Units industry electric machines of direct current
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- Alternating Current (AC) vs. Direct Current (DC)
- Power Electronics Solutions
- Alternating & Direct Current: AC DC Electricity
- Технический перевод для специальности 1004 "Электроснабжение" (по отраслям): Учебное пособие
- What is Alternating Current (AC)?
- Electromechanical constructions
- Electric machine
- Why isn’t there a standard voltage around the world?
- SIMOTICS electric motors for industry
Alternating Current (AC) vs. Direct Current (DC)
While some may claim that direct-current DC motors are no longer relevant, that is definitely not the case. Alternating-current AC motors have certainly decreased DC motor sales, and they do confer advantages in some applications. Understanding the differences between AC and DC motors reveals where each works best and helps guide selection and specification. The basic operation of all these designs is similar. A current-carrying conductor is placed in a magnetic field, and applying power through these conductors causes motor rotation.
The difference among the designs is how the electromagnetic fields are generated and where — in either the rotor or stator. In a permanent-magnet motor, the stator is stationary and mounted to the motor frame see Image 2. It holds permanent magnets mounted in proximity to the spinning current-carrying conductors in the rotor.
Applying a voltage through brushes contacting the armature on the rotor induces the current needed to produce mechanical force, which is rotation. Connecting two wires to the motor and supplying the proper DC voltage will cause the motor to run. Shunt, series, and compound-wound or stabilized-shunt motor designs have a rotor with electrical connections through a brush and commutator arrangement.
This configuration is different in AC induction and DC brushless motors. In these motor types, the magnetic field is generated in the fixed stator. Instead of the current-carrying coils being integrated into the spinning rotor, the coils are located in the fixed stator.
Instead of the permanent magnets mounted to the stationary stator, as in a DC motor, the magnets are mounted in the rotor. This design eliminates the need to provide electrical connections through brushes in both AC induction motors and DC brushless motors because the magnetic field is rotated instead of the current-carrying conductors. The rotor with the permanent magnets is forced to move by the current and related magnetic field generated by the AC voltage fed to the stator windings.
AC motors and DC brushless motors are popular and dominate many applications formerly occupied by standard DC motors. Although many reasons explain this change, one of the most notable is that AC motors require less maintenance. All motors require at least some minimal maintenance such as keeping the fan and motor clean or greasing non-sealed bearings.
However, DC motors also require monitored and scheduled replacement of the internal brushes. This is simple to perform on small motors. However, on higher horsepower hp DC motors, brush installation procedures are more complex and must be carefully followed.
On smaller, permanent-magnet DC motors, brushes easily and quickly can be changed. They are inexpensive and only take minutes to replace. A good rule of thumb is to replace the brushes once they reach one-third of their original length or every 2, hours of use, whichever comes first.
This will ensure the brushes are always within specification. Although brush maintenance is often seen as a disadvantage compared to AC motors, brushes in DC motors continue to improve.
Designs that reduce brush wear, such as smaller diameter commutators, extend motor operating time between brush replacements. The design of the brush — including the surface area, shape and contact pressure — can also extend brush change intervals. DC motors are often selected instead of AC motors for many reasons see Table 1. DC motors and controllers are often the low-cost option when compared to inverter-duty AC motors and drives.
This is especially true for fractional hp applications. DC motors have been around for more than years, so they have a large installed base and corresponding widespread familiarity with their operation and maintenance. For existing installations, replacing a DC motor with a new one — as opposed to redesigning the motor circuit to use an AC motor and drive — is almost always less expensive, quicker and easier. Along the same lines, the simple design of DC motors makes service, maintenance and control well understood and easily supportable.
Field excitation is not required, and brush replacement and motor service are well understood by the typical industrial electrician. Even speed control is simple: Just adjust the terminal voltage, often using a local potentiometer. Additionally, until the late s, when the variable frequency drive VFD was fully developed, DC motors were the best choice for variable speed control, and this remains a well-supported option.
While the ease of controlling motor speed was a big part of its early success, several other DC motor characteristics make them the best choice in certain applications. DC motors develop full torque at low speed and across the full operating range from zero to base speed see Figure 1. This makes DC motors a good choice for driving constant-torque loads — such as conveyor belts, elevators, cranes, ski lifts, extruders and mixers. These applications are often stopped when fully loaded, and the full torque of the DC motor at zero speed gets them moving again without the need for oversizing.
DC motors have a higher power density and are, therefore, smaller than an equivalent AC motor. They have no field coil in the stator, so the field coil space is saved, reducing the overall motor size. This becomes a substantial benefit in some space-constrained applications. Smaller form factors also mean DC motors have less inertia than AC motors, offering quicker acceleration and deceleration times. This can result in a quicker cycle time on production machines that start and stop often.
Although not often needed, DC motors can be manufactured to motor power ranges of more than 4, hp, whereas standard low-voltage induction motors do not go above to 1, hp. Above that, higher voltages are needed, which can greatly complicate installation and maintenance. Modern AC motors and drives have narrowed the performance gap with their DC counterparts, but general-purpose DC motors still outperform general-purpose AC motors by many measures.
Less electronics and rectification are required to build a DC-converter drive when compared to building an AC-inverter drive. DC motors can be directly fed from different power sources, even batteries. Depending on the type of DC drive, the quality of the output power varies dramatically and is typically measured by how much ripple current is produced by the drive.
High ripple current results in increased motor heating and possibly premature brush failure. Limiting the form factor to 1. A battery is an ideal current source because its form factor is 1. A pulse-width-modulated DC drive emulates pure DC closely with a form factor of 1. A single-phase, full-wave rectified DC drive is the most common form of DC drive used in the 0.
This drive takes an AC voltage and passes the positive half of the waveform and rectifies the negative part of the waveform to produce a waveform with a form factor of 1. These drives are commonly referred to as silicon-controlled rectifier SCR drives. A simple, single-phase, half-wave rectified DC drive has a much worse form factor.
These drives only pass the positive half of the AC sine wave and have a form factor of 1. These half-wave DC drives are not recommended for use with most DC motors. DC motors are suitable for many applications — including conveyors, turntables and others for which adjustable speed and constant or low-speed torque are required. They also work well in dynamic braking and reversing applications, which are common in many industrial machines.
Their quick acceleration, stopping and reversing — along with their linear-speed torque curve — make the DC motor a popular choice in many new designs, particularly for fractional hp applications.
He started his career with Rovema Packaging Machines as the electrical engineering manager and worked there for seven years. He may be reached at jkimbrell automationdirect. Joe Kimbrell. Image 1. Despite encroachment from AC designs, DC motors remain the best choice for many industrial applications. All graphics courtesy of AutomationDirect. Proactive pump fundamentals Manage the data and maximize efficiency. Tavis McVey. Processing Staff. Sponsored by Wilden. Submersible Pump selection considerations Six essential points to consider when choosing this type pump for industrial applications.
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Power Electronics Solutions
We cover the complete range of industrial motors — synchronous as well as asynchronous: from standard electric motors through servomotors for motion control applications up to high voltage and DC motors. This is all based on more than years of experience. In the meantime, Siemens electric motors are an integral component of Digital Enterprises. Extremely reliable and flexible electric motors in the power range up to MW and above.
It extends the scope of traditional control systems to include all automation functions within a single operations and engineering environment. Actuator: In electrical engineering, the term actuator refers to a mechanism that causes a device to be turned on or off, adjusted or moved, usually in response to an electrical signal. In some literature the terms actor or effector are also used. Actuators enable computers to control complex manufacturing processes without human intervention or supervision.
Alternating & Direct Current: AC DC Electricity
The rapid growth of the electric vehicle market has stimulated the attention of power electronics and electric machine experts in order to find increasingly efficient solutions to the demands of this application. The constraints of space, weight, reliability, performance, and autonomy for the power train of the electric vehicle EV have increased the attention of scientific research in order to find more and more appropriate technological solutions. In this chapter, it proposes a focus on the main subsystems that make a zero-emission vehicle ZEV , examining current features and topological configurations proposed in the literature. This analysis is preliminary to the various electric vehicle architectures proposed in the final paragraph. In particular, the electric drive represents the core of the electric vehicle propulsion. Particular attention will be devoted to power subsystems, which are the fundamental elements to improving the performance of the ZEV. Propulsion Systems. Until recently, electric cars were only small vehicles often designed with unusual shapes, able to move almost exclusively in the city area [ 1 , 2 ]. Nowadays, electric cars are available in every size and style, often derived from the corresponding petrol models, so leading to the same internal and external fittings, load capacity, and passenger transport. Over the past few years, several legislative provisions aimed at encouraging electric mobility, pushing above all the administrations to create the boundary conditions so that the switch from a traditional vehicle to a zero-emission vehicle ZEV occurs with reduced discomfort [ 3 ].
Технический перевод для специальности 1004 "Электроснабжение" (по отраслям): Учебное пособие
In this area the client can find all that is necessary to be able to build or to construct a machine such as manual coil winder and bobbin holder, winding machines for motors and transformers and also didactic one for motors, kits for the construction of transformers and asynchronous motors with set of slides as options, impregnating machine, radial vice to hold stators, rotor support bracket, stator and rotor tester and arc welder. The latter systems are supported by auxiliary modules such as a universal power supply, an electromagnetic brake, a base to fix or couple two machines, a load cell, tachometer and torque measuring units, electrical and mechanical digital measuring units, a contact tachometer and bracket for motor kit. They are recommended for technicians and high schools. To be fixed to the bench, it allows the manual winding of motor coil or of linear windings without wire guide.
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What is Alternating Current (AC)?
DC is the kind of electricity made by a battery with definite positive and negative terminals , or the kind of charge generated by rubbing certain types of materials against each other. Certain sources of electricity most notably, rotary electromechanical generators naturally produce voltages alternating in polarity, reversing positive and negative over time. Whereas the familiar battery symbol is used as a generic symbol for any DC voltage source, the circle with the wavy line inside is the generic symbol for any AC voltage source. One might wonder why anyone would bother with such a thing as AC.
To browse Academia. Skip to main content. You're using an out-of-date version of Internet Explorer. Log In Sign Up. Principles of Electrical Machines by V. Suresh Muthusamy.
Europe and most other countries in the world use a voltage which is twice that of the US. It is between and volts, whereas in Japan and in most of the Americas the voltage is between and volts. The system of three-phase alternating current electrical generation and distribution was invented by a nineteenth century creative genius named Nikola Tesla. He made many careful calculations and measurements and found out that 60 Hz Hertz, cycles per second was the best frequency for alternating current AC power generating. He preferred volts, which put him at odds with Thomas Edison, whose direct current DC systems were volts. When the German company AEG built the first European generating facility, its engineers decided to fix the frequency at 50 Hz, because the number 60 did not fit the metric standard unit sequence 1, 2, 5. At that time, AEG had a virtual monopoly and their standard spread to the rest of the continent. In Britain, differing frequencies proliferated, and only after World War II the cycle standard was established.
Forgot your Login info? Not registered yet? One also needs a set of tools to monitor and interact with the simulator to acquire data, and visualization tools to interpret results scope, graphs, data logging, etc. The FPGA Electric Machine Library includes a power electronic and motor library that lets you simulate all components forming the electrical motor drive system.
Why isn’t there a standard voltage around the world?
The present invention relates to a brushless direct-current DC motor fan that can be driven by an alternating-current AC power source. With technology advance, current brushless direct current motor fans can be mass-production in miniature size, light, weight, and compact with stable quality. Although widely used, they are still not suitable for household use, as they can not be driven by alternating current power sources which is available at ordinary house. It is a primary object of the present invention to provide a brushless DC motor fan that is not limited to be driven by direct current such that miniature brushless DC motor can be widely and conveniently used.
Alternator - A synchronous rotating AC machine used to change mechanical power into electrical power alternating current - AC. The usual waveform of an AC power circuit is a sine wave, as this results in the most efficient transmission of energy. Ambient Temperature - Ambient temperature is the temperature of water, air or surrounding medium where the equipment is used or stored. Asynchronous speed - The speed of an AC induction motor at full load and full voltage, also defined as the rated speed.
SIMOTICS electric motors for industry
Both AC and DC have their own characteristics and provide different advantages that can be used in different situations. As the name implies direct current, DC is a form of electricity that flows in one direction — it is direct and this gives it its name. The characteristic of direct current, DC can be shown on a graph. Here the current can be seen to be seen to be either positive or negative only. Alternating current, AC is different to direct current. As the name implies, it flows first in one direction and then the other.
In electrical engineering , electric machine is a general term for machines using electromagnetic forces , such as electric motors , electric generators , and others. They are electromechanical energy converters: an electric motor converts electricity to mechanical power while an electric generator converts mechanical power to electricity. The moving parts in a machine can be rotating rotating machines or linear linear machines.