Method to detect utility disturbance and fault direction

A method for detecting a voltage disturbance in an electrical power distribution network that includes an electrical system having one or more power sources that can be disconnected from the network by a disconnect switch provided in an electrical line, where the network provides three-phase electrical AC power signals to the electrical system, said method opening the disconnect switch in response to detecting the voltage disturbance only if the voltage disturbance is in the network outside of the electrical system, said method comprising:

• reading instantaneous voltage measurements of each of the three-phase power signals on the electrical line;
• reading instantaneous current measurements of each of the three-phase power signals on the electrical line;
• transforming the voltage measurements into first and second voltage values in a stationary reference frame using a Clarke transformation;
• transforming the first and second voltage values in the stationary reference frame to third and fourth voltage values in a rotating reference frame using a Park transformation, where the third voltage value defines an average magnitude of the three-phase power signals and the fourth voltage value provides an indication of whether the third voltage value is locked to a network voltage;
• transforming the current measurements into first and second current values in the stationary reference frame using a Clarke transformation;
• transforming the first and second current values in the stationary reference frame to third and fourth current values in a rotating reference frame using a Park transformation;
• multiplying the third current value by the third voltage value to obtain an instantaneous power value;
• multiplying the fourth current value by the third voltage value to obtain an instantaneous volt-ampere reactive (VAR) value;
• and
• opening the switch if the VAR value has a magnitude above a predetermined value and a sign indicating the voltage disturbance is outside of the electrical system in the network.

A detection system for detecting a voltage disturbance in an electrical power distribution network that includes an electrical system having one or more power sources that can be disconnected from the network by a disconnect switch provided in an electrical line, where the network provides three-phase electrical AC power signals to the electrical system, said method opening the disconnect switch in response to detecting the voltage disturbance only if the voltage disturbance is in the network outside of the electrical system, said detection system comprising:

• means for reading instantaneous voltage measurements of each of the three-phase power signals on the electrical line;
• means for reading instantaneous current measurements of each of the three-phase power signals on the electrical line;
• means for detecting whether a fault is occurring in the distribution network by using the voltage measurements to detect a voltage disturbance on the electrical line;
• means for transforming the voltage measurements into first and second voltage values in a stationary reference frame;
• means for transforming the first and second voltage values in the stationary reference frame to third and fourth voltage values in a rotating reference frame, where the third voltage value defines an average magnitude of the three-phase power signals and the fourth voltage value provides an indication of whether the third voltage value is locked to a network voltage;
• means for correcting the fourth voltage value over time to maintain the third voltage value locked to the network voltage;
• means for transforming the current measurements into first and second current values in the stationary reference frame;
• means for transforming the first and second current values in the stationary reference frame to third and fourth current values in a rotating reference frame;
• means for multiplying the third current value by the third voltage value to obtain an instantaneous power value;
• means for multiplying the fourth current value by the third voltage value to obtain an instantaneous volt-ampere reactive (VAR) value;
• and
• means for opening the switch if the VAR value has a magnitude above a predetermined value and a sign indicating the voltage disturbance is outside of the electrical system in the network.