JPH02285926A - Method and device for preventing overload of electrical equipment - Google Patents

Abstract

PURPOSE:To prevent overload properly by simulating temperature distribution based on the heat characteristics of a heat generating section in an electrical equipment, estimating the temperature of the heat generating section and outputting an alarm when the value of the temperature of the heat generating section exceeds a reference value. CONSTITUTION:Regarding a heat generating section 2 in an electrical equipment monitoring a temperature rise and a constitutional section continued to the heat generating section, a heat equivalent circuit 6 simulating the temperature distribution of each section on the basis of each heat characteristic is formed by using hardware or software, Joule loss generated in the heat generating section 2 is detected successively, and signals corresponding to the Joule loss are input to the heat equivalent circuit 6. The temperature rise of the heat generating section 2 is estimated from the voltage value of the input point of the heat equivalent circuit 6, and the alarm of overload is output when the temperature rise exceeds a specified threshold value. Accordingly, the high accurate temperature rise of the heat generating section 2 of the electrical equipment as an object to be protected can be estimated, thus outputting the alarm of precise overload.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an overload prevention method and device for preventing abnormal temperature rises in electrical equipment.

[Prior Art] Conventionally, this type of overload prevention method and its device have used a thermal relay or an electronic thermal relay using a distribution circuit. Fig. 7 is a circuit diagram showing a conventional example of an electronic thermal relay. FIG. 8 is an operating curve diagram showing its protective characteristics.

Thermal relays utilize the property of bimetals to deform when the temperature of the bimetal reaches a certain temperature due to the Joule loss generated by passing the current flowing through an electric device such as a motor through a heater. It is designed to obtain a signal to open the circuit. In addition, in the electronic thermal relay, as shown in FIG. 7, the motor 2 is driven by the power amplifier section 1, and the square circuit section 4 manually inputs the 11 charge current of the motor 2 detected by the current detector 3, and outputs the 'DC current'. 2
Multiply this by the internal resistance value of motor 2 to obtain motor 2
It is converted into Joule loss and output. Voltage current converter 5
is the Joule loss output from the square circuit section 4 and the motor rated current 1. The difference between the Joule loss due to If the output value for 41 minutes is less than 0, it is grounded and clamped. *The signal integral value is manually input to the non-inverting input terminal, and a predetermined reference value is input to the inverting input terminal, the two are compared, and when the integral value exceeds the reference value, it is output. A latch circuit section 8 made up of a memory circuit such as a flip-flop latches the output of the comparison section 7 and outputs an overload alarm.

Furthermore, Japanese Patent Application Laid-Open No. 18920/1989 discloses a similar overheat protection device, which detects the voltage value and current value of the winding of an electrical equipment, and divides the voltage value by the current value. The resistance value of the winding is calculated by , and the temperature of the winding is estimated using the relational expression between the resistance value and the temperature of the winding. When the temperature of the winding exceeds the maximum allowable temperature, overheat protection is activated. It outputs a signal for

[Problem 2III to be solved by the invention] The above-mentioned thermal relay utilizes the temperature characteristics of a bimetal, and it is difficult in principle to match this with the temperature rise characteristics due to motor overload. In addition, the electric current r shown in 8th r:A
“The protection characteristics of thermal relays are fixed when the saturation point C and one point on the graph are determined, so if you look at it from the perspective of actual thermal protection such as Chiyo.

This method is not sufficient because it merely shows the characteristics of the heat generating part with the highest required temperature rise. The published example of Japanese Patent Application Laid-Open No. 1999-01-1999 also estimates the uniform temperature value of the winding from the resistance value of the entire winding.
Similarly, the properties of the highest temperature parts are not so similar. As described above, conventional overload prevention methods and devices cannot completely estimate the overload characteristics of the target electrical equipment.
There are disadvantages in that an overload alarm is issued even when there is no overload, and conversely, there is a risk of burning out the target A-device because overload cannot be detected.

The L1 objective of the present invention is to construct a thermal equivalent circuit that closely reflects the temperature characteristics of the target electrical equipment, and to simulate the actual temperature rise with a high degree of opening, thereby estimating the accurate temperature rise of the heat generating part. It is an object of the present invention to provide a method and apparatus for estimating and appropriately preventing overload.

[Means for Solving the Problems] The overload prevention method according to claim 1 of the present invention prevents abnormal temperature rises in electrical equipment. A thermal equivalent circuit that simulates the temperature distribution of each component is formed using hardware or software based on the thermal characteristics of each component, and the Joule loss generated in the heat generating part is sequentially detected and applied. By inputting a corresponding signal to the thermal equivalent circuit, the temperature -F rise in the heat generating part is estimated from the voltage value at the input point of the thermal equivalent circuit, and when this temperature rise exceeds a predetermined limit value, The overload prevention device according to claim 2, which is characterized by a load alarm, includes a current detector that detects a current flowing through a heat generating part in an electrical device whose temperature rise is to be monitored, and a current value that is manually measured and squared. As shown in Fig. 6, there is a square circuit section that converts the value into Joule loss, which is the product of the electric resistance value of the heat generating section, and a voltage-current conversion section that manually converts the output of the square circuit section into a current signal. It has a ladder-shaped circuit configuration in which multiple L-shaped circuits consisting of resistors and capacitors are cascaded with resistors R8 to Rn in series and capacitors 01 to Cn in parallel. a thermal equivalent circuit section that compares the voltage value of the current signal human power point of the thermal equivalent circuit section with a set reference value, and outputs an overload alarm when the voltage value exceeds the reference value; The electrical resistance value of the resistor and the capacitance value of the capacitor of the unit rectangular circuit in the thermal equivalent circuit section are respectively the values of each unit rectangular circuit for the heat generating part and the component parts continuous thereto. The thermal resistance value and heat capacity value of each corresponding part are shown.

The overload prevention device according to claim 3 includes a current detector that detects a current flowing through a heat generating part in an electrical device whose temperature rise is to be monitored, and an A that inputs the detected current value and converts it into a digital signal.
The Joule loss generated in the heat generating section is calculated from the current values input manually from the A/D converter and the A/D converter, and the current signal value input to the thermal equivalent circuit section and the voltage value at the current signal input point are calculated. Using the calculation formula showing the relationship, calculate the voltage value of the current signal human power point using the calculated Joule loss as the current signal value, and compare it with the set reference value, and when the voltage value exceeds the reference value. It has a CPU that outputs an overload alarm.

[Function] The method for preventing overload of electrical equipment of the present invention uses a thermal equivalent circuit to check the heat generation part of the electrical equipment whose temperature rise is to be monitored and the constituent parts continuous thereto. By simulating the temperature distribution of each part based on the characteristics, the temperature of the heat generating part is estimated, and if this value exceeds a reference value, an alarm is output.

In the apparatus of claim 2, this thermal equivalent circuit is represented by a ladder circuit constructed by cascading a plurality of unit rectangular circuits corresponding to each part, and the construction thereof is shown in FIG. The electrical resistance value (Ω) of the resistors R1 to Ro of the L-shaped circuit is the thermal resistance value ("C/W)" of that part, and the capacitor C1 to c
The capacitance value (F) of n-1 is the heat capacity value (Joul
e/°C), respectively. Therefore, as the human power of this thermal equivalent circuit, by injecting a 7" current signal (A) corresponding to the Joule loss p (w) due to the detected current in the heat generating part, the voltage value (V
) corresponds to the temperature ("C") of the heat generating section, so by monitoring this voltage value in the comparison section, when it exceeds a predetermined reference value, it is determined that there is an overload and a 2 alarm signal is output. I can do it.

The third aspect of the present invention performs the same operation by software using a CPU, and calculates the relational expression between the input current signal value of the thermal equivalent circuit section used in the device of the second aspect and the voltage value at the input terminal. It is held in the memory of the CPU, and the current signal value corresponding to the Joule loss of the heat generating section is substituted into the relational expression to estimate the voltage value at the input terminal, that is, the temperature of the heat generating section. The following operations are also performed by the CPU, and when this temperature exceeds a reference value, an alarm signal can be output.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of an overload prevention device using the overload prevention method for electrical equipment of the present invention, and FIG.
The figure is a circuit diagram of the thermal equivalent circuit section of the embodiment, and FIG. 3 is an operating curve diagram showing the protection characteristics of the embodiment.

In this embodiment, the motor is subject to overload protection, and its configuration is such that, among the components of the conventional electronic thermal relay shown in FIG. 7, the integral circuit section 9 is replaced with a thermal equivalent circuit section 6. , all other circuit configurations are the same. As shown in FIG. 2, the thermal equivalent circuit section 6 has a thermal resistance value (t
/W) is the respective electrical resistance value (Ω) of the resistor R1
R,,R, and the heat capacity value of the core and frame (Joul
It is composed of a ladder-shaped circuit consisting of capacitors C, and C2, each with a capacitance value (F) of e/"C). Note that since the heat capacity of the winding is small, the corresponding capacitors are omitted. There is.

Next, the operation of this embodiment will be explained.

While the motor 2 is being operated by the power amplifier section 1, a load current is detected by the current detector 3, and the square circuit section 4 converts this current value into a product of the square value and the winding resistance, that is, a Joule loss P. Use IB. The voltage-current conversion section 5 converts this signal into a current signal (A) corresponding to Joule loss, and causes the current signal to flow into the thermal equivalent circuit section 6 . Therefore, since the thermal equivalent circuit section 6 simulates the thermal characteristics of the coil, core, and frame of the motor 2 with high accuracy, the temperature distribution °C can be estimated from the voltage value (V) of each part.

The comparison unit 7 compares the voltage at the input terminal lO of the #1 equivalent circuit unit 6 (
That is, the temperature value of the winding is inputted and compared with a set standard, and when it exceeds the standard value, a signal is output, and the latch circuit section 8 latches this signal and outputs alarm No. 43.

FIG. 3 shows the protection characteristics of this embodiment. The curve has two bending points A and B, and the slope changes before and after the bending points.
This more closely matches the overload temperature characteristics of the electrical equipment to be protected.

Next, other embodiments will be described.

FIG. 4 is a block diagram showing the configuration of this embodiment, and FIG. 5 is a flow chart showing its operation.

This embodiment uses a current detector 3 that detects the load current of the motor 2.
and A/D converter I! which performs A/D conversion of the detected current value. and CPU12.
has a formula for calculating the winding temperature in its memory.

In this embodiment, as in the previous embodiment, a ladder circuit similar to that shown in FIG. 2 is used as the thermal equivalent circuit, and the voltage value E at the human power point 10 and the input terminal value ! The relationship can be expressed by the following equation (1).

Here, x2= (:2R2R3-(R-2"R'J)T2
+++ (5°l-72) A better method for calculating equation (1) using the CPU 12 is to use equation (6) below.

Qo=R+j+e+oeXp(-,) ”K+j (1
-exp(-r, ))"ezoQXP(-%,t,
÷ r (, - e The end value of the previous calculation of the term, e2°, is based on the third term of equation (1) for the stud.

Next, the operation of this embodiment will be explained with reference to a flowchart.

At the start of the program, each part of the device is first initialized (step 51), and then the load current of the motor 2 is transferred to the C through the current detector 3, A/D converter 11, and bus.
The data is read into the PL 112 (step 52). CPU1
Step 2 is to calculate the Joule loss P generated in the windings from the read current value and the winding resistance of the motor 2.Step 53)
Using relational expression (6), Joule loss P is expressed as current signal value i
Then, the voltage value eo (ie, the temperature value of the winding) at the human power point 10 is calculated (step 54). This voltage value e. is compared with the set reference value e (step 55), and if the voltage value eo exceeds the reference value er, it is determined that there is an overload, and an alarm signal is output (step 56).
. If does not exceed the reference value e, , repeat step 5.
Return to step 2 and repeat the operation. In addition, as a modification of each of the above-mentioned embodiments, when performing overload protection for two electrical devices with different temperature characteristics (for example, a power amplifier and a motor), 2
It is possible to use overload protection devices in parallel.

[Effects of the Invention] As explained above, the present invention provides a thermal equivalent that simulates the temperature distribution of each part based on the thermal characteristics of the heat generating part and its continuous constituent parts in an electrical device whose temperature rise is to be monitored. By forming a circuit using hardware or software, sequentially detecting the Joule heat loss generated in the heat generating part, flowing it into the thermal equivalent circuit, and estimating the temperature of the heat generating part from the voltage value at the human power point. Since it is possible to estimate the temperature rise in the heat-generating parts of the electrical equipment to be protected, there is no need to issue an alarm even though there is no overload, or burn out the target equipment due to failure to detect overload, unlike in the past. , has the effect of being able to output accurate overload warnings.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of an overload prevention device using the overload prevention method for electrical equipment of the present invention, and FIG.
The figure is a circuit diagram of the thermal equivalent circuit of the embodiment, FIG. 3 is an operating curve diagram showing the protection characteristics of this embodiment, FIG. 4 is a block diagram showing the configuration of another embodiment of the present invention, and FIG. The figure is a flowchart showing the operation of the embodiment shown in Fig. 4, Fig. 6 is a general configuration diagram of a thermal equivalent circuit, Fig. 7 is a block diagram showing the structure of a conventional electronic thermal relay, and Fig. 8 is a block diagram showing the configuration of a conventional example of an electronic thermal relay. FIG. 3 is an operation curve diagram showing protection characteristics of a conventional example. 1...Power amplifier section, 2...Motor, 3...
・Current detector, 4... Square circuit section, 5...
Voltage-current conversion section, 6... Thermal equivalent circuit section, 7...
Comparison section, 8-...Latch circuit section, 9...
Integral circuit section, 10-...Human power point,...A/D
Converter, 12・-c p u, P... Joule loss R4~R,, +++ resistance, C1~C3,...
Capacitor, 51-56...step, A, B...bending point. Patent applicant: Yaskawa Electric Co., Ltd. Patent attorney: Tadashi Wakabayashi! Figure 6

Claims (1)

[Scope of Claims] 1. An overload prevention method for preventing abnormal temperature rises in electrical equipment, which includes the following: a heat generating part in the electrical equipment whose temperature rise is to be monitored and a component connected thereto; Based on thermal properties,
A thermal equivalent circuit that simulates the temperature distribution of each part is formed using hardware or software, and the Joule loss generated in the heat generating section is sequentially detected and a corresponding signal is input to the thermal equivalent circuit. An overload prevention method for electrical equipment that estimates the temperature rise in the heat generating part from the voltage value at the input point of the thermal equivalent circuit, and outputs an overload alarm when this temperature rise exceeds a predetermined limit value. 2. An overload prevention device for preventing abnormal temperature rises in electrical equipment, which includes a current detector that detects the current flowing through the heat generating part of the electrical equipment whose temperature rise should be monitored, and a current detector that detects the detected current value. a square circuit section that inputs the input signal and converts it into Joule loss, which is the product of the square value and the electrical resistance value of the heat generating section; a voltage-current conversion section that inputs the output of the square circuit section and converts it into a current signal; and a resistor. a thermal equivalent circuit section which has a ladder circuit configuration in which a plurality of L-shaped circuits each including a resistor in series and a capacitor in parallel are connected in cascade, and into which the current signal is input; a comparison section that compares the voltage value at the current signal input point of the section with a set reference value and outputs an overload alarm when the voltage value exceeds the reference value; The electrical resistance value of the resistor and the capacitance value of the capacitor of the unit L-shaped circuit are the thermal resistance value and heat capacity value of each corresponding part of each unit L-shaped circuit, respectively, regarding the heat generating part and the component parts continuous thereto. An overload prevention device for electrical equipment. 3. An overload prevention device for preventing abnormal temperature rises in electrical equipment, which includes a current detector that detects the current flowing through the heat generating part of the electrical equipment whose temperature rise should be monitored, and a current detector that detects the detected current value. A/D for input and digital conversion
The Joule loss generated in the heat generating section is calculated from the current values input from the converter and the A/D converter, and the relationship between the current signal value input to the thermal equivalent circuit section and the voltage value at the current signal input point is calculated. Using the formula shown, calculate the voltage value at the current signal input point using the calculated Joule loss as the current signal value, compare it with the set reference value, and when the voltage value exceeds the reference value, an overload alarm is issued. An overload prevention device for electrical equipment having a CPU that outputs.