Resistance reactance

Resistive reactance Capacitive reactance Inductive reactance... 

WJieii ilie impedance is a resistive reactance The peak voltage across R will be... 

Figure 5.3 Approximate deep-bar resistance reactance curves for four-pole motors rated from 10 kW to 10 MW.

The near-rectangular line currents will produce volt-drops in the series resistance-reactance cables, overhead lines and transformers. These volt-drops will be non-sinusoidal and will distort the waveform at their intermediate points of connection. At snch points there may be a switchboard or distribntion board and the loads connected to them will experience the distorted voltage waveform. 

The mathematical relationships are similar to those of a capacitor, but the inductor s effective resistance ("reactance") is given by eqn. 10.3 on page 113. 

The accuracy of a VT depends upon its leakage reactance and the winding resistance. It determines the voltage and the phase errors of a transformer and varies with the VA on the secondary side. With the use of better core material (for permeability) (Section 1.9) and better heat dissipation, one can limit the excitation cunent and reduce the error. A better core lamination can reduce the core size and improve heat dissipation. 

For ease of analysis we have ignored (without much error) the CT s own resistance and reactance. 

Olid cross- (Al) of PVC of common flat wire of PVC o.d. net u /. resistance a.c. resi- reactance capacitance circuit ... 

This value can be determined from the data available on a per km basis in cable manufacturers catalogues and as provided in the previous tables. For the given a.c. resistance and inductive reactance it can be determined by ... 

The influence of skin effects in a multi-core cable is almost the same as that of a multiphase busbar system, discussed in Sections 28.7 and 28.8. However, unlike a busbar system, the resistance and inductive reactance for various sizes of cables can be easily measured and are provided by leading manufacturers as standard practice in their technical data sheets. To this extent, making an assessment of skin effects in cables is easy compared to a busbar system. Since all the phases in a cable, of a 3-core or 3 72-core are in a regularly twisted formation throughout the length of the cable, they represent the case of an ideal phase transposition (Section 28.8.4(3)) and almost nullify the effect of proximity. 

On the load side, the interrupter is connected through a cable to the equivalent circuit, with the required quantities of lumped resistance and reactance, to represent the motor to be tested, under a locked rotor condition. The circuit would also represent an interruption immediately after a start, to check for the most onerous operating condition for the interrupter to generate the highest surges as discussed earlier. 

When the external impedance is a resistance or a capacitive reactance... 

X() = zero sequence reactance / () = zero sequence resistance X+ = positive sequence reactance... 

Ro = Zero sequence resistance Xg = Zero sequence reactance X, = Positive sequence reactance... 

The naturai zero phase sequence inductive reactance of the grounded neutral may be considered to be too small compared to this and ignored for ease of calculations. Thus the resistance Rq of the grounded neutral circuit may be considered as its impedance, i.e. 

Vg = voltage across the external resistance R R = external resistance X = ground capacitive reactance Vf = line voltage... 

It is therefore recommended that a small resistance of a low- /- R loss be introduced into the filter circuits as shown in Figure 23.15(a) to limit such an excessive flow of currents through them. Knowledge of the system parameters (resistance and reactance) is also essential to design an appropriate filter circuit to avoid a possible resonance in the first instance. If this occurs the resistance thus introduced will limit the excessive flow of current. 

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