Digital thermal protection device of alternating current motor

Abstract

The utility model relates to a digital thermal protection device of an alternating current motor, which is characterized in that each phase of power line is respectively connected with a voltage transformer and a current transformer, and voltage and current of a three-phase power supply are respectively provided for an electric energy metering chip through a corresponding sampling processing circuit; three-phase voltage, current, power, phase sequence and unbalance rate data collected in real time are provided for a connected MCU, and the MCU judges the working state of the motor according to program setting and drives the circuit in real time to control the alternating current contactor to be attracted / released so as to achieve control over the motor. The utility model has the advantages that the protection range, the sensitivity and the precision of the device are higher than those of a thermal overload relay, and the situation that the thermal relay does not act when the motor is burnt out in the past is effectively avoided; the load motor can be prevented from being damaged by overheating caused by overload, unbalanced input current, overvoltage, undervoltage, phase loss or locked-rotor, manual reset can be achieved, devices cannot be damaged, power consumption and voltage fluctuation can be recorded in real time, and the traceability of historical data is achieved.

Description

Technical Field

[0001] The utility model relates to the technical field of motor protection, in particular to a digital thermal protection device for an AC motor. Background Art

[0002] At present, motor protection at home and abroad is achieved by using traditional thermal overload relays. The main control element of the traditional thermal overload relay is a bimetallic strip. After the overload current passes through the thermal element, the bimetallic strip is heated and bent in one direction, driving the action mechanism to separate the contacts, thereby disconnecting the motor control circuit, realizing the power off of the motor and playing the role of overload protection.

[0003] It mainly has the following defects:

[0004] 1. When the bimetallic strip is heated and bent, it takes a long time for the heat to be transferred. Therefore, the thermal relay cannot be used for short-circuit protection, but can only be used for overload protection. In addition, its power consumption is relatively high.

[0005] 2. The protection method that uses current amplitude as the fault judgment criterion has certain defects in principle. It can only reflect symmetrical faults. It cannot effectively protect against asymmetrical faults such as grounding and unbalanced operation, or the action time is long.

[0006] 3. Due to thermal deformation, rust, looseness, long-term overload and other reasons, certain parameters of long-term operation will deviate from the original set values. In serious cases, they may fail or not operate, and the protective device will lose its proper protective function. Utility Model Content

[0007] The purpose of the utility model is to solve the technical problems existing in the prior art and to provide a digital thermal protection device and a protection method for an AC motor, which can provide more comprehensive protection for the AC motor, and the protection performance can be stable over a long period of time and will not fail to provide the proper protection due to differences in manufacturing process or time.

[0008] The utility model adopts the following technical solutions:

[0009] A digital thermal protection device for an AC motor comprises a three-phase power supply connected to an AC motor after passing through an AC contactor, and an MCU controls the AC contactor to close / release through a connected drive circuit to achieve control of the motor. The device is characterized in that each phase power line is respectively connected to a voltage transformer and a current transformer, and the output of each voltage transformer and current transformer passes through a corresponding sampling and processing circuit, and the sampling and processing circuit samples the voltage and output current of the three-phase power supply and provides them to an electric energy metering chip. After being processed by the electric energy metering chip, the three-phase voltage, current, power, phase sequence, and imbalance rate data collected in real time are provided to the connected MCU, and the MCU determines the working state of the motor according to a program setting and drives the circuit in real time to control the AC contactor to close / release, so as to achieve start and stop control of the motor, and record power consumption and voltage fluctuations.

[0010] The utility model discloses a digital thermal protection device for an AC motor. When the current and voltage data are normal and the motor is running stably, when the abnormal working conditions are as follows:

[0011] The MCU detects that the voltage is 437VAC, triggering the overpressure judgment condition. The MCU issues an alarm message, and the corresponding alarm message pops up on the human-machine interface. This alarm only pops up and records, and does not control the motor to stop;

[0012] When the detection voltage is below 323VAC, the undervoltage judgment condition is triggered, the MCU issues an alarm message, and the corresponding alarm message pops up on the human-machine interface. This alarm only pops up and records, and does not control the motor to stop;

[0013] If the detection voltage of any phase of A, B or C is below 100VAC, the phase loss judgment condition is triggered, the MCU issues an alarm message, the motor stops running, and the alarm indicator light on the control board lights up, and the corresponding alarm message pops up on the human-machine interface. After the fault is eliminated, the reset button on the control board must be pressed, and the fault light goes out. Only then can the motor start;

[0014] When the actual detected current is greater than 1.1 times the rated current, the thermal overload judgment condition is triggered. After the action time calculated by the software is exceeded, the MCU issues an alarm message, the motor stops running, and the alarm indicator on the control board lights up. The corresponding alarm message pops up on the human-machine interface. After the fault is eliminated, the reset button on the control board must be pressed. The fault light goes out and the motor can be started at this time.

[0015] When |actual current of a phase - rated current| / rated current>15%, the unbalanced input current judgment condition is triggered, the MCU issues an alarm message, and the motor stops running. After the fault is eliminated, the reset button on the control panel must be pressed, and the fault light goes out. Only then can the motor start;

[0016] When a phase loss, thermal overload or unbalanced input current fault occurs, the MCU will send out an alarm message and at the same time, it will send a signal to disconnect the AC contactor.

[0017] Due to the adoption of the above technical solution, the utility model has the following advantages and effects compared with the prior art:

[0018] 1. The protection range, sensitivity and accuracy of digital thermal protection are higher than those of thermal overload relays. It can effectively avoid the situation that the motor often burns out but the thermal relay does not work. It is an ideal upgrade product for thermal relays.

[0019] 2. It can prevent the load motor from being damaged by overheating due to overload, unbalanced input current, overvoltage, undervoltage, phase loss or stall. It can be reset manually without damaging the device.

[0020] 3. It can record power consumption and voltage fluctuations in real time, and has certain historical data traceability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a principle block diagram of the utility model;

[0022] Figure 2 It is a circuit principle diagram of an embodiment of the utility model.

[0023] like Figure 1 As shown, the utility model is a digital thermal protection device for an AC motor, comprising a three-phase power supply connected to an AC motor after passing through an AC contactor, and an MCU controls the AC contactor to close / release to control the motor through a connected drive circuit, characterized in that each phase power line is respectively connected to a voltage transformer and a current transformer, the output of each voltage transformer and current transformer passes through a corresponding sampling and processing circuit, the sampling and processing circuit is connected to an electric energy metering chip, and the voltage and output current of the three-phase power supply are sampled and provided to the electric energy metering chip respectively, and after being processed by the electric energy metering chip, the three-phase voltage, current, power, phase sequence, and imbalance rate data collected in real time are provided to the connected MCU, and the MCU determines the working state of the motor according to the program setting, and controls the AC contactor to close / release to control the motor in real time to control the motor, and records the power consumption and voltage fluctuation.

[0024] The determination conditions for various abnormal working conditions (alarms) are as follows:

[0025] Overvoltage judgment condition: When the actual detected phase voltage exceeds (1+15%)*380VAC, an overvoltage alarm is issued, but only an alarm is issued without any action;

[0026] Undervoltage judgment condition: When the actual detected phase voltage is lower than (1-15%)*380VAC, an undervoltage alarm is issued, but only an alarm is issued without action;

[0027] Phase loss judgment condition: When the voltage of all three phases, two phases or one phase is lower than 100VAC, a phase loss alarm will be issued, and the motor will stop and an alarm will be issued;

[0028] Thermal overload (overload) judgment conditions: When the detection current is greater than 1.1 times of the input rated current, there are different action times according to the excess multiples. When the actual current is less than 1.1 times of the rated current, the motor stops after 500 seconds in normal operation. When the actual current is 1.2 times of the rated current, the motor stops after 2 seconds. When the actual current is 7 times of the rated current, the motor stops instantly and an alarm is sounded.

[0029] Unbalanced input current judgment condition: |actual current of a certain phase - rated current| / rated current>15%, the action stops the motor and alarms; Example

[0030] The utility model is a digital thermal protection device and protection method for an AC motor. Figure 2 As shown, burn the program through the S2 interface. After the program is burned, connect the human-computer interaction device and set the relevant parameters on the human-computer interaction interface (the human-computer interface can set parameters: motor enable / disable, motor rated current input (setting range 0-100A), motor automatic control opening and closing time setting, alarm delay time setting (setting range 0-10 seconds), and the interface can display real-time voltage and real-time current. 3 sets of current transformers (ZMCT series) measure the three-phase current of the motor (each phase power line is connected in series in the transformer circle in turn, as shown in Figure 1). Figure 1 As shown in the figure, 3 sets of voltage transformers PT1-PT3 (DL-CT08CL2 series) are connected to each phase of the power line to detect the real-time three-phase voltage of the motor. The power metering chip RN8302B (a device that can automatically measure the grid voltage, current, active and reactive power, frequency, power factor, and energy) is used for data collection and monitoring. The measured data is transmitted in real time through SPI communication with the MCU. This data can be transmitted to the human-machine interface for real-time display through the MCU. When the motor is switched to automatic mode, the motor runs according to the human-machine interface settings. The specific process is to control V3 to be turned on through the MCU output signal. After V3 is turned on, the K1 relay is energized, and K1 controls the AC contactor to be energized, and further controls the motor to start, otherwise it stops; when it is switched to manual mode, the MCU also outputs a signal to control V3 to be turned on. After V3 is turned on, the K1 relay is energized, and K1 controls the AC contactor to be energized, and further controls the motor to start; when it is in non-automatic and non-manual state, the MCU outputs a signal to control V3 to be cut off. After V3 is cut off, the K1 relay does not energize, and K1 controls the AC contactor to be disconnected, and the motor stops.

[0031] When the current and voltage data are normal and the motor is running stably, the abnormal working conditions are as follows:

[0032] The MCU detects that the voltage is 437VAC, triggering the overpressure judgment condition. The MCU issues an alarm message, and the corresponding alarm message pops up on the human-machine interface. This alarm only pops up and records, and does not control the motor to stop;

[0033] When the detection voltage is below 323VAC, the undervoltage judgment condition is triggered, the MCU issues an alarm message, and the corresponding alarm message pops up on the human-machine interface. This alarm only pops up and records, and does not control the motor to stop;

[0034] If the detection voltage of any phase of A, B or C is below 100VAC, the phase loss judgment condition is triggered, the MCU issues an alarm message, the motor stops running, and the alarm indicator light on the control board turns on (red light), and the corresponding alarm message pops up on the human-machine interface. After the fault is eliminated, the "reset button" on the control board must be pressed, and the fault light goes out. Only then can the motor start;

[0035] When the actual detected current is greater than 1.1 times the rated current, the thermal overload judgment condition is triggered. After the action time calculated by the software is exceeded, the MCU issues an alarm message, the motor stops running, and the alarm indicator light on the control board lights up (red light), and the corresponding alarm message pops up on the human-machine interface. After the fault is eliminated, the "reset button" on the control board must be pressed, and the fault light goes out. Only then can the motor start;

[0036] When |actual current of a phase - rated current| / rated current>15%, the unbalanced input current judgment condition is triggered, the MCU issues an alarm message, the motor stops running, and the alarm indicator light on the control board lights up (red light), and the corresponding alarm message pops up on the human-machine interface. After the fault is eliminated, the "reset button" on the control board must be pressed, and the fault light goes out. Only then can the motor start;

[0037] When a phase loss, thermal overload or unbalanced input current fault occurs, the MCU will issue an alarm message and at the same time the MCU will output a low level to turn on V3 ( Figure 2 ), when V3 is turned on, the K1 relay coil will be energized and K1 will open its contacts.

[0038] Each control board corresponds to a different address and can communicate with the human-machine interface at the same time. The human-machine interface identifies different control boards through addresses. Different control boards can set currents with different functions to control different motors. The address setting can be performed through the 7-bit DIP switch D3, and up to 127 different addresses can be set.

Claims

1. A digital thermal protection device for an AC motor, comprising a three-phase power supply connected to an AC motor through an AC contactor, and an MCU controlling the AC contactor to close / release through a connected drive circuit to control the motor, characterized in that: Each phase of the power line is connected to a voltage transformer and a current transformer respectively. The output of each voltage transformer and current transformer passes through the corresponding sampling and processing circuit. The sampling and processing circuit samples the voltage and output current of the three-phase power supply respectively and provides them to the electric energy metering chip. After processing by the electric energy metering chip, the real-time collected three-phase voltage, current, power, phase sequence, and imbalance rate data are provided to the connected MCU. The MCU determines the working status of the motor according to the program settings and drives the circuit in real time to control the AC contactor to close / release, so as to realize the start and stop control of the motor.

Images