The open delta voltage transformer reduces the AC voltage and large current proportionally to a value that can be directly measured by the meter(automatic ac voltage regulator), which is convenient for direct measurement by the meter and provides power for relay protection and automatic devices.
A transformer for the power system is a special transformer that transmits information of high voltage and high current of the power grid to low voltage and low current secondary side metering, measuring instrument, relay protection, and automatic device. It is a primary system and a secondary system. The primary winding is connected to the power grid, and the secondary winding is connected with measuring instruments and protection devices.
The open delta voltage transformer can measure the voltage, current and electric energy of the primary system in conjunction with measuring instruments and metering devices; in conjunction with relay protection and automatic devices, it can form electrical protection and automatic control of various faults in the power grid. The performance of transformers directly affects the accuracy of power system measurement and metering and the reliability of relay protection devices.
The open triangle actually measures the zero sequence, mainly for insulation inspection. Under normal circumstances, there is no voltage on the open triangle. When a single-phase grounding occurs in the system, there will be no voltage on one phase of the primary winding of the voltage transformer, resulting in no voltage on the corresponding secondary winding, and 100V will appear on the open triangle. Voltage, voltage relay action, or alarm or trip.
The open delta refers to the connection of the three secondary windings of the three-phase voltage transformer. The three-phase secondary windings are connected according to the delta connection, but at the end, one point is not connected to form an open delta.
The secondary winding of the voltage transformer cannot be short-circuited. The open triangle PT is to detect whether a single phase-to-ground fault occurs(5kva single phase voltage stabilizer). When it is normal, the vector sum of the three phase-to-ground voltages is 0. When a phase-to-ground fault occurs, the three phases are no longer zero. Connected end to end, what is measured is the sum of this voltage vector. When a phase is completely grounded, the voltage of the open triangle is 100V. When the open triangle is running, the grounding voltmeter no longer opens but is closed.