IV. THE PROPOSED MODEL OF AN
ARCING HIF
The high impedance fault model proposed
by this paper shown in Figure 8 includes two DC
sources, DC1 and DC2 with voltages, Vp and Vn,
which represent the arcing voltage of air in soil
and/or between trees and the distribution line; two
resistances, Rp and Rn, between diodes which
represent the resistance of trees and/or the earth
resistance, and since most observed arcs occur in
highly inductive circuits [9] two inductances, Lp
and Ln were added to the circuit. The effect of the
inductances leads to the nonlinearity loop shape in
the V-I curve and the desired asymmetrical shape
for the HIF current. When the line voltage is
greater than the positive DC voltage Vp, the fault
current starts flowing towards the ground. The fault
current reverses backward from the ground when
the line voltage is less than the negative DC voltage
Vn. In the case when the line voltage is in between
Vp and Vn, the line voltage is counter-balanced by
Vp or Vn so that no fault current flows.
The characteristics shown by HIF are
studied and are reproduced using MATLAB
Simulink blocks. For studying HIF characteristics a
sample distribution system is taken into
consideration and HIF is simulated on this system
as shown in Fig 8.
The Emanuel model proposed is used as a
basic model and variable resistor is obtained using
MATLAB Simulink block. As given in Ref [5],
resistance ranges are brought in table 1. It can be
seen from table 1 that average varying resistance is
250ohm. Thus in matlab model for HIF, resistance
is varied up to 10% of original value. Fault is
initiated at instant of time of 0.2 sec.