Case Study: Repaid the High Voltage Ceramic Capacitor in CT Machine
The introduction of our hospital 1989 years Shimadzu SCT 3000TX CT machine, the high voltage secondary circuit tetrode
and high voltage capacitor voltage feedback mode, to 1995 years the cathode side of the high voltage capacitor (C2, the same below) breakdown, because no parts replacement, ordering the same time damage the capacitor to the shop home maintenance. After receipt of the capacitor, capacitors in order to verify repair performance quality, and will install it on the cathode side of the original, the new products installed on the anode side of the capacitor, the original capacitor (C1, Below) being placed; boot high voltage circuit and capacitance device status is normal, after 15 days of continuous operation, indicating that the C2 stable and reliable. To maximize its effectiveness, it proper storage for C1, C2 to maintain the current work status state. In August C2 O1 breakdown again, opening inventory to be C1 substitution, has been idle for seven years, the capacitance measuring device measure the two end points of "T" and "N" only between the capacity value to O. 2, cf nominal rating of O. 5 clear preference for low, suggesting that abnormal C1 technical indicators, poor performance. Needle can the use of its installed capacity, we conducted a large bile attempt, after numerous tests and active treatment, it recovery to normal charging and discharging state, put into operation.
1) Capacitor working condition:
For the oil-filled high-voltage capacitor metallized polypropylene film roll is made with good self-healing, voltage up to 125kV; in high voltage sub-polar circuit, from the regulator. And energy storage role. Although Cl idle a long time, the measured value abnormalities, according to the capacitor failure mechanisms and models, we think that this simply reflects the long-term disabled capacitor-like under the physical state, and capacitance measuring device for the instrument. "
Devices, built-in DC battery charge and discharge of its rated power voltage, current and capacity can not be sub-polar and high-pressure circuit. " state compared to the final identification of its strengths and weaknesses, should be adopted testing to determine.
2) Machine activation steps
(1) will be installed in high-voltage generator cathode C1side, the boot files from the control cabinet sub-switch control, mining with intermittent, gradually increase the charging voltage of the method, the real active recovery facilities, should be closely observed here refers kV charging display table, to charge the sub-block value, can be broken off from the capacitor wiring, Cl were measured capacity, electrical insulation resistance, whether the anomalies observed and recorded, so steady progress, not radical;
(2) activation charge when the gradual power value of 100kV, the measured capacitance value C1 has risen to O. 46, when charging up 12okV, C1 capacity has beenl close to the original rating, and no abnormal anti-capacitor mapping, then, can be turned off C1 disconnect wiring. Measured again fixed capacity value is still close to the rated value; (3) re-wiring and Power-up, when the anode side of the capacitor C1 are finished with CT machine to enter into the charge and the preparation state, divideddo not check kV positive and negative balance, no abnormal relations machine and then reboot, routine warm-up training, the size of current exposure to normal, calibration water phantom, the scanned image correctly, the instrument table shows the stable, high-pressure discharge and abnormal noise. Sweep various parts of the patient CT scan machine to run properly, the image quality as before.
3 Experience we learned
(1) high voltage capacitor is an important CT component, if damaged, the introduction of replacement is required, expensive, needle ailure of such poor, self-activate the repair. Savings by costs, shorten the maintenance cycle, economic and social benefits Significant
(2) high-voltage capacitors for a long time home, after a decline in capacity, can still be activated by the charge to upgrade to the rated capacity, return to normal use, the device should play performance.
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