Busbar voltage abnormality detection device and busbar voltage abnormality detection method

Abstract

To provide a bus voltage abnormality detection device and a bus voltage abnormality detection method, which can detect thermal influence to a load (auxiliary machine) due to minute voltage fluctuation in an early stage.SOLUTION: A bus voltage abnormality detection device 1 includes: a first voltmeter 111 for measuring voltage of an external power transmission system; a second voltmeter 105 for measuring voltage of a bus; an ammeter 108 for measuring current of a load connected to the bus; and a determination logic part 121 for determining voltage abnormality of the bus based on a voltage fluctuation amount of the external power transmission system which is measured by the first voltmeter, a voltage fluctuation amount of the bus which is measured by the second voltmeter, and a current fluctuation amount of the load which is measured by the ammeter.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a configuration of a bus voltage abnormality detection device and a detection method for detecting abnormalities in the bus voltage of a power supply panel in a power plant, and in particular to a technology that is effective when applied to abnormality detection in small-scale power systems such as those in remote islands. [Background technology]

[0002] In general, the power grid in Japan is constructed as a highly reliable network with a very large capacity, so under normal circumstances, there is a low possibility of voltage fluctuations that affect the load end occurring. On the other hand, in small-scale power grids in remote areas such as remote islands, and in the distributed networks that are expected to be developed in the future, the grid capacity is small and the system is more susceptible to voltage fluctuations, so the reliability of the power source is likely to deteriorate.

[0003] When the loads (auxiliary equipment) in a power plant receive power from the power grid, if a deterioration in quality is detected in the power grid, various protective relays detect the abnormality and protect the loads (auxiliary equipment).

[0004] Background art in this technical field includes, for example, a technology such as that described in Patent Document 1. Patent Document 1 discloses "a protection and control device for an AC / DC converter station capable of reliably protecting a DC line within an appropriate range in the event of an accident in an AC / DC converter station or a DC transmission system." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-68621 A Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, protection of electrical circuits in power plants is implemented mainly from the standpoint of short circuit accidents and earth fault accidents.

[0007] Taking electric motors as an example of a load (auxiliary equipment) in a power plant, when heat is generated by a current (overcurrent) larger than normal, there is a possibility of thermal damage, so generally, an overcurrent protection relay is installed to protect the motor from overcurrent. When a short circuit or other accident occurs at the motor end, the overcurrent protection relay detects the current rise, opening (tripping) the circuit breaker for the power supply and stopping the motor.

[0008] On the other hand, electric motors are generally not equipped with voltage-related protective relays specifically designed to protect the motor.The reason for this is that if a short circuit or other accident occurs in the power panel that supplies the power, the voltage drops significantly, the supplied current falls below the rated current, and the motor is unable to output electrical output (shaft power) commensurate with the load torque, causing it to stop.

[0009] As a special case, when a motor is operating near the rated speed and the voltage drops slightly by a few percent due to factors in the external power transmission system, the motor can output more than the load torque, so the motor will not stop and will continue to rotate at nearly the rated speed. Since motors have constant output characteristics at rated speed, in this state the current value will increase by the amount of the voltage drop.

[0010] Overcurrent protection for an electric motor does not function unless a current of a magnitude equal to or greater than a certain threshold value flows. Therefore, if the above-mentioned current increase falls below this threshold, a current greater than the rated current will flow through the circuit for a long period of time.

[0011] As a result, problems may occur such as motor and cable burning due to overcurrent and shortened lifespan due to heat, and it is necessary to detect the accident and cut off the power supply system before such problems occur.

[0012] The above-mentioned Patent Document 1 claims that when a ground fault or short circuit occurs on a DC line, the DC fault can be detected, the faulty line identified, and the DC circuit breakers on both ends of the faulty line opened using only information that can be measured at the AC / DC converter station, thereby minimizing the spread of the fault to the entire system.

[0013] However, Patent Document 1 does not describe the thermal effect on the load (auxiliary equipment) caused by the above-mentioned minute voltage fluctuations.

[0014] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a bus voltage abnormality detection device and a bus voltage abnormality detection method capable of detecting the thermal effect on a load (auxiliary equipment) caused by minute voltage fluctuations at an early stage. [Means for solving the problem]

[0015] In order to solve the above problems, the present invention is characterized in comprising a first voltmeter that measures the voltage of an external power transmission system, a second voltmeter that measures the voltage of a bus bar, an ammeter that measures the current of a load connected to the bus bar, and a judgment logic unit that judges a voltage abnormality of the bus bar based on the voltage fluctuation amount of the external power transmission system measured by the first voltmeter, the voltage fluctuation amount of the bus bar measured by the second voltmeter, and the current fluctuation amount of the load measured by the ammeter.

[0016] The present invention also provides a busbar voltage abnormality detection method for detecting a voltage abnormality in a busbar connected to an external power transmission system, comprising the steps of: (a) measuring the voltage of the external power transmission system and calculating a voltage fluctuation amount of the external power transmission system; (b) measuring the voltage of the busbar and calculating a voltage fluctuation amount of the busbar; (c) measuring a current of a load connected to the busbar and calculating a current fluctuation amount of the load; and (d) determining a voltage abnormality in the busbar based on the voltage fluctuation amount of the external power transmission system calculated in step (a), the voltage fluctuation amount of the busbar calculated in step (b), and the current fluctuation amount of the load calculated in step (c). Effect of the Invention

[0017] According to the present invention, it is possible to realize a bus voltage abnormality detection device and a bus voltage abnormality detection method that are capable of detecting the thermal effect on a load (auxiliary equipment) caused by minute voltage fluctuations at an early stage.

[0018] This makes it possible to protect the load (auxiliary equipment) from voltage imbalances and minute voltage changes in the power system.

[0019] Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments. [Brief description of the drawings]

[0020] [Figure 1] 1 is a diagram showing a schematic configuration of a bus-bar voltage abnormality detection device according to a first embodiment of the present invention. [Diagram 2] 2 is a diagram showing a determination logic in a low voltage state by a determination logic unit 121 of FIG. 1. FIG. [Diagram 3] 2 is a diagram showing a decision logic in an overvoltage state by a decision logic unit 121 of FIG. 1. FIG. [Figure 4] FIG. 11 is a diagram showing a judgment logic by a judgment logic unit 121 according to the second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and duplicated descriptions will be omitted as appropriate. EXAMPLES

[0022] A bus voltage abnormality detection device and a bus voltage abnormality detection method according to a first embodiment of the present invention will be described with reference to Fig. 1 to Fig. 3. Fig. 1 is a diagram showing a schematic configuration of a bus voltage abnormality detection device 1 of the present embodiment.

[0023] As shown in Fig. 1, this embodiment assumes a power supply bus 103 that receives power from an external power transmission system via a power receiving transformer 101 and a power receiving breaker 102. A motor 109 is connected to the power supply bus 103 as a load (auxiliary) via a motor circuit breaker 106.

[0024] The busbar voltage abnormality detection device 1 mainly comprises a busbar voltmeter 105 connected to a power supply busbar 103 via a busbar voltmeter transformer 104, a motor ammeter 108 connected to a motor 109 via a motor ammeter transformer 107, an external power transmission system voltmeter 111 connected to the external power transmission system via an external power transmission system voltmeter transformer 110, and a judgment logic unit 121.

[0025] The bus voltage meter 105 is a voltmeter for monitoring the bus voltage.

[0026] A motor ammeter 108 is connected in the power supply circuit of the motor 109 for monitoring the motor current.

[0027] An external power transmission system voltmeter 111 is connected to the primary side of the power receiving transformer 101 to monitor the voltage of the external power transmission system.

[0028] The judgment logic unit 121 evaluates the voltage state of the power supply busbar 103 based on each measurement signal 120 from the busbar voltmeter 105, the external power transmission system voltmeter 111, and the motor ammeter 108. If it is determined that the voltage state of the power supply busbar 103 is abnormal, a circuit breaker trip signal 122 is transmitted to the power receiving circuit breaker 102 to trip the power receiving circuit breaker 102.

[0029] The determination logic in a low voltage state by the determination logic unit 121 will be described with reference to Fig. 2. The control logic shown in Fig. 2 is a logic for determining an abnormality when the bus voltage drops.

[0030] In the judgment logic unit 121, the external power transmission system voltage fluctuation (voltage drop side) detection signal 201 outputs “1” when the voltage of the external power transmission system measured by the external power transmission system voltmeter 111 drops by −A% from the rated value.

[0031] The monitoring conditions for voltage drops in the external power transmission system are set to separate the conditions from accidents within the power plant. When the bus voltage drops significantly due to an accident within the power plant, the voltage on the bus side within the power plant drops significantly, but the system voltage does not drop to that extent. Therefore, this is set so that this control logic will not operate in the event of an accident within the power plant.

[0032] If a voltage abnormality occurs due to factors in the external power transmission system, the voltage of the external power transmission system will fluctuate in the same way as the voltage of the busbar in the power plant drops.

[0033] When a tap is installed in the power receiving transformer 101, the tap lower limit signal 202 of the power receiving transformer 101 outputs "1" on condition that the tap is at its lower limit.

[0034] The motor current increase detection signal 203 outputs "1" when the current of the motor 109 measured by the motor ammeter 108 becomes equal to or greater than the rated current.

[0035] Bus voltage fluctuation (voltage drop side) detection signal 204 outputs "1" when the bus voltage measured by bus voltmeter 105 drops by -B% from the rated value, which is a predetermined set value.

[0036] When either the signal 201 or the signal 202 indicating that the external power transmission system voltage has dropped outputs “1”, the OR circuit 205 outputs “1”.

[0037] In other words, if either the voltage fluctuation amount of the external power transmission system or the tap fluctuation amount of the power receiving transformer 101 connected between the external power transmission system and the power supply bus 103 exceeds a predetermined threshold, the OR circuit 205 determines that the voltage fluctuation amount of the external power transmission system has exceeded the predetermined threshold.

[0038] Furthermore, when an increase in current of the motor 109 is detected and a "1" is output in the signal 203, and also when a drop in the voltage of the busbar in the power plant is detected and a "1" is output in the signal 204, a "1" is output in the three-phase AND circuit 206, and a circuit breaker trip signal 208 is output via a delay timer 207 that is installed in consideration of preventing malfunction due to momentary behavior.

[0039] That is, the determination logic unit 121 determines that a current increase due to a bus voltage abnormality has occurred based on a voltage drop in the external power transmission system and the power supply bus 103 and a current increase in the load (motor 109).

[0040] Here, the set values ​​A and B indicating the voltage fluctuation rate and the setting value of the delay timer 207 are determined taking into consideration the configuration of the external power transmission system, the start time of the motor 109, and the like.

[0041] The determination logic in an overvoltage state by the determination logic unit 121 will be described with reference to Fig. 3. The control logic shown in Fig. 3 is a logic for determining an abnormality when the bus voltage rises.

[0042] In the judgment logic unit 121, the external power transmission system voltage fluctuation (voltage rising side) detection signal 301 outputs “1” when the voltage of the external power transmission system measured by the external power transmission system voltmeter 111 rises by C% from the rated value. Voltage monitoring of the external power transmission system is installed for the same reason as when a busbar drops.

[0043] When a tap is installed in the power receiving transformer 101, the tap upper limit signal 302 of the power receiving transformer 101 outputs "1" on condition that the tap is at its upper limit.

[0044] Bus voltage fluctuation (voltage increase side) detection signal 303 outputs "1" when the bus voltage measured by bus voltmeter 105 increases by D% from the rated value, which is a predetermined set value.

[0045] When either the signal 301 or the signal 302 indicating that the external power transmission system voltage has increased outputs “1”, the OR circuit 205 outputs “1”.

[0046] In addition, when an increase in the voltage of the busbar in the power plant is detected and a "1" is output in the signal 303, a "1" is output in the three-phase AND circuit 206, and a circuit breaker trip signal 208 is output via a delay timer 207 that is installed to prevent malfunction due to momentary behavior.

[0047] That is, the determination logic unit 121 determines from the voltage rise in the external power transmission system and the power supply bus 103 that an overvoltage caused by the external power transmission system has occurred.

[0048] Here, the set values ​​C and D indicating the voltage fluctuation rate and the setting value of the delay timer 207 are determined taking into consideration the configuration of the external power transmission system and voltage rise conditions (such as lightning strikes) taken into account on the system side.

[0049] As described above, the busbar voltage abnormality detection device 1 of this embodiment includes a first voltmeter (external power transmission system voltmeter 111) that measures the voltage of the external power transmission system, a second voltmeter (busbar voltmeter 105) that measures the voltage of the power supply bus 103, an ammeter (motor ammeter 108) that measures the current of a load (electric motor 109) connected to the power supply bus 103, and a judgment logic unit 121 that judges a voltage abnormality in the power supply bus 103 based on the voltage fluctuation of the external power transmission system measured by the first voltmeter (external power transmission system voltmeter 111), the voltage fluctuation of the power supply bus 103 measured by the second voltmeter (busbar voltmeter 105), and the current fluctuation of the load (electric motor 109) measured by the motor ammeter 108.

[0050] In addition, the bus voltage abnormality detection method of this embodiment includes a step of measuring the voltage of an external power transmission system and calculating a voltage fluctuation amount of the external power transmission system, a step of measuring the voltage of the power supply bus 103 and calculating the voltage fluctuation amount of the power supply bus 103, a step of measuring the current of a load (motor 109) connected to the power supply bus 103 and calculating a current fluctuation amount of the load (motor 109), and a step of determining a voltage abnormality in the power supply bus 103 based on the voltage fluctuation amount of the external power transmission system, the voltage fluctuation amount of the power supply bus 103, and the current fluctuation amount of the load (motor 109).

[0051] Then, if the voltage fluctuations of the external power transmission system and the power supply bus 103 exceed respective predetermined thresholds and the current of the load (motor 109) exceeds the rated current, it is determined that a current increase due to a bus voltage abnormality has occurred, and the power supply system to which the load (motor 109) is connected is disconnected or switched to another power supply system.

[0052] According to this embodiment, the thermal effect on the load (auxiliary equipment) caused by minute voltage fluctuations can be detected at an early stage, and the load (auxiliary equipment) such as an electric motor connected to the bus can be protected. EXAMPLES

[0053] Second Embodiment A bus voltage anomaly detection device and a bus voltage anomaly detection method according to a second embodiment of the present invention will be described with reference to FIG.

[0054] This embodiment is a modified example of Fig. 2 (determination logic in a low voltage state) of embodiment 1. The control logic of this embodiment shown in Fig. 4 is a logic in which, in addition to the signals 201 to 204 in Fig. 2, the effect on frequency is further taken into consideration as an effect of a voltage drop.

[0055] When the frequency drops, losses in the load (auxiliary equipment) increase, and the temperature rise caused by the losses can have a thermal effect on the load (auxiliary equipment).

[0056] Therefore, in this embodiment, in the determination logic unit 121, the bus frequency fluctuation (frequency drop side) detection signal 401 outputs "1" when the bus frequency drops by -E% of the rated frequency.

[0057] When either the signal 201 or the signal 202 indicating that the external power transmission system voltage has dropped outputs “1”, the OR circuit 205 outputs “1”.

[0058] In addition, when an increase in current of the motor 109 is detected and a “1” is output in the signal 203, or when a decrease in the bus frequency is detected and a “1” is output in the signal 401, a “1” is output in the OR circuit 205.

[0059] Furthermore, when a voltage drop in the busbar in the power plant is detected and a "1" is output in the signal 204, a "1" is output in the three-phase AND circuit 206, and a circuit breaker trip signal 208 is output via a delay timer 207 that is installed to prevent malfunction due to momentary behavior.

[0060] As described above, in the bus voltage abnormality detection device 1 of this embodiment, when the frequency of the bus voltage exceeds a predetermined threshold, the judgment logic unit 121 judges that a current increase due to frequency fluctuation has occurred, and disconnects the power supply system to which the motor 109 is connected, or switches the power supply to another system, based on the AND condition of the voltage fluctuation amount of the external power transmission system and the voltage fluctuation amount of the power supply bus 103.

[0061] Although it is assumed that the bus frequency is calculated based on the voltage waveform, a frequency meter may be installed to directly measure the bus frequency.

[0062] In addition, in the above, an example in which the bus frequency decreases has been described, but the same applies when the bus frequency increases, since the output torque of the motor decreases, resulting in increased losses due to increased slip.

[0063] In addition, in each of the above embodiments, it is assumed that the power receiving breaker 102 on the power supply panel is tripped to disconnect the power supply system or switch the power supply to another system, but if the power supply system is not disconnected or switched, the motor circuit breaker 106 may be tripped to stop the motor 109.

[0064] The present invention is not limited to the above-described embodiments, and includes various modified examples. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the configurations described. It is also possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace a part of the configuration of each embodiment with another configuration. [Explanation of symbols]

[0065] 1. Bus voltage abnormality detection device 101...Receiving transformer 102... Power receiving circuit breaker 103…Power busbar 104... Busbar voltmeter transformer 105...Busbar voltmeter 106...Motor circuit breaker 107...Motor ammeter transformer 108...Motor ammeter 109...Electric motor 110…External power transmission system voltmeter transformer 111…External power grid voltage meter 120…Measurement signal 121...Decision logic section 122…Breaker trip signal 201…External power transmission system voltage fluctuation (voltage drop side) detection signal 202: Lower limit tap signal of receiving transformer 101 203…Motor current increase detection signal 204... Bus voltage fluctuation (voltage drop side) detection signal 205...OR circuit 206…3-phase AND circuit 207...Delay timer 208…Breaker trip signal 301…External power grid voltage fluctuation (voltage rise side) detection signal 302: Upper tap limit signal of receiving transformer 101 303... Bus voltage fluctuation (voltage rise side) detection signal 401... Bus frequency fluctuation (frequency drop side) detection signal

Claims

1. a first voltmeter that measures a voltage of an external power transmission system; a second voltmeter for measuring the bus voltage; an ammeter for measuring a current of a load connected to the bus; a determination logic unit that determines a voltage abnormality of the bus bar based on a voltage fluctuation amount of the external power transmission system measured by the first voltmeter, a voltage fluctuation amount of the bus bar measured by the second voltmeter, and a current fluctuation amount of the load measured by the ammeter; and A bus voltage abnormality detection device comprising:

2. The bus voltage abnormality detection device according to claim 1, The bus voltage abnormality detection device is characterized in that when the voltage fluctuation amount of the external power transmission system and the voltage fluctuation amount of the bus exceed a predetermined threshold value and the current of the load exceeds a rated current, the judgment logic unit determines that a current increase due to a bus voltage abnormality is occurring, and disconnects the power supply system to which the load is connected or switches to another power supply system.

3. The bus voltage abnormality detection device according to claim 2, A bus voltage abnormality detection device characterized in that the judgment logic unit determines that a current increase due to a bus voltage abnormality is occurring based on a voltage drop in the external power transmission system and the bus, and an increase in current in the load.

4. The bus voltage abnormality detection device according to claim 2, The busbar voltage abnormality detection device, characterized in that the judgment logic unit judges that an overvoltage caused by an external power transmission system is occurring based on a voltage increase in the external power transmission system and the busbar.

5. The bus voltage abnormality detection device according to claim 2, The busbar voltage abnormality detection device is characterized in that the judgment logic unit has an OR circuit that determines that the voltage fluctuation amount of the external power transmission system has exceeded a predetermined threshold when either the voltage fluctuation amount of the external power transmission system or the tap fluctuation amount of a receiving transformer connected between the external power transmission system and the busbar exceeds a predetermined threshold.

6. The bus voltage abnormality detection device according to claim 2, the load is an electric motor, The bus voltage abnormality detection device is characterized in that the judgment logic unit determines that a current increase due to frequency fluctuation is occurring when the frequency of the bus voltage exceeds a predetermined threshold, and disconnects the power supply system to which the motor is connected based on the AND condition of the voltage fluctuation amount of the external power transmission system and the voltage fluctuation amount of the bus.

7. A bus voltage abnormality detection method for detecting a voltage abnormality in a bus connected to an external power transmission system, comprising: (a) measuring a voltage of an external power transmission system and calculating a voltage fluctuation amount of the external power transmission system; (b) measuring a voltage of a bus bar and calculating a voltage fluctuation amount of the bus bar; (c) measuring a current of a load connected to the bus and calculating a current fluctuation amount of the load; (d) determining a voltage abnormality of the busbar based on the voltage fluctuation amount of the external power transmission system calculated in the step (a), the voltage fluctuation amount of the busbar calculated in the step (b), and the current fluctuation amount of the load calculated in the step (c); A bus voltage abnormality detection method comprising:

8. A bus voltage abnormality detection method according to claim 7, a busbar voltage abnormality detection method, characterized in that in step (d), if the voltage fluctuation amount of the external power transmission system and the voltage fluctuation amount of the busbar each exceed a predetermined threshold value and the current of the load exceeds a rated current, it is determined that a current increase due to a busbar voltage abnormality is occurring, and the power supply system to which the load is connected is disconnected or switched to another power supply system.

9. A bus voltage abnormality detection method according to claim 8, A bus voltage abnormality detection method, characterized in that in the step (d), it is determined that a current increase due to a bus voltage abnormality is occurring based on a voltage drop in the external power transmission system and the bus, and an increase in current in the load.

10. A bus voltage abnormality detection method according to claim 8, A busbar voltage abnormality detection method, characterized in that in the step (d), it is determined that an overvoltage caused by an external power transmission system is occurring based on a voltage increase in the external power transmission system and the busbar.

11. A bus voltage abnormality detection method according to claim 8, a busbar voltage abnormality detection method, characterized in that in the step (d), if either a voltage fluctuation amount of the external power transmission system or a tap fluctuation amount of a power receiving transformer connected between the external power transmission system and the busbar exceeds a predetermined threshold, it is determined that the voltage fluctuation amount of the external power transmission system has exceeded a predetermined threshold.

12. A bus voltage abnormality detection method according to claim 8, the load is an electric motor, a bus voltage abnormality detection method, characterized in that in the step (d), if the frequency of the bus voltage exceeds a predetermined threshold, it is determined that a current increase due to frequency fluctuation is occurring, and the power supply system to which the motor is connected is disconnected under an AND condition of the voltage fluctuation amount of the external power transmission system and the voltage fluctuation amount of the bus.

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