In addition to the previous article, we will consider an example of compiling a network model with isolated neutral. Consider the simplest power line with one-way power supply (Fig. 1). It is necessary to draw up a power transmission model that will give out currents and voltages at the beginning of the line in short circuit modes and in single-phase earth fault modes.
Phase coordinates method
The phase coordinate method for modeling electrical networks with a grounded and isolated neutral, calculation of short circuit currents.
The phase coordinate method allows you to simulate networks with isolated neutral. In Russia, networks of 6-10-35 kV (sometimes 110 kV) operate with isolated neutral. Such networks are accompanied by small currents and significant overvoltages during single-phase earth faults.
According to the “Electrical Installation Rules”, one full transposition cycle should be performed on overhead power transmission lines with a voltage of 110-500 kV and a length of more than 100 km to limit asymmetry of currents and voltages.
Consider an example of compiling a power transmission model using the phase coordinate method. In fig. 1 shows the power transmission, a mathematical model of which must be compiled. It is necessary to determine the currents in the short circuit mode at the beginning of the line.
Some complex types of damage can occur in power lines, for example, a short circuit with a wire break. This mode can occur when a wire of any phase falls to the ground (Fig. 1).