The frequency converter of a certain ship malfunctioned and tripped during navigation, causing the ship to lose power. Based on the fault symptoms, information, and damaged components, a fault tree analysis was conducted to find a solution, eliminate the fault, and restore power.
The communication electric propulsion system is the mainstream of ship electric propulsion today, with various forms.
A certain ship adopts two sets of "AC-DC-AC frequency converters+AC synchronous motors" type AC propulsion systems. The frequency converter plays a bridge role in the power conversion of this propulsion system and is a key equipment of the electric propulsion system. Once a fault occurs, it will cause the ship to lose power.
Therefore, how to troubleshoot and solve frequency converter faults is an important issue to ensure the normal operation of this type of propulsion system. This article explains the process of solving a fault in the frequency converter of a ship's electric propulsion system.
Fault phenomenon
The main circuit of a certain ship's frequency converter adopts an AC-DC-AC topology structure. The input is two sets of three-phase 690 V 50 Hz AC power, which is converted into DC power through uncontrolled rectification, and then converted into three-phase AC power required by the load through inverter and output filtering.
During the navigation test of the ship's electric propulsion system, during the transition from dual engine to three working conditions to dual engine to one working condition test:
After running for a few minutes under the dual engine operating condition, the left propulsion frequency converter made a strange noise, and the lower part of the inverter cabinet made a sound and black smoke emitted from the ventilation port. The frequency converter malfunctioned and stopped, and the main propulsion system circuit breaker tripped;
During the single axis three navigation test, a sound occurred in the middle of the inverter cabinet of the right propulsion frequency converter, and black smoke emerged from the ventilation port. The frequency converter malfunctioned and stopped, and the main propulsion system circuit breaker tripped.
2)Fault information
The centralized control panel recorded the faults and alarm information that occurred successively during the fault shutdown:
① Left frequency converter
Abnormal propulsion circuit breaker; Controller hardware protection; Inverter unit C2 fault; Main switch malfunction.
② Right frequency converter
Controller hardware protection; Fault in inverter units B1, B2, and A2; Control power failure and water cooling unit failure.
③ The fault information of the left frequency converter mentioned above indicates that
Excessive current in the left propulsion circuit breaker causes overcurrent tripping protection; And the right push circuit breaker was opened normally without any overcurrent phenomenon.
Fault damaged components
Disassemble the frequency converter, and the damaged components are as follows:
Left frequency converter:
The C2 phase IGBT is damaged, and some DC support capacitor shells are damaged and deformed. The buffer capacitor terminals are severely damaged, and the DC bus terminals connected to the buffer capacitor are melted; The C-phase stacked busbar is damaged; Other phase components are normal, and the control hardware and software status is normal.
Right frequency converter
A2 phase IGBT driver interface board drops out; The B1 and B2 shared inverter busbar and the A1 and A2 shared inverter busbar are damaged; Other phase components are normal, and the control hardware and software status is normal.
Cause analysis of left frequency converter
① On site disassembly revealed:
The C-E pins of the C2 phase buffer capacitor have a burning phenomenon, but the internal capacitance and series diodes of the buffer capacitor are intact, indicating that the short-circuit current flows through the external pins of the buffer capacitor at the moment of fault, without flowing through the internal capacitance of the buffer capacitor. Based on this, it can be determined that there is a short-circuit phenomenon between the external pins of the buffer capacitor at the moment of fault;
The supporting capacitor of the C2 phase inverter component is damaged and deformed, indicating that a short period of high current discharge has occurred, and the excessive heat accumulated in a short period of time has led to the deformation of the supporting capacitor shell;
The C2 phase IGBT casing is slightly damaged, indicating that the short-circuit energy has not been released in large quantities inside the IGBT module;
② From the fault information of the circuit breaker, it can be determined that:
During the fault, overcurrent occurred on the input side of the transformer, causing the circuit breaker to trip; Hardware protection of the controller indicates the occurrence of overvoltage on the internal DC side;
The terminal connection between the stacked busbar and the C2 phase IGBT in the C-phase inverter unit is severely eroded, indicating a short circuit and accompanied by high-energy discharge;
③ During the operation of the equipment, due to the agitation of the internal wind path and the shaking of the ship, conductive impurities present in the cabinet overlapped at the pins of the C2 phase buffer capacitor before the fault, resulting in a short circuit of the buffer capacitor pins;
The short circuit fault first occurs in the external part of the IGBT module adjacent to the stacked busbar. After the short circuit, it causes a long short-circuit discharge of hundreds of milliseconds, which generates an arc between the buffer capacitor pins. The high current causes the incoming circuit breaker to actively protect and trip, and the energy input on the incoming side is cut off, causing the energy flowing between the buffer capacitor pins to rapidly decrease;
When the discharge energy of the supporting capacitor is insufficient to maintain the arc, the electric arc is extinguished. At the moment of arc extinction, a high voltage is generated between the pins of the buffer capacitor, causing the overvoltage of the C2 phase IGBT to break through and pass through. The remaining discharge energy of the supporting capacitor flows through the IGBT module, causing the C2 phase IGBT to overheat and burst;
After the system wiring was advanced, the protection measures of the frequency converter were not followed, and corresponding inspections and cleaning work were not carried out before the test. Conductive impurities entered the interior of the frequency converter, and the conductive impurities overlapped between the positive and negative DC terminals, forming a short circuit arc and generating overvoltage. The overvoltage will breakdown the IGBT connected in parallel between the positive and negative terminals, causing IGBT to pass through directly and causing IGBT damage.
(2) Analysis of the causes of the right frequency converter
① On site disassembly revealed:
The B1 phase IGBT was severely damaged, indicating that a large current flowed through the IGBT module during the fault process, and the accumulated high energy in a short period of time caused the IGBT to explode and be damaged;
The A-2 phase IGBT driver detached and was not severely damaged compared to the B1 phase, indicating that the energy flowing through the A2 phase IGBT during the fault process was smaller than that of the B1 phase IGBT;
The B2 phase IGBT is almost undamaged, but the internal parameters of the IGBT are abnormal, indicating that there is no large energy flowing through the B2 phase IGBT during the fault;
From the analysis of fault information:
Hardware protection of the controller indicates the occurrence of overvoltage on the internal DC side;
There is severe burning inside the B1 phase IGBT, and the DC bus terminal connected to it has been melted, indicating that the burned out part of the IGBT is at the moment of the fault and a short circuit occurs. The short circuit current flows through the IGBT and bus connection terminal in a short period of time, accumulating a large amount of heat and causing the B1 phase IGBT to explode;
The B1 phase IGBT explosion caused the upper A2 phase IGBT driver interface board to fall off, further causing damage to the A2 phase IGBT;
Due to the B2 phase IGBT and B1 phase IGBT being connected to the main circuit through the same stacked busbar, the B1 phase IGBT exploded, causing damage to the B2 phase IGBT
During the operation of the electric propulsion equipment, the internal wind path and ship sway of the equipment cause conductive impurities in the cabinet to overlap at the positive and negative terminals of the B1 phase IGBT DC, causing a circuit short circuit. At the moment of the short circuit, a high-energy arc is generated between the B1 phase IGBT DC terminals, melting the conductive impurities, increasing the electrical gap of the DC terminals, and extinguishing the arc;
At the moment of extinction, a high voltage is generated between the short-circuit points, causing the B1 phase IGBT to break through and pass through. The input energy on the AC input side and the energy stored in the supporting capacitor are all released through the IGBT, causing the B1 phase to explode and be damaged. The shock wave of the explosion causes the A2 phase IGBT driver board directly above to fall off, making it unable to control the normal conduction and shutdown of the A2 phase IGBT. The gate is in a state of loss of control, and static electricity accumulates to a certain extent, causing the IGBT to conduct. The remaining energy on the DC side will flow through the A2 phase IGBT, causing it to be damaged;
The arc voltage generated by the DC terminal of the B1 phase IGBT interferes with the DC terminal of the B2 phase IGBT through the stacked busbar, causing damage to the B2 phase IGBT.
Fault handling measures
Based on the analysis of the cause of the malfunction, the following corresponding corrective measures will be taken:
(1) Replace damaged inverter components; Thoroughly clean other components and main circuit components, especially the IGBT surface and related wiring; Tighten and inspect all connectors and wiring terminals for confirmation; Perform static and status checks on the restored frequency converter, and confirm according to the static power on process, keeping corresponding records;
(2) Further revise and improve the "Construction Technology for Equipment Protection of Comprehensive Electric Power Propulsion System", do a good job in the protection and cleaning of electric propulsion equipment, timely supervise and actively cooperate with manufacturers to conduct comprehensive inspections of the wiring, maintenance, and cleaning of electric propulsion equipment, to ensure safe and smooth testing;
(3) After the rectification was completed, various working condition tests were carried out for single axis and double axis, and the test results met the requirements of the test outline and test book.
5.Conclusion
The troubleshooting of the frequency converter and the restoration of power indicate that the analysis method and handling process in this article are correct.
The daily maintenance of electrical equipment is an important link to ensure its normal operation, and any negligence may cause equipment failure, resulting in serious consequences.