The impact of modernising the municipal heating plant’s internal load on the selection of settings and the selectivity of power protection devices

Abstract

This paper presents a case study of the modernisation of the internal power supply system of a district heating plant with a 6 kV switchyard. The modernisation involved a change in the facility’s power structure, the decommissioning of part of the previous infrastructure, the connection of a cogeneration system, and the adaptation of the power supply system to current operational requirements. Particular attention was paid to the impact of reduced power demand and the presence of a local generation source on the selection of current transformers and protection settings in the supply bays of the 6 kV switchyard – GPZ.

The article also discusses the issue of protection selectivity, using the example of a short circuit in a cable joint on the 6 kV substation Bay 5 – GPZ Bay 34 line, which caused the I>>> protection to trip in the 110/6 kV transformer bay. This case indicates that the modernisation of the internal power supply system should cover not only the primary circuits, but also the transformers, settings and coordination of the protection systems with the master system.