Measurement of Tip Clearance of All Blades and the Maximum Tip Clearance Using Discharge-Type Tip Clearance Measurement System.

Abstract

The discharge-type blade tip clearance measurement system has a high accuracy and characteristics as a standard reference device. However, this method can not measure the tip clearance of all blades nor the maximum tip clearance. Therefore, such measurements were attempted in this study. The principles for measuring the tip clearance of all 'the blades are as follows. The electrode is brought near to the tip of the blade and discharge occurs at the longest blade, then the movement of the electrode is stopped. Next, the applied voltage is increased until all the blades are in a discharging state. The gap of each blade can be measured by identifying the order of discharge at the blades and the discharge voltage at each blade. The principles for measuring the maximum tip clearance are as follows. In the same manner as the above method, the electrode is brought near to the blade tip and discharge occurs when supplied voltage is increased. Under this condition, the current corresponding to the supplied voltage is measured. The measured current curve has an inflection point. The inflection point corresponds to the minimum current where the discharge of all the blades occurs. The maximum tip clearance is determined by converting the measured voltage of the inflection point into length. The operations of these methods are automated.