In the use of the inverter, due to improper selection and use of the inverter, the inverter will not be able to operate normally or even cause equipment failure, resulting in production interruption and unnecessary economic loss. This article takes Fuji FRNP7/G7 inverter as an example to describe several problems that should be paid attention to when using the inverter.
1 selection
A feed oil pump is controlled by frequency conversion. The motor type is JR127_10, 115kW, Ue=380V, Ie=231A, and the FRNll0P7-4EX inverter is used. During operation, it is found that although the given frequency is high, the actual frequency cannot be adjusted, the inverter trips frequently, and the fault indication is “OLlâ€, that is, the inverter is overloaded. After inspection, the rated current of the inverter is 210A, and the running current of the oil pump motor is fluctuating around 220A when the material is high, the driving torque reaches the limit setting, the frequency can not be adjusted, and the running current is greater than the rated current of the inverter. The inverter over-current trips. The analysis believes that the reason is that the inverter capacity selection is too small.
The selection of the inverter should meet the following conditions:
(1) The voltage level is consistent with the control motor.
(2) The rated current is 1.1~1.5 times of the rated current of the motor.
(3) Select the type of inverter according to the load characteristics of the controlled device.
The oil isolation pump is a constant torque load, and it is better to use a G7 inverter with a wide driving torque limit range. Select FRNl60G7_4EX, the rated voltage of the inverter is 400V, the rated output current is 304A, the driving torque limit is 150%, and the above problem is no longer occurred after switching to FRNl60G7. 4EX.
2 installation environment
Due to the high integration of the frequency converter, the overall structure is compact, and its own heat dissipation is large, so the temperature, humidity and dust content of the installation environment are required to be high. The inverter of Shanxi Aluminum Factory is installed in the operation room. Because the installation workshop belongs to the dry process workshop, the operating environment of the inverter is poor, the operation room has a lot of dust, and the indoor temperature in summer is high. The inverter has been faulty many times. After sealing and cooling the operating room, the situation has greatly improved. Later, due to the large amount of condensed water in the centralized air conditioning in the operating room, the cabinet was too close to the cabinet, and a fault of the inverter control board components was damaged. It can be seen that the inverter must be provided with a good operating environment while installing the inverter.
3 parameter setting
There are many setting parameters of the inverter, and each parameter has a certain range of selection. In use, it is often encountered that the inverter cannot work normally due to improper setting of individual parameters.
(1) The start and stop button and the potentiometer frequency modulation are invalid. When the inverter is shipped from the factory, it is set to operate through the keyboard panel. The external control is invalid, and the terminal FWD_CM is shorted by the shorting tab. When the external start and stop and FM control are selected, the shorting tab must be removed. The above problem may occur, it may be FWD, the CM shorting piece is not removed, the operation mode and the FM mode parameter selection are incorrect, and the part should be checked.
(2) The inverter works normally when the motor is unloaded, but it cannot be started with load. This problem often occurs with constant torque loads. A FRNl60P7.4EX inverter of Shanxi Aluminum Factory has a normal air test during the test run, but it trips with load, which can not be loaded after the acceleration and deceleration time is increased. Continue to check the torque boost value and change the torque boost value from "2" to "7" to increase the voltage output at low frequencies. The load characteristics at low frequencies are improved and the motor is loaded normally. When encountering the above problems, it is important to check the acceleration and deceleration time setting and the torque boost setting value.
(3) The inverter is put into operation, and the motor is not started, and the overload is tripped. A 7.5kW_6 pole motor of Shanxi Aluminum Plant adopts frequency conversion control, and the frequency converter frequently stops when it is put into operation. When checking the original setting, the offset frequency is set to 2H2. Before the inverter receives the running command but does not give the FM signal, the controlled motor will always receive the low frequency running command of 2H2 and cannot start. It is determined that the stall current of the motor reaches 47A, which is about 3 times of the rated current of the motor, and the overload protection action of the inverter is normal. Change the bias frequency to 0Hz and the motor starts normally.
(4) The frequency has reached a large value, but the motor speed is still not high. The frequency setting of a newly used inverter is already very large, but the motor speed is significantly lower than other motors at the same frequency. Check that the frequency gain setting is 150%. It is known from the definition of the frequency setting signal gain that the setting gain is the ratio of the analog frequency signal to the output frequency. Assuming the set frequency is 30 Hz, the actual output frequency is only 20H2. After changing the set gain to 100%, the problem is solved.
(5) The frequency rises to a certain value. When the upward adjustment is continued, the frequency keeps jumping at a certain value and the rotation speed cannot be increased. When the inverter is working, the output torque is automatically calculated and the output torque is limited to the set value. If the drive torque setting value is too small, the output torque may be limited, so that the inverter output frequency does not reach the given frequency. In case of the above problem, check whether the drive torque setting value is too small, and whether the inverter capacity is too small, and then try to solve it.
4 Troubleshooting
The inverter has a strong fault diagnosis function to protect the internal rectification, inverter part, CPU and peripheral communication and motor faults of the inverter. The fault code will always be displayed until the inverter resets after the protection trip. According to the fault indication code, the cause of the fault is determined, which can narrow the fault finding range and greatly reduce the fault finding time.
(1) When a frequency converter starts up after cleaning, it displays “OH2†fault indication trip, OH2 means external fault of the inverter. The terminal "THR" and "CM" connected to the external fault signal at the factory are short-circuited with shorting tabs. Since this inverter is not equipped with external protection, THR_CM should be shorted. Upon inspection, the short tab between 66THR" and "CM" is loose and falls during cleaning. The inverter runs normally after the shorting is restored.
(2) When the inverter starts, it will trip. The fault indication is “OClâ€. If the OCl is overcurrent during acceleration, it is suspected that the motor is faulty. Disconnect the inverter from the motor connection line and check the short circuit between the motor windings. The inverter runs normally after replacing the motor.
(3) In the summer, if the cooling and ventilation effects of the inverter operating room are poor, and the ambient temperature rises, the “OHl†and “OH3†overheat protection trips often occur. At this time, it should be checked whether the fan inside the inverter is damaged, and whether the operating room temperature is too high, measures should be taken to force cooling to ensure that the inverter is safe for summer.
(4) When the frequency converter is adjusted to above 15Hz, the "LU" undervoltage protection action. The "LU" protection signal means that the rectified voltage is insufficient. We checked from the rectification part to the input end of the inverter power supply and found that there was no phase on the input side of the power supply. Since the voltmeter took the signal from the other two phases, the voltmeter indicated normal, and the phase loss of the input side of the inverter was not found in time. After the input phase is missing, the inverter's rectified output voltage drops. In the low frequency region, the charging capacitor is also adjustable in frequency. However, after the frequency is adjusted to a certain value, the rectified voltage drops rapidly, causing the inverter "LU" to trip.
5 maintenance
During the running of the inverter, you can visually check the running status from the outside of the device for abnormality. The full-time inspector can check the operating parameters of the inverter through the keyboard panel conversion keys, such as output voltage, output current, output torque, motor speed, etc. , Master the range of daily operation values ​​of the inverter, in order to find the inverter and motor problems in time. In addition, pay attention to the following points:
(1) Set up special personnel to clean and blow the inverter regularly to keep the internal cleaning of the inverter and the smooth flow of the air duct.
(2) Keep the environment around the inverter clean and dry. Do not place debris near the inverter.
(3) After each maintenance of the inverter, carefully check for missing panel screws and wires to prevent short-circuit accidents caused by small metal objects.
(4) When measuring the insulation of the inverter (including the motor), a 500V megger should be used. If only the inverter is tested, remove all external wiring connected to the inverter terminals. After cleaning the device, short the main circuit terminals by wires, and test them with the ground meter. If the megohmmeter indicates 5M or more, the instructions are normal. The purpose of this is to reduce the number of shakes.
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