The precondition for the common access to benefits of electricity is the efficient and properly operating complex system of facilities for power generation, transmission and distribution. Electricity supplied to each household is generated at power plants. In Poland, they are chiefly coal- and lignite-fired thermal power plants. It is only possible to transmit energy from power plants to the customer due to the extensive network of power transmission lines and substations. However, this process entails losses. The key method to minimize such losses involves increasing the transmission line voltage.Line voltages vary according to power transmission distances. They are as follows:
- 220 - 400 - 750 kV (extra high voltage, EHV), in the case of the longest transmission distances,
- 110 kV (high voltage, HV), in the case of transmission distances of not more than several dozen kilometres,
- 10 - 30 kV (medium voltage, MV), used for local distribution lines.
In order to increase voltage for the transmission purposes and subsequently lower it to the level allowing use of common electrical appliances designed for 230V or 380 V voltage ratings, is necessary to use EHV substations, numerous HV distribution substations and transformer stations, where medium voltage (used for distribution purposes) is transformed to low voltage used commonly by customers' appliances (230/380 V). All of these facilities, i.e. power lines and substations, make up the power system.
PSE perform the duties of the transmission system operator using its own transmission grid of the highest voltage, which consists of (as at 1 January 2018):
- 258 lines with a total length of 14 195 km, including:
- 1 line of 750 kV voltage with a length of 114 km,
- 93 lines of 400 kV voltage with a total length of 6 326 km,
- 164 lines of 220 kV voltage with a total length of 7 755 km,
- 106 extra-high voltage (EHV) substations
- under-sea 450 kV DC connection between Poland and Sweden, with a total length of 254 km (127 km belongs to PSE).