Transient voltage

Whenever frequent swilehings are likely, high transient voltages may develop and harm the motor windings and the capacitors. Fast discharge facilities must be provided across the capacitor terminals to damp such transients quickly. Sec Section 25.7. for more details on discharge devices. 

To damp the transient voltages on the primary side. For markings refer to Section 15.10.1 and Figure 15.35. 15.4.5 Control transformers... 

The first few turns of the line end coil of a motor or transformer and short lengths of interconnecting cables and overhead lines and their associated terminal equipment, will thus be subject to severe stresses and will be rendered vulnerable to damage by such sleep-fronted transient voltages. 

Figure 17.14 A transient voltage stress across the first (entrance) coil of an induction motor as a function of front time (/,) and length of entrance coil (from Slamecka, 1983)...

By the immediate first current zero it is assumed that the contacts have travelled sufficiently apart to achieve the required deionization and have built up adequate dielectric strength to withstand at least 0.95 V, . If the circuit does not interrupt at the immediate current zero at a which is so near to the point of chopping Vt , the interruption will take place only by the next current zero at point h and result in another 260 strikes by then. To study more accurate behaviour of an intenupter, with the number of restrikes and the formation of the actual transient voltage waveforms on current chopping, oscillograms similar to those during a short-circuit test may be obtained (Section 14.3.6). 

The following are the recommended values of the switching transient voltages that may be considered to select the switching device ... 

The diffusivity is independent of the motion of any other species (e.g. electrons or holes) and is not influenced by internal electrical fields as in the case of chemical diffusion processes which require the simultaneous motion of electronic or other ionic species. The partial ionic conductivity of the mixed ionic and (predominantly) electronic conducting electrode is given by the product of the concentration and the diffusivity and may be related to the variations of the steady state and transient voltage ... 

Fig. 9.2 Transient voltage (a) and current (b) behavior of an SOFC cell due to changes in load resistance (Qi et al., 2005).

Transient — Subcycle disturbance in the AC waveform evidenced by a sharp, brief discontinuity of the waveform. This may be of either polarity and may be additive or subtractive from the nominal waveform. Transients occur when there is a sudden change in the voltage or the current in a power system. Transients are short-duration events, the characteristics of which are predominantly determined by the resistance, inductance, and capacitance of the power system network at the point of interest. The primary characteristics that define a transient are the peak amplitude, the rise time, the fall time, and the frequency of oscillation. Figure 1.12 shows a transient voltage waveform at the output of a power transformer as the result of switching-in of a motor containing power factor correction capacitors. 

FIGURE 1.12 Motor starting transient voltage waveform. 

Figure 3.20 shows the transient voltage response at the main electrical switchboard for a commercial building due to capacitor bank switching by the utility. A moderate... 

The a value for a ZnO varistor is 15 and ki = 9.3 x 10 31i, the potential dilference and current being measured in volts and amps respectively. Calculate the p.d. across the varistor for currents of 0.1, 1, 10, 100 and 1000 A. If a device needs protection against transient voltages in excess of 300 V, show how a varistor having the characteristic defined above can be connected to afford protection. [Answers 252, 294, 343, 400, 466 V]... 

For selection of protection components and devices, the transient voltage withstand level of equipments and circuit components must be known or conservatively estimated. For most equipment and circuit components, standards do not exist for lightning transient levels. Therefore, information available from manufacturers must be obtained, laboratory testing performed or conservative engineering estimates used. Limits for common types of equipments and components are provided for guidance. 

Nor can we rely on TVS s (silicon transient voltage suppressors) because the latter often can t even handle the type of energy a single 8/20 xs spike throws at them, least of all a succession of spikes at a certain constant rate per minute. 

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