Bipolar photovoltaic array grounding apparatus and method
View Patent ↗The invention is an apparatus and method for safely disconnecting a bipolar photovoltaic array from earth ground under normal static operating conditions. The invention senses the voltage to earth on all three terminals of a bipolar photovoltaic array and uses a set of operable contacts to selectively couple or uncouple the DC neutral point of the array (the center tap) to earth ground. When all three terminals of the bipolar array are within the rated voltage capability of the photovoltaic array the DC neutral point is allowed to float.
1. A direct current electrical power system comprising a bipolar solar photovoltaic array and a means for grounding said bipolar solar photovoltaic array wherein;
said bipolar solar photovoltaic array comprises two monopolar arrays, each sourcing an associated DC current, solidly coupled in a series aiding arrangement with a common center coupling to configure a three-wire DC circuit and wherein;
said common center coupling is coupled to earth ground through said means for grounding and wherein;
said means for grounding comprises a saturable reactor wherein;
said saturable reactor is of a type that saturates when biased with a predetermined level of DC ground fault current and wherein;
said DC ground fault current is the difference in said associated DC currents of each of said monopolar arrays.
2. The direct current electrical power system according to claim 1 further comprising a set of operable contacts electrically connected across said reactor wherein said reactor is short-circuited when said set of operable contacts are closed.
3. The direct current electrical power system according to claim 2 further comprising; voltage sensors, current sensors and a control circuit and wherein said set of operable contacts is closed under command of the control circuit when a fault condition is determined based on a fault voltage or a fault current sensed by at least one of the voltage sensors or the current sensors, respectively.