Energisation of an MV electric boiler for load control in power systems with large share of renewables

The intermittence of some renewable energy sources, mainly wind and solar, leads to rapid power variations, which have to be controlled in order to maintain the system stable. Controllable loads, like MW range electric boilers, are a good solution for this problem, as the warmed water can be reused, minimising energy losses.
The boilers under analysis in this paper operate by increasing/decreasing the water level. Electric arcs appear between the electrodes and the water surface for a period of approximately 2s during the energisation. These arcs can be seen as faults to ground by the protections relays and trigger the ground fault protection. This paper uses field measurements made in a boiler installed in a power plant for the analysis of this issue.
The measurements are used to design a simulation model of the electric arc, which is used to study different energisation scenarios: With/without isolating transformer, different generator groundings and different grounding resistances. Monte Carlo method is used in order to simulate the randomness of the electric arcs, while the maximum zero-sequence current and voltage is registered.
The simulations show a good agreement with the measurements and can be used to estimate worst-case scenarios