Motors direct torque

If a greater reduction in line current is required for starting ac motors than is possible with reac tor starting, autotrausformers may be used. Because of transformer action, the reduction in motor-starting torque is directly proportional to the reduction in line current. Table 29-3 compares reactor and autotrausformer starting with respect to... 

Direct torque measurement requires installation of strain gages on the impeller shaft or on the coupling between the motor and impeller shaft (Fig. 2). As the shaft is rotating, a device called slip ring is used to transmit the signal to the stationary data acquisition system. 

Reaction torque is a less expensive alternative to direct impeller torque and is recommended for mixers that have the motor and impeller shafts axially aligned (in this case, the reaction torque is equal to direct torque and is opposite in sign). 

Tj direct stress due to agitator mass Tp ( peak torsional shear stress in shaft due to 2.5 times motor rated torque Ts working stress... 

Duty cycle calculations where motor current is derived directly from the motor torque requirements are accurate for separately excited DC motors and synchronous motors, where torque current and armature current are equal. A double drum mine hoist operating at depth will typically have a duty cycle as represented in Figure 1. This duty cycle shows a transition from motoring to regeneration in the full speed zone of the shaft. 

Each motor is provided with an anti-reverse rotation device. The device is designed to prevent impeller rotation in the reverse direction due to each of the following conditions motor starting torque, if the motor was incorrectly wired for reverse rotation and, reactor coolant flow through the pump in the reverse direction due to the largest remaining pipe break after application of leak before break as described in Section 3.6, which could result in reverse flow through the pump. 

Battery-Electric Equipment. This is mechanically simpler in design than engine-driven equipment. Typically, the high-torque dc electric-drive motor is coupled directly to the drive axle through a constant-mesh drive train. An electronic silicon-controlled rectifier (SCR) speed-control device regulates the motor s revolutions per minute through operator foot control. Direction is reversed electrically with a delay interlock to avoid reversing motor direction while in motion. 

Reduced-voltage starting. A reactor, resistor, or transformer is temporarily connected ahead of the motor during start to reduce the current inrush and limit voltage dip. This is accompanied by reduced starting torque. For reactor or resistor start, the torque decreases as the square of current for transformer start, the torque decreases directly with line current. The reactor, resistor, or transformer can be adjusted to give a proper balance between torque and current. 

Thyristors have been replacing saturable reactors they are small, efficient, and easily controlled by a wide variety of control systems. A modern crane control drive uses fixed secondary resistors and two sets of primaiy thyristors (one set for hoist, one for lower). With tachometer feedback for speed sensing, the control for the motor provides speed regulation and torque hmiting in both directions, all with static-devices. A wide variety of control systems is possible the control should be designed for the specific application. 

Direct-current motor fields are on the stator. The rotor is the armature. The magnetic field does not rotate like the field in ac machines. Current in the armature reacts with the stator field to produce torque. 

Plugging By changing any two of the phases the motor will develop a torque in the reverse direction and provide the necessary braking. The voltage across... 

Where stray currents are involved, several measurements have to be taken that are continually changing with time, simultaneously with each other. A double recorder is most suitable for this. Linear recorders with direct indication of the measurements cannot be used for potential measurements because the torque of the mechanism is too small to overcome the friction of the pen on the paper. Amplified recorders or potentiometer recorders are used to record potentials. In amplified recorders, as in amplified voltmeters, the measured signal is converted into a load-independent impressed current and transmitted to the measuring mechanism, which consists of a torque motor with a preamplifier. The amplifier results in an... 

One of the critical measurements is torque or shaft power. A variety of methods is recognized direct methods such as torque meters or reaction mounted drivers (dynamometers) and indirect methods such as electrical power input to drive motors, heat balance, or heat input to a loop cooler. See Part 7, Measurement of Shaft Power, PTC 19.7 1961 [3] for additional information. 

The device of Figure 2-70 can also operate as a motor if a DC current is applied to the rotor windings as in the alternator and an AC current is imposed on the stator windings. As the current to the stator flows in one direction, the torque developed on the rotor causes it to turn until the rotor and stator fields are aligned (5 = 0°). If, at that instant, the stator current switches direction, then mechanical momentum will carry the rotor past the point of field alignment, and the opposite direction of the stator field will cause a torque in the same direction and continue the rotation. 

All four designs can withstand full-voltage starting directly across the power lines, that is, the motors are strong enough mechanically to withstand magnetic stresses and the locked-rotor torques developed at the time the switch is closed. 

Important advantages of direct-current motors for machine drives are the adjustable speed over a wide range, the fact that speeds are not limited to synchronous speeds, and the variation of speed-torque characteristics [8]. 

Direct Indicating Viscometer. This is a rotational type instrument powered by an electric motor or by a hand crank. Mud is contained in the annular space between two cylinders. The outer cylinder or rotor sleeve is driven at a constant rotational velocity its rotation in the mud produces a torque on the inner cylinder or bob. A torsion spring restrains the movement. A dial attached to the bob indicates its displacement. Instrument constants have been so adjusted that plastic viscosity, apparent viscosity, and yield point are obtained by using readings from rotor sleeve speeds of 300 and 600 rpm. 

Air (or Gas) Downhole Motors. Some positive displacement mud motors can be operated on unstable foam. In general, these mud motors must be low-torque, high-rotalional-speed motors. Such motors have found limited use in air and gas drilling operations where directional boreholes are required. Recently a downhole turbine motor has been developed specifically for air and gas drilling operations. This downhole pneumatic turbine motor is a high-torque, low-rotational-speed motor. 

Rotary speed of the positive displacement motor is directly proportional to flowrate. Torque is directly proportional to pressure. Thus, normal surface instruments can be used to monitor the operation of the motor downhole. 

A typical MWD bottomhole assembly used in rotary drilling is as follows from bottom to top drill bit, stabilizer, resistivity, WOB torque, directional and telemetry system, neutron-density Pe. The typical distances are seen in Figure 4-296a. When a mud motor is inserted between the lower stabilizer and the drill bit, the distances are increased as shown in Figure 4-296b. 

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