Abstract : This paper mainly introduces the current operation and maintenance status of the frequency converter for condensate pumps at Yungang Thermal Power Plant, the existing problems and the measures taken. It focuses on the faults that have occurred in the company's frequency converters, the causes of the faults, and the countermeasures.
Keywords: frequency converter; fault analysis; troubleshooting
Application of 6 kV High Voltage Frequency Converter in Yungang Thermal Power Co. Ltd. Zhao Ning—ning (Shanxi Datang International Yungang Thermal Power Co. Ltd., Datong 037039, China)
Abstract： Frequency converter for condensation pump in Yungang Thermal Power Co. Ltd. Was introduced in terms of operation, maintenance, existing problems and solutions, especially the fault, fault causes of frequency converter and countermeasures were presented．
Key words : frequency converter dault analysis; treatment
1. Basic Information on High Voltage Frequency Converters
Shanxi Datang International Yungang Thermal Power Co., Ltd. (hereinafter referred to as Yungang Thermal Power) has a total of 10 6 kV high-voltage frequency converters (all of which were put into operation in 2003). Among them, there are 2 primary air fans for boilers No. 1 and No. 2, which are PH-6-6-1250 perfect harmonic-free high-voltage frequency converters manufactured by Robicon Corporation of the United States; and 3 condensate pumps for boilers No. 1 and No. 2, which are HARSVERT-A type high-voltage frequency converters manufactured by Beijing Leadway Electric Technology Co., Ltd.
2. Design, operation, and maintenance of frequency converters
Two of the three frequency converters for the condensate pumps are in operation, with one on standby. Initially, due to insufficient understanding of the frequency converters' performance, operating characteristics, and environmental requirements, the installation design had certain shortcomings. The condensate pump frequency converter room was located under an air-cooled fan, resulting in a poor environment with significant dust. Furthermore, the six frequency converters were installed in a small, low-ceilinged room, hindering ventilation and heat dissipation. This poor operating environment led to equipment overheating, rapid aging of electronic components, and a high probability of failure. To improve ventilation and heat dissipation, ventilation ducts were added to the top of the frequency converter cabinets, and axial flow fans were installed through openings in the walls to expel the heat generated by the frequency converters outdoors. The manufacturer recommends that maintenance personnel clean the frequency converter filters every 15 days. However, given the windy and dusty environment in the area where Yungang Thermal Power Plant is located, maintenance personnel clean the filters approximately every 10 days to ensure good ventilation and reduce the likelihood of frequency converter failure.
3. Typical Fault Cause Analysis, Handling, and Countermeasures
The Leadway frequency converters used in Yungang Thermal Power Plant are relatively early products, so there are still some deficiencies in technical details, product quality, and program design. In addition, the operation and maintenance personnel are not familiar with the operation and adjustment of the frequency converter devices, so many problems were encountered in the early stage of production. The following are some representative faults and defects.
3.1 DCS remote startup fails
Fault phenomenon: The DCS remote start fails. When the operator starts the frequency converter on the central control console, the frequency converter does not respond.
Cause analysis:
(1) The starting logic of the Yungang Thermal Power Condensate Pump is designed to first close the 6 kV high-voltage switch, and after 10 seconds, the DCS system automatically sends a starting pulse to start the frequency converter. In the early stage of commissioning, due to insufficient training of the operators, some operators were not familiar with the starting operation of the frequency converter. After closing the high-voltage switch, they immediately started the frequency converter. At this time, the frequency converter was in the self-test state after high voltage power-on and did not accept any instructions, resulting in the failure of the frequency converter to start.
(2) Because the company’s frequency converter is controlled by an industrial computer, and the industrial computer is working continuously, it crashes when there is a lot of dust, and does not accept any instructions, thus causing the frequency converter to fail to start.
Handling and countermeasures :
(1) Strengthen the training of operators to ensure they are proficient in the operation procedures of the frequency converter and avoid abnormal operating conditions of the frequency converter due to human error.
(2) When the industrial computer crashes, disconnect the power, thoroughly clean the inside of the industrial computer, and power it back on. It will then function normally. Strengthen the monitoring of the industrial computer's operation and clean the industrial computer's filter screen in a timely manner.
3.2 Tripping during operation
Fault Phenomenon: The frequency converter was running normally when it suddenly tripped. Cause Analysis: Checking the frequency converter's fault log revealed no abnormal alarm information. The manufacturer's personnel analyzed that the controller program was malfunctioning, causing a trip due to lack of response. Solution: Powering the unit back on resolved the fault.
3.3 Startup failed
Fault Symptom: The device reported drive faults in A1, A2, B2, and C2, suspecting damage to the power unit drive board. After cleaning the main control box and fiber optic cables, and replacing units A1 and A2, the inverter still failed to start after power-on and high voltage application. Cause Analysis: The manufacturer's technicians determined that the program block on the main control board was worn out and damaged. Solution: The manufacturer's technicians replaced the program block with a spare, and the fault disappeared.
3.4 Simulation given and feedback do not match
Fault Symptom: The DCS display shows a significant discrepancy between the analog input and feedback frequency of the frequency converter. Cause Analysis: Upon checking the frequency converter's parameter settings and verifying the 4-20 mA analog setting with thermal control personnel, a mismatch was found. Solution: Reset the frequency converter parameters.
3.5 Touchscreen black screen
Fault symptom: The frequency converter is running normally, but the operation and inspection personnel found that the touch screen was black. Cause analysis:
(1) The industrial computer crashed and data transmission was interrupted.
(2) After restarting the industrial control computer, it was found that the startup was unsuccessful. Upon inspection, it was found that the hard drive was damaged.
(3) Horizontal colored bars appear on the touch screen, indicating that the touch screen is aging and damaged.
Handling and countermeasures:
(1) The device is powered off, the industrial computer is removed, the inside of the industrial computer is thoroughly cleaned, and the power is turned on again. The touch screen displays normally.
(2) Replace the industrial control computer.
(3) Replace the touch screen.
3.6 The device alarms "Unit cabinet fan failure".
Fault Phenomenon: During operation, the frequency converter alarms "Unit Cabinet Fan Fault". Cause Analysis: Initially, a loose auxiliary contact of the unit cabinet fan was suspected. After stopping the equipment, the contact was checked and found to be normal. The fan was removed and inspected, revealing it to be burnt out. Solution and Countermeasures: Replace the top fan of the unit cabinet and increase equipment inspections.
3.7 No voltage or current display on the touchscreen
Fault Symptom: During equipment operation, the touchscreen showed no output, input current, or voltage display. Cause Analysis: Inspection revealed a loose connection at the data cable connector between the main control box and the industrial computer. Solution: Reconnect the data cable securely and tighten the connector screws.
3.8 No voltage output
Fault symptom: After starting the frequency converter and closing the high-voltage switch, the frequency converter has no output voltage. Cause analysis: The controller program is malfunctioning. Solution and countermeasures: Open the high-voltage switch, thoroughly clean the inside of the frequency converter, and it should function normally after power is restored. Regularly clean the frequency converter's filters.
3.9 Tripping during operation
Fault Symptom: The frequency converter tripped during operation. Checking the device records revealed no alarms or fault information. Cause Analysis: To further determine the cause of the fault, high voltage was restored for restarting. The frequency converter immediately tripped, and the B1 unit reported a "drive fault," indicating that the power unit drive circuit board was damaged. Solution: Replace the power unit.
3.10 Mismatch between remote commands and local feedback
Fault Symptom: The remote command reaches 100, but the inverter feedback only reaches 92. Cause Analysis: All parameter settings were checked and found to be correct. The manufacturer's technicians analyzed that the optocoupler components on the analog receiver board inside the main control box were aging, resulting in poor linearity. Solution: Replace the analog receiver board inside the main control box.
4. Current Problems
Due to design and installation limitations, as well as environmental factors, the inverter's heat dissipation has consistently been poor, resulting in significant dust accumulation and potential equipment hazards. It is necessary to further strengthen the monitoring of the inverter's operation, cleaning the inverter filters every 10 days and thoroughly cleaning the inverter unit, including important components such as the power unit, main control box, and industrial computer, every six months. The Leadway inverters at Yungang Thermal Power are controlled by industrial computers, which and touchscreens are prone to failure, resulting in high maintenance requirements and poor stability. An upgrade is planned, replacing the industrial computer with a single-chip microcomputer controller to reduce maintenance and potential malfunctions.
5. Requirements and recommendations for the design and manufacturing of frequency converters
When designing the installation location of the frequency converter, the installation space of the frequency converter room should be fully considered. Ideally, a separate frequency converter room should be provided, which should be large and high to facilitate air circulation. At the same time, the frequency converter room should be well-sealed to prevent dust from entering. Installing an air conditioner with sufficient capacity can reduce the probability of frequency converter failure. The frequency converter design should be simple and practical; the number of functions is not important, but ease of maintenance should be prioritized to minimize maintenance and enhance equipment reliability.
For details, please click: Application of 6kV High Voltage Frequency Converter in Yungang Thermal Power Plant
