Voltage overvoltage

Electrolysis is employed industrially to isolate elements from their ores. In some cases, a product (usually a gas) may form so slowly (high activation energy) that a higher-than-expected voltage (overvoltage) must be applied. (Section 21.7)... 

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. 

Fig. 5. Energy requirements of the HaH-Hfiroult cell (23—25). E, decomposition of alumina Eg, depolarization by carbon E, anode overvoltage E, counter electromotive force E, bath voltage drop E, bath bubble voltage F/, anode voltage drop Eg, cathode voltage drop E, external voltage drop ...

Seconday Current Distribution. When activation overvoltage alone is superimposed on the primary current distribution, the effect of secondary current distribution occurs. High overpotentials would be required for the primary current distribution to be achieved at the edge of the electrode. Because the electrode is essentially unipotential, this requires a redistribution of electrolyte potential. This, ia turn, redistributes the current. Therefore, the result of the influence of the activation overvoltage is that the primary current distribution tends to be evened out. The activation overpotential is exponential with current density. Thus the overall cell voltages are not ohmic, especially at low currents. 

Overvoltages and voltage surges caused by disturbances in an LT system 6/130... 

The motor may also fail due to system overvoltages, such as during a fast bus transfer (Section 7.19) or due to voltage surges (Section 17.3). 

Momentary overvoltages due to a sudden load rejection, which may overspeed the generator and develop higher voltages or... 

This class may be selected for protective devices where their operation does not depend upon the phase relationship between the voltage and the cuiTcnl phasors,. such as for an overvoltage, overcurreni or an undervollage protection. For instance, a residual VT should have this accuracy class. 

In actual operation, disturbances on a power system, causing sudden changes in the system parameters, are quite frequent and may generate temporary overvoltages and voltage surges, as summarized above. The system disturbances may be of two types, external or internal, as explained below. 

The general practice to express an overvoltage is in p.u. This abbreviation will be used frequently in our discussions. One p.u. is the maximum voltage between the phase and the neutral, i.e. 

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