Series Capacitive Compensation to Increase the Railway Traction Power Supply System Transmission Capacity

Abstract

The article addresses the problem of improving the numerical analysis and operation of series capacitive compensation (SCC) units in the return wire of 25 kV power supply system traction substations to increase the railway capacity. Numerical analyses of the SCC impedance for two versions are considered: according to the condition of voltage equalization in the traction substations power supply arms and according to the condition of minimizing the negative sequence voltage. It is shown that the existing regulatory documents correctly place focus on the SCC impedances determined from the condition of ensuring equal power supply arm voltages. It is also shown that for numerical analyses of SCC impedance, the connection of the 110(220) kV power supply line impedances should be taken into account. To this end, it is proposed to connect, in the equivalent analysis circuit diagrams, two adjacent substations to the external power supply system through an equivalent delta of the impedances of 110(220) kV power lines. To effectively increase the voltage in the traction network while maintaining the minimum equalizing current values, it is advisable to connect the SCCs at both adjacent substations. In so doing, the no-load voltage values should be kept at the same level to reduce the equalizing current first component, which is determined by the difference of the transformers’ no-load voltages. It is shown that the connection of the SCC does not entail a growth in the equalizing current second component, which is determined by the difference of voltage losses at adjacent substations, including the voltages across the SCCs. If the SCC is connected at only one substation of the inter-substation zone, it is advisable to introduce automated control of the transformer OLTC at the substation without an SCC with a limited number of switching operations (up to 10 per day) with increased loads in the traction network.