JPS5875495A - Controlling and protecting device for electric motor - Google Patents

Abstract

PURPOSE:To contrive a controlling device with its overall size compact by a method wherein a thyristor is provided making and breaking the electric motor main circuit and electric currents detected by current transformers are used to decide on an excessive load, open phase, or inverted phase, for the controlling of the gate of said thyristor. CONSTITUTION:A triac 16, a double-throw thyristor, is connected to the R and T phases of a 3-phase iduction motor IM, and each of the three phases is provided with a current transformer CT whose output is supplied to an excess current decision circuit 18 of a 3E relay or the like detecting an excess load, open or inverted phase. The output of the decision circuit 18 triggers the gate G of the triac 16 to break the power supply. The device being thus constructed, the motor IM is protected with an extremely compact device without using such a complicated means as an electromagnetic contact means, which results in a great reduction in the space a controlling board occupies.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control and protection device for an electric motor, and more specifically, a thyristor is used as a switching element for starting and stopping an electric motor, and the thyristor and a protection circuit for the electric motor are compactly integrated. This invention relates to a motor control switchboard.

Many large-capacity three-phase induction motors are used as mechanical drive sources in industrial equipment such as various factories.

With this type of motor, if you apply the rated voltage directly at the time of starting,
Since an overcurrent of 5 to 7 times the full load current temporarily flows, causing problems such as burning out the motor, various reduced voltage starting methods are employed. In addition, some small-capacity electric motors use a full-voltage starting method in which the motor is started by applying power supply voltage from the beginning. Even if the falling motor starting method is adopted, the main power circuit to the motor is normally opened and closed by the mechanical operation of a magnetic contactor, and therefore it is used where three-phase induction motors are required. In most cases, this electromagnetic contactor is always installed on the motor control switchboard.

Further, in order to protect the motor from overload operation and other destructive factors, a protection circuit is incorporated in each motor starting control circuit. For example, a thermal overcurrent relay (thermal relay) is used as a 4N protection circuit when an overcurrent flows through the motor. As shown in Figure 1, a bimetal is used as the thermal element, a relay heater is placed in each of the three phases R, S, and T, and the thermal relay contacts are activated to open and close the electromagnetic contactor MC. It is a device element that prevents the motor from being overloaded and burnt out under restricted conditions.
(Indicated by reference symbol ThR in the figure) 0 This thermal overcurrent relay only performs overload protection, and cannot provide open phase protection or anti-phase protection. Further, since bimetal is used, the response is slow, and there are also problems such as lack of reliability due to dust etc. adhering to the bimetal, which may cause the device to become inoperable.

Another motor protection circuit is a motor breaker.

This does not activate immediately even if an overcurrent exceeding the rated current (for example, an overcurrent when starting a motor directly) flows, but only if the overcurrent continues to flow for a preset time lag or more. It operates to protect the electric motor. In this route (b), overload protection and open phase protection are possible, but anti-phase protection is not possible, and the response time is slow because a bimetal is used as the thermal element.

Therefore, in order to completely protect electric motors from the three elements of overload, open phase, and anti-phase, electric motors used in major equipment such as factories are equipped with a current converter in combination with the electromagnetic contactor in the control panel. is incorporated. This system uses a current transformer (CT) to detect overcurrent, which is a symptom of an abnormal state of the motor, and opens and closes the electromagnetic coil of the electromagnetic contactor using an overcurrent determination circuit, generally referred to as a 3E IJ circuit. This is due to the three protection factors for electric motors: overload, phase loss,
It is now widely used because it protects the electric motor by quickly and reliably detecting antiphase. A typical example is shown in FIG. In the figure, R, S, and T are each phase of three-phase AC, MCB is a molded circuit breaker, MCFiim is a magnetic contactor, PBS is a pushbutton switch, MC is a magnetic coil, Me-a and Mc-b are magnetic contactors opening and closing auxiliary contacts, CT is current transformer, IM
10 designates an induction motor and reference numeral 10 designates a 3E relay, respectively. By the way, it was mentioned earlier that the motor control protection circuit shown in Figure 2 is widely used in motor control panels of major equipment such as factories because it has thorough failure prevention measures and is reliable. As mentioned above, the control panel is equipped with various devices such as the circuit breaker (MCB), magnetic contactor (MC), current transformer (CT), and 3EIJ relay 10, so it is made of extremely bare wires. I'm stuck with the wiring configuration and taking up a lot of space. In particular, since the electromagnetic contactor (MC) has a mechanical structure for the most part, it becomes larger as the capacity increases, and the combustor (CT) and 3E relay can accommodate various capacities. Commercially available products with general versatility such as When connecting the control protection circuits of many motors into the control panel from one three-phase power line, the number of control devices such as magnetic contactors (MC) and current transformers (CT) used for this is It becomes overwhelming.

An example of this is shown in FIG. 3 using a thermal overcurrent relay. It is assumed that the induction motor (IM) is branch-connected from n three-phase power lines.

At this time, a no-fuse breaker (NFB) is installed on the main power line.
) are inserted, and as many circuit breakers (M) as there are electric motors (IM) are inserted.
CB), magnetic contactor (Me), thermal relay (ThR
) is required, and therefore it is easy to understand that the number of control devices on the control panel will be enormous.

In addition, it has been pointed out that the conventional motor control protection circuit shown in FIGS. 2 and 3 has the following drawbacks. First, since a magnetic contactor (MC) mechanically turns on and off electrical contacts, the contacts must be replaced when they wear out, but each time the contacts are worn out, the electric motor and therefore the production line must be stopped. This means that in production lines that run day and night, if even part of the line stops, it will have a big impact on the factory operating rate, and it will cause extremely large losses that cannot be covered by a simple comparison of the unit cost of the contacts that need to be replaced and the labor required. It is caused as a whole.

Another difficulty is that when the main contacts of a magnetic contactor (MC) open and close, electric sparks inevitably fly, and the radio waves generated at this time become induced noise. The problem is that the sequencer's electronic circuitry is used to malfunction. In other words, recent sequencers are IC
(Integrated circuits), LSI (Large scale integrated circuits), and other devices are used in large numbers in logic circuits, but these devices are susceptible to radio interference that causes them to malfunction due to the influence of external radio waves. .

The inventor of this application is an electrical engineer who has been engaged in the design and management of control panels and power distribution facilities in large-scale factory equipment for many years.
In order to fully protect against the three negative elements of overload, open phase, and anti-phase, the number of control devices has become enormous, and the space they occupy cannot be ignored. Large losses are occurring due to production line stoppages when replacing contacts, and sequencer failures due to other radio interference.
We are acutely aware of the need for proper alignment, such as the occurrence of malfunctions in electronic circuits, etc.
In order to solve these drawbacks, an apparatus according to the present invention has been devised. In other words, it forms the main element in the control equipment,
In addition, a thyristor, which is a power switching element, is used in the motor starting circuit instead of an electromagnetic contactor that causes contact replacement and radio wave interference, and it protects the motor from the three negative elements of overload and phase loss ψ antiphase. We have focused on the fact that the above-mentioned drawbacks can be solved at once by manufacturing an overcurrent determination circuit according to the rating of the motor being used and by stacking it on the thyristor so that it can be compactly packaged. in this case,
When installing a new motor control panel, by adopting the device according to the present invention, it goes without saying that the control panel space can be drastically reduced by /J%.
Compatibility is achieved by having the same mounting dimensions as the Lfkk contactor and by keeping the terminal arrangement approximately the same as the current one. Therefore, it is also possible to completely replace the magnetic contactor or electromagnetic switch with the device according to the present application each time it is time to replace the contacts of the T magnetic contactor in the existing control panel yc.

Therefore, the present invention has a thyristor element that opens and closes the main circuit of the motor, a current transformer inserted into the main circuit of the motor, and a current value detected by the current transformer to detect overload, phase loss, and resistance of the motor. A control and protection device for a motor is provided, comprising an overcurrent determination circuit that determines the phase and sends a trigger signal to the gate electrode of the thyristor element.

Next, preferred embodiments of the motor control and protection device according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 4 schematically shows the connection state of the device according to the present invention, in which reference numeral 12 is an input side terminal board, 14
indicate the output side terminal board, respectively. Further, in the figure, R, S, and T indicate three-phase connection terminals, U, V, and W indicate connection terminals to an induction motor (IM), and Me-a+Mc=b each indicates an auxiliary contact terminal.

A thyristor 16 as a power switching element is connected between at least two of the connection terminals R, S, and T of the three-phase power line and at least two corresponding connection terminals of the induction motor (IM). . As this thyristor 16,
A triac, which is a bidirectional thyristor, is preferably used, and a panel mounting type G3A standard solid state relay (SSR) manufactured by Shigeishi Electric Co., Ltd. can be used as a commercially available product. The opening/closing capacity of the try book 16 is selected depending on the capacity of the induction motor to be controlled.

Note that this triac 16 may be inserted in each phase of the three-phase power line, but even if it is inserted in only two of the three phases as in the embodiment, the starting control of the electric motor can be performed.

Since this can be done satisfactorily, it is recommended to use two of these from the viewpoint of cost reduction.

In addition, as shown in the figure, a current transformer (CT) is installed in each phase of the three-phase power line.
), and the output of this current transformer (CT, ) is connected to an overcurrent determination circuit 18 generally referred to as a 3E relay, so that the overcurrent determination circuit 18 triggers the gate electrode G of the triac 16. do.

That is, when a problem such as overload, open phase, or reverse phase occurs in the induction motor (IM), which is the controlled object, the current transformer (CT) detects this, and the overcurrent determination circuit 18 detects the problem of the triac 16. The gate electrode G is triggered to instantaneously cut off the power supply, and the image layer of the electric motor (IM) is performed. Although not shown, the gate electrode G of the triac 16 can turn on and off the triac 16 in response to an external control signal. In addition, when this device is installed in a control panel, it is necessary to perform a wiping test, but in order to avoid sudden rated operation, an inching switch (not shown) is installed. It is more preferable to trigger the gate electrode G several times for a short period of time.

In addition, in Fig. 4, the contact relay (MC) and the contact M
e-a + Me-b is provided because the device according to the present invention is compatible with conventional electromagnetic contactors. In other words! In addition to the main contacts for opening and closing the original circuit, the magnetic contactor has auxiliary contacts for opening and closing the self-holding or interlocking operation circuit, and the triac 16 replaces the main contacts of the magnetic contactor. Therefore, in order to provide compatibility with an electromagnetic contactor, this contact relay (MC) is provided as an auxiliary contact as necessary.

The device according to the invention shown in FIG. 4 can be packed into extremely compact external dimensions. For example, if two triacs 16 and 16 are attached to a heat sink and a current transformer (CT) and an overflow judgment circuit 18 are stacked on top of the two triacs 16. They can be integrated to a slightly larger height, and the number and location of the terminals are the same, so they are completely compatible with electromagnetic contactors. Multiple motor start control devices according to the present invention can be connected to a three-phase power line. An example of this is shown in Figure 5. It is obvious at a glance that the configuration is extremely simple, with just a no-fuse breaker (NFB) on the main power line.

In other words, thermal relays (ThR), molded circuit breakers (MCB), or three
E IJ relay control equipment is no longer required, it is significantly smaller, and it is also effective for motor starting control, overload, phase loss,
The function of picking against antiphases is not impaired at all compared to the conventional one. In addition, by being miniaturized and simplified in this way, significant labor savings can be achieved when designing and manufacturing a new motor control panel. Furthermore, since it does not use an electromagnetic contactor with mechanical contacts, there is no need for maintenance and inspection work to replace the contacts, and there is no need to replace the thyristors until their service life is over, so the power to the production line can be stopped. This also greatly reduces production opportunities and contributes to an overall improvement in production efficiency. Also, it is dangerous to use mechanical electrical contacts that can cause sparks, which can cause induced noise.
There is no risk of radio interference causing malfunction of electronic circuits such as sequencers as peripheral devices (small contact relays are used as auxiliary contacts, but their current capacity is extremely low compared to the current flowing through the auxiliary contacts). Because it is small, there is no large spark when the contact opens, and it does not lead to radio interference.Furthermore, since the contact is sealed, there is no chance of contact failure due to dust, etc.)

The electric motor control system according to the present invention has been described above with reference to the preferred embodiments and in relation to the prior art.
The present invention is not limited to the configuration of this embodiment,
Many modifications may be made within the spirit of the invention.

[Brief explanation of the drawing]

Figure 1 shows a motor starting circuit as a conventional example, and a second
The figure shows a conventional motor starting circuit as yet another embodiment, FIG. 3 shows a conventional motor starting circuit connected in parallel to a control panel in large numbers, FIG. 4 shows an electrical wiring diagram of a motor control protection device according to the present invention, FIG. 5 is a circuit diagram of a control panel using the device shown in FIG. 4. 10... Overcurrent judgment circuit 12.14... Terminal board 1
6... Thyristor (TRIAC) 18... Overcurrent judgment circuit Patent applicant Seiichi Shiraki 1 Figure R5T i3 Figure C 箭40 9 435- Figure 5

Claims (1)

[Claims] (1) A cyrisk element that opens and closes the main circuit of the motor,
A current transformer is inserted into the main circuit of the motor, and an overload controller that determines whether the motor is overloaded, open phase, or out of phase based on the current value detected by the current transformer and sends a trigger signal to the gate electrode of the thyristor element. A motor control protection device comprising a current determination circuit.