JPH06105452A - Load control apparatus - Google Patents

Abstract

PURPOSE:To obtain a load control apparatus which can automatically set a optimum reference value for decision of fault for the protection condition by storing a drive time and a drive current of a motor. CONSTITUTION:A storing circuit 17 is provided in a control circuit 11 for storing a current value sampled in the constant interval from the start of drive and the time thereof. A logical arithmetic circuit 14 computes the reference value for fault decision on the basis of the data stored in this storing circuit 17 and sets the computed value in an automatic setting circuit 18. A detection current of the main circuit 1 outputted from a current converter 5 and a zero-phase current transformer 6 is converted by a current detecting circuit 12 and it is then logically computed in various manners by the logical arithmetic circuit 14 based on the control program in view of always monitoring a fault such as overload, phase missing and grounding or the like. That is, since the reference value for fault decision is set automatically from the drive characteristic obtained by the running of motor, the optimum reference value can always be set and moreover automatically, making the setting work easier very much.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load control device for controlling opening and closing of a motor and protection by using a switch such as an electromagnetic contactor, and more particularly to automatically determining a reference value for judgment for performing a protection operation. The present invention relates to a load control device that can be set.

[0002]

2. Description of the Related Art Recently, some control center unit devices have a load control device having a number of functions such as operation / stop control, protection and monitoring of an induction motor by applying a microcomputer. Have been served. The protection function of this type of load control device is to constantly monitor the main circuit current of the electric motor for comparison with the reference value for abnormality determination,
When an abnormality such as an overload, open phase, or ground fault is detected, the electromagnetic contactor connected to the main circuit is opened to protect the electric motor and display the cause of the abnormality to the outside.

[0003]

By the way, in such a control center, the reference value for abnormality determination is set by actually measuring the starting current, the starting time and the steady-state current of the electric motor at the installation site. The standard value is decided and this is set. However, in this case, if the set current is larger than the steady value, overload protection cannot be performed, and if the set time is short, malfunction occurs at start-up, and conversely, if the set current is too long, there is a problem that the motor cannot withstand and the protection cannot be performed. Therefore, an object of the present invention is to provide a load control device capable of automatically setting a reference value for abnormality determination that is optimum for a protection condition.

[0004]

A load control apparatus according to the present invention comprises an electromagnetic contactor for opening and closing a main circuit between a power bus and an electric motor, a current converter for detecting a main circuit current, and a current converter from the current converter. In a load control device that has a logic operation circuit that compares the detection signal with a reference value for abnormality determination to determine whether there is an abnormality and outputs a command to open the electromagnetic contactor in the event of an abnormality A storage circuit for sampling and storing the startup time and startup current is provided, and the logical operation circuit has a function of calculating the protection characteristic based on the storage data of the storage circuit, while the calculation result is set in the automatic setting circuit. It is characterized by having a function to obtain.

[0005]

In the first operation such as the test operation of the electric motor, the current value is automatically measured at every constant time after the start of the operation, and the current and time at this time are stored in the memory circuit. The logical operation circuit uses this stored data and, for example, according to the following equation (1), I ² It is calculated as t is constant, and the maximum value is set in the automatic setting circuit as a reference value for abnormality determination. (Sampling current value i × k) ² X (sampling time t) (1) Here, k is a coefficient in consideration of variations in starting characteristics obtained by the test.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a control center will be described below with reference to the drawings. That is, FIG. 1 shows a circuit configuration for one unit of the control center. In FIG. 1, reference numeral 1 denotes a three-phase main circuit that supplies power to an induction motor 2 that is a load. The main circuit 1 includes a circuit breaker 3 for wiring, an electromagnetic contactor 4, and a main circuit current for detecting the current. The current converter 5 and the zero-phase current transformer 6 for detecting the zero-phase current of the main circuit are interposed as main circuit devices. The primary winding 7a of the operation transformer 7 is connected between the two phases of the main circuit 1 between the load side of the wiring breaker 3 and the current side of the electromagnetic contactor 4. The output voltage of the secondary winding 7b of the operating transformer 7 serves as a power source for the operating circuit and is used as a bus 8
Applied to. The bus bar 8 has a coil 4a of the electromagnetic contactor 4 and an auxiliary contact 4 so that it can be used as one power supply line.
b, the start operation switch 9 and the stop operation switch 10 are connected to one ends thereof, and the other ends thereof are connected to the operation signal output terminal 11a and the operation signal input terminal 11b of the control circuit 11. As a result, the control circuit 11 receives the start signal from the start operation switch 9 and the stop signal from the stop operation switch 10 to turn on and off the coil 4a, thereby opening and closing the electromagnetic contactor 4 and the current converter 5 as well. , Has a function of inputting a current signal from the zero-phase current transformer 6 and performing protection operations such as overload protection, open-phase protection, and ground fault protection of the induction motor 2. The power supply of the control circuit 11 is to prevent intrusion of switching noise generated by the coil 4a of the electromagnetic contactor 4, etc.
It is supplied from a tertiary winding 7c which is insulated from the secondary side of the operating transformer 7.

The control circuit 11 also inputs a detection current according to the magnitude of the main circuit current output from the current converter 5 and the zero-phase current transformer 6, and a current detection circuit 12 from this current detection circuit 12. A drive circuit 13 that operates the electromagnetic contactor 4 while calculating the detection signal to monitor the abnormality of the main circuit current
It is composed of a logical operation circuit 14 for outputting a command, a display circuit 15 for displaying the main circuit current value and the cause of abnormality of the main circuit 1, and an external output circuit 16 for outputting the content of the abnormality to the outside.

The control circuit 11 is further provided with a memory circuit 17 corresponding to the object of the present invention. The memory circuit 17 has a current value i (sampled at a constant interval t _s from the start of activation shown in FIG. 2). i ₁ ...... i _n ) and its time t (t ₁ ......
t _n ) is stored. The logical operation circuit 14 calculates an abnormality determination reference value based on the data stored in the storage circuit 17. The abnormality determination reference value is set in the automatic setting circuit 18, and such automatic setting is performed only when the switch 19 is manually turned on.

The automatic setting circuit 18 has a storage section,
Not only the above abnormality judgment reference value is stored, but overcurrent,
A control program for executing protection operations such as open-phase, undercurrent, ground fault, and control operations such as instantaneous power failure restart, timed restart, and function data for determining protection operations are stored.

Therefore, to automatically set the reference value for abnormality determination
First, with the setting switch 19 turned on, the electric motor 2
Is tested for the first time under actual load, the current converter 5
Via the fixed interval t_sAnd the current value i (i₁
...... i_n) And its time t (t₁...... t_n) Is a fixed period of time
It is sampled and stored in the storage circuit 17. This day
It is the current value of the steady state in the logical operation circuit 14 based on the
Steady current I_cAnd the steady current I_cN₁Doubled n
₁× I_cIs the overload protection characteristic I in the steady current state₁When
Become. Next, from the start of activation, the sampling current value i is n₁×
I_cUntil t_aThe variation of the starting characteristics
(I × k) characteristic is obtained by using the coefficient k in consideration of the above. This
(2) at each sampling value of the (i × k) characteristic of
To I² A constant t characteristic is calculated. (I × k)² × t …… (2) [0 <t <t_a]

I ^{2 found at} each sampling value of the (i × k) characteristic The maximum value of the constant t characteristic is used as the reference value for abnormality determination. Here, a region of n ₂ × I _c or more is a protection region of the circuit breaker for wiring in order to avoid inrush current of the electric motor. The overload protection characteristic I ₁ is obtained from the above calculation formula, and this is automatically set in the automatic setting circuit 18 as a reference value for abnormality determination, and thereafter this reference value for abnormality determination is used for abnormality determination. In FIG. 2, I _MCCB represents the operating characteristic curve of the circuit breaker for wiring, and I _M represents the motor current.

In a normal state, the detected current of the main circuit 1 output from the current converter 5 and the zero-phase current transformer 6 is converted into a predetermined signal by the current detection circuit 12, and this is calculated by the logical operation circuit 14. Based on the control program stored in the storage unit of the automatic setting circuit 18, a logical operation is performed to compare with various function data and reference values for abnormality determination to check whether there is an abnormality such as overload, open phase, or ground fault. Always monitor. When an abnormality occurs, the logic operation circuit 14 determines that the drive circuit 13 and the display circuit 1
A command for opening the electromagnetic contactor 4 and a command for displaying the content of the abnormality are output to 5.

In the above-mentioned embodiment, the above-mentioned I ² for automatic calculation is used.
Although the constant t is used as the calculation formula, other calculation formulas may be used. The slope of the protection characteristic can be changed according to the sampled current value and time.

[0014]

According to the load control apparatus of the present invention, the starting characteristic of the electric motor is obtained by the operation of the electric motor, and the reference value for abnormality determination is automatically set by automatically calculating from the starting characteristic. Since the value can be set and the value can be automatically set, it is possible to obtain an excellent effect that the setting work becomes extremely easy.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a motor current characteristic and a current characteristic which is a protection condition.

[Explanation of symbols]

1 is a main circuit, 4 is an electromagnetic contactor, 5 is a current converter, 6 is a zero-phase current transformer, 11 is a control circuit, 12 is a current detection circuit, 14
Is a logical operation circuit, 17 is a memory circuit, and 18 is an automatic setting circuit.

Claims (1)

[Claims] 1. An electromagnetic contactor that opens and closes a main circuit between a power bus and an electric motor, a current converter that detects a main circuit current, and a detection signal from the current converter is compared with a reference value for abnormality determination. In a load control device having a logical operation circuit that determines the presence / absence of an abnormality and outputs an electromagnetic contactor opening command when an abnormality occurs, the starting current of the electric motor is sampled at regular intervals from the start of starting and the starting time and starting current are stored. A storage circuit is provided, and the logical operation circuit has a function of calculating a protection characteristic based on the storage data of the storage circuit,
A load control device having a function of setting the calculation result in an automatic setting circuit.