Electric motor systems direct current

Power Take-Off From Engine or Transmission. This type of system is limited to tmcks and there are several take-off means available. Most are some form of electric power generation equipment, belt-driven from the engine crankshaft, which produces either a regulated a-c voltage or rectified direct current for the compressor and fan motors in the body. 

This is a very good motor for direct connection to certain loads, particularly where constant speed is required. NEMA defines it as a synchronous machine which transforms electrical power from an alternating-current system into mechanical power. It usually has direct-current field excitation by a separately driven direct-current generator or one directly connected to the motor. This motor remains synchronous with the supply frequency and is not affected by the load. Proper application requires consideration of the following ... 

The tip is first brought near to the sample via a coarse Z positioner, such as a controlled approach piezo-electric motor. This provides a 10 A step size and so is capable of very precise and controlled movement. As soon as a tunnelling current is detected, the tip is stopped and the fine control system is operated. Thus the lip is mounted on the end of a hollow, cylindrical piezo crystal, a tube scanner (a piezo-electric crystal can be made to deform under the influence of a voltage applied across it). The tube scanner has four strip electrodes on the outside, providing movement in the x and y directions (lateral movement), and one electrode covering the whole of the inside. A... 

Electrical System. The conductors in the hose-cable carry power and control signals down to the underwater vehicle and return information. The drive-pump motor is powered by three-phase, 220 V carried down three paired conductors. The solenoid valve, which controls the clean pump, is energized by 24 V direct current (DC), which is controlled on deck. The submersible pump that circulates water through in situ sensors uses 110 V alternating current (AC) power from the hose-cable. 

Most electronic equipment shares the television set s need for a number of differing voltages for the operation of individual components. This alone may be sufficient justification for the inclusion of a direct current to alternating current converter in fuel cell power systems. In addition, alternating current electric motors are more suitable in most applications. They tend to operate at a rotational speed controlled by the frequency of the current. If completely unloaded they speed up to this fixed velocity and accelerate no further. Many types of direct current motors, if operated unloaded, will continue to accelerate until they fail. A belt driven fan operated by an alternating current motor is undamaged by the failure of the belt. A direct current motor will require a special safety circuit to shut it down in case of belt failure. If the belt and the safety circuit both fail, the motor will speed up until it destroys itself. 

The produced electric power of the stack is used to power the electric motor as well as all the auxiliary components of the fuel cell system and some high voltage components of the vehicle. The current ramification to single components is provided from a power distribution unit (PDU), which is directly coimected to the electrical poles of the fuel cell stack. 

Extruder motors are usually electric, but some systems utilize hydraulic motors. For example, injection molding machines use hydraulics to develop clamp tonnage. Electric motors may be of the direct current (DC) or alternating current (AC) types. Traditionally, DC motors, which regulate speed through voltage control, have been more popular because they could provide the necessary power at a lower cost. However, recent advances in frequency control - the technique used to regulate speed in AC motors - have caused this type of motor to become more widely used. 

In this type of system the a.c. electric motor is first disconnected from its supply and a d.c. current injected into its windings for sufficiently long to stop the motor. The circuit diagram in Fig. 13. 25 shows the basic features of this type of system. Pressing the start button energises relay R and closes the direct-on-line starter contacts to supply three-phase power to the induction motor, which will then accelerate to its working speed. The starter is held on via contacts Rl. 

The direct current (DC) output of a fuel cell stack will rarely be suitable for direct connection to an electrical load, and so some kind of power conditioning is nearly always needed. This may be as simple as a voltage regulator, or a DCIDC converter. In CHP systems, a DC to AC inverter is needed, which is a significant part of the cost of the whole system. Electric motors, which drive the pumps, blowers, and compressors mentioned above, will nearly always be a vital part of a fuel cell system. Frequently also, the electrical power generated will be destined for an electric motor - for example, in motor vehicles. 

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