Contact voltage

It provides complete protection for operating personnel troni high touch or step voltages (for details on contact voltages, see Section 22.9) across the enclosure and the metallic structures caused by parasitic (electromagnetic) currents. 

Contact Voltage Protection Overvoltage protection against ... 

To prevent unacceptably high contact voltages [1,2], metal sheathing of power cables in transformer and switching stations and in the distribution network is connected to grounded installations, which have a low grounding resistance. This increases the danger of corrosion and makes corrosion protection more difficult if ... 

Fig. 14-3 Allowable contact voltages t/g as a function of the period tp of the failure current.

Tracks on wooden sleepers in ballast have a relatively low leakage load that is a hundred times smaller for a ballast bed than for tracks in the street. Good electrical insulation is, however, only ensured if the rails have no electrical contact with other installations with low grounding resistance. Overhead conductor poles should in principle not be connected to the rails. Exceptions are overhead conductor poles with electrical equipment that is connected to the rails to avoid inadmissibly high contact voltages in the event of a failure. Such overhead conductor poles should be... 

With long-term interference from operational currents of high-voltage power lines or railway power and supply lines, the contact voltage must not exceed 65 V [9]. The relevant operational current has to be stated by the operator responsible for the basic calculation. If the calculated pipeline potentials are above 65 V, connection with grounds is always necessary. 

Fig. 4. Scheme of the p—n photoefiect (according to S9>) explaining the generation of photo-emf. Note Ue = contact voltage between metal and photoconductor VD = diffusion voltage in the p—n junction Fph = reverse internal photo voltage (in relation to Vq)... 

As the equilibrium betv een the sample and the metal electrodes is maintained by the electron exchange, the equality of the electrochemical potentials of electrons in these phases leads to the follo ving expressions for the contact voltage drop and the heterogeneous thermovoltage coefficient ... 

DCP. The design of the DCP source is shown in Fig. 7.25. Two jets of argon issue from graphite anodes. These join and form an electrical bridge with the cathode, which is made of tungsten. In operation, the three electrodes are brought into contact, voltage is... 

An especially simple example of Galvani potential differences is the so-called contact potential dijference (or contact voltage) between two metals. The electrons e in a metal can be assigned a chemical potential, similar to ions in a solution. In this case it is the electron potential (We will only attach an index indicating charge such as etc., to formulas and names of substances when it is necessary or useful for clarity. Expressions like e and e will be treated as equal.) will be different depending upon the metal in question. 

Fig. 22.1 Illustration of contact voltage and electrochemical equilibrium for two metals I and II in contact.

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