Abstract: The present invention relates to a bidirectional 3 phase power meter for compensating reverse load flow and a method for metering thereby. According to the present invention, there is provided a bidirectional 3 phase power meter for compensating reverse load flow which allows calculating power receiving and power transmitting apparent power and power factor using the detected voltage/current and a method for metering thereby.

Abstract: Provided is an apparatus and method for preventing reverse power flow of an over current relay. When a neutral line current is greater than a phase current, it is determined that a reverse power flow occurs, and thus a protection relay is prevented from malfunctioning. The apparatus for preventing reverse power flow of an over current relay includes: a detecting unit which detects a phase current and a neutral line current; a reverse power flow determining unit which is electrically connected to the detecting unit and compares the phase current and the neutral line current which are detected by the detecting unit to determine whether or not a reverse power flow occurs; a setting unit which is electrically connected to the reverse power flow determining unit and sets an operation time and the number of operation times of a protection relay; and an operation unit which is electrically connected to the setting unit and operates the protection relay in a manner set by the setting unit.

Abstract: The present invention relates to a bidirectional 3 phase power meter for compensating reverse load flow and a method for metering thereby. According to the present invention, there is provided a bidirectional 3 phase power meter for compensating reverse load flow which allows calculating power receiving and power transmitting apparent power and power factor using the detected voltage/current and a method for metering thereby.

Abstract: A switching device for a transformer allows stable power supply without power interruption when a secondary winding voltage of the transformer is changed in the case of voltage drop on a distribution line due to a load characteristic. The switching device having an uninterruptible power supply function includes a plurality of switches operated by an external signal, a current circulation unit for multiple switches electrically connected to a large-current path of the switches to perform a switch-on function in place of the switches upon switching on and off between the switches, and a control unit electrically connected to the switches and current circulation unit to read voltage values and to apply signals to the switches depending on the voltage values to sequentially switch the switches. Accordingly, the switching device can stably supply power to power consumption sources without power interruption.

Abstract: Provided is an apparatus and method for preventing reverse power flow of an over current relay. When a neutral line current is greater than a phase current, it is determined that a reverse power flow occurs, and thus a protection relay is prevented from malfunctioning. The apparatus for preventing reverse power flow of an over current relay includes: a detecting unit which detects a phase current and a neutral line current; a reverse power flow determining unit which is electrically connected to the detecting unit and compares the phase current and the neutral line current which are detected by the detecting unit to determine whether or not a reverse power flow occurs; a setting unit which is electrically connected to the reverse power flow determining unit and sets an operation time and the number of operation times of a protection relay; and an operation unit which is electrically connected to the setting unit and operates the protection relay in a manner set by the setting unit.

Abstract: Disclosed herein is a replacement system of a distribution transformer and a low-voltage power line without outage. A distribution-line uninterruptible power supply includes a transformer primary bypass cable, a transformer secondary bypass cable, and a low-voltage power line bypass cable. Further, the uninterruptible power supply includes a combined phase-shifter and three-phase transformer, a transformer primary bypass switch, a transformer secondary bypass switch, a phase-based power adjuster, an energy converter, and a three-phase AC/DC converter. The capacity of the target transformer can be extended to one and half times that of the existing transformer. The energy conversion process of this system allows the utilization ratio of the transformer to be adjusted according to the phases, and has an advantage of extending the replaceable range at a low voltage without outage. Practical equipment can be secured at a low cost by replacing only the transformer in the existing uninterruptible power supply.

Abstract: A control method for preventing malfunction of an over current ground relay is disclosed. The control method includes: determining directions of per-phase power flows by measuring the magnitudes and phases of per-phase voltages and currents in an electric power system; checking occurrence of a load fault or a power source fault using the determined directions of per-phase power flows; and controlling an over current ground relay (OCGR) or an over current relay (OCR) to transmit a trip signal to a circuit breaker, after, upon occurrence of a load fault, checking occurrence of a ground fault and checking occurrence of a short circuit fault, and, upon occurrence of a power source fault, checking occurrence of a short circuit fault without checking occurrence of a ground fault, by turning on or off the OCGR or the OCR according to occurrence of a ground fault or a short circuit fault.

Abstract: A switching device for a transformer allows stable power supply without power interruption when a secondary winding voltage of the transformer is changed in the case of voltage drop on a distribution line due to a load characteristic. The switching device having an uninterruptible power supply function includes a plurality of switches operated by an external signal, a current circulation unit for multiple switches electrically connected to a large-current path of the switches to perform a switch-on function in place of the switches upon switching on and off between the switches, and a control unit electrically connected to the switches and current circulation unit to read voltage values and to apply signals to the switches depending on the voltage values to sequentially switch the switches. Accordingly, the switching device can stably supply power to power consumption sources without power interruption.