Protection of low-voltage distribution networks

A system for protecting a low-voltage distribution network comprising a low-voltage side of a three-phase distribution transformer configured to supply electrical power to at least one single-phase load through a respective distribution line of a plurality of three-phase distribution lines, the system comprising:

• a memory having processor-readable instructions stored therein;
• and
• a numerical relay coupled to the three-phase distribution transformer, the numerical relay comprising one or more processors configured to access the memory and execute the processor-readable instructions, which, when executed by the one or more processors configures the one or more processors to perform a method, the method comprising:
• measuring, utilizing the numerical relay, variations of a periodic neutral-to-ground voltage between a neutral terminal of the three-phase distribution transformer and a local ground node by sampling the variations at a sampling frequency;
• performing an iterative measurement procedure on the low-voltage distribution network responsive to the variations of the periodic neutral-to-ground voltage being larger than a variation threshold by performing each iteration of the iterative measurement procedure M times at each respective period of the periodic neutral-to-ground voltage where
• M
• =
• F
• s
• F
• ν
• where Fv is a frequency of the periodic neutral-to-ground voltage and Fs is the sampling frequency;
• detecting a fault in the low-voltage distribution network responsive to the iterative measurement procedure satisfying a fault condition for a predefined number of iterations of the iterative measurement procedure;
• disconnecting, utilizing the numerical relay, the low-voltage side of the three-phase distribution transformer from the low-voltage distribution network responsive to the fault being detected;
• performing the iterative measurement procedure for a period of at least 200 ms responsive to the low-voltage side of the three-phase distribution transformer being disconnected;
• and
• disconnecting, utilizing the numerical relay, a high-voltage side of the three-phase distribution transformer responsive to the iterative measurement procedure satisfying the fault condition during the period of at least 200 ms.