Short Circuit System

As botli processes, reduction and oxidation, take place on tlie same electrode surface (a short-circuited system), it is not possible to directly measure tlie corrosion current. Experimentally, only tlie sum of tlie anodic and catliodic... 

Conventional methods for establishing the existence of active transport are to analyze the effects of metabolic inhibitors, to correlate the rate of metabolism with the extent of ion flow or the concentration ratio between the inside concentration and the outside concentration of the cells, and to measure the current needed in a short-circuited system having identical compositions solution on each side. Measurements indicate that the flow contributing to the short-circuited current, and ary net flow detected are due to active transport, since the electrochemical gradients of all ions are zero (A // = 0, c0 = c,). 

Upon further polarization, the anodic and cathodic curves intersect at a point where the potentials are the same (Ecorr) and the external current is maximized. The electrode potentials at this point are numerically equal for copper and zinc and the current is /con-Physically, this point on Fig. 3.5 is attained when the load in the external circuit is extremely low or when the system is short circuited. Systems undergoing corrosion can be explained on a very similar basis. The measured output potential in a corroding system, often called the mixed potential or the corrosion potential (Ecorr)> is the potential at the intersection of the anodic and the cathodic polarization curves. 

Procedure. Titrate 5 mg of thiol sulphur in 100 ml. of 95 per cent ethanol, containing 0-25 n ammonia and 0-1 N ammonium chloride, at the potential of a saturated calomel electrode (a short circuit system) with an aqueous solution of 0-005 M silver nitrate. Deoxygenate both solutions. 

The number of unsaturated bonds can be determined by a titration with a standard solution of bromine dissolved in glacial acetic acid. The sample is also dissolved in glacial acetic acid to which sodium and ammonium acetate are added, so as to give a final concentration of 0-5 and OT M respectively. The cathodic current of bromine is measured with a short circuit system using a rotating platinum indicator, and a calomel or chloranil reference electrode at the potential of the reference electrode. Several unsaturated open chain compounds and terpenes have been titrated in this way.( ) Other modifications of this technique have been used to determine the amount of unsaturation in fats in methanolic solutions. The standard solution of bromine is prepared in methanol, saturated with sodium bromide, and the methylester of stearic acid is added to suppress the maxima. If the methanolic solution is acidified, OT M potassium bromate with OT M sodium bromide can be used instead of bromine. The bromine generated in homogeneous solution can be used to analyse xylenol and cresol fractions of coal-tars. Other phenolic compounds may be similarly determined. The method was used for the determination of small concentrations of styrene... 

It is easy to notice, that the protection against a short-circuit failure in the X-ray tube circuit implements due to the "soft" outer characteristic of the apparatus main circuit. The overvoltage protection at emergencies in the control system happens due to the redistribution of the magnetie flow, created by power winding I, between the 3,6 control yokes. Therefore the voltage on the X-ray apparatus anode drops approximately two times. 

Protection of the electrical supply system in the event of a motor or motor-feeder short circuit. The fault must be cleared from the rest of the system to prevent further trouble,... 

It is observed that there may be asymmetry in the system as long as the short-circuit condition lasts, as illustrated in Figure 13.20, i.e. up to the opening of the interrupting device. (For opening times of interrupters, refer to Table 19.1.) But the content of the asymmetry may be quite feeble after three or four cycles. Flowever. if the short-circuit condition still prevails, such as when... 

The generation of an asymmetrical current on an a.c. system, leads to the inference that a short-circuit condition will give rise to a d.c. component due to a shift in its zero axis. During the sub-transient state the value of the asymmetrical current will be the phasor sum of the symmetrical /sc and the asymmetrical current components. For details refer to Section 14.3.6. 

For more clarity we have reproduced in Figure 14.3 an actual test circuit and in Figure 14.4, the oscillograms of the test results of a short-circuit test successfully carried out on an LT power distribution panel (Figure 14.8) for a system fault level of 50 kAfor 1 second, at CPRI (Central Power Research Institute). From a study of these oscillograms (Figure 14.4), we can infer the following test results ... 

In most applications, a bar primary CT is generally used and a normal CT may be suitable. But for too small ratings, where the use of a wound primary CT is imperative, short-circuit effects must be considered, except the CTs for an LT system, where the fault level for such small ratings may be very low and may not matter (Section 13.4.1(5)). For applications on an HT system, where a wound primary CT is imperative, choice of a CT from standard wound primary CTs may still be possible, meeting the minimum requirements of class of accuracy, VA burden and short-time rating. lEC 60044-1 indicates for measuring and protection CTs the maximum short-time factors (STF) that can be obtained economically for a normal wound primary CT where... 

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