JPH09327179A - Abnormality detector and protector for ac/dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to detect a commutation failure even when all three phases become a conduction state by providing a means which determines that an AC/DC converter has a trouble when such a state that absolute values of AC currents of all the phases of the AC/DC converter is a predetermined value or above continues for a given period of time. SOLUTION: DC current Idc and AC currents Ia-Ic of respective phases are input into level judging circuits 4-7 to determine the levels of these currents. Then, logical products of the output of the level judging circuit 4 and those of the level judging circuits 5-7 are calculated by AND circuits 8, respectively. When current is normally commutated, DC current Idc flows and AC current of one phase is nearly zero. However, when there is a commutation failure and a bypass pair state or a two-phase conduction state continues, such a state continues that DC current Idc may flow and AC currents of one or more phases may not flow. By this method, therefore, a commutation failure wherein DC current Idc flows from an OR circuit 10 and AC currents of one or more-phases do not flow can be detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abnormality detection device and a protection device for an AC / DC converter.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing an abnormality detecting device for an AC / DC converter disclosed in, for example, Japanese Patent Application No. 7-222956. In FIG.
It is an AC / DC converter composed of a to 1f. Reference numeral 2 is a current transformer (hereinafter referred to as CT) that detects the DC current Idc of the AC / DC converter 1.
3a to 3c are current transformers (hereinafter referred to as CT) that detect the alternating currents Ia to Ic of the respective phases of the AC / DC converter 1.
7 to 7 are level determination circuits for comparing the currents detected by the CTs 2 and 3a to 3c with predetermined values K1 to K4, 8 is an AND circuit, 9 is an on-delay timer, and 10 is an OR circuit.

Next, the operation will be described. The DC current Idc detected by CT2 and the alternating currents Ia-Ic of the respective phases detected by CT3a-3c are input to the level judgment circuits 4-7 for level judgment. When the DC current Idc is larger than the predetermined value K1, the level determination circuit 4
In addition, the level determination circuits 5 to 7 use the alternating currents Ia to I of the respective phases.
Predetermined values K2 to K4 having absolute values of c such that almost (0) of the alternating currents Ia to Ic can be detected.
If it is smaller, it outputs "1".

Next, the logical product of the output of the level judging circuit 4 and the outputs of the level judging circuits 5 to 7 is obtained by the logical product circuit 8. Normally, when the commutation is normally performed, the DC current Idc is flowing, and one phase of the AC currents Ia to Ic is substantially (0), that is, the AND circuit 8
The output of '1' goes around each phase every 60 °, but commutation failure occurs due to an accident in the AC system, and for example, the electric valves 1a, 1d of the same system of the AC / DC converter 1 are In the case of a bypass pair (hereinafter, referred to as BPP) state in which they are simultaneously conducted and the DC side is short-circuited, or a two-phase flow state in which a current continuously flows in two phases of an alternating current, The state where the DC current Idc is flowing and the AC current is not flowing in one or more phases continues.

FIG. 5 shows the electric valves 1a, 1 of the AC / DC converter 1.
This shows a state in which b is kept conducting and two-phase current is flowed. At this time, the direct current Idc and the alternating currents Ia, Ic
Current flows, but the alternating current Ib does not flow. The output of the logical product circuit 8 is input to the on-delay timer 9 for each phase, and it is detected that the logical product circuit 8 continues to output "1" for a predetermined time or more and is input to the logical sum circuit 10. To do. A direct current Idc is flowing from the output of the OR circuit 10,
Moreover, it can be detected that commutation failure continues such that no AC current is flowing in one or more phases.

[0006]

Since the conventional abnormality detecting device for the AC / DC converter is constructed as described above, the BPP
It is possible to detect the continuation of the commutation failure in the state and the commutation failure in the two-phase conduction state. However, the commutation failure occurs in three phases and the current continuously flows in three phases of the AC system. When the phase conduction state continued, there was a problem that the alternating current (0) could not be detected and the commutation failure could not be detected.

The present invention has been made to solve the above problems, and an object thereof is to obtain an abnormality detection device and a protection device for an AC / DC converter that can detect a commutation failure even in a three-phase flow state. To aim.

[0008]

An abnormality detecting apparatus for an AC / DC converter according to claim 1, wherein the DC current of the AC / DC converter is a predetermined value or more, and the AC current of at least one phase of the AC / DC converter is detected. First abnormality determining means for determining an abnormality when a state in which the absolute value is equal to or less than a predetermined value continues for a predetermined time,
A case where the direct current of the AC / DC converter is a predetermined value or more, and the state in which the absolute value of the AC current of all phases of the AC / DC converter is a predetermined value or more continues for a predetermined time. The second abnormality determining means is provided.

According to a second aspect of the present invention, there is provided a protection device for an AC / DC converter.
An abnormality detecting device for an AC / DC converter according to claim 1, an accident detecting means for detecting an accident in the AC system based on a change in voltage or current of the AC system, and an abnormality detecting device for the AC / DC converter detects an abnormality. And first protection means for transmitting a protection operation signal to the AC / DC converter when the fault detection means detects a fault.

According to a third aspect of the present invention, there is provided the abnormality detecting device for an AC / DC converter, wherein the DC current of the AC / DC converter is a predetermined value or more, and the absolute values of the AC currents of all the phases of the AC / DC converter are a predetermined value or more. Second abnormality determining means for determining that the state is abnormal when the state continues for a predetermined time, and the DC current of the AC / DC converter is a predetermined value or more and the AC currents of all phases of the AC / DC converter are Third abnormality determining means for determining an abnormality when a state in which the absolute value is equal to or less than a predetermined value continues for a predetermined time, and the absolute value of the alternating current of at least one phase of the AC / DC converter is a predetermined value or more. And a fourth abnormality determination means for determining an abnormality when the second abnormality determination means has not determined that the abnormality has occurred for a predetermined time.

According to a fourth aspect of the present invention, there is provided a protection device for an AC / DC converter.
An AC / DC converter abnormality detecting device according to claim 3, an AC / DC converter abnormality detecting device for detecting an AC system error based on a change in the AC system voltage or current, and a second AC / DC converter abnormality detecting device. A second protection unit that sends a protection operation signal to the AC / DC converter when the abnormality determination unit detects an abnormality and the accident detection unit detects an accident; and an abnormality detection device for the AC / DC converter. A third protection means for sending a protection operation signal to the AC / DC converter when the third abnormality determination means detects an abnormality and the accident detection means detects an accident; and an abnormality of the AC / DC converter. And a fourth protection means for transmitting a protection operation signal to the AC / DC converter when the fourth abnormality determination means of the detection device detects an abnormality and the accident detection means detects an accident. It is.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1. 1 is a block diagram showing an abnormality detecting device for an AC / DC converter according to Embodiment 1 of the present invention. In the figure, reference numeral 1 is an AC / DC converter composed of electric valves 1a to 1f made of thyristors. Reference numeral 2 is a current transformer (hereinafter referred to as CT) for detecting the DC current Idc of the AC / DC converter 1. 3
a to 3c are current transformers (hereinafter referred to as CT) that detect the alternating currents Ia to Ic of the respective phases of the AC / DC converter 1, and 4 to 7 are CTs.
2, 3a to 3c detected current and predetermined value K1
Level determination circuit for comparing with K4, 8 is a logical product circuit, 9
Is an on-delay timer, and 10 is an OR circuit. As described above, it is the same as that of FIG. 5 shown as the prior art, and by the level determination circuits 4 to 7, the AND circuit 8, the on-delay timer 9 and the OR circuit 10, It constitutes a first abnormality determination means. Further, 11 is a logical product circuit that takes the logical product of the input from the level determination circuit 4 and the negation of the inputs of the level determination circuits 5 to 7, and 12 is an on-delay timer, which is the level determination circuits 4 to 7 and the logical product circuit. 11, the on-delay timer 12 and the OR circuit 10 constitute second abnormality determining means.

Next, the operation will be described. The DC current Idc detected by CT2 and the alternating currents Ia-Ic of the respective phases detected by CT3a-3c are input to the level judgment circuits 4-7 for level judgment. When the DC current Idc is larger than the predetermined value K1, the level determination circuit 4
In addition, the level determination circuits 5 to 7 use the alternating currents Ia to I of the respective phases.
Predetermined values K2 to K4 having absolute values of c such that almost (0) of the alternating currents Ia to Ic can be detected.
If it is smaller, it outputs "1".

Next, the logical product circuit 8 takes the logical product of the output of the level judgment circuit 4 and the outputs of the level judgment circuits 5 to 7, respectively. Normally, when the commutation is normally performed, the direct current Idc is flowing, and one phase of the alternating currents Ia to Ic is substantially (0), that is, the logical product circuit 8
The output of '1' goes around each phase every 60 °, but commutation failure occurs due to an accident in the AC system, and for example, the electric valves 1a, 1d of the same system of the AC / DC converter 1 are In the case of a bypass pair (hereinafter, referred to as BPP) state in which the currents are simultaneously conducted and the DC side is short-circuited, or a two-phase flow state in which a current continuously flows in two phases in the AC system, The state where the DC current Idc is flowing and the AC current is not flowing in one or more phases continues.
That is, the state where the AND circuit 8 outputs "1" continues.

Therefore, the output of the AND circuit 8 is input to the on-delay timer 9 for each phase, and the AND circuit 8 outputs "1".
Is continuously output for a predetermined time or longer and is input to the logical sum circuit 10, a direct current Idc is flowing from the output of the logical sum circuit 10 and an alternating current is generated in one or more phases. It can be detected that the commutation failure continues such that the non-flowing state continues.

Further, the logical product circuit 11 calculates the logical product of the output of the level judgment circuit 4 and the inverted outputs of the level judgment circuits 5 to 7. FIG. 1 shows a state in which the electric valves 1a to 1c of the AC / DC converter 1 remain conductive and three-phase flow occurs. At this time, the direct current Idc and the alternating currents Ia to Ic continue to flow. Therefore, the AND circuit 1
The output of 1 is input to the on-delay timer 12, and it is detected that the AND circuit 11 continues to output "1" for a predetermined time or longer, and it is input to the OR circuit 10 that takes the logical sum.
From the output of the AND circuit 11, it is possible to detect that the DC current Idc is flowing and the AC currents Ia to Ic are continuously flowing in the three phases, that is, the three-phase flowing state is continued.

As described above, according to the first embodiment, the logical product circuit 11 for adding the logical product of the output of the level judging circuit 4 and the inverted outputs of the level judging circuits 5 to 7 is added. So that BPP and 2
In addition to the detection of commutation failure in the phase current state, the DC current Idc,
There is an effect that a commutation failure in a three-phase flow state in which the alternating currents Ia to Ic continue to flow can be detected. In addition, since it can be configured by simply adding the AND circuit 11 and the on-delay timer 12 to the conventional device, there is an effect that it can be easily configured.

Embodiment 2. FIG. 2 is a configuration diagram showing a protection device for an AC / DC converter according to Embodiment 2 of the present invention.
In the figure, 13 is a transformer for conversion, 14 is an AC bus, 1
Reference numeral 5 is the abnormality detection device shown in the first embodiment. Reference numeral 16 is a transformer (hereinafter referred to as PT), 17 is an accident detector (accident detection means) that detects an accident in the AC system based on the output of PT 16, and 18 is an abnormality detection device 15 for detecting an abnormality of the AC / DC converter 1. This is a logical product circuit (first protection means) that detects and outputs a protection operation signal to the AC / DC converter 1 when the accident detector 17 detects an accident.

Next, the operation will be described. For example, in the case where a commutation failure continues due to a continuous AC system accident such as a ground fault accident at the nearest end of the AC / DC converter, and the electric valve is continuously energized, the abnormality detection device according to the first embodiment. The commutation failure is detected at 15, and the accident detector 17 detects that the AC system accident continues. The AC system accident detector 17 constantly monitors the bus voltage of the AC bus 14 with the PT 16 and determines that the AC system failure is a condition that the bus voltage is lower than a predetermined value for a predetermined time. There is one that Then, the output of the abnormality detection device 15 and the output of the accident detector 17 are input to the AND circuit 18. A logical product circuit 18 takes a logical product of these outputs and outputs a protection operation command for continuation of commutation failure to protect the electric valve. As the protection operation, there is one that issues a stop command to the converter control device (not shown) of the AC / DC converter 1 to stop the operation of the DC system. In the second embodiment, as the accident detector 17, an AC system accident is taken as a judgment condition that the condition that the bus voltage becomes smaller than a predetermined value continues for a predetermined time. An AC system fault may be set on the condition that the condition in which the current becomes larger than the predetermined value continues for a predetermined time.

As described above, according to the second embodiment, the abnormality detecting device 15 detects the abnormality of the AC / DC converter 1,
In addition, since the AND circuit 18 that sends a protection operation signal to the AC / DC converter 1 when the accident detector 17 detects an accident is provided, the electric valve of the AC / DC converter 1 can operate when an AC system accident occurs. When an abnormality such as three-phase flow is detected, there is an effect that it is possible to shift to the protection operation and protect the electric valve of the AC / DC converter 1. Further, since an accident in the AC system is detected and the logical product is taken, even if the abnormality detection device 15 malfunctions, the reliability of stable operation of the DC system can be improved without shifting to the protection operation. is there.

Embodiment 3 FIG. 3 is a configuration diagram showing an abnormality detecting device for an AC / DC converter according to Embodiment 3 of the present invention. In the figure, reference numerals 21 to 23 denote currents Ia to Ic detected by the CTs 3a to 3c and predetermined values K2 to K4. A level determination circuit for comparing with
.About.23 and a logical product circuit for taking the logical product of outputs, 25 is an on-delay timer, and these level determination circuits 4, 21 ...
23, the logical product circuit 24, and the on-delay timer 25 constitute a second abnormality determining means. 26 is a logical sum circuit for calculating the logical sum of the outputs of the level judgment circuits 21 to 23;
Is a negation circuit, 28 is a logical product circuit that takes the logical product of the output of the level judgment circuit 4 and the output of the negation circuit 27, and 29 is an on-delay timer.
23, OR circuit 26, NOT circuit 27, AND circuit 28
And the on-delay timer 29 constitutes a third abnormality determining means. Further, 30 is an on-delay timer, 31
Is a logical sum circuit, and 32 is a logical product circuit that takes the logical product of the negation of the output of the on-delay timer 25 and the logical sum circuit 31, and these level judgment circuits 21 to 23, the on-delay timer 30, the logical sum circuit 31 and the logical circuit. The product circuit 32 constitutes fourth abnormality determining means.

Next, the operation will be described. First, CT
The level determination circuits 4, 21 and 2 receive the direct current Idc and the alternating currents Ia to Ic of the respective phases taken in from the circuits 2 and 3a to 3c.
Input to 3 to judge the level. Here, in the level determination circuit 4, when the direct current Idc exceeds the predetermined value K1, in the level determination circuits 21 to 23, the absolute values of the alternating currents Ia to Ic of the respective phases exceed the predetermined values K2 to K4. '1' is output to. These level judgment circuits 4, 21 ...
The logical product of the outputs of 23 is taken by the logical product circuit 24, the output is input to the on-delay timer 25, the direct current Idc is flowing, and the alternating currents Ia to I are generated in all the phases on the alternating current side.
It is detected that the state in which c is flowing continues for a predetermined time, that is, the commutation failure due to the three-phase flow state continues.

For commutation failure due to the BPP state, the outputs of the level determination circuits 21 to 23 are changed to the logical sum circuit 2
6 is a circuit for time-determining by an on-delay timer 29 what is obtained by a logical product circuit 28 of a logical product of a signal obtained by inverting the logical sum in 6 by a NOT circuit 27 and the output of the level determination circuit 4, Further, regarding the commutation failure due to the two-phase flow state, the outputs of the level determination circuits 21 to 23 are input to the on-delay timer 30, and the outputs are ORed by the OR circuit 31, and the output and the above-mentioned 3 are obtained. It can be detected by a logical product circuit 32 which performs a logical product with the inversion signal of the output of the on-delay timer 25 which determines the phase flow state.

As described above, according to the third embodiment, the cause of the commutation failure can be detected separately for the three-phase flow state, the BPP state, and the two-phase flow state, so that the protection is performed corresponding to each state. There is an effect that the operation can be performed.

Embodiment 4 FIG. 4 is a configuration diagram showing a protection device for an AC / DC converter according to Embodiment 4 of the present invention.
In the figure, reference numeral 33 denotes the abnormality detection device shown in the third embodiment. Reference numeral 34 denotes a protection operation for the AC / DC converter 1 when the abnormality detection device 33 detects an abnormality of the AC / DC converter 1 in the 3-phase flow state and the accident detector 17 detects an accident. An AND circuit (second protection means) for transmitting a signal, and 35 is a BPP of the AC / DC converter 1 in which the abnormality detection device 33 is provided.
An AND circuit (third protection means) that detects a state abnormality and sends a protection operation signal corresponding to the BPP state to the AC / DC converter 1 when the accident detector 17 detects an accident,
Reference numeral 36 indicates a protection operation according to the two-phase flow state of the AC / DC converter 1 when the abnormality detection device 33 detects an abnormality in the two-phase flow state of the AC / DC converter 1 and the accident detector 17 detects an accident. It is an AND circuit (fourth protection means) that sends out a signal.

Next, the operation will be described. For example, when the commutation failure continues due to the continuation of an AC system accident such as a ground fault accident near the AC / DC conversion station and the electric valve is continuously energized, the abnormality detection device according to the third embodiment is used. 33 at 3
The commutation failure of the phase-current, BPP or two-phase flow is detected, and the accident detector 17 detects that the AC system accident continues. The three outputs of the abnormality detection device 33 are respectively combined with the outputs of the accident detector 17 to obtain the logical product circuits 34 to 36.
Is input to The AND circuits 34 to 36 take logical products and divide them into a protection operation command for a three-phase flow state, a protection operation command for a BPP state, and a protection operation command for a two-phase flow state to convert the AC / DC converter 1. To a controller (not shown) to protect the valve according to each state.

As described above, according to the fourth embodiment, the AC / DC converter 1 has three electric valves in the event of an AC system accident.
When the continuous conduction state of the phase conduction, the BPP or the two-phase conduction is established, there is an effect that the protection valve can be protected according to each state and the electric valve can be protected. In addition, since an accident in the AC system is detected and AND is performed, even if the abnormality detection device 33 malfunctions, the operation does not shift to the protection operation, and the effect of improving the reliability of the stable operation of the DC system can be improved. is there.

[0028]

As described above, according to the first aspect of the present invention, the direct current of the AC / DC converter is a predetermined value or more, and the absolute values of the AC currents of all the phases of the AC / DC converter are the predetermined values. Since it is configured to include a second abnormality determination means for determining an abnormality when the state of being equal to or greater than the value of continues for a predetermined time,
In addition to detection of commutation failure in BPP and two-phase flow, 3
There is an effect that it is possible to detect a commutation failure in a state of mutual flow.

According to the second aspect of the present invention, when the abnormality detecting device of the AC / DC converter detects an abnormality and the accident detecting means detects an AC system accident, a protection operation signal is sent to the AC / DC converter. Since it is configured to have the first protection means for sending out, when an abnormality such as a three-phase flow state of the AC / DC converter is detected at the time of an AC system accident, the protection operation is performed by shifting to the protection operation. There is an effect that can be. Also,
Since the protection operation is performed only when the AC system accident is detected, even if the abnormality detection device malfunctions, the reliability of the stable operation of the DC system can be improved without shifting to the protection operation.

According to the third aspect of the present invention, there is provided a state in which the DC current of the AC / DC converter is a predetermined value or more and the absolute values of the AC currents of all the phases of the AC / DC converter are the predetermined values or more. The second abnormality determining means for determining an abnormality when continuing for a predetermined time, the direct current of the AC / DC converter is a predetermined value or more, and the absolute values of the AC currents of all phases of the AC / DC converter are predetermined. And a state in which the absolute value of the alternating current of at least one phase of the AC / DC converter is greater than or equal to a predetermined value. Since it is configured to include a fourth abnormality determining unit that determines the abnormality when the second abnormality determining unit continues for a predetermined time and the second abnormality determining unit does not determine the abnormality, the cause of the commutation failure is communicated in three phases. Flow status, BPP status and two-phase flow status are detected separately Kill Therefore, there is an effect capable of performing protection operation in response to each state.

According to the fourth aspect of the invention, the second abnormality determining means of the abnormality detecting device for the AC / DC converter detects the abnormality,
A second protection unit for transmitting a protection operation signal to the AC / DC converter when the accident detection unit detects an AC system accident; and a third abnormality determination unit of the AC / DC converter abnormality detection device. Third protection means for detecting an abnormality and transmitting a protection operation signal to the AC / DC converter when the accident detection means detects an AC system accident; and a third protection means for detecting the abnormality of the AC / DC converter. And a fourth protection means for transmitting a protection operation signal to the AC / DC converter when the abnormality determination means detects an abnormality and the accident detection means detects an AC system accident. Therefore, when the AC / DC converter is in a continuous energized state of three-phase flow, BPP or two-phase flow in the event of an AC system accident, the protection valve can be shifted to a protection operation corresponding to each state to protect the electric valve. effective. In addition, since the protection operation is performed only when an AC system accident is detected, even if the abnormality detection device malfunctions, the operation does not shift to the protection operation, and the effect of improving the reliability of the stable operation of the DC system can be improved. is there.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an abnormality detection device for an AC / DC converter according to Embodiment 1 of the present invention.

FIG. 2 is a configuration diagram showing a protection device for an AC / DC converter according to Embodiment 2 of the present invention.

FIG. 3 is a configuration diagram illustrating an abnormality detection device for an AC / DC converter according to Embodiment 3 of the present invention;

FIG. 4 is a configuration diagram showing a protection device for an AC / DC converter according to Embodiment 4 of the present invention.

FIG. 5 is a configuration diagram showing a conventional AC / DC converter abnormality detection device.

[Explanation of symbols]

1 AC / DC converter, 4 level determination circuit (first to third abnormality determination means), 5 to 7 level determination circuit (first and second abnormality determination means), 8 AND circuit (first abnormality determination means) ), 9 on-delay timer (first abnormality determining means), 11, 24 AND circuit (second abnormality determining means), 12, 25 on-delay timer (second abnormality determining means), 15, 33 abnormality detection Device, 18 AND circuit (first protection means), 21-23 level determination circuit (second-fourth abnormality determination means), 26 OR circuit (third abnormality determination means), 27 NOT circuit (first) 3 abnormality determination means), 28 AND circuit (third abnormality determination means), 29
On-delay timer (third abnormality determination means), 30
On-delay timer (fourth abnormality determination means), 31 OR circuit (fourth abnormality determination means), 32 AND circuit (fourth abnormality determination means), 34 AND circuit (second protection means), 35 AND circuit (third protection means), 36 AND circuit (fourth protection means).

Claims (4)

[Claims] 1. When the direct current of the AC / DC converter is a predetermined value or more and the absolute value of the AC current of at least one phase of the AC / DC converter is a predetermined value or less for a predetermined time. First abnormality determining means for determining an abnormality, and a state in which the DC current of the AC / DC converter is a predetermined value or more and the absolute values of AC currents of all phases of the AC / DC converter are a predetermined value or more. An abnormality detecting device for an AC / DC converter, comprising: a second abnormality determining unit that determines an abnormality when continuing for a predetermined time. 2. An abnormality detection device for an AC / DC converter according to claim 1, an accident detection means for detecting an accident in the AC system based on a change in voltage or current of the AC system, and an abnormality detection for the AC / DC converter. A protection device for an AC / DC converter, comprising: a first protection unit that sends a protection operation signal to the AC / DC converter when the device detects an abnormality and the accident detection unit detects an accident. 3. Abnormality when the DC current of the AC / DC converter is a predetermined value or more and the absolute value of the AC currents of all the phases of the AC / DC converter is the predetermined value or more for a predetermined time. And a second abnormality determining means for determining that the DC current of the AC / DC converter is a predetermined value or more and the absolute value of the AC currents of all phases of the AC / DC converter is a predetermined value or less. A third abnormality determining means for determining an abnormality when continuing for a period of time, and a state in which the absolute value of the alternating current of at least one phase of the AC-DC converter is equal to or greater than a predetermined value for a predetermined time, and An abnormality detecting device for an AC / DC converter, comprising: a fourth abnormality determining means that determines an abnormality when the second abnormality determining means does not determine that the abnormality is occurring. 4. An abnormality detection device for an AC / DC converter according to claim 3, an accident detection means for detecting an accident in the AC system based on a change in voltage or current of the AC system, and an abnormality detection for the AC / DC converter. A second protection unit for transmitting a protection operation signal to the AC / DC converter when the second abnormality determination unit of the device detects an abnormality and the accident detection unit detects an accident; and the AC / DC converter. Third protection means for transmitting a protection operation signal to the AC / DC converter when the third abnormality determination means of the abnormality detection device detects an abnormality and the accident detection means detects an accident; A fourth protection means for transmitting a protection operation signal to the AC / DC converter when the fourth abnormality determination means of the AC / DC converter abnormality detection device detects an abnormality and the accident detection means detects an accident. Protection device for AC / DC converter with Place.