A protection and monitoring system, device, and method for an electric power system, including a capacitor bank having multiple strings in each phase, voltage and current measuring devices, and relays to protect this capacitor bank. Each string can have multiple capacitor units and each unit can consist of multiple capacitor elements. The method may include: determining steady state operating condition using the obtained current and voltages, calculating and storing present time impedance value of each string into memory, calculating the string per unit impedance incremental quantity, detecting capacitor element failure based at least in part on this incremental quantity and calculating number of failed capacitor elements for each event, accumulating the number of failed capacitor elements, and performing a protection action when healthy capacitor elements are subject to an overvoltage limit. The method may be inherently immune or otherwise insensitive to capacitor variations due to aging, temperature change, instrument transformers errors, inaccuracy in data acquisition, and inherent manufacturing unbalance.

A protection and monitoring system, device, and method for an electric power system, including a capacitor bank having multiple strings in each phase, voltage and current measuring devices, and relays to protect this capacitor bank. Each string can have multiple capacitor units and each unit can consist of multiple capacitor elements. The method may include: determining steady state operating condition using the obtained current and voltages, calculating and storing present time impedance value of each string into memory, calculating the string per unit impedance incremental quantity, detecting capacitor element failure based at least in part on this incremental quantity and calculating number of failed capacitor elements for each event, accumulating the number of failed capacitor elements, and performing a protection action when healthy capacitor elements are subject to an overvoltage limit. The method may be inherently immune or otherwise insensitive to capacitor variations due to aging, temperature change, instrument transformers errors, inaccuracy in data acquisition, and inherent manufacturing unbalance.

A protection circuit including an inrush current detector operable to detect an inrush current from a DC link is disclosed herein. The inrush current detector includes a transistor switch that is turned on in normal operation of the protection circuit. The protection circuit operates to detect when the voltage across the transistor switch exceeds a threshold voltage in response to a detected inrush current, and in response operates to turn off the transistor switch.

An electronic circuit includes: a first series-connection of DC link capacitors (C.sub.A1, . . . , C.sub.Am) and a second series-connection of DC link capacitors (C.sub.B1, . . . , C.sub.Bn) connected in parallel between DC bus bars (DC+, DC−), wherein the first series has a first node (A) between the DC link capacitors thereof and the second series has a second node (B) between the DC link capacitors thereof; and a short-circuit module (301; 401, 407) configured to receive a voltage difference (UM) between the first node and the second node and to cause the DC bus bars short circuited in response to the received voltage difference being greater than a predetermined threshold.

An electronic circuit includes: a first series-connection of DC link capacitors (C.sub.A1, . . . , C.sub.Am) and a second series-connection of DC link capacitors (C.sub.B1, . . . , C.sub.Bn) connected in parallel between DC bus bars (DC+, DC−), wherein the first series has a first node (A) between the DC link capacitors thereof and the second series has a second node (B) between the DC link capacitors thereof; and a short-circuit module (301; 401, 407) configured to receive a voltage difference (UM) between the first node and the second node and to cause the DC bus bars short circuited in response to the received voltage difference being greater than a predetermined threshold.

The invention relates to a grounding fault protection method for a high-voltage capacitor of a direct-current filter. The method comprises the following steps of acquiring a head end voltage u and an unbalanced current i.sub.T2 of a direct-current filter, and acquiring a discrete head end voltage and unbalanced current sequence; calculating a virtual capacitance C.sub.zd; determining a protection setting value C.sub.set according to the bridge arm capacitance of the high-voltage capacitor, and when the virtual capacitance C.sub.zd is larger than the protection setting value C.sub.set, protecting and judging to be an internal fault; otherwise, protecting and judging to be an external fault.

The invention relates to a grounding fault protection method for a high-voltage capacitor of a direct-current filter. The method comprises the following steps of acquiring a head end voltage u and an unbalanced current i.sub.T2 of a direct-current filter, and acquiring a discrete head end voltage and unbalanced current sequence; calculating a virtual capacitance C.sub.zd; determining a protection setting value C.sub.set according to the bridge arm capacitance of the high-voltage capacitor, and when the virtual capacitance C.sub.zd is larger than the protection setting value C.sub.set, protecting and judging to be an internal fault; otherwise, protecting and judging to be an external fault.

A protection circuit including an inrush current detector operable to detect an inrush current from a DC link is disclosed herein. The inrush current detector includes a transistor switch that is turned on in normal operation of the protection circuit. The protection circuit operates to detect when the voltage across the transistor switch exceeds a threshold voltage in response to a detected inrush current, and in response operates to turn off the transistor switch.

Systems and methods for integrated control and monitoring of charging and cell balancing in a group of ultracapacitors. Monitoring and control circuitry can be configured for built-in monitoring feedback to the charger and the balancing circuits to dynamically improve performance, extend system lifetime, decrease charging time, increase available power and/or energy, and/or enhance safety and reliability of the group of ultracapacitors.

A connection-and-protection device having two capacitively connected conductors respectively connected in use to a supply cable at one end and a load cable at the other end is provided, the connection and protection device including a connection terminal for connection to either of the supply or load cables, a pair of cable terminals for the respective capacitively connected conductors, a direct connection within the device between the connection terminal and one of the pair of cable terminals, the other of the pair cable terminals not normally being connected to the connection terminal and means for connecting the other of the pair of cable terminals to the connection terminal to protect the capacitive connection of the two conductors, if the voltage between the pair of cable terminals exceeds a threshold and event detection means comprising means for detection the voltage between the pair of cable terminals exceeding a threshold.