Arc horn

An arc horn flashover model, (a) A linear inductance model, (b) A nonlinear model. 

Most transmission lines in Japan are of double-circuit vertical configuration with two GWs and thus are composed of eight conductors. It is recommended to represent the line by a frequency-dependent line model in a numerical simulation. But a distributed line model with a fixed propagation velocity, attenuation, and surge impedance, that is, fixed-parameter distributed line model explained in [23], is often used. 

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Unknown XHE Maintenance on CTG 11-1 DC fuel oil pump was inadequate arcing horn clearances were not checked. 

Unknown XEQ The CTG 11 -1 DC fuel oil pump starter contactor began to stick open against its arcing horn. 

An arc horn flashover is represented either by a piecewise linear inductance model with time-controlled switches as illustrated in Figure 2.41a, or by a nonlinear inductance as shown in Figure 2.41b, based on a leader progression model [29,30]. The parameters L,- (i = 1-3) and... 

Figure 2.41a shows a lumped circuit model of an arc horn flashover proposed by Shindo and Suzuki [29]. Inductance and resistance values and closing times of switches are determined from a given voltage wave-form across the arc horn gap based on a theory of a discharge mechanism. 

The results obtained from using a frequency-dependent (distributed) line model and a frequency-independent line model are shown in Figure 2.45 for the case of no flashover of an arc horn. In the latter model, line parameters are calculated at the dominant transient frequency given by... 

The parameters were the same as those in Table 2.4 for a 77-kV system, except for a lightning current of 40 kA based on the field measurement [33]. The lower phase arc horn voltage was relatively smaller than those of the other phases on the 500-kV (EHV) line compared with those on the 77-kV line. Thus, an arc horn flashover phase on an EHV line is independent of the AC source voltage, and the lower phase flashover is less probable than those of the other phases. On the contrary, flashover probability is the same on each phase, and a flashover is dependent on the AC source voltage on a low voltage line. 

Measured results of arc horn flashover phases on a 77 kV transmission line. Single-phase FO, x two-phase FO, and O three-... 

Figure 2.51 shows simulation results of arc horn flashover phases by a simple distributed line "tower model," that is, neglecting the RL circuit in... 

Figure 2.39 with the parameters in Table 2.4, and by the recommended model illustrated in Figure 2.39. This figure should be compared with the field test result shown in Figure 2.50. It is clear that the recommended model cannot duplicate the field test result, while the simple distributed line model shows a good agreement with the field test result. The reason for the poor accuracy of the recommended model [28] is that the model was developed originally for a 500 kV line on which the lower phase flashover was less probable as explained in the previous section [23]. Thus, the recommended tower model tends to result in lower flashover probability of the lower phase arc horn. An R-L parallel circuit between two distributed lines in Figure 2.39 represents traveling wave attenuation and distortion along a tower. The R and L values were determined originally based on a field measurement (a in Equation 2.9), and thus those are correct only for the tower on which the measurement...

The first four chapters describe a transient analysis/simulation, which is based on a circuit theory derived by a transverse electro-magnetic (TEM) mode of wave propagation. When a transient involves a non-TEM mode of wave propagation, a circuit theory-based approach cannot provide an accurate solution. Typical examples include arcing horn flashover considering... 

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