JPH0628484B2 - Overload detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an overload detection device for monitoring a load amount for load protection.

[Prior Art] FIG. 5 is an explanatory view showing a conventional overload detecting device shown in an instruction manual of "DB type DC overcurrent relay" of Mitsubishi Electric Corp., for example, where 1 is fixed. A coil wound around the core 2, 3 is a movable core that is attracted to and removed from the fixed core 2, 4 is a saddle that is pushed according to the movement of the movable core 3, and 5 is on / off by the saddle 4. A micro switch to be operated, 6 is a rod whose one end is connected to the movable core 3, 7 is a diaphragm of an air dashpot type time delay element 8 which is connected to the other end of this rod 6, 9 is a valve whose opening can be adjusted, and 10 is a reset. A valve, 11 is a knob for long-time suction scale setting, 12 is a knob for instantaneous suction scale setting, and 13 is a secondary armature that responds to the knob 12.

Next, the operation will be described. First, settling knob 1 for load
When an overload current more than the long-time suction scale setting by 1 flows, the movable core 3 is attracted upward, and thus the saddle 4 is also pushed upward. The moving speed of the movable core 3 and the diaphragm 7 connected to the movable core 3 via the rod 6 is determined by the internal pressure of the air chamber 14 due to the amount of air sucked through the time delay valve 9. Reset valve 10 is coil 1
When the exciting current of 1 disappears or becomes close to it, the movable part including the movable core 3 is promptly restored. On the other hand, when a large overcurrent, for example, a short-circuit current, which is equal to or greater than the instantaneous suction scale setting value by the setting knob 12, flows, the secondary armature 13
Are attracted to the movable core 3, the timed valve 9 is wide open, the movable core 3 is freed, and the movable core 3 and the saddle 4 are
Instantly operates to quickly open the micro switch 5.

[Problems to be solved by the invention]

Since the conventional overload detection device is configured as described above, the overload setting for the timed operation or the instantaneous operation must be performed by the mechanical manual operation by the knobs 11 and 12, and the mechanical error thereof is caused. As a result, the deviation of the overload set value becomes large, and the motion area of the movable part is required, so that the size of the device cannot be avoided. In addition, there is a problem that the quality and the function of the friction part are significantly deteriorated due to the use environment.

The present invention has been made to solve the above problems, and detects and processes the load amount of the main circuit with high accuracy in a digital manner, and also calculates the average value of the detected value and the reference value. To obtain an overload detection device that can electrically and reliably perform overload detection in a wide time range from short time to long time without causing an overload setting error. With the goal.

[Means for solving problems]

An overload detection device according to the present invention includes a current transformer that detects a main circuit current of a DC load, an analog / digital converter that converts the main circuit current into a digital amount, and a converted digital signal that is sampled at regular intervals. Then, an averaging processor for further averaging processing, an instantaneous overcurrent detection comparator for comparing the average current obtained by the averaging processing with the instantaneous overcurrent determination reference value, and control by this comparator output. An overload relay, a first calculator that squares the average current and multiplies the calculated value by the load resistance, a first primary delay calculator that obtains a temperature rise from the multiplied value, and the average current And a reset circuit for resetting the first primary delay calculator based on the above, a temperature comparator for comparing the rising temperature with a set reference rising temperature, and controlling the overload relay by this comparison output, An averaging processor that squares the average current obtained by the averaging process, further samples the calculated value for a predetermined period of time, and averages the averaged value, and the average value is multiplied by the DC load resistance of the main circuit. The second computing unit, the second first-order lag computing unit that obtains the rising temperature from the multiplication value, and the rising temperature are compared with a preset reference rising temperature,
It comprises a long-time overload detection temperature comparator which controls the above-mentioned overload relay by this comparison output.

[Work]

The overload detection device according to the present invention converts the main circuit current detected by the current transformer into a digital signal by analog-to-digital conversion, and the digitalized main circuit current signal is sampled and integrated at regular intervals, and then averaged. Obtain the averaged current value. Next, this average current is compared with the instantaneous overcurrent determination reference value, and if this average current is greater than the instantaneous overcurrent determination reference value, it is determined to be an instantaneous overload and the overload relay is activated to detect overload. . On the other hand, the square value of the average current is calculated, and this is multiplied by the load resistance to obtain the power consumption that is consumed due to this load resistance and is converted to the temperature rise value of the load corresponding to this power consumption. To do. This temperature rise value is compared with the reference temperature, and when it is larger than this reference value, it is judged as an overload and the overload relay is activated.
Performs timed overload detection.

In addition, the reset circuit for timed overload detection operates according to the value of the average current, and when this average current becomes zero, the timed overload detection circuit is reset to zero and the temperature rise due to timed overload is reset to zero. .

On the other hand, the square value of this average current is calculated, and the calculated value is integrated over time, and then averaged, and this average value is multiplied by the load resistance, and this load resistance forms a jule heat. The consumed power consumption is obtained, and the temperature rise value of the load corresponding to this consumed power is converted. Next, this temperature rise value is compared with a reference temperature, and when it exceeds this reference temperature, it is judged that there is an overload, the above-mentioned overload relay is operated, and long-time overload detection is performed.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. First
In the figure, 21 is a DC motor as a DC load, 22
Is a rectifier thyristor converter, 23 is a current transformer placed on the AC side, 24 is a current detector of the main circuit current I connected to the current transformer 23, and 25 is an A / D converter for digitally converting the main circuit current. , 26 are first averaging processors provided in the arithmetic unit 27, which sample the digitalized current signal at regular intervals and obtain the average value I _A of the sampled current signal. 28 is an instantaneous overcurrent detection comparator that compares the averaged current I _A that has been averaged with the instantaneous overcurrent determination reference value I ₀ ; 29 is a calculator that calculates the squared value I _A ² of the average current I _A ; _A first computing unit for multiplying the value I _A ² by the load resistance R to obtain the power consumption (juule heat) I _A ² R of the load, 3
1 is the first for calculating the temperature rise θ of the load from the calculated value I _A ² R
, A time delay overload detection temperature comparator 32 that compares the rising temperature θ and the reference temperature θ _0, and a first first-order delay calculator 31 and 36 when the average current value is zero. A reset circuit for resetting the rising temperature θ, 37 is an average current I
_An arithmetic unit for obtaining a squared value I _A ² of _{A, a} ^second averaging processor 38 for sampling and averaging the squared value I _A ² of the average current I _A for a predetermined time t, and 39 an averaged output Power consumption of the load by multiplying the load resistance R (juule heat) Second arithmetic unit for calculating A second primary delay calculator for calculating the temperature rise θ of the load from
Reference numeral 41 is a long-time overload detection temperature comparator for comparing the rising temperature θ and reference temperature θ _0, and 33 is each of the comparators 28, 32, 4
1, 34 is an output circuit of the output signal of the mixer 33, 34 M is an amplifier (inverter), and 35 is an overload relay whose operation is controlled by the output of the mixer 33.

Next, the operation will be described, but first, the relationship between the temperature increase of the load used for overload detection and the size of the load will be described.

As is well known, the general formula for increasing the temperature is as follows.

Qdt = Cdθ + θ · Adt (10) Where, Q: amount of heat generated in an object per unit time (W) C: heat point (J / K) A: amount of heat transferred per unit time per 1K ( W / K) θ: Temperature (10) is transformed to obtain the following equation. When the Laplace transform is performed with the initial value 0, the following equation is obtained.

On the other hand, the calorific value is expressed by the following equation, considering that it is due to Jouille heat.

Q (t) = I ² (t) R …………………… (13) I (t): Current value (A) R: Circuit resistance (Ω) As a result, I ² R becomes It is found that they are closely related, and accordingly, the first and second first-order delay calculators 31,
It becomes possible to calculate the overload detection temperature by 40.

Next, to describe the operation of the above circuit, the current value I detected by the current detector 24 is converted into an analog / digital converter (A /
The digital signal is converted into a digital signal by a D converter 25), and the first averaging processor 26 samples M digital signals at regular time intervals. This sampling process is shown in the flow diagram of FIG. Next, M pieces of sampled data are added, and the added value is divided by the number of additions M to obtain the average current I _A. Then, the calculation of overload detection is started. This averaging process is shown in the flow diagram of FIG. The calculation of overload is executed by the following method based on the average current I _A thus obtained.

For overload protection of the DC motor 21, instantaneous overcurrent detection that regulates the commutation capability of the commutator, timed overload detection that regulates the temperature rise, and temperature rise leading to insulation deterioration and breakdown of the armature winding are performed. It suffices to monitor the three points of the specified long-time overload detection.

First, the instantaneous overcurrent detection will be described with reference to the flowchart of FIG. The determination reference value I ₀ of the instantaneous overcurrent is stored in advance in the memory of the arithmetic unit 27, and the comparator 28 compares the average current I _A with the determination reference value I ₀ read from the memory, and I _A > I If it is determined to be ₀ (step a), it is determined to be in the overload state and the overload relay 35 is activated (step b). In step a, if it is determined that I _A I ₀ is automatically entered in the process of time limit overload detection, obtains the square value I _A ² of the I _A in the arithmetic unit 29 (step c), further the load resistance in one of the arithmetic unit 30 (armature circuit resistance) is multiplied by I _a ² to R seek I _a ² R (step d). Further, the temperature rise θ corresponding to this I _A ² R is calculated by the first first-order delay calculator 31 (step e).

Here, it is determined whether or not the average current I _A has a value near zero (step f), and if so, the reset circuit 36.
With the reset output of, the output term .theta. And the integral term of the first first-order delay calculator 31 are reset to zero (step g). Next, the rising temperature θ thus obtained is compared with the reference temperature θ ₀ defined as the rated item in the comparator 32 (step h), and when it is determined that θ> θ ₀ , the overload relay 35
To detect an overload condition. On the other hand, θ
When it is determined to be θ ₀ , the process of long-time overload detection is automatically started, the square value I _A ² of the average current I _A is calculated by the calculator 37 (step i), and the square value I _A is calculated. ² is sampled at a time interval t which is wider than the sampling interval in the first averaging processor 26 and added (step j), and the added value is divided by the number N of additions for time t. Average value of The second averaging processor 38 performs an averaging process to obtain (step k), and the second computing unit 39 further sets the load resistance (armature circuit resistance) R to the above average value. Multiply by (Step 1). Also this Is calculated by the second primary delay calculator 40 (step m).

Then, the temperature rise theta thus calculated compared in the comparator 41 with the reference temperature theta ₀ and the same reference temperature theta ₀ used in the comparator 32 is defined as a rated item (step n), theta>
When it is determined to be θ ₀ , the overload relay 35 is operated to detect the overload state (step b), and when it is determined to be θθ _0, it is determined to be the normal operation state (step o). ). As described above, when the overload relay 35 operates in step b, it is determined that the overload relay 35 is in the overload state, and control of power supply to the load and other load protection measures can be taken.

Although the armature resistance R is input to the first and second arithmetic units 30 and 39 in the above embodiment, since this is always a constant value, the first and second primary delay arithmetic units are always present. It may be included in the gain terms of the calculations of 31 and 40. Further, in the above embodiment, the processor or the like dedicated to the digital signal processing is provided in the arithmetic unit 27, but a processor or the like of another control arithmetic unit may be used, and the same effect as the above embodiment is obtained. Play.

〔The invention's effect〕

As described above, according to the present invention, the main circuit current for overload detection is input to the arithmetic unit by the processor,
This is digitally converted and then averaged, and based on the average value output, automatic calculation for instantaneous overload detection and timed overload detection, and automatic long-time overload detection by averaging processing for a predetermined time The overload relay is configured to be automatically operable according to the result of any calculation, so that it is possible to detect an instantaneous overload condition and the overload that should be protected in a relatively short time by continuous overload current. The condition detection and the accurate detection of the overload condition which is allowed for a relatively long time by the repeated overload current by the overload current and the no-load current (current near zero) can be detected by the conventional manual overload setting. There is an effect that what can be automatically carried out without any operation. In addition, the averaging process of the predetermined time of the long-time overload detection calculation can be determined by the cycle of the load current repetition time, and the operating characteristics of each target system can be set, and the mechanism part exists. Since it does not cause problems of wear and deterioration,
It has the effect of obtaining a product with little change over time.

In addition, the digital signal processing can prevent the overload detection system from malfunctioning due to noise in the main circuit current, and also electrically detect the overload state based on the averaged current value. Since the overload relay is electrically and automatically controlled based on the detection data, the overload detection point can be set accurately, and there is an effect that a detection error does not occur. Further, since the reset circuit for resetting the first temporary delay calculator when the value of the average current by the first averaging processor is zero is provided, there is an effect of having a reset function equivalent to the conventional reset valve. . Further, the second averaging processor for sampling the output of the first averaging processor at an interval larger than the sampling interval of the first averaging processor and performing averaging processing is provided. Can be processed at a large sampling interval once averaged by the averaging processor of
This has the effect of reducing the load on the processing of the averaging processor.

[Brief description of drawings]

1 is a circuit diagram of an overload detection device according to an embodiment of the present invention, FIG. 2 is a flow chart of a sampling process according to an embodiment of the present invention, and FIG. 3 is an averaging process according to an embodiment of the present invention. FIG. 4 is a flow chart of a process, FIG. 4 is a flow chart of an overload detection process according to an embodiment of the present invention, and FIG. 5 is an explanatory diagram of a conventional overload detection device. 21 is a DC motor (DC load), 23 is a current transformer, 25 is an A / D converter, 26 is a first averaging processor, 28 is an instantaneous overcurrent detection comparator, and 30 is a first computing unit. , 31 is the first
First-order delay calculator, 32 is a temperature comparator for detecting timed overload,
35 is an overload relay, 36 is a reset circuit, 38 is a second
Averaging processor, 39 is a second computing unit, 40 is a second primary delay computing unit, and 41 is a long-time overload detection temperature comparator.

Claims (1)

[Claims] 1. A current transformer for detecting a main circuit current of a DC load, an analog / digital converter for converting the detected main circuit current into a digital amount, and a main circuit current of the digital amount for every constant period. A first averaging processor that performs sampling and averaging processing, an instantaneous overcurrent detection comparator that compares the average current obtained by this averaging processing with an instantaneous overcurrent determination reference value, and this comparison output A controlled overload relay, a first arithmetic unit that squares the average current obtained by the averaging process, and multiplies the calculated value by the DC load resistance of the main circuit to obtain power consumption; A first temporary delay calculator for obtaining a rising temperature from electric power, a reset circuit for resetting the first temporary delay calculator when the value of the average current is zero, and a rising temperature for a preset reference rise Compare this to the temperature A temperature comparator for detecting a timed overload which controls the overload relay by a comparison output, and the average current is squared, and the calculated value is sampled at an interval larger than the sampling interval in the first averaging processor. A second averaging processor for performing averaging processing, a second computing unit for multiplying the calculated value obtained by the averaging processing by the DC load resistance of the main circuit to obtain power consumption, and A second first-order delay calculator for obtaining the temperature rise from the electric power, and a long-time overload detection temperature comparator for comparing the temperature rise with the reference temperature rise and controlling the overload relay by this comparison output are provided. Overload detection device.