Over-voltages

IEEE, Results of an investigation on the over voltages due to a vacuum circuit breaker when switching an H. V. motor, IEEE 85 SM 370-2(1985). 

Kaufmann, R.H. and Halberg, M.H., System over- voltages, causes and protective measures. 

Switching over voltages phenomena in MV bwiichgears. Workshop on MV Switchgear and CPRI. 1-43. (1987). 

Spark gap These have a pair of conducting rods with an adjustable gap, depending upon the spark over voltage of the arrester. Precise protection is not possible, as the spark-over voltage varies with polarity, steepness and the shape of the wave. These arresters are also now obsolete for the same reasons. 

To apply the corrective measures to limit the Ferranti effect it is essential to first study its over voltage (OV) status at the far end of the line. Consider the earlier system TZ of 400 kV 50 Hz and draw a voltage profile as illustrated in Figure 24.17, for the voltages worked out as in equation (24.7), at different lengths of the line. The voltages, for the sake of simplicity, are also shown in Table 24.4. 

Such protection can be used on a power transformer, a motor or generator, or a single feeder. In addition, other types of relay are used for particular applications (e.g. transformer Buchholz gas, neutral voltage displacement and over-voltage). 

Investigation of alloying components and their effect on over voltage... 

Into a freshly charged cell, as previously prepared, place 300 milliliters (10.1 fluid oz.) of ice-cold tap water into the anode compartment (clay pot), and then add and dissolve 50 grams (1.8 oz.) of sodium chlorate into this water. Thereafter, place 500 milliliters (17 fluid oz.) of ice-cold tap water into the cathode compartment, and then add and dissolve 50 grams (1.8 oz.) of sodium chlorate there into. Thereafter assemble the cell as illustrated below, and then place the cell into an ice bath, and then begin the electrolysis process. The desired dimensions of the titanium electrodes may vary, but it is recommended to use rectangular bars of 10 to 15 millimeters in width of surface area (0.39 inches by 0.59 inches), and the electrodes should be placed about 127 millimeters apart (5 inches). The current should be 1.5 to 2.7 volts DC current at about 50 amps. Over voltage should be minimum, and the cell temperature should be kept below 5 Celsius at all times. Electrolyze the solution for about 18 to 24 hours. 

CCEs have also been used in conjunction with enzymes. Glucose oxidase was encapsulated within the methyl silicate (or silica)-graphite composite [216, 220]. Reduced oxygen from the enzymatic reaction results in the production of H2O2, which is oxidized at the electrode. Palladium and rhodium catalysts have been added to the electrode to help lower the over voltage required for hydrogen peroxide oxidation [219, 221]. Glucose oxidase and horseradish peroxidase have been simultaneously entrapped within a CCE for a biosensor that does not require a... 

Short-term measurements are based on the relation between current and voltage. It is possible to observe the system and wait for a defined event (e.g., open-circuit operation, starting of an engine, etc.), or it is possible to inject a defined current and measure the voltage response. Most methods are based on an electric circuit that consists of a voltage source, an over-voltage network, and a side-reaction current (Fig. 8.9). 

Over-current and over-voltage conditions should also be detected by the safety-management system. 

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