JP2601003Y2 - Accident motor disconnection detector - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a system for operating a large number of motors by an inverter, and a detector for separating an accident motor for separating an accident motor without causing a system down when a short circuit occurs in the motor. About.

[0002]

2. Description of the Related Art FIG. 7 shows a circuit in which a number of motors M _{1 to} Mn are operated by an inverter 1. If short circuit on one of the motor occurs, the accident motor current flows I _M as shown in FIG. In the figure, the motor current _IM is the output current I of the inverter 1. The reason for the increase is that a normal motor other than the accident motor supplies current to the accident motor.

When such an accident occurs, the inverter 1 is stopped by the operation of the overcurrent protection circuit. For this reason, the system is down due to the accident of one motor.

In order to prevent this system down, after the inverter is stopped due to overcurrent interruption, the inverter is restarted while the rotation speed of the motor rotated by the inertia moment is within the allowable rotation speed, thereby preventing the system down. A method has been proposed.

To restart the inverter and operate the system smoothly, it is necessary to disconnect the accident motor. Conventionally, as a method of disconnecting an accident motor, a circuit breaker or a fuse is provided in series in each motor circuit, and the accident motor is disconnected from the inverter by tripping the circuit breaker or fusing the fuse due to the accident motor current.

[0006]

The operating characteristics of the breaker or the fuse tripping depend on the squared product of the current. However, when the motor is inserted directly and started, the rated current flows even with a normal induction motor. Also, a load with a large moment of inertia results in a longer start-up time of the motor.Therefore, there is a problem that the number of motors depends on the selection of breakers and fuses that endure the start-up current and trip with an accident current. It is difficult.

[0007] The present invention has been made in view of such a conventional problem, and an object thereof is to provide an accident that can selectively shut off an accident motor without being limited by the number of operating motors. An object of the present invention is to provide a motor disconnection detector.

[0008]

In order to achieve the above object, a fault motor disconnection detector according to the present invention comprises a current detector for detecting a current flowing through a load motor, and an overcurrent set level of the motor. An overcurrent detector which is set to be equal to or more than a starting current and which is set to be equal to or more than a cutoff allowable value of an external motor start switch and detects an overcurrent from the current signal; And an output circuit for outputting a signal for opening an external switch for starting the motor at the time of disappearance.

[0009]

A large current flows for one or two cycles from a normal motor that rotates with an inertia moment to a faulty motor even if the faulty motor occurs during the operation of the motor and the power is cut off. The current detector detects this current. When this current signal exceeds the overcurrent detection set level, the overcurrent detector outputs. The output circuit prepares for operation when the overcurrent signal is input, and outputs when the fault motor current falls below the overcurrent set level and there is no overcurrent signal to input, and turns off the external motor start switch. Therefore, the accident motor can be selectively cut off without being affected by the number of load motors and the starting current.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings.

Embodiment 1 Referring to FIGS. 1 and 2, M is a motor operated by an inverter 1, 2 is a current sensor provided in a motor circuit, and MS
The electromagnetic switch for opening and closing the motor circuit, TH is the thermal relay connected in series with the motor circuit, RY ₁ is a current sensor unit output relays, RY ₂ is its contacts operated by the ON contact Ry ₁ of the relay RY ₁ Electromagnetic switch MS by Ry ₂₁
Relay is self held by the contact Ry ₂₂ with an OFF the, S1 and S2 are operated switch and stop switch connected to the electromagnetic switch MS series, S3 are relay RY
Reset switch connected in series with ₂ .

[0012] CT ₁ to CT ₂ is a current transformer, DB is a current transformer CT ₁ to CT ₃ of the secondary current 3-phase full wave rectifier diode bridge for detecting the phase current flowing to the motor M, 3 denotes a diode a current detection resistor circuit composed of a resistor R _1, R _2, which are connected to the bridge, so that the switch current detection sensitivity by the resistor R _1, R _2.

[0013] C ₁ is the current capacitor for removing a harmonic component from the terminal voltage V ₁ of the detection resistor circuit 3, the fourth resistance R _4, the variable resistor VR _1, the capacitor C ₁ including a resistor R ₅ of the voltage V _C A voltage dividing circuit, CP, calculates a voltage V _C from the divided voltage.
Is a timer for outputting a predetermined time when the comparator CP operates, and 5 is a time constant circuit comprising a resistor R ₈ for delaying the operation of the timer T and a capacitor C _2. , TR is a transistor turned ON by the operation of the timer T for biasing the relay Ry _1.

Next, the operation of the current sensor unit 2 will be described with reference to FIGS. Phase currents flowing through the motor M detected by the current transformer CT ₁ to CT ₃ are all three phases in the diode bridge DB is rectified through the resistor R _1, R _2.

For this reason, a voltage V ₁ proportional to the current flowing through the motor M is generated at both ends of the resistors R ₁ and R ₂ . The detection voltages V ₁ charges the capacitor C ₁ through the resistor R _3. The voltage V _C of the capacitor C ₁ has a first-order lag due to the time constant of R ₃ and C ₁ (FIG. 3C), and is a voltage that is not affected by harmonic components included in the motor current operated by the inverter. .

This voltage V _C is divided by the voltage dividing circuit 4 and compared with the set voltage of the comparator CP. When the voltage V _C exceeds the set level, the output CP _{0 of the} comparator CP is output.
Becomes low level (FIG. 3 (d)). As a result, the input pin 2 of the timer T goes low and the output T of the timer T goes low.
₀ becomes high level (FIG. 3 (e)). Since the terminal of the capacitor C ₂ of the time constant circuit 5 is connected to the input terminal (pin 2) via the diode D ₃ , the output T of the timer T
Output to that time of ₀ is determined by the constant R8, C ₂ of the time constant circuit 5.

The output T _{0 of the} timer T is applied to the base of the transistor TR. Since the base of the transistor TR is connected to the input pin 2 of the timer T via the diode D ₄ , the output CP _{0 of the} comparator CP is output. Is low, the transistor TR does not turn on. Therefore, the transistor TR turns on when the output CP _{0 of the} comparator CP returns from the low level to the high level, and the relay Ry ₁
Is operated (FIG. 3 (1)). When the relay RY ₁ is operated, and the operation relay RY ₂ in FIG. 1, not dropped away to electromagnetic switch the MS, and selective tripping fault motor.

Here, the breaking capacity of the electromagnetic switch MS poses a problem in application. As shown in FIG. 8, the current flowing through the accident motor is the inverter 1 and other normal motors M ₁ to M ₁ .
The sum of the currents from the Mn group, and the current I
₀ the inverter but is 0 when interrupting the overcurrent, a current I _MS from the motor group peak current value of approximately Ip = √2I _S 0.7 × when the starting current of the motor and I _S (n-1) As shown in FIG. 4, it has been experimentally confirmed that a current attenuating below the rating flows in about two cycles.

Therefore, if the number of motors n is large, the peak current I
As a result of the increase in p, it is necessary to increase the breaking capacity of the electromagnetic switch MS. This problem is to become possible to increase the application on unnecessarily electromagnetic switch MS, if the motor current is above a set level of the comparator CP so as not to capacitor C ₂ charged by the diode D ₃ in FIG. 2, the diode O the transistor TR by D ₄
Figure 3 the operation of the relay RY ₁ so as not N let (g)
Like to delay.

[0020] Thus the fault current at the time of operation relay RY ₁ becomes below the detection level, and is between the constant R _8, C ₂ determined by the time T ₀ when the constant circuit 1 when the timer T. Here, the constants of R ₈ and C ₂ are selected as the time required for the electromagnetic switch MS to separate.

Therefore, according to this embodiment, by setting the fault current detection level (operating level of the comparator CP) to be equal to or higher than the starting current of the motor and equal to or lower than the cut-off allowable current of the electromagnetic switch MS, only the fault motor is detected. Selection can be cut off.

Embodiment 2 In Embodiment 2, the current sensor shown in FIG.
It is changed like this. In FIG. 5, the same components as those in FIG. 2 are denoted by the same reference numerals, and the description thereof will not be repeated.

[0023] In FIG. 5, DB ₁ to DB ₃ phase current transformer CT ₁ to CT single-phase diode bridge for individually full-wave rectifying the secondary output currents of the _3, 3 ₁ to 3 ₃ are each diode bridge A current detection resistor circuit comprising resistors R ₁ and R ₂ for detecting an output current and a protection Zener diode ZD ₁ , D ₁₁
To D ₁₃ is a current detecting resistor circuit 3 ₁ to 3 ₃ terminal voltage V ₁₁ ~V
₁₃ is a logical OR configuration and the highest voltage is
Diode output to P, C ₁ is a capacitor for absorbing higher harmonic component contained in the voltage input to the comparator CP.

Further, a resistor R ₁₂ is provided between the second pin of the output pin 7 and the timer T of the comparator CP, the resistor R ₇
And a diode D ₆ and capacitor C ₄ is provided between the input 2 and # This pin 2 and pin and O potentials of timer T, the base potential of the transistor TR is output CP ₀ of the comparator CP is the high level from the low level At some point, regardless of the time constants R ₈ and C ₂ of the timer, the resistor R ₇ and the capacitor C ₄
The time constant is set to rise. Other configurations are the same as those of the circuit of FIG.

In the circuit of FIG. 2, since the outputs of the current transformers CT _{1 to} CT ₃ are subjected to three-phase full-wave rectification, the voltage V ₁ detected by the current detection resistor circuit 3 is as shown in FIG. becomes whereas the, in example 2, current transformer CT ₁ to CT ₃ of each single-phase output was single-phase full-wave rectification, respectively, the current detecting resistor 3 ₁
3 ₃ detects the voltage V ₁₁ ~V ₁₃ in the detection voltage by the circuit of the diode D ₁₁ to D ₁₃ of the OR configuration, since the detection voltages V ₁ takes out the highest voltage among the voltages V ₁ is as shown in FIG.

[0026] Thus, voltages V ₁ because it is flowing sum of the secondary currents of the current transformers CT ₁ to CT ₃ is the detection resistor R _1, R ₂ of the circuit of FIG. 2 is high at the same current. Further, in the circuit of FIG. 2, when a current flows through only one phase, the detection voltage becomes low, so that a ground fault detection may not be performed.

For this reason, for example, when the selective cutoff level is protected against a one-phase overcurrent, the circuit of FIG. 2 is twice as large as that of FIG. to detect the voltages V ₁ at the peak, it is necessary to set to twice the case of an accident motor shedding level 1 phase detection. However the detection voltages V ₁ in overcurrent only one phase as ground or the like will not work to become 1/2.

On the other hand, according to the second embodiment, since the voltage V ₁ does not decrease even with a current of only one phase, all fault currents can be detected.

[0029]

[Effects of the Invention] Since the present invention is configured as described above, the following effects can be obtained.

(1) It is possible to selectively cut off motors without restriction by the number of load motors.

(2) By adding a current sensor section to the conventional load motor starting circuit, it becomes possible to selectively cut off the faulty motor, so that the conventional system can be improved at low cost.

(3) The current sensor section can be composed of a current transformer and a printed circuit board, and the printed circuit board can be downsized by using an IC.

(4) Since only the faulty motor is selectively cut off, the cause of the fault can be easily clarified, and the maintenance of the system using a large number of motors can be simplified, so that the technical level of the maintenance staff can be low.

(5) By adjusting the current detection resistor according to the magnitude of the primary current of the current transformer, the detection voltage can be made constant and V
Since A can be kept constant, it can be applied to a wide primary current range.

(6) According to the second aspect, the output of each phase current transformer is rectified by a diode bridge and the output is formed into a logical sum so that an overcurrent of only one phase can be detected. Output, the motor can be selectively cut off even in the event of a ground contact.

[Brief description of the drawings]

FIG. 1A is a configuration diagram of a load circuit according to an embodiment of the present invention. (B) is a configuration diagram of a sequence circuit in the embodiment.

FIG. 2 is a circuit configuration diagram of a current sensor unit according to the first embodiment.

FIG. 3 is a time chart illustrating an operation of a current sensor unit.

FIG. 4 is a curve diagram showing a change in a peak current value of a current flowing from a normal motor group to a failed motor.

FIG. 5 is a circuit configuration diagram showing a current sensor group according to a second embodiment.

FIGS. 6A and 6B are waveform charts for explaining detection voltages according to the first and second embodiments.

FIG. 7 is a connection circuit diagram of a load motor showing a conventional example.

FIG. 8 is a diagram illustrating a current flowing through a failed motor.

[Explanation of symbols]

1 ... inverter 2 ... current sensor unit 3, 3 ₁ to 3 ₃ ... current detection resistor circuit. 4 ... dividing circuit 5 ... time constant circuit CP ... Comparator CT ₁ to CT ₃ ... current transformer DB, DB ₁ ~DB ₃ ... diode bridge M, M ₁ to Mn ... motor MS ... electromagnetic switch RY _1, RY ₂ ... Relays S1-S3 ... Switch T ... Timer TH ... Thermal relay

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01R 19/165 H02H 7/06-7/097 H02P 7/67-7/80

Claims (2)

(57) [Scope of request for utility model registration] A current detector for detecting a current flowing through a load motor; and an overcurrent setting level set to be equal to or more than a starting current of the motor and equal to or more than a cutoff allowable value of an external motor start switch. An overcurrent detector that detects an overcurrent, and an output circuit that prepares for operation based on the input of the overcurrent signal and outputs a signal that opens an external motor start switch when the overcurrent signal disappears. A detector for disconnecting an accident motor, comprising: 2. The current detector comprises: each current transformer for detecting each phase current of a load motor; each current detection resistor connected to the secondary side of each current transformer; 2. The fault motor disconnection detector according to claim 1, further comprising: an OR circuit that outputs each of the generated terminal voltages by an OR operation.