage level. The instrument transformer is further divided into two types which are current transformer and potential transformer. Current transformer The current transformer is used for measuring electricity and also for protection. When the current is high to apply directly to the measuring instrument, the current transformer is used to transform the high current into the current required value in the circuit. Potential transformer The potential transformer is an instrument transformer used to transform voltage from a higher value in the primary windings to a lower value in the secondary windings. This transformer steps down the voltage to a safe limit value that the ordinary low voltage instrument like wattmeter, voltmeter, and watt-hour meters can easily measure. Windings: Two- winding transformer Also called conventional winding transformer has a fixed number of turns. It is a static machine that transfers electrical energy from one end to another without changing frequency. A two-winding transformer has two separate winding, which is the primary and secondary winding. Auto-transformer It shares the same turns of wire between the input and the output connections. The primary and secondary winding are not electrically insulated. Insulation: Dry type transformer The dry-type transformer is a type of transformer not using any insulating liquid where its winding or core is immersed in liquid. Instead, the windings and core are kept within a sealed tank that is pressurized with air. They are still very safe without liquid. We have two types of the dry-type transformer, that is Cast Resin Dry Type Transformer (CRT) and Vacuum pressure Impregnated Transformer (VPI). Oil immersed transformer It's also called an oil-filled transformer, a kind of voltage transformation device using an oil cooling method to reduce the transformer temperature. Unlike the dry-type transformer, the body of an oilimmersed transformer is installed in the welded steel oil tank filled with insulation oil. Phases: Single phase transformer A single-phase transformer is an electrical device that accepts single-phase AC power and outputs singlephase AC. A single-phase transformer is used in non-urban areas. They decrease the home voltage to a suitable value without a change in frequency, so it's used as a step-down transformer. Three-phase transformer A three-phase transformer is made of three sets of primary and secondary windings. Each set of windings wound around one leg of an iron core assembly. It looks like three single-phase transformers sharing one joined core as in the image below. AC MOTORS An AC motor is an electric machine that converts alternating current into mechanical rotation. AC motor applications range from industrial bulk power conversion from electrical to mechanical to household small power conversion. AC motors have two types which are synchronous and induction or asynchronous. Induction types can be categorized as single phase or three phase. DC MOTORS A direct current (DC) motor is a motor that turns energy from a direct current and turns this into mechanical energy. The first DC motor was developed around the 1830's-1840s. They were commercially unsuccessful, because these motors were battery powered and batteries were still very expensive, and the quality was low. It has two types which are brushless and brushed, the brushed type is further divided into series wound, shunt wound, compound wound, and permanent magnet.
