Step voltages

Maximum touch and step voltages of a grounding station 22/712... 

The safe step voltage, j, should not be more than the total resistance to ground through the body, f 2isb (Section 22.10.1) X safe body current, 4, as a function of time, where... 

The step voltage falls sharply at higher depths. 

After the final designs are complete it is recommended that the actual touch (actual) and step voltage (actual) are rechecked for both power plant and switchyard areas separately, to ensure that they are within the tolerable limits as determined above. After the ground stations have been finally installed the actual step and touch voltages must be measured to verify the designs. 

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. 

Exposure of a human body to touch and step voltages and methods to deal with these are also covered. Grounding and ground fault protection schemes are described in detail with illustrations to help an engineer to select the most appropriate grounding method and ground fault protection scheme for a machine or system. 

The inverters are either voltage source or current source (see Figure 7-7a and b). There are other variations, but they apply to drivers smaller than the ones used with compressors. However, pulse-width-modulated (PWM) (see Figure 7-7c), transistorized units are less complicated and are relatively maintenance-free with reliable units available to at least 500 hp. For all but the smaller compressors, the current source inverter is the one typically used. With a six-step voltage source, a rule of thumb has been to size the motor at two-thirds of its rating so as not to exceed the insulation temperature rise. For current source motors, the output torque is not constant with decreased speed, which fortunately is compatible with most compressors, as torque tends to follow speed. For current source drives, one needs to upsize the motor captive transformer by approximately 15% to account for harmonic heating effects. 

Figure 94 (a) The SCL transient currents for various normalized trapping times (R = Ttrap/t0) as calculated from theory (see Ref. 26) R = oo denotes the trap-free case is the steady-state current without trapping, (b) t trap-free SCL transient current injected from ITO under a positive step voltage applied to an IT0/PPV/TPD PC/A1 device jScl corresponds to in part (a). Bottom TOF photocurrent transient for holes generated by a light pulse at the A1/(TPD PC) interface (the negative polarity applied to ITO). (From Ref. 428). 

Figure 14 Separation of the test mixture using a step voltage gradient and a short packed column. Capillary 75 mm i.d., 8 cm packed with Dionex AS9-HC (8.5 cm to detector, 34.5 cm total). Mobile phase 2.5 mM hydrochloric acid (titrated to pH 8.05 with Tris). Flow is a combination of 10-bar pressure and EOF with -30 kV added at 1.3 min. All other conditions as given in Figure 1. (Reprinted from Ref. 75, with permission.)...

Fig. 5.17 Transient currents from step voltages across (a) a loss-free dielectric, (b) a conductor, (c) a dielectric with dipolar relaxation, and (d) a dielectric with dipolar relaxation and conduction.

When the conductivity in question is very low, there are other experimental difficulties too. On application of a step voltage across a specimen, the initial current may be dominated by a displacement current due to polarisation of the material. Since some dipole orientation may be very slow to reach equilibrium, the displacement current can swamp a small conduction current for a long... 

Results for a 20 pm thick sample of polycarbonate containing 50 mass% TPD for a field of 1.5 x 107Vm-1 at 296 K with charges injected from an indium tin oxide (ITO) electrode coated with a 0.1 pm thick layer of PPV are shown in Fig. 8.30(b). The limiting current is close to the trap-free SCLC, indicating that the PPV-coated ITO acts as an efficient hole-injecting electrode. The lower curve is the TOF transient recorded under identical conditions. The arrow on the lower curve indicates the transit time and that on the upper curve is 0.8 of this value. The step-voltage response is therefore close to the theoretical prediction. 

In Chapter 1 we had discussed a simple series resistor-capacitor (RC) charging circuit. What we were effectively doing there was that by closing the switch we were applying a step voltage (stimulus) to the RC network. And we studied its response — which we defined as... 

But sometimes, we do want to know what happens at the moment of application of a stimulus — whether subsequently repetitive, steady, or otherwise. Like the case of the step voltage applied to our RC-network. If this were a power supply, for example, we would want to ensure that the output doesn t overshoot (or undershoot ) too much. 

DC Transient-Current Method. In this method a step voltage is applied to the sample and the current response is measured by a fast-response electrometer. For the single- relaxation-time model, the current response would be given by equation (7-9). In recent years this method has been of renewed interest because with the advent of modem computing methods, it is possible to Fourier-transform the response in the time domain to obtain the frequency response. Several Fourier-transform dielectric spectrometers have been designed. We may note the one of historical significance due to Johnson et al.15, as well as modem commercial instruments.16 The method has the great... 

Fig. 9.7. Example of multi-step voltage-limited CC charge ( pseudo-CC ) with a 2.45 VPC step trigger and pure CC finishing step (no voltage limit).

Figure 3. Admittance data from a K +-conducting membrane and curve fits (solid curves) of eqs 2, 3, and 4 with Y /jf,) = 0 plotted in the complex plane [X(f) vs. R(f)] as impedance [Z(jf) = R(f) + jX(f) = Y 1(jf/)] loci (400 frequency points) over the 12.5 5000-Hz frequency range. These data were acquired rapidly as complex admittance data, as illustrated in Figure 1, at premeasurement intervals of 0.1 and 0.5 s after step voltage clamps to each of the indicated membrane potentials from a holding of —65 mV. The near superposition and similarity in shape of the two loci at 0.1 and 0.5 s, at each voltage, indicates that the admittance data reflect a steady state in this interval after step clamps. Axon 86-41 internally perfused with buffered KF and externally perfused in ASW + TTX at 12 °C. The membrane area is 0.045 cm2.

The appearance of the admittance-derived Tn(V) curve is qualitatively similar to that produced by a HH analysis of large step-voltage responses. However, a quantitative comparison (12) showed significant discrepancies between the values at corresponding potentials and variability in the discrep-... 

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