Resistance units

Duty cycle and duty rating of resistance units 5/90... 

To obtain this rotor current, the required rotor circuit resistance can be calculated as below for the various configurations of the rotor windings and the resistance units. It may be noted that, when the resistance configuration is not the same as that of the rotor, it must... 

The simplest method is performing it manually. Once the total external resistance is known, the resistance unit can be built with a hand-operated mechanism to manually cut-off the external resistance. However, this method is suitable only for applications where the magnitude of torque during the pick-up period (torque at different... 

Consider Figure 5.5 with six steps (rotor resistance unit with five steps) and assume the maximum and minimum torques as and between each step, to suit a particular load demand (Figure 5.6(a)). Let the corresponding rotor currents be / ,a and Then by a simple hypothesis using equation (1.7). 

Consider a rotor resistance unit with five sections (total number of steps is six). Then in the previous example (Figure 5.4), considering Tj, as 200% and the corresponding slip S ai as roughly 14% then... 

The power and schematic diagram for this configuration of resistance unit is given in Figure 5.6(b). 

The resistance units, when used only for starting purpose, are in the circuit for only a short time and are thus short-time rated. However, when they are employed for speed control, braking or plugging operations, in addition to the starting duty, they may be rated for continuous duty. The resistance units are thus classified according to their duty demand, i.e. number of operations per hour (c/h). See Chapter 3 on the duty cycle. 

The following information is essential to decide the duty class of the resistance units ... 

By referring to NEMA publication ICS 2-213 with the above details, the resistance class can be found. The resistance units are designated by class number, current and resistance. NEMA tables ICS 2-213 to ICS 2-213-5 can be referred to for this purpose. 

Table 5.1 Recommended number of starling steps of a resistance unit to switch a slip-ring motor...

As in NEiVIA/ICS-2-21.1. tlie exposed conduclor resistance units can attain a temperature rise up to 375°C. whereas wlieti they are enclosed iti i housing, the tetiiperature rise must be restricted to 350°C. Accordingly, the temperature rise of the air in the vicinity of the housing, when measured at it gap of I inch from the enclosure, should not exceed I75 C. 

Very high temperature-rise permissible limits of resistance units render them unsuitable for installations which are fire-prone, such its pulp and paper industries, chemical industries, refineries, textile mills, etc. For specific iipphcations and surroundings, however, resistance design can be altered (derated) to restrict the temperature rise to within desirable limits. 

For small brake power, resistance unit is small and can be located within the main enclosure. But for higher power that may call for large resistance units and have to dissipate excessive heat, it is mounted as a separate unit. The resistance units are shod-time rated depending upon the duty they have to perform. 

Wlderstands-briicke, /. (Elec.) resistance bridge, -blichse, /. resistance box., -draht, m. (Elec.) resistance wire, -einheit, /. resistance unit. 

Now, if R is much greater than R2, we can assume that R2 is zero without compromising the accuracy of the rate calculation. In electric circuits, two resistances applied in series are simply added together in calculating the line resistance. The same is true for resistance to chemical transport. If is 1,000 resistance units and R2 is 1 resistance unit, we can ignore R2 and still be within 99.9% of the correct answer. For most environmental transport and fate computations, it is sufficient to be within 99.9% of the correct answer. 

Resistivity units are used almost exclusively to describe ultrapure water in the 10 megohm-cm to 18 megohm-cm (0.1 microsiemens/cm to 0.055 microsiemens/cm) range generated by mixed bed ion exchange and used as boiler feed water and in certain critical washing applications. 

An electrical diagram for a Pirani gauge is shown in Fig. 7.47, where V and D comprise the Pirani tube. D is the dummy filament tube that is sealed off, and V is the tube that is exposed to the vacuum system. The filaments in the V tube are connected to a bridge circuit called a Wheatstone bridge with two resistance units called Rj and R2. Power from the power supply passes across the Wheatstone bridge and is adjusted to the proper setting by R3, whose value is read on the mil-... 

As erosion progresses, by whatever means, some rock units will be more resistant than others. These will be left exposed at higher elevations, and may protect underlying rock. Depending on the orientation and shape of the resistant unit, and the agents of erosion acting on it, various landforms may develop. 

A resistant unit may also be nearly vertical, because sometimes it is formed that way. Molten rock can flow into vertical cracks deep beneath the surface, and then solidify into resistant igneous rock bodies called dikes. When surrounding rocks weather away, the resistant rocks can form vertical walls extending many miles. The Spanish Peaks of south central Colorado have classic swarms of such dikes dominating the topography. 

Electrical conductivities of typical shallow groundwater in glacial terrain (Shoot Zone gold property, northwestern Ontario) and those of common bedrock materials converted from the usual resistivity units (from Keller and Frischknecht, 1966)... 

By electrical we mean the phenomena of an induced current of electricity passing through a conductor and producing a useful effect in the form of heat or energy. An example of an electrical device would be the household iron. In this article, useful heat is produced by the passage of a current of electricity through a resistance unit imbedded within the iron itself. 

Three times the Elements must circulate in the fire resistant, united, mixed, putrefied, gloriously fixed, penetrating and cleansed, through which the Seed of Gold is being bom again, and the power is also preserved indeed in actuality. This rotation must occur three times, so that the Medicine of the third order can be seen."... 

Ni 60, Cr 16 Heating and electrical resistance units Nichrome heating elements... 

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