JP2015033306A - Three-phase open-phase protection device, and three-phase open-phase protection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To resolve a problem of increase in cost without increasing a size of a mounting area for a protection relay, and to protect an apparatus with certainty without increasing the number of components.SOLUTION: A three-phase open-phase protection device comprises: a current detector for detecting currents of two phases of a three-phase AC power supply; an analog input unit to which the currents of the two phases of the three-phase AC power supply that are detected by the current detector are inputted; an analog digital conversion unit converting a signal from the analog input unit into a digital signal; a calculation processing unit calculating a current value of a remaining one phase of the three-phase AC power supply on the basis of an input current value and a phase angle of the two phases of the three-phase AC power supply that is a digital signal from the analog digital conversion unit, and determining open-phase of a three-phase balanced load on the basis of the calculated current value of the respective phases; and a control signal output unit giving an AC circuit breaker an opening command in a case where the open phase of the three-phase balanced load is detected by the calculation processing unit.

Description

  The present invention relates to a three-phase open phase protection device and a three-phase open phase protection method, and in particular, connected to a power system in which a three-phase balanced load is connected to a three-phase AC power source via an AC circuit breaker. The present invention relates to a three-phase phase loss protection device and a three-phase phase loss protection method suitable for detecting a phase failure of a load and protecting a device.

  Normally, when three cables are correctly connected from a three-phase AC power source to a three-phase balanced load (mainly a rotating machine) and the three-phase balanced load does not exceed the rated output, the three-phase balanced load is operating normally. Continue. However, when an open phase of a three-phase balanced load occurs, overcurrent flows in the remaining two phases, and if the operation is continued while the overcurrent continues to flow, there is a risk that the insulator or the like will burn out.

  In addition, when the three-phase balanced load is in an open-phase state, the two-phase that is still connected to the three-phase AC power supply will have about twice as much overcurrent, but the three-phase during operation with a moderate load factor. If phase loss occurs in the balanced load, burnout may not be prevented by overcurrent protection alone, so phase loss protection for a three-phase balanced load is required.

  For example, Patent Documents 1 and 2 disclose the phase loss protection of such a three-phase balanced load.

  This patent document 1 relates to a phase loss determination method and a phase loss determination circuit of a power supply device, and two current transformers are provided in two phases of an output line for the purpose of reducing the number of parts (current transformers). The current signal detected by the current transformer may be taken in, and the addition and sign inversion operation may be performed to obtain the current signal of the phase not provided with the current transformer. The weak current signal obtained on the secondary side of the generator is A / D converted and taken into the control unit, and the addition and sign inversion operations are performed by the digital calculation function of the control unit, and the generator output current is directly It is described that the current transformers to be detected can be saved from 3 to 2 and contribute to the cost reduction of the power supply device.

  On the other hand, Patent Document 2 relates to a three-phase open phase detection circuit that protects a device that uses a three-phase AC power source as a power source, and aims to reduce the effect on the mounting area and reduce the cost. An R-phase current detection circuit and an S-phase current detection circuit that detect current of two phases (R-phase and S-phase) of each phase (R-phase, S-phase, and T-phase) are provided, and their phases are compared. In addition, it is described that the comparison output is input to the control unit, and the control unit controls the switch according to the input to perform the phase loss protection.

JP 2009-55739 A JP 2006-109670 A

  Conventionally, it has been necessary to take in the current of each phase of the three-phase AC power source and to determine the phase loss of the load based on the current of each phase for the three-phase phase loss protection. Therefore, in order to capture the three-phase current and detect the three-phase, it is necessary to arrange a current transformer for each phase, and also to install a three-phase current capturing circuit in the protective relay.

  Therefore, in the conventional configuration, there is a problem that it is necessary to increase the mounting area of the panel on which the instrumental current transformer is arranged and the protective relay, and there is a problem that the cost is increased. In addition, if there are many current capturing circuits for current transformers and protective relays, the number of components increases, resulting in a problem that leads to an increase in failure rate.

  In order to solve these problems, those described in Patent Documents 1 and 2 have been proposed. However, in any case, it is difficult to say that the determination of the phase loss in the control unit is performed reliably, and it is reliable. Equipment protection was desired.

  The present invention has been made in view of the above points, and the object of the present invention is to solve the problem of cost increase without increasing the mounting area of the protective relay, and without increasing the number of parts. An object of the present invention is to provide a three-phase phase loss protection device and a three-phase phase loss protection method that can reliably protect the device.

  In order to achieve the above object, the three-phase open phase protection device of the present invention is a three-phase open phase protection connected to a power system in which a three-phase balanced load is connected to a three-phase AC power source via an AC circuit breaker. The three-phase open phase protection device includes a current detector that detects a two-phase current of the three-phase AC power source, and a two-phase AC power source detected by the current detector. Of the three-phase AC power source that is the digital signal from the analog-to-digital converter, and the analog-to-digital converter that converts the signal from the analog-input unit into a digital signal. The current value of the remaining one phase of the three-phase AC power supply is calculated based on the input current value and the phase angle, and the phase loss of the three-phase balanced load is determined based on the calculated current value of each phase. An arithmetic processing unit, and the arithmetic processing unit When an open phase balanced load is detected, characterized in that a control signal output unit for providing the opening command to the AC circuit breaker.

  In addition, the three-phase open phase protection method of the present invention is a three-phase connected to a power system in which a three-phase balanced load is connected to a three-phase AC power source via an AC circuit breaker in order to achieve the above object. A three-phase phase loss protection method for detecting a phase loss of the three-phase balanced load with a phase loss protection device and protecting the device, and detecting a current of two phases of the three-phase AC power source with a current detector. The signal from the analog input unit to which the two-phase current of the three-phase AC power source detected by the current detector is input is converted into a digital signal by the analog-digital conversion unit, and the digital signal from the analog-digital conversion unit is converted. Based on the two-phase input current value and phase angle of the three-phase AC power source that is a signal, the arithmetic processing unit calculates the current value of the remaining one phase of the three-phase AC power source, and for each of the calculated phases. Judgment of phase loss of the three-phase balanced load based on the current value And, when the phase loss of the three-phase balanced load is detected by the arithmetic processing unit, the control signal output unit gives an opening command to the AC circuit breaker to open the AC circuit breaker. And

  According to the present invention, it is possible to reliably protect a device without increasing the number of parts, as well as solving the problem of cost increase without increasing the mounting area of the protective relay.

It is a block diagram which shows Example 1 of the three-phase phase loss protection apparatus of this invention.

  Hereinafter, the three-phase phase loss protection device and the three-phase phase loss protection method of the present invention will be described based on the illustrated embodiments.

  FIG. 1 shows a first embodiment of the three-phase phase loss protection device of the present invention. As shown in the figure, the three-phase phase loss protection device 11 of this embodiment is connected to a power system 10 in which a three-phase balanced load 2 is connected to a three-phase AC power source 1 via an AC circuit breaker 4. .

  The three-phase phase loss protection device 11 according to the present embodiment detects a current of two phases of the first phase (R phase) and the third phase (T phase) of the three-phase AC power source 1. Two current transformers 3A and 3B, which are measuring instruments, and the first phase (R phase) and third phase (T phase) of the three-phase AC power source 1 detected by the current transformers 3A and 3B. ), An analog input circuit 6 that is an analog input unit to which a current is input, an analog-digital conversion circuit 7 that is an analog-digital conversion unit that converts a signal from the analog input circuit 6 into a digital signal, and the analog-digital conversion circuit The remaining one phase of the three-phase AC power source 1 based on the input current values and phase angles of the first phase (R phase) and the third phase (T phase) of the three-phase AC power source 1 which are digital signals from 7 And calculating the current value of the second phase (S phase) which is An arithmetic processing unit 8 that determines the phase loss of the three-phase balanced load 2 based on the current values of the phases (R phase, S phase, T phase), and the arithmetic processing unit 8 detects the phase loss in the three-phase balanced load 2 The control output circuit 9 is a control signal output unit that gives an opening command to the AC circuit breaker 4 when it is configured.

  More specifically, in the power system 10, a three-phase balanced load 3 is connected to the three-phase AC power source 1 via an AC circuit breaker 4. Current transformers 3 </ b> A and 3 </ b> B for detecting the current are arranged in the first phase (R phase) and the third phase (T phase). The current outputs of the current transformers 3A and 3B are connected to the analog input circuit 6 of the protective relay 5 and converted into a small current, and the output is input to the analog / digital conversion circuit 7, where the arithmetic processing unit 8 is converted into a digital signal that can be calculated.

  In addition, the arithmetic processing unit 8 calculates the effective value of the current of the first phase (R phase) and the third phase (T phase), and indirectly calculates the second phase (S Phase) current. From this calculated current value of each phase (R phase, S phase, T phase), an unbalance rate is obtained, and the missing phase of the three-phase balanced load 2 is determined.

  The above-mentioned unbalance rate is calculated by the following formula 1. Here, when the unbalance coefficient (K) exceeds a preset set value, it is determined that the phase is out of phase, and the control output circuit 9 outputs a disconnection command for the AC circuit breaker 4 so that the AC circuit breaker 4 is turned on. It is opened to interrupt the load current.

  According to the present embodiment, it is possible to reliably protect the device without increasing the number of parts, as well as solving the problem of cost increase without increasing the mounting area of the protective relay 5. There is an effect that can be done.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  DESCRIPTION OF SYMBOLS 1 ... Three-phase alternating current power supply, 2 ... Three-phase balanced load, 3A, 3B ... Current transformer for instrument, 4 ... AC circuit breaker, 5 ... Protection relay, 6 ... Analog input circuit, 7 ... Analog-digital conversion circuit, 8 ... Arithmetic processing unit, 9... Control output circuit, 10... Power system, 11.

Claims (8)

A three-phase open phase protection device connected to a power system in which a three-phase balanced load is connected to a three-phase AC power source via an AC circuit breaker,
The three-phase open phase protection device receives a current detector that detects a two-phase current of the three-phase AC power source, and a two-phase current of the three-phase AC power source detected by the current detector. An analog input unit, an analog / digital conversion unit that converts a signal from the analog input unit into a digital signal, and a two-phase input current value and phase of the three-phase AC power source that is a digital signal from the analog / digital conversion unit An arithmetic processing unit that calculates a current value of the remaining one phase of the three-phase AC power source based on an angle, and determines an open phase of the three-phase balanced load based on the calculated current value of each phase; A three-phase phase loss protection device, comprising: a control signal output unit that gives an opening command to the AC circuit breaker when a phase loss of the three-phase balanced load is detected by the arithmetic processing unit . In the three-phase phase loss protection device according to claim 1,
The three-phase open phase protection device, wherein the current detector is connected to any two phases of the three-phase AC power source. In the three-phase phase loss protection device according to claim 1 or 2,
In the arithmetic processing unit, an unbalance rate is obtained from the calculated current value of each phase, and when the unbalance rate exceeds a preset set value, it is determined that the three-phase balanced load is missing. A three-phase open-phase protection device. In the three-phase phase loss protection device according to claim 3,
As for the unbalance rate, the unbalance coefficient (K) is calculated by the following equation, and when the calculated unbalance coefficient (K) exceeds a preset value, the lack of the three-phase balanced load is calculated. A three-phase open phase protection device characterized by determining a phase.

The three-phase AC load is connected to the three-phase AC power supply through the AC circuit breaker and the three-phase AC load is connected to the power system. A three-phase phase loss protection method,
A two-phase current of the three-phase AC power supply is detected by a current detector, and a signal from an analog input unit to which the two-phase current of the three-phase AC power supply detected by the current detector is input, The analog-to-digital conversion unit converts the digital signal into a digital signal, and the arithmetic processing unit converts the three-phase AC power The current value of the remaining one phase is calculated, the phase loss of the three-phase balanced load is determined based on the calculated current value of each phase, and the three-phase balanced load is detected by the arithmetic processing unit. When a phase is detected, a control signal output unit gives an opening command to the AC circuit breaker to open the AC circuit breaker. In the three-phase phase loss protection method according to claim 5,
The three-phase open phase protection method, wherein the two-phase current of the three-phase AC power source detected by the current detector is a current of a first phase and a third phase of the three-phase AC power source. In the three-phase phase loss protection method according to claim 5 or 6,
An unbalance rate is obtained from the current value of each phase calculated by the arithmetic processing unit, and when the unbalance rate exceeds a preset value, it is determined that the three-phase balanced load is missing. Characteristic three-phase open phase protection method. In the three-phase phase loss protection method according to claim 7,
As for the unbalance rate, the unbalance coefficient (K) is calculated by the following equation, and when the calculated unbalance coefficient (K) exceeds a preset value, the lack of the three-phase balanced load is calculated. A three-phase phase loss protection method characterized by determining a phase.

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