Source of supply

Shaped products used for adsorbent purposes are generally less sophisticated and therefore less expensive than catalytic products. In 1985, it was reported that 10,000 t/yr of activated alumina adsorbents were produced in the United States. North American producers of Bayer process-based activated aluminas include Alcoa, La Roche (formerly Kaiser Chemicals), Discovery, and Alcan. Gel-based activated aluminas are produced by La Roche, Vista, and several of the major catalyst manufacturers. In Europe, principal sources of supply are Rhc ne-Poulenc and Condea. 

The benzene feedstock contains nonaromatics, ranging from 50 to 2000 ppm, depending on the source of supply. The nonaromatics do not directly contaminate the product because their boiling points are typically 40—60°C lower than that of ethylbenzene. However, part of these nonaromatics... 

An in vitro ensymatic synthesis of sucrose was carried out ia 1944 (5). A successful chemical synthesis was performed by Lemieux and Huber (6) ia 1953 from acetylated sugar precursors. However, the economics and chemical complexities of both processes make them unlikely sources of supply. 

These are series motors and are relatively compact and lightweight compared to an a.c. motor. The use of such motors is therefore common for hand tools and home appliances and also for such applications that require a high speed (above 3200 r.p.m.) which is not possible in an a.c. machine. Likely applications are polishers, grinders and mixers. This motor runs equally well on both a.c. and d.c. sources of supply. 

The pay-off roll is unwound by the tension of the sheet, caused by the speed of the recoiler at the finishing line and the bridles positioned at different locations. The pay-off roll motors therefore operate in a regenerative mode and can feed-back the energy thus saved to the source of supply, if desired. This can be done by using a full-wave synchronous inverter, as shown in Figures 6.31 or 6.33. 

Regenerative braking If the motor be run beyond synchronous speed by some external means it will work as a generator and feed back useful energy to the supply system. It will draw only the necessary excitation current, / , for the generator action from the source of supply. In such a condition, the motor... 

In this method simultaneous readings of voltage at motor terminals and current are taken while using a d.c. source of supply and the resistance of Ihe windings is calculated. Current must be restricted to 10% of the rated current of the windings. Errors introduced into the measurement, by the resistance of leads and contacts must be compensated. 

These may receive power from one or more sources of supplies and distribute them to different load centres, which may be a motor control centre (MCC) or a distribution board (DB), as illustrated in Figures 13.2... 

Nole The actual fault at any point will be much lower than calculated with the above impedances 41.42. 4a and Z14 because other impedances from the source of supply (Transformers in the above case) up to the point of fault, are not considered while designing a system. 

A transformer is not a source of supply (it only transforms one voltage to another) but it is considered so, in terms of fault level calculations. In fact, it provides a means to add to the impedance of a circuit on the lower voltage side, and limits the fault level of the network to which it is connected. One will appreciate that the capacity of the actual source of supply, on the higher voltage side, will be much larger. On the LV side it is controlled by the impedance of the transformer. It is customary to consider this impedance to determine the fault level on the LV side. The fault level is measured as the dead... 

The philosophy to assume the impedance of the source of supply (generator or a transformer) as the impedance of the faulty circuit may be far from reality and may give a very high fault current. In actual operation, the fault intensity may be far less, as every device and component connected in the circuit will tend to add to the effective impedance of the faulty circuit and limit the magnitude of the fault current. Figure 13.15 also subscribes to this theory. But it is customary to design the systems for the worst fault conditions which, in all likelihood, may not arise, and decide the protective scheme and the current settings of the protective relays for the minimum possible fault current. 

To establish the minimum fault level, impedances of the feeding lines from the source of supply up to a selected point, at which the fault level is to be determined, must be added. For a step-by-step calculation to arrive at such a fault level refer to lEC 60909 and the literature on the subject as well as the references at the end of this chapter. 

When there are more than one sources of supply, it is recommended to distribute the loads also in as many sections as the incomers, and provide a tie-circuit between every two sections, to obtain more flexibility. Now fault on one section or source of supply will not result in the loss of power to the entire system. Figures 13.16 and 13.17 illustrate this type of distribution. 

Figure 13.41 Three sources of supply and two bus couplers Figures 13.39-13.41 are mechanical interlocking schemes...

The preferred way to achieve interlocking between more than one. source of supplies is through electrical schemes only, wherever possible. They are foolproof and can also be operated remotely. Mechanical schemes are generally for smaller installations where, as a result of smaller ratings or cost considerations, a breaker is not used and that imposes a limitation on adopting an electrical interlocking scheme. 

The electrical interlocking should preferably be provided through shunt trip releases. It must have a separate a.c. or d.c. source of control supply, such that the operation of the scheme is independent of the main source of supply. For the same reason, interlocking through undervoltage (U/V) releases is not recommended as its... 

Figure 13.42 Electrical interlocking scheme for manually operated breakers for two sources of supplies...

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