Method for coordinating protective devices in a distribution grid

A method for coordinating a distribution network of different levels of electromechanical switches and automatically electrically closable apparatuses in a DC circuit, the distribution network being arranged between feed-in devices and loads, and having at least one busbar, wherein each of the apparatuses includes an electrical switch to open or close the DC circuit, a fault current detection device, a tripping unit, and a pre-charging apparatus, wherein if a fault current is detected by the fault current detection device, the electrical switch opens the DC circuit via the tripping unit and the pre-charging apparatus restores a voltage on the at least one busbar before the electrical switch is closed, and wherein each of the apparatuses further includes a control unit to automatically close the electrical switch after successful pre-charging, the method comprising:

• in the case of a first apparatus at a feed-in device
• setting a counter for the first apparatus to a number of a level in the distribution network;
• detecting, using the fault current detection device, whether there is a fault;
• if there is a fault, determining whether the fault current exceeds a current threshold;
• if the fault current exceeds the current threshold, opening the apparatuses;
• determining a direction of the fault current;
• in the case of a second apparatus at a load
• terminating the method in the case of a positive direction of the fault current;
• or
• in the case of a negative direction of the fault current, checking whether the voltage on the at least one busbar has been restored and, if this is the case, automatically closing the second apparatus;
• or
• in the case of a third apparatus at a feed-in device
• terminating the method in the case of a negative direction of the fault current;
• or
• in the case of a positive direction of the fault current, decrementing the counter for the third apparatus by one;
• and
• if the counter for the third apparatus is less than or equal to zero, terminating the method;
• or
• if the counter for the third apparatus is greater than zero, waiting for a switch-off time of the electromechanical switches;
• charging, using the pre-charging apparatus, to test whether the fault has been eliminated;
• checking whether the charging is possible on a side of the loads using the pre-charging apparatus;
• and either
• if the charging is possible, recharging the distribution network, automatically switching on the third apparatus, and suppressing the switching transient, or
• if the charging is not possible, decrementing the counter for the third apparatus by one.