Cable impedance

Ambient temperature range -40°C Tamb =s +80°C Cable impedance Z = 50... 

Comparing the values in Table 25.2 to those of typical fire sets, we see that for cables longer than a few feet, the cable impedance quickly becomes much larger than that of the fire set. The cable, therefore, becomes the limiting factor in both current level and current rate of rise. 

The frequency signal is coupled out via DT2 and buffer 2, amplified and adapted to the coaxial cable impedance. The circuit is adjusted to a resonance frequency near/r. However, driving the quartz crystal at a phase of - 40° has been found to be optimal for under-liquid sensing [44]. Temperature dependence of the circuit is essentially due to the temperature dependence of the quartz crystal. Dependence on voltage supply of approximately 20 Hz has been found for a quartz crystal in air and 80 Hz in water [45]. Thus common stabilizing methods for current supply are sufficient. 

For AC systems the calculation of the short-circuit current is more complicated, particularly when generators and motors are both present in the system. The simplest calculations occur when the source of voltage can be assumed to be of constant magnitude during the fault duration. In AC systems the source impedance will be the addition of the cable impedance, busbar impedance, transformer internal impedance, the appropriate internal impedance of the generator, the appropriate internal impedance of the motors in system and the impedance of the overhead transmission lines. 

Neglect high voltage cable impedances nnless the route distances are long. 

Now add the feeder cable impedance in series to obtain the total series impedance between the MCC and the motor. Call this total impedance Zmnic-... 

In the proposed system, used as the example above, it is acceptable to ignore the cable impedance Rem + jXcm and the transformer impedance Rc + jXc for approximate calculation purposes. This is only allowable for the following reasons -... 

Keywords. Scattering parameters the input impedance of the cable Impedance Spectroscopy global optimization technique wire fault location... 

It is quite clear that cable impedance is far more complicated than overhead line impedance... 

If the lengths of the three minor sections are different, an imbalance in the induced voltages will result that causes sheath currents. However, when there are more than a few major sections, it is a common practice to design cross-bonding after considering the best balance for the induced voltage. This results in the socalled homogeneous nature of cable impedance [4,5]. 

Voltage and current deviations are expressed by using the cable impedance [Z] and admittance [Y] in the following example ... 

If the cable impedance and admittance per unit length are provided by the cable manufacturer, the data of the n-equivalent circuit can be easily calculated with the cable length. The cable impedance and admittance can be calculated by cable constants or cable parameters installed in the EMTP using the physical parameters of the cable. The parameters shown in Table 4.2 are generally provided by the manufacturer. 

The data for cable impedance and admittance calculation using the EMTP are shown in List 4.1. Table 4.3 lists the calculated cable parameters of the XLPE cables. The parameter of the positive sequence is employed for the steady-state voltage simulation. If the cable parameters are provided by the cable manufacturer, parameter calculation by cable constants or cable parameters is not required. The model parameters are obtained from the cable parameters and length as shown in Table 4.4. 

It is well-known that a semiconducting layer exists on the surface of a cable conductor, which occasionally produces a significant effect on a cable transient. The impedance of the semiconducting layer was derived in Reference 22 and may be implemented into a cable-impedance calculation. It should be noted that the admittance of the semiconducting layer is far more important than its impedance, from a transient analysis viewpoint. 

The data for the cable impedance and admittance calculation for EMTP is shown in List 4.1. Table 4.3 shows calculated cable parameters of fhe XLPE... 

Current mode preamplifiers can provide reliable counting up to 10 counts per second. They are specially suited for use with fission chambers.Voltage sensitive preamplifiers, with low gain, have high input impedance and low output impedance. They are useful for use with scintillation detectors, and also for matching of cable impedance. 

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