The present disclosure relates to a protective relay detecting disconnection in a circuit comprising a disconnection detection unit including a plurality of nodes connected to both ends of an output of a transformation unit, a reference voltage generation unit forming a reference voltage, and a plurality of resistors forming a voltage dividing resistor and connecting the plurality of nodes and the reference voltage generation unit; a sensing voltage generation unit applying a voltage for forming a predetermined voltage difference with respect to the reference voltage; and a disconnection determination unit connected to a first node, in which the magnitude of a voltage signal applied by the voltage dividing resistor varies depending on whether at least one of the transformation unit and the circuit connected to the transformation unit is disconnected, and detecting whether at least one of the transformation unit and the circuit connected to the transformation unit is disconnected.

A system for distribution transformer monitoring may comprise a distribution transformer that includes a transformer fluid tank, a monitoring unit that includes a plurality of sensors, wherein the monitoring unit is coupled to the distribution transformer, and wherein the plurality of sensors comprises a fluid sensor that includes a sensor probe that extends out of the monitoring unit into the transformer fluid tank of the distribution transformer, and a communication unit coupled to the distribution transformer and communicatively coupled to the monitoring unit. The monitoring unit may further comprises a sensor module to receive sensor data from the plurality of sensors, a storage module to store the sensor data in an internal data storage device of the monitoring unit, an analysis module to analyze the sensor data to determine generated data, and a communication module to communicate the sensor data or the generated data to a remote computing device.

The present disclosure relates to a protective relay detecting disconnection in a circuit comprising a disconnection detection unit including a plurality of nodes connected to both ends of an output of a transformation unit, a reference voltage generation unit forming a reference voltage, and a plurality of resistors forming a voltage dividing resistor and connecting the plurality of nodes and the reference voltage generation unit; a sensing voltage generation unit applying a voltage for forming a predetermined voltage difference with respect to the reference voltage; and a disconnection determination unit connected to a first node, in which the magnitude of a voltage signal applied by the voltage dividing resistor varies depending on whether at least one of the transformation unit and the circuit connected to the transformation unit is disconnected, and detecting whether at least one of the transformation unit and the circuit connected to the transformation unit is disconnected.

An arrangement contains a polyphase transformer which has primary windings and secondary windings. The secondary windings are connected to form a star circuit, the star point of which is connected to earth potential by means of an overvoltage-limiting device. The overvoltage-limiting device has a first overvoltage-limiting component. A switch, which electrically bridges the first overvoltage-limiting component in its closed state, is assigned to the first overvoltage-limiting component.

A current detection circuit capable of compensating for detection accuracy of a switching current through switching of a connection state of a resistor even when the switching current has a component in a direction opposite to a predetermined direction is provided. A current detection circuit for detecting a value of a component in a predetermined direction of a switching current using a current transformer, wherein, when the switching current flowing in a primary side of the current transformer has a component in a direction opposite to the predetermined direction, a connection state of reset elements on a secondary side of the current transformer is switched such that an impedance of a magnetic reset on the secondary side of the current transformer is decreased.

A power harvesting system employs a saturable core transformer having two primary windings and at least one secondary winding. One of the primary windings is a high impedance winding, and the other primary winding is a low impedance winding. The two primary windings are connected with the load (motor). The secondary winding provides power to the circuit components of a replacement electronic thermostat. Relay contacts connects A/C power to either the high impedance primary winding or to the low impedance primary winding. When the relay is de-energized, A/C power is applied to the high impedance winding so that a relatively small amount of current flows through both the high impedance winding. This current is low enough that it does not energize the motor but is sufficient to generate the required voltage to transfer power to the secondary winding and is used to power the electronic thermostat. When the relay is energized, A/C power is applied directly to the low impedance primary winding, energizing the motor. At the beginning of each A/C cycle, the current through the low impedance winding builds up rapidly until the core saturates. The result is that a short pulse is generated in the secondary on both the positive and negative A/C cycle. This pulse has an amplitude determined by the turns ratio of the low impedance winding to the secondary winding and is used to power the electronic thermostat. After the core saturates, the impedance of the low impedance winding is only the resistance of the wire of the winding which is very small and results in negligible impact on the motor operation and also results in very low power dissipation.

System and method for detecting turn-to-turn faults in one or more windings of various objects are provided. In one implementation, a fault detector receives a set of current measurements associated with a transformer and uses these measurements to execute a procedure for detecting a turn-to-turn fault in the transformer. The procedure can include dividing a steady-state differential current value by a steady-state voltage value to obtain one or more compensating factors, determining a magnetizing current amplitude indicator by multiplying the steady-state voltage value by the one or more compensating factors, determining a compensated differential current value by combining the steady-state differential current value with a modifier value that incorporates the magnetizing current amplitude indicator, comparing the compensated differential current value against a threshold value, and declaring an occurrence of the turn-to-turn fault in the transformer when the compensated differential current value exceeds the threshold value.

A method for protecting a low-voltage distribution network. The low-voltage distribution network includes a low-voltage side of a three-phase distribution transformer that is 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 distribution lines. The method includes measuring 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, detecting a fault in the low-voltage power distribution network based on the variations of the periodic neutral-to-ground voltage, and disconnecting the low-voltage side from the low-voltage power distribution network responsive to the fault being detected.

A current transformer connector (10; 102) for connecting a current transformer of an electrical network to a protection relay via a current transformer data acquisition board (12; 104), is provided. The current transformer connector (10; 102) comprises first and second pairs (14, 20) of first and second current contacts (16, 18, 22, 24), each current contact pair (14, 20) being connectable in use to the current transformer so as to permit current flow from the electrical network through the current contact pairs (14, 20) to the protection relay. Each current contact pair (14, 20) is arranged to be in a short circuit configuration. The first current contact (16, 22) in each current contact pair (14, 20) is arranged to be independently moveable relative to the corresponding second current contact (18, 24) so that during initial insertion of the current transformer data acquisition board (12; 104) into the current transformer connector (10; 102) in use the first current contact (16) of the first current contact pair (14) is configured to separate from the second current contact (18) of the first current contact pair (14) to permit breaking of the short circuit configuration of the first current contact pair (14) and making of an electrical connection between the first current contact pair (14) and the current transformer data acquisition board (12; 104), while the second current contact pair (20) remains in the short circuit configuration. The first current contact (16, 22) in each current contact pair (14, 20) is further arranged to be independently moveable relative to the corresponding second current contact (18, 24) so that during further insertion of the current transformer data acquisition board (12; 104) into the current transformer connector (10; 102) in use the first current contact (22) of the second current contact pair (20) is configured to separate from the second current contact (24) of the second current contact pair (20) to permit breaking of the short circuit configuration of the second current contact pair (20).

Methods and systems for controlling a circuit designed to protect electrical equipment, in particular sensitive power grid equipment such as transformers, are disclosed. In particular, methods of local and remote control of operation of protection circuits are provided that allow for remote access to change an operational mode of such protection circuits, while ensuring that power grid equipment is protected locally regardless of any configuration instructions received from a remote or centralized facility. Override levels may be set to ensure power grid transformer protection, regardless of operational mode or remote instruction.