JPH04164262A - Power supply switching device - Google Patents

Abstract

PURPOSE:To enable high-accuracy detection of an excessive current and phase interruption by constituting the device in such a way that first and second monitoring actions are alternately repeated, and when the currents of respective phases of a three-phase alternating current have exceeded a prescribed value, or when the current of one phase has gone down beyond a prescribed level than those of the other phases, the switches are turned off respectively. CONSTITUTION:The currents of respective phases of a three-phase alternating current continuously flowing in the closed condition of an electromagnetic switch 1 are detected by current detecting parts 21a to 21c, and these are monitored by a monitoring control part 23. The control part 23 carries out alternately first and second monitoring actions in a prescribed time cycle. In the first monitoring action, it is judged whether or not the current values of respective phases have exceeded a prescribed value, and when the condition exceeding the prescribed value continues, the switch 1 is turned off. In the second monitoring action, when the current of either one of three phases has gone down that the other phases and when such a condition has continued, the switch 1 is turned off. Thus, the presence of excessive current and phase interruption can be detected with high accuracy.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a power supply switching device that opens and closes a three-phase alternating current input for, for example, driving a motor. The present invention relates to a power switchgear equipped with a supervisory control unit that performs both phase-based supervisory control.

[Conventional technology]

For example, a power supply unit for driving a three-phase AC motor is provided with a switch for opening and closing the three-phase AC input, and an electromagnetic switch is generally used as this switch. In this electromagnetic switch, an actuator is electromagnetically driven by a push button operation, and contacts corresponding to each phase of a three-phase alternating current are opened and closed by this actuator.

When using this type of switch, a protection device may be provided to cut off the supply of current when an excessive current flows or when one phase of the three-phase alternating current is missing.

A conventional example of this type of protection device is known as a thermal relay. This thermal relay is equipped with a bimetal that deforms due to Joule heat depending on the amount of current flowing through each phase of the three-phase alternating current.The deformation of this bimetal drives a lever, etc., and the lever opens and closes the contacts. . In this thermal relay, when an excessive current flows through any phase, the contacts open due to the deformation of the bimetal, and the supply of three-phase alternating current is cut off. Further, when any phase of the three-phase alternating current is in an open-phase state, the contact opens due to deformation of the bimetal of the phase where the current amount has decreased, and the supply of the three-phase alternating current is cut off.

[Problems to be Solved by the Invention] However, in the protection device using the thermal relay, since the contacts are opened and closed by deformation of the bimetal, there is a certain range in the amount of current when the interrupting operation is performed. However, it has the disadvantage that high-precision characteristics cannot be obtained.

Furthermore, the deformation state of the bimetal changes depending on the so-called cold start, in which power supply is started after a long period of no current supply, and the so-called hot start, in which power supply is resumed after a short period of interruption. ,
Therefore, the power cutoff characteristics change during both starts. Further, since the power cutoff characteristics depend on the deformation characteristics of the bimetal, it is also impossible to change the level (threshold value) of the cutoff current at the time of power cutoff.

Furthermore, in the bimetal system, after the power is cut off due to excessive current, the bimetal cools down naturally and the contact returns.
There is also the drawback that the bimetal may flap if the cause of the excessive current is not completely eliminated.

The present invention solves the above-mentioned conventional problems, and can cut off the power supply by detecting the presence or absence of excessive current and open phase with high precision, and can also switch the setting of the amount of current to be cut off. The purpose is to provide a power switchgear that provides a reliable power supply.

[Means to solve the problem]

The power switchgear according to the present invention includes a switch that opens and closes the input of three-phase AC, and a switch that is located on the output side of the switch and that controls the amount of current in each phase of the three-phase AC that flows when the switch is in a closed state. A power supply switching unit that is provided with a current detection unit that detects the current, a monitoring control unit that monitors the amount of current based on the detection output of the current detection unit, and a switching unit that operates the switch according to the judgment of the monitoring control unit. In the apparatus, in the monitoring control unit, a first monitoring operation and a second monitoring operation are alternately repeated in a predetermined cycle, and in the first monitoring operation, the amount of current of each phase of the three-phase alternating current is When a predetermined value is exceeded, a command signal for opening the switch is output to the switching unit, and in a second monitoring operation, the amount of current in any phase of the three-phase alternating current changes to the current in the other phase. The present invention is characterized in that a command signal for opening the switch is output to the switching unit when the amount falls below a predetermined level.

[Operation] In the above means, the amount of current of each phase of the three-phase alternating current that continues to flow with the switch in the closed state is detected by the current detection section, and this amount of current is monitored by the monitoring control section. In the supervisory control section,
For example, the first and second
monitoring operations are performed alternately. In the first monitoring operation,
It is determined whether the current value of each phase has exceeded a predetermined value, and when a current of a predetermined value or more flows, for example, when this occurs continuously during a predetermined number of cycles of monitoring operation, the switch is opened. Control is performed to cut off the power. In addition, in the second monitoring operation, when the amount of current in any phase of the three-phase alternating current falls below a predetermined level than the amount of current in other phases, for example, when this occurs continuously during a predetermined number of cycles of monitoring operation, etc. Control is performed to open the switch and cut off the power supply.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block and circuit diagram of a power switchgear according to the present invention.

In FIG. 1, the reference numeral 1 is an electromagnetic switch, the reference numeral 20 is a protection part, and the reference numeral 30 is an operation switch.

In the above-mentioned electromagnetic switch 1, symbols 1a and 1b.

1c is an input terminal. This input terminal 1a.

1b and 1c each phase of three-phase AC (U phase, ■ phase, W phase)
are input. Inside the electromagnetic switch 1, switching contacts 2a, 2b, '2c and switching contacts 3 are provided, and the switching contacts 2a, 2b, 2c and 3 are simultaneously driven to open and close by an electromagnetic actuator 4. Of the switching contacts 2a, 2b, and 2c are used to open and close each phase of the three-phase alternating current, and 3 is an auxiliary contact. The symbol 5 on the right side of FIG. 1 is a drive input terminal.

DC power for driving the electromagnetic actuator 4 in the electromagnetic switch 1 is applied to the drive input terminal 5 . The operation switch 30 is provided in the supply path of the driving DC power. Turn on this operation switch 30
By the operation, the electromagnetic actuator 4 in the electromagnetic switch 1 is driven, and the switching contacts 2a, 2b, 2c, and 3 are switched to the closed state. Further, when the electromagnetic actuator 4 is driven by turning off the operation switch 30, the opening/closing contacts 2a, 2b, 2c, and 3 are in an open state.

Reference numerals 6a, 6b, and 6c are three-phase AC output terminals from the electromagnetic switch 1. A current detection unit 2 is installed in the protection unit 20.
1 is provided. This current detection section 21 includes three sensors 21a and 21b.

21c is provided. These three sensors 21a, 2
1b and 21c are switching contacts 2a and 2b in the electromagnetic switch 1
, 2c and the output terminals 6a, 6b, 6c. These sensors 21a, 21b, 21
c detects the amount of current in each phase of the three-phase alternating current flowing in the direction of the output terminals 6a, 6b, 6c when the switching contacts 2a, 2b, 2c are closed. Sensor 21a.

21b and 21c are composed of a ring made of permalloy material and a winding wire wound around the ring. Output terminals 6a, 6b from switching contacts 2a, 2b, 2c
, 6c are connected to the respective sensors 21a, 21
It is provided so as to pass through the rings b and 21c. Each sensor 21. The detection outputs from a, 21b, and 21c are input to the monitoring control unit 23 in the protection unit 20 via amplifiers 22a, 22b, and 22c.

The monitoring control section 23 is a microcomputer. The monitoring control unit 23 includes the sensors 21a and 2 installed in each phase.
A multiplexer 23a to which current detection outputs from 1b and 21c are input in parallel, an A/D converter 23b, a CPU, a memory, etc. are provided. The switching contact 3 provided as an auxiliary contact in the electromagnetic switch 1 is used to control the operation of the supervisory control section 23. This monitoring control unit 23 performs a first monitoring operation and a second monitoring operation, which will be described later. A control output resulting from the monitoring and control by the monitoring and controlling section is supplied to the switching section 24 .

When a control output is output to the switching unit 24 based on the supervisory operation control by the supervisory control unit 23, the switching contacts 2a, 2b, 2c, and 3 of the electromagnetic switch 1 are brought into an open state. The phase current supply is cut off. That is, the switching section 24 has a pair of contacts 24a, and this contact 24a.
An electromagnetic actuator 24b for opening and closing a is provided. - pair of contacts 24. a is connected in parallel to the operation switch 30 in a supply path of DC power input from the drive input terminal 5. When the electromagnetic actuator 24b is operated by the control output from the monitoring control section 23 and the contact 24a is opened, the operating switch 30 is turned off.
The state becomes the same as the FF state, and the operating state of the electromagnetic actuator 4 of the electromagnetic switch 1 is switched, and the switching contacts 2a, 2b,
2c is in an open state, and the three-phase alternating current is cut off.

Note that the actuator 2 of the switching section 24 is attached to the protection section 20.
A power supply unit 25 is provided for supplying power to 4b.

Next, the operation of the power switchgear will be explained.

For example, when supplying three-phase AC power to a load such as a three-phase morph, the operation switch 30 is turned on. As a result, the DC power supplied from the drive input terminal 5 is supplied to the electromagnetic actuator 4 of the electromagnetic switch 1, and each switching contact 2a in the electromagnetic switch 1 is
2b.

2c and 3 close. Therefore, the supply parts of each phase (U phase, ■ phase, W phase) of the three-phase AC are connected, and the output terminals 6a, 6b, 6
Three-phase alternating current is supplied to loads such as a three-phase motor via c.

The amount of current in each phase of the three-phase alternating current is measured by three sensors 21a and 21b.
, 21c, and the detection outputs are sent to amplifiers 22a, 22b.

22c and supplied to the multiplexer 23a of the supervisory control section 23. The detection output of the amount of current of each phase input in parallel to the multiplexer 23a is sent to the A/D converter 2.
3b, the signal is converted into a digital signal, and a current amount monitoring operation is executed according to a program set in advance.

FIG. 2 shows the monitoring operation in the monitoring control section 23 in the form of a time chart.

FIG. 2 fA) shows the operation of the auxiliary contact 3 of the electromagnetic switch 1. The electromagnetic actuator 4 of the electromagnetic switch 1 causes the switching contacts 2a, 2b, and 2c of each phase to close, and at the same time, the switching contact 3, which is an auxiliary contact, opens. The monitoring operation is started at .

A timer is provided in the monitoring control section 23, and the first monitoring operation and the second monitoring operation are alternately switched according to this timer. FIG. 2 FB+ shows a switching pulse for the first monitoring operation, and (C) shows a switching pulse for the second monitoring operation. As shown in FIG. 2 fB) (C), the first monitoring operation and the second monitoring operation are repeated alternately at predetermined cycles (for example, every 10 seconds). FIG. 2 (D) (E) (Fl indicates a timing pulse for sampling the amount of current of each phase of the three-phase alternating current.

The detection output of the amount of current output from each of the sensors 21a, 21b, and 21c is shown in FIG. 2FD+ (E).
It is detected according to the timing pulse shown for each of FF+. In other words, each phase of three-phase AC (U phase, ■ phase, W
The amount of current in FD+ (E
It is detected according to the timing of lFF+.

Figure 2 [G) (H) (Il indicates the first monitoring operation, and Figure 2 (J) indicates the second monitoring operation. Accordingly, the first monitoring operation and the second monitoring operation are repeated alternately every 10 seconds.

First, the first monitoring operation will be explained. In the first monitoring operation, the detection output of the current amount of each phase (U phase, ■ phase, W phase) is sampled according to the timing pulse shown in FIG. (G) indicates the current detection output of the U phase, (I() indicates the current detection output of the V phase, and (Il indicates the current detection output of the W phase.) In the first monitoring operation, each phase The determination is made based on whether the current value exceeds a predetermined level, and the set threshold value is indicated by L. Fig. 3 shows the above threshold value. It is set to allow inrush current when the operation switch 30 is first turned on and three-phase AC is connected. For example, for the first second, the rated current of the load such as a three-phase morph is The threshold value is set to several times the rated current, and after 10 seconds, it is set to 1 times the rated current, and from 1 second to 10 seconds, the threshold value is set to gradually decrease. The setting level of this threshold value can be changed externally.In Fig. 3, L2 and L3 are switchable respectively.
It shows the threshold level of deviation. For example, Ll is the so-called cold start threshold when the electromagnetic switch 1 is closed after being stopped for a long time, and L
2 is the threshold value at the time of a so-called hot start when the supply is stopped for a short time from the AC supply state and the electromagnetic switch 1 is closed again, and L3 indicates a threshold value between L+ and L2. . Each of these threshold values, ,L2. L3
The level may be switched externally using a manual switching unit, but for example, the switching contact (auxiliary contact) of the electromagnetic switch l
It is also possible to monitor the opening/closing time of 3, determine the optimum threshold value when turning on the three-phase alternating current, and automatically change the threshold value to L2 or L3 according to this determination.

The first monitoring operation is performed as follows.

First, the switching contacts 2a and 2b of the electromagnetic switch 1.

In the monitoring period T1 immediately after 2c becomes closed, the amount of inrush current is monitored. During the monitoring period T1, as shown in Figure 4 (Al), if the current value of any of the U phase, ■ phase, and W phase exceeds the threshold during this monitoring period T1, the inrush current It is determined that it is excessive and the switching unit 2
4, the actuator 24b in the switching section 24 opens the contact 24a, and the DC power to the electromagnetic actuator 4 of the electromagnetic switch 1 is cut off. As a result, the switching contacts 2a, 2b, and 2c become open, and the supply of three-phase alternating current is cut off. Furthermore, after the period T3 of the first monitoring operation in the next cycle, the amount of current in each phase is similarly monitored using the threshold value L (L, , L2, or). In the monitoring period after T3, if the amount of current exceeds the threshold even once, the control ratio J is output to the switching section 24 to cut off the supply of three-phase alternating current. Furthermore, even if the current does not exceed the threshold in the first monitoring operation of the cycle after T3, if the current exceeds the rated current as shown in Figure 4 (B), the next During period T, 1 of the first monitoring operation, whether or not the current value exceeds the rated current is similarly monitored. Then, when the amount of current exceeds the rated current for a predetermined number of consecutive periods (for example, six consecutive periods), the switching unit 24
A control output is output to the switching contacts 2a, 2 of the electromagnetic switch 1.
b and 2c are opened, and the supply of three-phase alternating current is cut off.

Next, the second monitoring operation will be explained. As shown in FIG. 2(J), the second monitoring operation includes a rest period T2 . . . of the periods T+, Ts, T, . T...
This is carried out at T6..., and it is determined whether there is an open phase in any phase of the three-phase alternating current during this period.

During this second monitoring operation, for example, during a 10 second period, as shown in FIG.
D) (E) Sample the current detection output of each phase (U phase, ■ phase, W phase) at least once based on the timing pulse shown in Compare the quantity detection output. FIG. 5 shows threshold values La, Lb, Lc, and Ld for comparing the current amount of each phase during a monitoring period of, for example, 10 seconds. In the example shown in the figure, the threshold value La is adjusted to the rated current of a load such as a three-phase motor, Lb is set to 08 times the threshold value, and LC is set to 0.8 times the threshold value.
5 times and ted is set to 0.3 times. With this threshold value, for example, as shown in Figure 6 (A), the peak value of the detected current amount of each phase is set to be within one threshold value (Lb in Figure 6 (A)). If the peak value of the detection output of the current amount of each phase does not sandwich the threshold value, it is determined that there is no open phase. Also, Figure 6+B)
As shown in Figure 6, there are two thresholds (a (in Figure 6 FBl, Lb and L
If c) is present, the same detection state is monitored during the next second monitoring operation. If there are two threshold values between the peak values of the detected output of the current amount as shown in FIG. It is determined that there is an open phase state, and a control output is output to the switching unit 24,
Opening/closing contacts 2a, 2b of the electromagnetic switch 1.

2c is opened to cut off the supply of three-phase alternating current.

In the illustrated embodiment, the monitoring period T2 of the second monitoring operation is
T4. The detection output of the current amount of each phase is sampled once at T, , ..., but the detection output of the current amount of each phase is sampled at least twice during this monitoring period, and Two threshold values may be present between any peak values of all the sampling detection outputs, and when these thresholds occur a predetermined number of times in succession, it may be determined that an open phase state exists.

〔effect〕

As described above, according to the present invention, the presence or absence of an excessive current and the presence or absence of an open phase are alternately and repeatedly detected in the supervisory control section, so that the presence or absence of these can be reliably detected. Moreover, since the monitoring level is set by the control means, there is no variation in operating characteristics as in conventional thermal relays using bimetals, and highly accurate monitoring and control can be performed. Furthermore, it is also possible to switch the setting level that serves as a criterion for determining excessive current.

[Brief explanation of drawings]

FIG. 1 is a block and circuit diagram showing an embodiment of the power switchgear according to the present invention, FIG. 2 is a time chart showing its monitoring operation, FIG. 3 is an explanatory diagram of the threshold value of the first monitoring operation, and FIG. Figure 4+A+ (B) is an explanatory diagram of the first monitoring operation, and Figure 5 is an explanatory diagram showing the threshold value of the second monitoring operation.
FIG. 6 (A1 FB+ is an operation explanatory diagram of the second monitoring operation. 1... Electromagnetic switch, 2a, 2b, 2c... Switching contacts, 3... Switching contacts (auxiliary contacts), 4 ... Electromagnetic actuator, 5 ... Drive input terminal, 20 ... Protection part,
21.=Current detection section, 21a, 21b, 21cm sensor, 23.. Monitoring control section, 24.. Switching section.

Claims (1)

[Claims] 1. A switch that opens and closes the input of three-phase alternating current, and a current detection section that is located on the output side of this switch and detects the amount of current in each phase of the three-phase alternating current that flows when the switch is in a closed state. ,
A power switchgear is provided with a monitoring control unit that monitors the amount of current based on a detection output of the current detection unit, and a switching unit that operates the switch according to a judgment of the monitoring control unit, In the control unit, the first monitoring operation and the second monitoring operation are alternately repeated in a predetermined cycle.
In the second monitoring operation, when the amount of current in each phase of the three-phase alternating current exceeds a predetermined value, a command signal is output to the switching section to open the switch. A power source switching device characterized in that a command signal for opening the switch is output to a switching unit when the amount of current in any phase of alternating current is lower than the amount of current in other phases by a predetermined level. Device