Short-time duties

Rating of short-time motors 3/59 Equivalent output of short-time duties 3/63... 

If a short-time duty is performed on a Continuous Maximum Rating (CMR) motor with some no-load or idle running, the temperature rise 0 may not reach its maximum value, 0 , us shown in curve (c) of Figure... 

I. A CMR motor therefore can be operated at higher outputs on short-time duties as shown in curve (d). The extent to which a CMR motor cun be over-rated to perform a particular short-time or intermittent duty is considered in the follow ing example. While evaluating the rating for such duties, the heat during start-up and during braking and their frequency of occurrence should be considered. 

J)- Thermal curves for intermittent loads, the average heating not exceeding the permissible temperature rise Figure 3.16 Equivalent output of short-time duties... 

Figure 3.17 Determining the motor rating (CMR) for a short-time duty...

In this case the regulating resistance grids arc normally continuous duty, unlike those for stail-up, which arc short-time duty. Equations (5.1 a-d) can be used, for determining the total rotor circuit resistance for a particular speed variation, i.e. 

Duty cycles Continuous duty (CMR) (S ) Periodic duties Factor of inertia (FI) Pleating and cooling characteristic curves Drawing the thermal curves Rating of short motors Equivalent output of short time duties Shock loading and use of a flywheel... 

The mechanical engineer will also advise on the necessary duplication of machinery, e.g. continuous duty, maximum short-time duty, standby duty and out-of-service spare machines. He will also give some advice on the proposed method of operation and control of rotating machines, and this may influence the choice of cooling media, construction materials, types of bearings, ducting systems, sources of fresh air, hazardous area suitability, etc. 

Note Short-time loading is higher than the CMR and it is true lor all duties S2 - S o... 

If the cycle has a short-time rating, with a period of energization and one of rest, the motor will obviously cool during the de-energizing period, and depending upon the peak load and tlie rest periods, a comparatively lower output motor can perform duties at higher loads. The equivalent output for the load cycle of Figure 3.16 is... 

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. 

Since will be too low (< 5 ms for a 50 Hz system) 1. will be much less than 7% of 1 in all situations. To assign a short-time rating to the protected devices and components in such cases is therefore of little relevance. As noted above, current is the cause of heat, for which is assigned the thermal duty of a current-carrying device, component or part. Also note the following ... 

As a conclusion, it can be said that TV-systems are not suited for time-resolved measurements with time frames as short as milliseconds. Even the fast scan is still much too slow to achieve an acceptable duty cycle with short time frames. 

The specific reference to the Home Guard in this order is an implicit recognition of its reputation, if not notoriety, for over-zealous officiousness, already prominent so shortly after its foundation. It was not uncommon for serving Army Officers, policemen and ARP wardens about their night-time duties to be stopped and searched by Home Guard volunteers, or even for them to be stopped repeatedly on the same night by the same volunteer. 

The reboiler duty Q2 has a strong and fast effect on all impurities (Figure 17.18b). The curves show two competing effects, stripping-out and accumulation through recycles. The first is faster at very short time, but is balanced by the second at longer times. The most important effect is on the impurity Ii, both dynamically and at steady-state. 

Two employees of a North Carolina company were helping to unload a truck on a warm sunny day when they inadvertently punctured a container of an unknown liquid chemical. A quick check of the contents revealed they had spilled a concentrated pesticide, intended to be mixed with water before application. Their first response was to grab a garden hose and use the water pressure to push it to one side. In a short time, they began to feel faint and short of breath, so they decided to ask for help. Since no one at the facility had specialized training to deal with the spill, the manager on duty called the local fire department. 

The community amongst the primitive Christians was voluntary, not coactive. They brought their goods and laid them at the apostles feet. They were not enjoined to bring them it was the effect of their charity and heavenly mindedness which the blessed apostles begot in them and not the injunction of any constitution, which, as it was but for a short time done (and in but two or three places) that the scripture makes mention of, so does the very doing of it there and the apostle s answer to him that detained a part, imply that it was not esteemed a duty but reckoned a voluntary act occasioned by the abundant measure of faith that was in those Christians and apostles. ... 

When used in conjunction with rechargeable batteries, can supply energy for short time, reducing battery cycling duty and extending life... 

Sound level meters measure noise only at a given point at the time of observation. If the noise being measured is constant in both space and time, meters will give an accurate representation of the situation. However, if the sound level changes with time and location (for instance, as an operator moves around), it will be necessary to record either the sound level manually using short time intervals (5 to 10 s) or the noise data for later analysis of the time history of the noise. The second approach is preferable when a worker s noise exposure is related to duty cycles or product flow. In this case, extrapolations can be made on the basis of total day production to determine the noise exposure of an employee over a full day. 

Duty Specific controller functions. Continuous constant load, indefinitely long time period. Short time constant load, short or specified time period. Intermittent varying load, alternate intervals, specified time periods. Periodic intermittent duty with recurring load conditions. Varying varying loads, varying time intervals, wide variations. 

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