SCIENCE EDUCATION > Engineering

Electrical Engineering

This collection starts with an electrical safety video that introduces the best practices for commonly used equipment in an electrical laboratory. Subsequent videos introduce elements such as inductors, transformers, convertors, rectifiers, and inverters.

  • Electrical Engineering

    09:35
    Electrical Safety Precautions and Basic Equipment

    Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

    Electric machines and power electronics experiments involve electrical currents, voltages, power, and energy quantities that should be handled with extreme diligence and care. These may include three-phase AC voltage (208 V, 230 V, or 480 V), up to 250 V DC voltages, and currents that can reach 10 A. Electrocution occurs when an electrical path is established through the body with very low currents that can damage vital organs, such as a person’s heart, and may cause immediate death. All experiments must be performed in the presence of personnel trained to handle electricity at these voltage and current levels. In case of emergency, evacuate the lab through any of the exits and dial 911.

  • Electrical Engineering

    10:40
    Characterization of Magnetic Components

    Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

    The objective of this experiment is to achieve hands-on experience with different magnetic components from design and material perspectives. This experiment covers B-H curves of magnetic material and inductor design through identifying unknown design factors. The B-H curve of a magnetic element, such as an inductor or transformer, is a characteristic of the magnetic material forming the core around which windings are wrapped. This characteristic provides information about the magnetic flux density that the core can handle with respect to the current flowing in the windings. It also provides information about limits before the core is magnetically saturated, i.e. when pushing more current through the coil leads to no further magnetic flux flow.

  • Electrical Engineering

    08:56
    Introduction to the Power Pole Board

    Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

    DC/DC converters are power electronic converters that convert DC voltages and currents from a certain level to another level. Typically, voltage conversion is the main purpose of DC/DC converters and three main types of conversion exist in a single converter: stepping up, stepping down, and stepping up or down. Among the most common step-up converters are boost converters (Refer to this collections video: DC/DC Boost Converter), while among the most-common step-down converters are buck converters. (Refer to this collections video: DC/DC Buck Converter.) Buck-boost converters are also common to perform both step-up and step-down functionalities, and flyback converters can be considered as special types of buck-boost converters where electrical isolation is achieved between the input and output ports. (Refer to this collections video: Flyback Converter.) DC/DC converter topologies are numerous, and their control, modeling, and operational improvements (e.g. efficiency, reliability, performance, etc.) are areas of continuous interest. The HiRel Power Pole board presented in this experiment provides a very flexible tool to study and analyze the performance of boost, buck, and flyback converter, all on a single board. The objective of this experiment is to introduce the major components and capabilities of the

  • Electrical Engineering

    12:17
    DC/DC Boost Converter

    Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

    Boost converters provide a versatile solution to stepping up DC voltages in many applications where a DC voltage needs to be increased without the need to convert it to AC, using a transformer, and then rectifying the transformer output. Boost converters are step-up converters that use an inductor as an energy storage device that supports the output with additional energy in addition to the DC input source. This causes the output voltage to boost. The objective of this experiment is to study different characteristics of a boost converter. The step-up capability of the converter will be observed under continuous conduction mode (CCM) where the inductor current is non-zero. Open-loop operation with a manually-set duty ratio will be used. An approximation of the input-output relationship will be observed.

  • Electrical Engineering

    10:25
    DC/DC Buck Converter

    Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

    While it is simple to step up or down AC voltages and currents using transformers, stepping up or down DC voltages and currents in an efficient and regulated manner requires switching power converters. The DC/DC buck converter chops the input DC voltage using a series input switch, and the chopped voltage is filtered through the L-C low-pass filter to extract the average output voltage. The diode provides a path for the inductor current when the switch is off for part of the switching period. The output voltage is this less than or equal to the input voltage. The objective of this experiment is to study different characteristics of a buck converter. The step-down capability of the converter will be observed under continuous conduction mode (CCM) where the inductor current is non-zero. Open-loop operation with a manually-set duty ratio will be used. An approximation of the input-output relationship will be observed.

  • Electrical Engineering

    09:34
    Flyback Converter

    Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

    A flyback converter is a buck-boost converter, which can both buck and boost. It has electrical isolation between the input and the output using a coupled inductor or a "flyback transformer." This coupled inductor enables a turns ratio that provides both voltage step-up and step-down capability, like in a regular transformer but with energy storage using the air-gap of the coupled inductor. The objective of this experiment is to study different characteristics of a flyback converter. This converter operates like a buck-boost converter but has electrical isolation through a coupled inductor. Open-loop operation with a manually-set duty ratio will be used. An approximation of the input-output relationship will be observed.

  • Electrical Engineering

    10:49
    Single Phase Transformers

    Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

    Transformers are stationary electric machines that step up or down AC voltage. They are typically formed of primary and secondary coils or windings, where the voltage on the primary is stepped up or down at the secondary, or the other way around. When a voltage is applied to one of the windings and current flows in that winding, flux is induced in the magnetic core, coupling both windings. With an AC current, AC flux is induced, and its rate of change induces voltage on the secondary winding (Faraday's law). Flux linkage between both windings depends on the number of turns of each winding; therefore, if the primary windings have more turns than the secondary winding, voltage will be higher on the primary than on the secondary, and vice versa. This experiment characterizes a single-phase transformer by finding its equivalent circuit parameters. Three tests are performed: open-circuit test, short-circuit test, and the DC test.

  • Electrical Engineering

    11:14
    Single Phase Rectifiers

    Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

    A DC power supply is generally considered to be a device that supplies DC, or unidirectional, voltage and current. Batteries are one such power supply, however, they are limited in terms of lifetime and expense. An alternative method to providing unidirectional power is to transform AC line power to DC power using a rectifier.

    A rectifier is a device that passes current in one direction, and blocks it in the other direction, enabling the transformation of AC to DC. Rectifiers are important in electronic circuits as they only allow current in a certain direction after a certain threshold forward voltage across them is overcome. A rectifier can be a diode, a silicon controller rectifier, or other types of silicon P-N junctions. Diodes have two terminals, the anode and the cathode, where current flows from anode to cathode. Rectifier circuits use one or more diodes that change AC voltages and currents, which are bipolar, to unipolar voltages and currents that can be easily filtered to achieve DC voltages and currents.

  • Electrical Engineering

    10:27
    Thyristor Rectifier

    Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

    Similar to diodes, thyristors, also called silicon controlled rectifiers (SCRs), pass current in one direction from the anode to cathode, and block current flow in the other direction. However, current passage can be controlled through a "gate" terminal, which requires a small current pulse to turn on the thyristor so it can start conducting. Thyristors are four-layer devices, composed of alternating layers of n-type and p-type material, thereby forming PNPN structures with three junctions. The thyristor has three terminals; with the anode connected to the p-type material of the PNPN structure, the cathode connected to the n-type layer, and the gate connected to the p-type layer nearest the cathode. The objective of this experiment is to study a controlled thyristor-based half-wave rectifier at different conditions, and understand how different timings of the gate pulse affect the DC output voltage.

  • Electrical Engineering

    09:51
    Single Phase Inverter

    Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

    DC power is unidirectional and flows in one direction, whereas, AC current alternates directions at a frequency of 50-60 Hz. Most common electronic devices are designed to run off of AC power; therefore an input DC source must be inverted to AC. Inverters convert DC voltage to AC through switching action that repeatedly flips the polarity of the input DC source at the output or load side for part of a switching period. A typical power inverter requires a stable DC power input, which is then switched repeatedly using mechanical or electromagnetic switches. The output can be a square-wave, sine-wave or a variation of a sine-wave, depending on circuit design and the user needs. The objective of this experiment is to build and analyze the operation of DC/AC half-bridge inverters. Half-bridge inverters are the simplest form of DC/AC inverters, but are the building blocks for H-bridge, three-phase, and multi-level inverters. Square-wave switching is studied here for simplicity, but sinusoidal pulse width modulation (SPWM) and other modulation and switching schemes are typically used in DC/AC inverters.

  • Electrical Engineering

    09:28
    DC Motors

    Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

    The DC machine operates with DC currents and voltages as opposed to an AC machine, which requires AC currents and voltages. DC machines were the first to be invented and utilize two magnetic fields that are controlled by DC currents. The same machine can be easily reconfigured to be a motor or generator if appropriate field excitation is available, since the DC machine has two fields termed field and armature. The field is usually on the stator side and the armature is on the rotor side (opposite or inside-out compared to AC machines). Field excitation can be provided by permanent magnets or a winding (coil). When current is applied to the armature or rotor coil, it passes from the DC source to the coil through brushes that are stationary and slip rings mounted on the rotating rotor touching the brushes. When the rotor armature coil is a current-carrying loop, and is exposed to an external field from the stator or field magnet, a force is exerted on the loop. Since the loop is "hanging" on both sides of the motor using bearings, the force produces a torque that will rotate the rotor's shaft rather than move it in any other direction. This rotation causes the magnetic fields to align but at the same time, slip rings switch sides on the brushes, or "commute," and this is what is known as the commutation process.

  • Electrical Engineering

    11:17
    AC Induction Motor Characterization

    Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

    The objectives of this experiment are to find the equivalent circuit parameters of a three-phase induction motor using the per-phase equivalent circuit and tests similar to those used in transformer characterization. In electrical engineering, an equivalent circuit (or theoretical circuit) can be determined for a given system. The equivalent circuit retains all characteristics of the original system, and is used as a model to simplify calculations. Another objective is to operate the motor in the linear torque-speed region.

  • Electrical Engineering

    10:26
    VFD-fed AC Induction Machine

    Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

    Variable frequency drives (VFDs) are a type of adjustable speed drive, which are becoming standard equipment to power most AC induction motors. VFDs are common in industrial and automation applications and typically provide robust control of the motor in speed, torque, or position modes. The VFDs tested and simulated in this experiment focus on speed and open-loop control with constant voltage to frequency ratio (V/f) control. The induction motor typically operates at a rated stator flux, and this flux is approximately proportional to the V/f ratio. To maintain constant stator flux, the voltage and frequency applied to the stator are maintained at a constant ratio, which is the V/f ratio. The VFD used in this experiment is a 1 hp Yaskawa V1000 drive, but the procedure applies to most commercially available general purpose drives.

  • Electrical Engineering

    09:01
    AC Synchronous Machine Synchronization

    Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

    Three-phase wound-rotor synchronous generators are the main source of electrical power worldwide. They require a prime mover and an exciter in order to generate power. The prime mover can be a turbine spun by fluid (gas or liquid), thus the sources of the fluid can be water running off a dam through a long nozzle, steam from water evaporated using burned coal, etc. Most power plants including coal, nuclear, natural gas, fuel oil, and others utilize synchronous generators. The objective of this experiment is to understand the concepts of adjusting the voltage and frequency outputs of a three-phase synchronous generator, followed by synchronizing it with the grid. The effects of field current and speed variations on the generator output power are also demonstrated.

  • Electrical Engineering

    11:18
    AC Synchronous Machine Characterization

    Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

    Three-phase wound-rotor synchronous motors are less popular than permanent magnet rotor synchronous motors due to the brushes required for the rotor field. Synchronous generators are much more common and available in most existing power plants, as they have excellent frequency and voltage regulation. Synchronous motors have the advantage of almost 0% speed regulation due to the fact that the rotor speed is exactly the same as the stator's magnetic field speed, causing the rotor speed to be constant, irrespective of how much the motor's shaft is loaded. Thus, they are very suitable for fixed speed applications. The objectives of this experiment are to understand the concepts of starting a three-phase synchronous motor, V-curves for various loads where the load affects the motor power factor, and the effect of loads on the angle between the terminal voltage and back e.m.f.

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