Discussion on various protection and fault handlin

Abstract: as a very important energy-saving equipment in today's industrial field, high-voltage inverter plays a huge role, but because of its high cost and the importance of its location, it must be protected to ensure the normal operation of the inverter, This paper introduces the various protection devices and protection principles of ipower series frequency converters produced by Harbin Jiuzhou electric, as well as the solutions to common faults, which also provide a reference for the daily inspection and maintenance of frequency converters

key words: high voltage inverter protection fault handling

1 Introduction

ipower series high-voltage inverter is an AC-DC-AC voltage source inverter with multi unit series structure. It realizes the sinusoidization of input and output voltage and current waveforms through multi overlap addition technology, effectively controls harmonics, and reduces the pollution of electricity and load. It is an environmental friendly high-voltage inverter that does not need a filter. At the same time, it also has complete protective devices and measures to protect the frequency converter and load, so as to eliminate and avoid losses caused by various complex working conditions and create greater benefits for users

2. Protection of high-voltage frequency converter

2.1 incoming line protection of high-voltage frequency converter

incoming line protection is the protection of the user's incoming line and frequency converter, including lightning protection, grounding protection, phase loss protection, phase reversal protection, imbalance protection, overvoltage protection, transformer protection, etc. These protective devices are generally installed at the input end of the frequency converter. Before running the frequency converter, first protect 2 Only when there is no problem with the incoming line protection of the aerospace license can it be operated

2.1.1 lightning protection refers to the lightning protection through the lightning arrester installed at the input end of the bypass cabinet or frequency converter. The lightning arrester is an electrical device that can release lightning or release the operating overvoltage energy of the power system at the same time, protect electrical equipment from instantaneous overvoltage hazards, and cut off the continuous current without causing the grounding short circuit of the system. The lightning arrester is connected between the incoming line of the frequency converter and the ground, and is connected in parallel with the protected frequency converter. When the overvoltage value reaches the specified action voltage, the lightning arrester will act immediately to flow charge, limit the overvoltage amplitude and protect the equipment insulation; After the voltage value is normal, the lightning arrester will quickly return to its original state to ensure the normal operation of the system and prevent damage caused by lightning strike

2.1.2 grounding protection is achieved by installing a zero sequence transformer device at the incoming end of the frequency converter. The principle of zero sequence current protection is based on the Kirchhoff current law, and the algebraic sum of the complex current flowing into any node in the circuit is equal to zero. When the circuit and electrical equipment are normal, the vector sum of each phase current is equal to zero. Therefore, the secondary winding of the zero sequence current transformer has no signal output, and the actuator does not act. When a phase grounding fault occurs, the vector sum of the currents of each phase is not zero. The fault current causes magnetic flux to be generated in the annular core of the zero sequence current transformer, and the induced voltage at the secondary side of the zero sequence current transformer is fed back to the main monitoring box, and then the protection command is issued to achieve the purpose of grounding fault protection

2.1.3 phase loss, phase reversal, imbalance protection, if the accuracy of the strain gauge is not high, or the anti-aging ability of the glue used to fix the strain gauge is not good, or the material of the sensor is not good, it will affect the accuracy and service life of the sensor overvoltage protection. Phase loss, phase reversal, imbalance protection, overvoltage protection is mainly to collect the incoming voltage from the incoming voltage feedback version of the frequency converter or the voltage transformer, and then determine whether it is phase loss, phase reversal, whether the incoming voltage is balanced, and whether it is overvoltage through the calculation of the CPU board, because if the input is phase loss, or phase reversal, and the voltage is unbalanced or overvoltage, it is easy to cause the transformer to burn out, or the power unit to damage, or the motor to reverse

2.1.4 the main reason for transformer protection is that it is solid, easy to use and simple to protect. Ippower series high-voltage frequency converter is only composed of three parts: transformer cabinet, power unit cabinet and control cabinet. The transformer uses a split dry-type transformer to convert high-voltage AC into a series of low voltages from different angles to supply power to the power unit. The transformer can only be cooled by air cooling. Therefore, the protection of the transformer is mainly through the temperature of the transformer to prevent the transformer from overheating, And cause the transformer coil to burn. Place a temperature probe in the three-phase coil of the transformer, and connect the leading end of the temperature probe to the temperature control device, which can automatically start the temperature, alarm temperature, and trip temperature of the fan at the bottom of the transformer, and display the temperature of each phase coil. If the temperature reaches the alarm or trip value, the temperature controller will send a signal to PLC, display the alarm information in the user interface, and PLC will carry out alarm or trip protection

2.2power series high-voltage inverter outlet side protection

ippower series high-voltage inverter outlet protection is the protection of the inverter output side and load, including output overvoltage protection, output overcurrent protection, output short circuit protection, motor overtemperature protection, etc

2.2.1 output overvoltage protection. Output overvoltage protection is to collect the output voltage through the output side voltage sampling plate. If the output voltage is too high, the system will automatically alarm

2.2.2 output overcurrent protection. Output overcurrent protection is to compare and judge whether overcurrent is caused by detecting the output current collected by the output hall

2.2.3 output short-circuit protection. The protective measures taken against the short-circuit fault between the stator winding and its outgoing line of the motor. If the frequency converter judges that the output is short circuited, it will immediately block the power unit and stop the operation at the place where it is placed (the distance between the back of the box and the wall) to meet the requirements (as specified in the equipment operation instructions)

3 fault handling method of ippower series high voltage inverter

ippower series high voltage inverter has a highly intelligent calculation level and perfect fault detection circuit, and can provide accurate positioning of all faults and make clear instructions on the main control interface. In practical application, we found that common faults can be divided into control channel abnormality, IGBT overcurrent, overvoltage fault and so on. Here, common faults, causes and treatment methods are analyzed

3.1 abnormal fault of control channel

abnormal fault of control channel is usually caused by optical fiber communication between PWM board and power unit board, which is generally caused by the following situations:

1, poor contact of optical fiber connection parts or falling off of optical fiber head

2. Dust is accumulated inside the optical fiber signal transmitter/receiver

3, fiber breakage

4. The optical fiber communication control board is damaged

in the case of optical fiber failure, it is first necessary to determine whether it is the power unit failure or the controller side failure, which can be determined by adjusting the optical fiber. Switch the optical fiber corresponding to any power unit of the same phase on the optical fiber board in the controller with the optical fiber reporting the fault. If the optical fiber fault located on the power on monitoring interface is still in the original position, it indicates that the optical fiber board is damaged. On the contrary, if the optical fiber fault displayed on the monitoring interface has been replaced, it indicates that it is a power unit fault. At this time, it can be considered to replace or repair the faulty power unit

3.2 causes and solutions of IGBT overcurrent fault

igbt is the most critical power device in high-voltage inverter. As a high-power composite device, IGBT may be locked and damaged during overcurrent. In order to improve the reliability of the system, some measures are taken to prevent damage due to overcurrent. Generally, the causes of IGBT overcurrent fault are as follows:

1. Inverter output short circuit

2. IGBT in power unit is broken down

3, the drive detection circuit is damaged

4, the detection circuit is disturbed

the detection method is to find the corresponding module according to the fault location displayed on the monitoring interface, disassemble and check whether the IGBT is damaged. The judgment method is to find the positive v+ and negative v- of the DC bus inside the power unit, connect the black lead of the multimeter to v+, and the red lead to u and V respectively. With the diode gear, it should display a value of about 0.4V, and the reverse phase shows infinity; Connect the red probe to v- and repeat the above steps to get the same result. Otherwise, it can be judged that IGBT is damaged and needs to be replaced

3.3 cause and solution of overvoltage fault

the cause of overvoltage is generally the overvoltage from the input side of the power supply. Under normal circumstances, the fluctuation of electric voltage is within -10% to +10% of the rated voltage, but under special circumstances. As the DC bus voltage rises with the power supply voltage, when the voltage rises to the protection value, the frequency converter will trip due to overvoltage protection. In order to avoid the overvoltage at the input side, the tap of the transformer can be changed for regulation. This method is only suitable for the situation that the field voltage is always high. In addition, it can also consider adding an absorption device at the input side of the power supply to reduce the overvoltage factor at the input side of the frequency converter

4 conclusion

high voltage and high power frequency converters play a more and more critical role in industrial production, and the daily maintenance of frequency converters is also more important. Therefore, only by understanding the various protection functions and fault handling methods of high voltage frequency converters, can we properly deal with various problems during operation. With the continuous development of science and technology, the functions and protection of high voltage frequency converters will be more perfect, China's high-voltage inverter will also be in the forefront of the world

References:

[1] Jiuzhou electric ipower frequency converter technical manual, Harbin Jiuzhou electric 2004

[2] Application Manual of high voltage frequency converter, Zhong Mingzhen, Zhao Xiangbin, 2009, 04 Machinery Industry Press (end)