JP2004147393A - Protective relay against overcurrent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To materialize cost reduction and low current consumption by stabilizing a trip time and lessening used parts. <P>SOLUTION: An arithmetic processing unit 14 calculates the thermal data having simulated the heat generation of a motor, based on a DC voltage signal outputted from an AC/DC converting circuit 1, and controls a switching element SW1 so that the calculated thermal data and the charge voltage of a capacitor C1 may accord with each other; and outputs a tripping signal in case that the calculated thermal data come to a preset tip level or over. This protective relay reads in the charge voltage of the capacitor C1, and switches on or switches off the switching element so that it may conform to the thermal data to perform closed loop control, so this can materialize high precision without cost up. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electronic overcurrent protection relay used to protect a motor from overcurrent.
[0002]
[Prior art]
A conventional overcurrent protection relay includes, for example, a current transformer for detecting a current of a motor, and an output of the current transformer being converted into a DC voltage signal by an AC / DC conversion circuit, and converting the voltage signals Er, Es, Et into a DC voltage signal. The maximum voltage phase is selected from the input voltage signals according to the interruption characteristic calculation program of the calculation processing unit, and the eddy current level is determined based on the voltage of the maximum voltage phase to set the time. After a lapse of a predetermined time, a trip signal is output to the trip circuit to excite the trip coil and cut off the current supply to the motor.
[0003]
However, since the arithmetic processing unit uses the secondary current of the current transformer as a power source, when the load current is intermittently applied in a short time, the reset function of the arithmetic processing unit repeatedly operates to set the time according to the eddy current. However, since a trip operation cannot be obtained, the motor generates heat due to intermittent eddy currents, causing a burnout accident, and there is a problem that the motor cannot be reliably protected.
[0004]
Therefore, conventionally, for example, one shown in FIG. 1 is known (see Patent Document 1). In FIG. 1, 8 is a three-phase circuit, CT1, CT2, and CT3 are current transformers, 1 is an AC / DC conversion circuit, and 2 is a power supply unit. An arithmetic processing unit 3 includes a voltage / frequency conversion unit and an A / D conversion unit, and converts a DC voltage signal output from the AC / DC conversion circuit 1 into coarse / fine pulses corresponding to the voltage level. . Reference numeral 4 denotes a voltage / current conversion circuit, which converts a pulse output from the arithmetic processing unit 3 into a current. The output current of the voltage / current conversion circuit 4 charges the time-limit capacitor 11 through the diode 9. Reference numeral 10 denotes a charging resistor connected in parallel with the capacitor 11.
[0005]
The charge voltage of the capacitor 11 is compared with a preset voltage of the constant voltage diode 13 in the comparator 12, and when the charge voltage of the capacitor 11 is higher than the set voltage, the comparator 12 turns on and trips the trip signal. Supply to circuit 5. The tripping circuit 5 drives the trip unit 6 in response to the input tripping signal, and the driven trip unit 6 controls the switching mechanism 7 to open and close the switching contacts of the three-phase electric circuit 8 to supply current to the motor. Shut off supply.
[0006]
[Patent Document 1]
JP-A-7-170651
[Problems to be solved by the invention]
However, in the above-described conventional example, the charging voltage of the time-limit capacitor 11 is controlled by the coarse and fine pulse currents. The accuracy of the time deteriorates. In addition, a circuit for discriminating between the capacitor voltage for the time limit and the trip level is required, and there is a problem that the cost is increased.
[0008]
Accordingly, an object of the present invention is to provide an overcurrent protection relay that has solved the above-mentioned problems.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides an overcurrent protection relay for supplying a trip signal to tripping means for protecting a motor, wherein the current transformer detects a current of the motor; First converting means for converting the output of the heater into a DC voltage signal, arithmetic processing means for calculating heat data simulating heat generation of the motor based on the output of the first converting means, switching means, and the switching means. A capacitor for charging the power supply voltage via the power supply, and the arithmetic processing means controls the switching means so that the calculated heat data and the charging voltage of the capacitor coincide with each other. The overcurrent protection relay outputs the tripping signal when the trip level exceeds a preset trip level.
[0010]
Further, in the present invention, the arithmetic processing means can further read the capacitor voltage at power-on and continue the arithmetic of the thermal data.
[0011]
Further, the arithmetic processing unit receives the output from the first conversion unit and the charging voltage of the capacitor and converts them into digital data. The second conversion unit converts the digital data into digital data. Load current calculation means for calculating the magnitude of the motor current based on the output from the first conversion means, heat data calculation means for calculating heat data from the load current data obtained by the load current calculation means, First comparing means for comparing the charging voltage of the capacitor converted to the digital data with the calculation result of the thermal data calculation means and controlling the switching means so that the charging voltage matches the calculation result; The trip level is compared with the calculation result of the thermal data calculation means, and when the calculation result is equal to or higher than the trip level, the tripping is performed. It may have a second comparing means for outputting a signal.
[0012]
Further, the heat data calculation means can calculate the heat data from the charging voltage of the capacitor converted into the digital data when the power supply rises.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 2 shows an embodiment of the present invention.
In FIG. 2, reference numeral 8 denotes a three-phase circuit, CT1, CT2, and CT3 denote current transformers provided in the three-phase circuit 8, 1 denotes an AC / DC conversion circuit, and 2 denotes a power supply unit. C1 is a charging capacitor that charges the voltage of the power supply unit 2 through the charging resistor R1 and the switching element SW1. R2 is a discharging resistor connected in parallel with the capacitor C1.
[0014]
An arithmetic processing unit 14 receives the DC voltage signal output from the AC / DC conversion circuit 1 and the charging voltage of the capacitor C1, controls the switching element SW1, and outputs a trip signal to the trip circuit 5. . The tripping circuit 5 drives the trip unit 6 in response to the input tripping signal, and the driven trip unit 6 controls the switching mechanism 7 to open and close the switching contacts of the three-phase electric circuit 8 to supply current to the motor. Shut off supply.
[0015]
The arithmetic processing unit 14 calculates heat data that simulates heat generation of the motor based on the DC voltage signal output from the AC / DC conversion circuit 1, and calculates the calculated heat data, the charging voltage of the capacitor C1, And a function of outputting a trip signal when the calculated thermal data becomes equal to or higher than a preset trip level, and changing a charging voltage of the capacitor C1 when the power is turned on. A function of reading and continuing the calculation of the heat data. Since thermal data is calculated by the arithmetic processing unit 14, the time constant is a very long time of about several tens of seconds. If this is to be realized with a time-limited capacitor voltage as in the prior art, the constant of a capacitor or a resistor is reduced. Although the variation greatly affects the trip time, the arithmetic processing unit 14 in the present embodiment reads the charging voltage of the charging capacitor C1 and turns on / off the switching element so as to match the thermal data to perform closed-loop control. By doing so, high precision can be achieved without increasing the cost.
[0016]
FIG. 3 shows details of the arithmetic processing unit 14. That is, an A / D conversion circuit 15 that inputs the outputs Er, Es, Et from the AC / DC conversion circuit 1 and the charging voltage of the capacitor C1 and converts them into digital data, respectively. Load current calculating means 16 for calculating the magnitude of the motor current based on the outputs Er, Es, Et converted to the above, and heat data calculating means for calculating heat data from the load current data obtained by the load current calculating means 16 And comparing means 18 for comparing the charging voltage of the capacitor C1 converted into digital data with the calculation result of the thermal data calculation means 17 and controlling the switching element SW1 such that the charging voltage matches the calculation result. Comparing the trip level with the calculation result of the thermal data calculation means 17 and determining that the calculation result exceeds the trip level. And a comparing means 19 for outputting a trip signal to. Further, the thermal data calculating means 17 reads the charging voltage of the charging capacitor C1 converted into digital data by the A / D conversion circuit 15 when the power is turned on, and continues to calculate the thermal data using the read charging voltage. .
[0017]
In this way, variations in the constants of capacitors and resistors of external components do not significantly affect the trip time, and even if the reset function of the arithmetic processing unit is repeatedly activated, the charge stored in the charging capacitor can be reduced. Discharge simulates the heat radiation of the load, so that the time can be set according to the load current and trip operation can be obtained, thus avoiding the problem that the motor generates heat due to intermittent eddy currents and burns out Can be. In addition, variations in the constants of external components do not significantly affect the trip time, so that cheaper components can be used and fewer components are used, so that cost reduction and current consumption can be reduced. It is possible to realize the miniaturization and space saving of the device.
[0018]
【The invention's effect】
As described above, according to the present invention, the trip time can be stabilized, the number of components used can be reduced, the cost and current consumption can be reduced, and the current transformer can be reduced in size and space can be saved. Can be realized.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a conventional overcurrent protection relay.
FIG. 2 is a circuit diagram of the overcurrent protection relay of the present invention.
FIG. 3 is an internal block diagram of an arithmetic processing unit of the overcurrent protection relay.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 AC / DC conversion circuit 2 Power supply unit 5 Tripping circuit 6 Trip unit 7 Opening / closing mechanism 8 Three-phase circuit 14 Operation processing unit 15 A / D conversion circuit 16 Load current calculation means 17 Thermal data calculation means 18, 19 Comparison means

Claims (4)

An overcurrent protection relay for supplying a trip signal to trip means for protecting a motor,
A current transformer for detecting a current of the motor, a first converter for converting an output of the current transformer into a DC voltage signal, and heat data simulating heat generation of the motor based on an output of the first converter. An arithmetic processing unit for performing an operation, a switching unit, and a capacitor that charges a power supply voltage via the switching unit,
The arithmetic processing means controls the switching means so that the calculated heat data matches the charging voltage of the capacitor, and when the calculated heat data becomes equal to or higher than a preset trip level. An overcurrent protection relay for outputting the trip signal. In claim 1,
The overcurrent protection relay, wherein the arithmetic processing means further reads the capacitor voltage at power-on and continues the arithmetic of the thermal data. In claim 1,
The arithmetic processing unit is configured to input the output from the first conversion unit and the charging voltage of the capacitor and convert them into digital data, respectively, and the second conversion unit converts the digital data into digital data by the second conversion unit. Load current calculating means for calculating the magnitude of the motor current based on the output from the first converting means; heat data calculating means for calculating heat data from the load current data obtained by the load current calculating means; First comparing means for comparing the charging voltage of the capacitor converted into data with the calculation result of the thermal data calculating means and controlling the switching means so that the charging voltage coincides with the calculation result; And the calculation result of the thermal data calculation means, and when the calculation result is equal to or higher than the trip level, the trip signal is output. Overcurrent protection relay, characterized in that a second comparison means for force. In claim 2,
The arithmetic processing unit is configured to input the output from the first conversion unit and the charging voltage of the capacitor and convert them into digital data, respectively, and the second conversion unit converts the digital data into digital data by the second conversion unit. Load current calculating means for calculating the magnitude of the load current based on the output from the first converting means; and load current data obtained by the load current calculating means and charging of the capacitor converted to the digital data at the time of power supply rise A heat data calculating means for calculating heat data from the voltage, and comparing a charge voltage of the capacitor converted into the digital data with a calculation result of the heat data calculation means so that the charge voltage matches the calculation result. First comparing means for controlling the switching means, and comparing the trip level with the calculation result of the thermal data calculating means. Overcurrent protection relay in which the operation result; and a second comparator means for outputting the trip signal when it is above the trip level.

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