Siemens 6SE70 inverter fault handling example

The AC speed control system composed of frequency converter and AC motor has a wider allowable voltage fluctuation range, smaller size, stronger communication capability, and better speed control performance, and has been widely used in industrial and mining enterprises.

There will be various fault phenomena. With the help of the perfect self-diagnosis protection function of the inverter and the experience accumulated in daily work to improve the technical level of inverter fault handling, this will significantly shorten the time of inverter fault handling. Siemens 6SE70 series inverters are affected by the surrounding environmental conditions such as temperature, humidity, dust, hydrogen sulfide corrosive gas, etc., and there are many fault alarm phenomena in the application.

The fault countermeasures table in the inverter operation manual introduces common faults. When some codes not mentioned above appear, the inverter should be fully checked. The inverter maintenance method adopts two methods: online voltage detection and DC resistance measurement. The voltage of each key point is measured and compared with the normal value to narrow the scope of the fault and make analysis and judgment; the DC resistance of the components is measured, and the judgment and comparison are made according to the color ring of the chip resistor. Then the suspected components are removed and the DC resistance of the components is measured again. The comparison method is used to determine whether the components are good or bad.

We will take the letter "E" alarm fault displayed on the PMU LCD screen of the Siemens 6SE70 inverter control panel as an example to illustrate how to handle the inverter fault.

When the letter "E" alarm is displayed on the PMU LCD screen of the Siemens 6SE70 inverter control panel, the inverter cannot work. Pressing the P key and restarting the power supply are ineffective. There is no relevant introduction in the operation manual. When checking the external DC 24V power supply, it is found that the voltage is low. After solving the problem, the inverter works normally. However, the "E" alarm generally means that the CUVC board is damaged. Replacing a CUVC board will work normally. The following situations of "E" alarm are caused by the failure of the bottom board and CUVC communication board.

(1) Siemens 6SE70 inverter fault phenomenon: The PMU LCD screen of the operation control panel displays an "E" alarm.

Inspection and treatment: Replace a new CUVC board, power on and start the machine. The LCD screen still displays the "E" alarm, indicating that the cause of the fault is not the CUVC board but the bottom board. Check the bottom board, use a digital multimeter to measure the external DC24V voltage, and the reference voltage of the integrated block N3 is abnormal. The output voltage of the integrated block N220 is 0.1V, which is obviously low. The normal value is 15V. Check the integrated block N2's pin 1 is 11.3V, the pin 8 is 0.20V, and the power input of the pin 11 is 27.5V, which is normal. After analysis, it is determined that pins 1, 8, and 20 are abnormal. Test the voltage of the integrated block N3's pin 1 to be 0.31V, and the voltage of the pin 2 to be 1.8V, which are also low. Remove the N3 integrated block MC340 with a hot air gun, and measure the resistance between pins 2 and 3 to be 84 ohms. After replacing a new N3 integrated block MC340, test the voltage of each pin, pin 1 is 2.1V, and pin 2 is 5.1V, which is normal. The voltages of each pin of N2 integrated block were also normal. The output voltage of integrated block N3 was abnormal, which caused the voltages of each pin of N2 integrated block to be offset. The input parameters of the inverter wiring were restored and the inverter was started and operated normally.

(2) Siemens 6SE70 inverter fault phenomenon: The PMU LCD screen of the operation control panel displays an "E" alarm.

Inspection and treatment: Use a digital multimeter to measure the voltage of each pin of the bottom plate N2 and N3 integrated blocks. The voltage of N3's 1 pin and N2's 8 pin are both low. The base bias resistor of the V28 transistor has changed from 4.7K ohms to 150K ohms. Replace the new chip resistor and measure the voltage of each pin of N2 and N3. It is normal. Because the base bias resistor of V28 changes, the V28 transistor is cut off, causing the N2 and N3 integrated blocks to not work properly.

(3) Fault phenomenon: The PMU LCD screen on the operation control panel displays an "E" alarm.

Inspection and treatment: For an inverter with "E" alarm, the CBT communication board on the original CUVC board of the inverter was removed and installed on a new CUVC board. After the inverter was installed with the CUVC board and started, the LCD screen still displayed the "E" alarm. After removing the CUVC board and checking, it was found that the chip resistor on the CBT communication board was burned out. After replacing the new CBT communication board, the inverter started and worked normally.

(4) Fault phenomenon: The PMU LCD screen on the operation control panel displays an "E" alarm.

Inspection and treatment: Check the power-on voltage of the first pin of the bottom power block N2, which is 11.32V, while the normal value is 26.7V. The output voltage of the 20th pin is 0.117V, while the normal value is 15.31V. The voltage of the first pin of the reference voltage block N3 is 0.315V, while the normal value is 2.1V. The voltage of the second pin varies between 1.5V and 1.8V, while the normal value is 5.1V. Check the relay K4, the coil circuit is connected in series with two diodes V16 and V15, with resistance values ​​of 3.67 ohms and 5.5 ohms respectively, which are short-circuited. The base resistance of the transistor V28 (5C) has changed from the normal value of 4.7K ohms to 150K ohms, which is burned out. After replacing the new resistor and diode, it runs normally.