Capacitance phase

The tangent of the capacitance phase angle has been shown to be a measure of the completeness of the anneal (2.) Based on this technique, we have data which would predict 30 minutes at 300°C is sufficient to obtain optimum dielectric properties. However, we have found chronogravimetric analysis of polyimide films to be more useful in defining optimum anneal conditions. 

L1, L2, L3 phase conductors 1/1, 1/2, 1/3 voltages phase to neutral C1, C2, C3 capacitances phase to earth PE protective earthed conductor RF earth fault resistance UN, PE voltage between neutral N and PE in case of an earth fault... 

The plot of impedance Z = R+jX with R = Rg and X = j(coLs - ) is shown in terms of impedance magnitude, Z = y/R +X, and phase, tan cp = X/R in Fig. 9. The values given in Table 1 for a 10 MHz AT-cut quartz crystal have been taken for computation. The quartz impedance is inductive (phase shift + 90°) between/s and/p, and capacitive (phase shift -90°) outside this interval. The phase shift is very steep. 

Historically, the first and most important capacitance method is the vibrating capacitor approach implemented by Lord Kelvin in 1897. In this technique (now called the Kelvin probe), the reference plate moves relative to the sample surface at some constant frequency and tlie capacitance changes as tlie interelectrode separation changes. An AC current thus flows in the external circuit. Upon reduction of the electric field to zero, the AC current is also reduced to zero. Originally, Kelvin detected the zero point manually using his quadrant electrometer. Nowadays, there are many elegant and sensitive versions of this technique. A piezoceramic foil can be used to vibrate the reference plate. To minimize noise and maximize sensitivity, a phase-locked... 

Approx. Current rating capacitance per Direct in In duct phase ground... 

If Cg = electrostatic or leakage capacitance to the ground per phase, providing the return path to the fault current / , in the event of a ground fault on the system. This current will be capacitive in nature. 

This is same as Cor resistive impedance. In these two cases, when the external impedance is resistive or capacitive, there is no excessive v oltage rise across the healthy phases of the system beyond The voltage... 

The phenomenon of saturation of the magnetic core of such a device during normal operation and its resonance with the ground capacitive reactance, X. , is known as ferro-resonance. It would have the same effect on the healthy phase,s/system as in (i) above. 

If = fault current through the healthy phases due to ground capacitive reactance X , then the current through the ground capacitive reactances... 

Tlte value of / can thus be varied in magnitude and phase displacement to suit a particular location of installation or pi otective scheme by introducing suitable R and /Y into the neutral circuit. When the impedance is inductive, the fault current will also be inductive and will offset the ground capacitive current /". In such a grounding, the main purpose is to offset the fault current as much is possible to immunize the system from the ha/ai ds of an arcing ground. This is achieved by providing an inductor coil, also known as an arc suppression coil, of a suitable value in the neutral circuit. 

L = inductor coil inductance in henry Cj, = ground capacitance per phase in farad and f = system frequency in Hz... 

L - iiuluctor coil indtictance in henry = ground capacitance )er phase in farad atid / = system fret uency in Hz... 

To determine the basic parameters of a 6% series reactor and its capacitive compensation, consider Example 23.6 with 3000 kVAr banks (1000 kVAr per phase) rated for 33.4 kV ... 

There will be three such parallel circuits to make it 60 kVAr. To calculate equivalent capacitance and reactance in delta, we may convert it into an equivalent star as shown in Figure 23.24(b) by maintaining the same line parameters as in Figure 23.24(a). If the impedance of each phase in delta is Z, then to maintain the same steady-state line current, 4 , in star also let the equivalent impedance of each phase in star be Z. Then,... 

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