Direct current source for testing thermal relay
By using adjustable voltage-regulated switching power supply group and linear constant current source in thermal relay testing equipment, combined with real-time adjustment of the controller, the detection accuracy and cost in the existing technology are solved, and different current levels and testing are achieved The flexible adaptation of time improves the accuracy of test results and the efficiency of equipment use.
Patent Information
- Application Number
- CN202411359808.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-27
- Publication Date
- 2025-01-03
AI Technical Summary
Due to the limited output voltage range of the switching power supply and errors, the accuracy of the detection results is reduced, which cannot meet the testing requirements of different current levels. In addition, the autothermal effect in a long-term test leads to an increase in resistance, affecting the accuracy.
A DC current source including an adjustable voltage-regulating switching power supply group and a linear constant current source is designed. The voltage and current are adjusted in real time through the controller to ensure the constant output current, reduce voltage ripple, and adapt to the increase in resistance to achieve different currents. Flexible adaptation of grades and test durations.
It improves the accuracy and accuracy of the test current, reduces the cost requirements of the test equipment, avoids the necessity of purchasing multiple range equipment, and meets the overload protection testing needs of different models of thermal relays.
Smart Images
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Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of testing current sources, and in particular relates to a direct current source for testing thermal relays. Background Art
[0002] The main purpose of thermal relays is to provide overload protection, phase failure protection and asymmetric protection for motors. However, every year, motors burn out due to faults and even cause major safety accidents. Therefore, in order to ensure the normal operation of motors, the overload protection of thermal relays is very important. Thermal relays use the thermal effect of current to protect motors from overload and reflect the overload heating state of the controlled equipment. That is, the overload protection test of thermal relays requires passing 1.1 to 1.25 times the rated current for a certain period of time. At present, thermal relay test equipment often uses switching power supplies as power supplies. The impedance of thermal relays is purely resistive. By changing the output voltage of the switching power supply, the test current flowing through the thermal relay can be adjusted.
[0003] However, the impedance of thermal relays of different models is different. The higher the current level, the smaller the impedance. Since the output voltage range of the switching power supply is limited and the power supply has errors within the maximum range, when the large-range test equipment outputs a small current for testing, the range error causes the accuracy of the test results to be reduced. The same model of switching power supply cannot meet the overload protection test of thermal relays of different current levels. Thermal relay manufacturers are often required to purchase a variety of test equipment with different ranges from small to large, which increases the cost of the test equipment. At the same time, there are many different test methods for thermal relays, such as standard testing and equivalent testing. Different test methods output current to the thermal relay to be tested for different durations, ranging from tens of seconds to more than 1 hour. During long-term testing, the thermal relay heats up due to the self-heating effect, resulting in an increase in resistance and a decrease in test accuracy. In addition, the switching power supply changes the output voltage by pulse width modulation, and the output voltage has a large ripple, which affects the accuracy of the test current.
[0004] Therefore, designing a DC current source for thermal relay testing that can reduce power supply voltage ripple, flexibly adapt current levels, and eliminate self-heating interference during the test has become a technical problem that needs to be solved urgently. Summary of the invention
[0005] In order to solve the above problems, the present invention provides a direct current source for testing a thermal relay.
[0006] The technical solution of the present invention is a direct current source for testing a thermal relay, comprising: The adjustable voltage-stabilized switching power supply group converts 220V AC mains power into a DC voltage within the corresponding voltage range, and is used to output DC voltages of different voltage levels; Linear constant current source, the input end is connected to the output end of the switching power supply group, and the output end is connected to the thermal magnetic relay R to be tested L , generates the load current I for testing load , realize constant current output, and send corresponding current sampling signal to the controller; Controller, based on manually set test current I set , send a control signal to the adjustable voltage-stabilized switching power supply group to control the voltage output of the adjustable voltage-stabilized switching power supply group, send a voltage reference signal to the linear constant current source to control the output current of the linear constant current source and maintain the current constant, and use the current sampling signal to obtain the load current I output by the linear constant current source load , and then detect the linear constant current source output voltage V out , calculate the load current I load With the output voltage V out The thermal magnetic relay R to be tested is obtained L resistance value.
[0007] As a further improvement of the present invention, the adjustable voltage-stabilized switching power supply group comprises a plurality of switching power supply monomers A1, A2, ..., A m The input end of the switching power supply unit is connected to the 220V AC mains, and the output positive pole corresponds to the contactor switches K1, K2, ..., K m The controller is used to send a control signal S that matches the contactor switch K1 , S K2 ,……,S Km , adjust the on and off of each contactor switch.
[0008] As a further improvement of the present invention, the positive and negative input terminals of the linear constant current source are connected to the positive output terminal VCC and the negative output terminal GND of the switching power supply group, and the output terminals OUT_A and OUT_B are connected to the thermal magnetic relay R to be tested. L The linear constant current source is composed of a number of linear constant current source monomers B1, B2, ..., B n The linear constant current source monomer sends a corresponding current sampling signal V to the controller. s1 、V s2 ,……,V sn The controller is used to send a voltage reference signal V that matches the linear constant current source monomer. ref1 、V ref2 ,……,V refn , adjust the on and off of each linear constant current source monomer.
[0009] As a further improvement of the present invention, each of the linear constant current source monomers is provided with a power switch tube N for constant current regulation. mos , respectively Q1, Q2, ..., Qn , obtain the current sampling signal of the constantan wire current sampling resistor R s1 , R s2 ,……,R sn , operational amplifier U o1 , U o2 ,……,U on , and the driving resistor R d1 , R d2 ,……,R dn .
[0010] As a further improvement of the present invention, the power switch tube N mos The drain terminal is connected to the output terminal OUT_B, the source terminal is connected to one end of the constantan wire current sampling resistor, and the gate terminal is connected to one end of the driving resistor; the other end of the constantan wire current sampling resistor is connected to the input terminal GND of the linear constant current source; the other end of the driving resistor is connected to the output terminal of the operational amplifier; the positive input terminal of the operational amplifier is used to input a reference voltage signal, and the negative input terminal is connected to the power switch tube N mos The intersection of the current sampling resistor and the constantan wire, the operational amplifier controls the power switch tube N mos In the constant current working area.
[0011] As a further improvement of the present invention, the load current I load The load current I is obtained by superimposing the output current of the linear constant current source monomer. load The relationship between the current sampling signal and
[0012] As a further improvement of the present invention, the controller converts the load current I load With test current I set Perform calculations and adjust the reference voltage signal in real time to maintain the load current I load Stable tracking test current I set .
[0013] As a further improvement of the present invention, the controller sets the test current I set Generate a small current in proportion and input it to the thermal magnetic relay R to be tested. L , detect the thermal magnetic relay R to be tested L The voltage data is used to generate a feedback voltage signal, and the estimated resistance value of the thermal magnetic relay RL to be tested is calculated by calculating the small current and the feedback voltage signal to test the current I set The test voltage data with margin is calculated with the estimated resistance value, and a corresponding voltage reference signal is generated and sent to the linear constant current source.
[0014] As a further improvement of the present invention, the magnitude of the small current is judged to be no greater than the test current I set 5%.
[0015] After adopting the above method, the input end of the linear constant current source is connected to the output end of the switching power supply group, and the output end is connected to the thermal magnetic relay RL to be tested. The controller sends a control signal to the adjustable voltage-stabilized switching power supply group to control the adjustable voltage-stabilized switching power supply group to output a constant voltage to the linear constant current source. The controller then sends a voltage reference signal to the linear constant current source to keep the output current of the linear constant current source under control and maintain the current constant, so that the output voltage will not produce large ripples, thereby improving the accuracy of the output test current.
[0016] The adjustable voltage-stabilized switching power supply group is composed of a plurality of switching power supply monomers A1, A2, ..., Am connected in parallel, the output positive pole of the switching power supply monomer is connected in series with a contactor switch, and the linear constant current source is composed of a plurality of linear constant current source monomers B1, B2, ..., Bn connected in parallel, so that the current source has a large voltage and current range at the same time. The controller sends a control signal and a voltage reference signal to control different contactor switches to be connected with the linear constant current source monomers, so that the maximum range of the adjustable voltage-stabilized switching power supply group and the linear constant current source changes to match the output value required by the test current Iset, so as to avoid the range error being too large when the set test current Iset value changes greatly, resulting in a decrease in the accuracy of the output current, and at the same time meet the overload protection test of thermal relays of different current levels, and the thermal relay manufacturer does not need to purchase both large and small range equipment at the same time, thereby reducing the cost of purchasing test equipment.
[0017] The controller generates a small judgment current in proportion to the test current Iset, inputs the small judgment current into the thermal-magnetic relay RL to be tested, and detects to obtain a feedback voltage signal, calculates the estimated resistance of the thermal-magnetic relay RL to be tested, and generates test voltage data with a margin. Under test modes of different durations, after the resistance of the thermal-magnetic relay RL to be tested increases due to the self-heating effect, the voltage reference signal sent to the linear constant current source has a margin, which adapts to the influence of the increased resistance and improves the accuracy of the test results. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 Shown is a schematic diagram of the DC current source principle of the present invention.
[0019] Figure 2 Shown is a schematic diagram of the linear constant current source circuit structure. DETAILED DESCRIPTION
[0020] like Figure 1-2 A DC current source for testing a thermal relay is shown, comprising: The adjustable voltage-stabilized switching power supply group converts 220V AC mains power into a DC voltage within the corresponding voltage range, and is used to output DC voltages of different voltage levels; Linear constant current source, the input end is connected to the output end of the switching power supply group, and the output end is connected to the thermal magnetic relay R to be tested L , generating the load current I for testing load , realize constant current output, and send corresponding current sampling signal to the controller; Controller, based on manually set test current I set , send a control signal to the adjustable voltage-stabilized switching power supply group to control the voltage output of the adjustable voltage-stabilized switching power supply group, send a voltage reference signal to the linear constant current source to control the output current of the linear constant current source and maintain the current constant, and use the current sampling signal to obtain the load current I output by the linear constant current source load , and then detect the linear constant current source output voltage V out , calculate the load current I load With output voltage V out The thermal magnetic relay R to be tested is obtained L resistance value.
[0021] The adjustable voltage-stabilized switching power supply group comprises a plurality of switching power supply monomers A1, A2, ..., A m The input end of the switching power supply unit is connected to the 220V AC mains, and the output positive pole corresponds to the contactor switches K1, K2, ..., K m The controller is used to send a control signal S that matches the contactor switch K1 , S K2 ,……,S Km , adjust the on and off of each contactor switch.
[0022] The positive and negative poles of the input terminal of the linear constant current source are connected to the positive pole VCC and the negative pole GND of the output terminal of the switching power supply group, and the output terminals OUT_A and OUT_B are connected to the thermal magnetic relay R to be tested. L The linear constant current source is composed of a number of linear constant current source monomers B1, B2, ..., B n The linear constant current source monomer sends a corresponding current sampling signal V to the controller. s1 、V s2 ,……,V sn The controller is used to send a voltage reference signal V that matches the linear constant current source monomer. ref1 、V ref2 ,……,V refn , adjust the on and off of each linear constant current source monomer.
[0023] Each of the linear constant current source monomers is provided with a power switch tube N for constant current regulation.mos , respectively Q1, Q2, ..., Q n , obtain the current sampling signal of the constantan wire current sampling resistor R s1 , R s2 ,……,R sn , operational amplifier U o1 , U o2 ,……,U on , and the driving resistor R d1 , R d2 ,……,R dn .
[0024] The power switch tube N mos The drain terminal is connected to the output terminal OUT_B, the source terminal is connected to one end of the constantan wire current sampling resistor, and the gate terminal is connected to one end of the driving resistor; the other end of the constantan wire current sampling resistor is connected to the input terminal GND of the linear constant current source; the other end of the driving resistor is connected to the output terminal of the operational amplifier; the positive input terminal of the operational amplifier is used to input a reference voltage signal, and the negative input terminal is connected to the power switch tube N mos The intersection of the current sampling resistor and the constantan wire, the operational amplifier controls the power switch tube N mos In the constant current working area.
[0025] The load current I load The load current I is obtained by superimposing the output current of the linear constant current source monomer. load The relationship between the current sampling signal and
[0026] The controller converts the load current I load With test current I set Perform calculations and adjust the reference voltage signal in real time to maintain the load current I load Stable tracking test current I set .
[0027] The controller passes the test current I set Generate a small current in proportion and input it to the thermal magnetic relay R to be tested. L , detect the thermal magnetic relay R to be tested L The voltage data is used to generate a feedback voltage signal, and the estimated resistance value of the thermal magnetic relay RL to be tested is calculated by calculating the small current and the feedback voltage signal to test the current I set The test voltage data with margin is calculated with the estimated resistance value, and a corresponding voltage reference signal is generated and sent to the linear constant current source.
[0028] The magnitude of the small current is judged to be no greater than the test current I set 5%.
[0029] The input end of the linear constant current source is connected to the output end of the switching power supply group, and the output end is connected to the thermal magnetic relay RL to be tested. The controller sends a control signal to the adjustable voltage-stabilized switching power supply group to control the adjustable voltage-stabilized switching power supply group to output a constant voltage to the linear constant current source. The controller then sends a voltage reference signal to the linear constant current source to keep the output current of the linear constant current source under control and maintain the current constant, so that the output voltage will not produce large ripples, thereby improving the accuracy of the output test current.
[0030] The adjustable voltage-stabilized switching power supply group is composed of a plurality of switching power supply monomers A1, A2, ..., Am connected in parallel, the output positive pole of the switching power supply monomer is connected in series with a contactor switch, and the linear constant current source is composed of a plurality of linear constant current source monomers B1, B2, ..., Bn connected in parallel, so that the current source has a large voltage and current range at the same time. The controller sends a control signal and a voltage reference signal to control different contactor switches to be connected with the linear constant current source monomers, so that the maximum range of the adjustable voltage-stabilized switching power supply group and the linear constant current source changes to match the output value required by the test current Iset, so as to avoid the range error being too large when the set test current Iset value changes greatly, resulting in a decrease in the accuracy of the output current, and at the same time meet the overload protection test of thermal relays of different current levels, and the thermal relay manufacturer does not need to purchase both large and small range equipment at the same time, thereby reducing the cost of purchasing test equipment.
[0031] The controller generates a small judgment current in proportion to the test current Iset, inputs the small judgment current into the thermal-magnetic relay RL to be tested, and detects to obtain a feedback voltage signal, calculates the estimated resistance of the thermal-magnetic relay RL to be tested, and generates test voltage data with a margin. Under test modes of different durations, after the resistance of the thermal-magnetic relay RL to be tested increases due to the self-heating effect, the voltage reference signal sent to the linear constant current source has a margin, which adapts to the influence of the increased resistance and improves the accuracy of the test results.
Claims
1. A direct current source for testing a thermal relay, characterized in that: include, The adjustable voltage-stabilized switching power supply group converts 220V AC mains power into a DC voltage within the corresponding voltage range, and is used to output DC voltages of different voltage levels; Linear constant current source, the input end is connected to the output end of the switching power supply group, and the output end is connected to the thermal magnetic relay R to be tested L , generates the load current I for testing load , realize constant current output, and send corresponding current sampling signal to the controller; Controller, based on manually set test current I set , send a control signal to the adjustable voltage-stabilized switching power supply group to control the voltage output of the adjustable voltage-stabilized switching power supply group, send a voltage reference signal to the linear constant current source to control the output current of the linear constant current source and maintain the current constant, and use the current sampling signal to obtain the load current I output by the linear constant current source load , and then detect the linear constant current source output voltage V out , calculate the load current I load With the output voltage V out The thermal magnetic relay R to be tested is obtained L resistance value.
2. A direct current source for thermal relay testing according to claim 1, characterized in that: The adjustable voltage-stabilized switching power supply group comprises a plurality of switching power supply monomers A1, A2, ..., A m The input end of the switching power supply unit is connected to the 220V AC mains, and the output positive pole corresponds to the contactor switches K1, K2, ..., K m The controller is used to send a control signal S that matches the contactor switch K1 , S K2 ,……,S Km , adjust the on and off of each contactor switch.
3. A direct current source for thermal relay testing according to claim 1, characterized in that: The positive and negative poles of the input terminal of the linear constant current source are connected to the positive pole VCC and the negative pole GND of the output terminal of the switching power supply group, and the output terminals OUT_A and OUT_B are connected to the thermal magnetic relay R to be tested. L The linear constant current source is composed of a number of linear constant current source monomers B1, B2, ..., B n The linear constant current source monomer sends a corresponding current sampling signal V to the controller. s1 、V s2 ,……,V sn The controller is used to send a voltage reference signal V that matches the linear constant current source monomer. ref1 、V ref2 ,……,V refn , adjust the on and off of each linear constant current source monomer.
4. A direct current source for thermal relay testing according to claim 3, characterized in that: Each of the linear constant current source monomers is provided with a power switch tube N for constant current regulation. mos , respectively Q1, Q2, ..., Q n , obtain the current sampling signal of the constantan wire current sampling resistor R s1 , R s2 ,……,R sn , operational amplifier U o1 , U o2 ,……,U on , and the driving resistor R d1 , R d2 ,……,R dn .
5. A direct current source for thermal relay testing according to claim 4, characterized in that: The power switch tube N mos The drain terminal is connected to the output terminal OUT_B, the source terminal is connected to one end of the constantan wire current sampling resistor, and the gate terminal is connected to one end of the driving resistor; the other end of the constantan wire current sampling resistor is connected to the input terminal GND of the linear constant current source; the other end of the driving resistor is connected to the output terminal of the operational amplifier; the positive input terminal of the operational amplifier is used to input a reference voltage signal, and the negative input terminal is connected to the power switch tube N mos The intersection of the current sampling resistor and the constantan wire, the operational amplifier controls the power switch tube N mos In constant current working area.
6. A direct current source for thermal relay testing according to claim 4, characterized in that: The load current I load The load current I is obtained by superimposing the output current of the linear constant current source monomer. load The relationship between the current sampling signal and 7. A direct current source for testing a thermal relay according to any one of claims 1 to 6, characterized in that: The controller converts the load current I load With test current I set Perform calculations and adjust the reference voltage signal in real time to maintain the load current I load Stable tracking test current I set .
8. A direct current source for testing a thermal relay according to any one of claims 1 to 6, characterized in that: The controller passes the test current I set Generate a small current in proportion and input it to the thermal magnetic relay R to be tested. L , detect the thermal magnetic relay R to be tested L The voltage data is used to generate a feedback voltage signal, and the estimated resistance value of the thermal magnetic relay RL to be tested is calculated by calculating the small current and the feedback voltage signal to test the current I set The test voltage data with margin is calculated with the estimated resistance value, and a corresponding voltage reference signal is generated and sent to the linear constant current source.
9. A direct current source for testing a thermal relay according to claim 8, characterized in that: The magnitude of the small current is judged to be no greater than the test current I set 5%.