Operation & maintenance |


Air gap and generator capacity range for the T15 and T35 inspection robots (Source: Toshiba ESS)


Air cooled generator


Generator capacity [MVA]


plants and it is now available for the full range of applications. The multi-functional robots have been available for inspection services as from fiscal 2023. In the past, turbine generator rotors were typically pulled from stators every four years for precision inspections, but the use of robotics, as well as NDT inspection technology that does not require a liquid contact medium, has reduced the need for rotor removal when looking for cracks and contributed to improved power plant load factors. The T15 and T35 robots are equipped with top, bottom, front and rear high resolution cameras for VT (visual testing) of rotor and stator. Examples of what visual examination of the stator core inner surface might show include: foreign material; scratches/damage; heating and arc indications. Rotor surface visual inspection can yield similar findings, as well as rotor wedge positions and plugging condition of rotor ventilation holes.


The types of inspection that can be carried out by the T15 and T35 robots (Source: Toshiba ESS)


Inspection target Rotor


Surface Vent


Wedge Teeth


Surface Stator


Wedge Core


lamination


Robot type T15 T35


Inspection methods Visual test


Ultrasonic test Visual test


Acoustic analysis EL CID


Camera Ultrasonic probe Camera Hammer Microphone Leakage flux


Detection coil


Potential findings


Scratches / overhead marks


Clogged


ventilation holes Internal defects


Scratches / overheat marks


Loosening of wedges


Electrical


insulation damage of core lamination


Examples of T15/T35 visual inspections (Source: Toshiba ESS)


The robots enable cameras to be positioned on the centre lines of rotor ventilation holes, which is necessary for high quality inspection and diagnosis of rotor ventilation plugging issues (including automated image diagnostics). The T35 robot can perform ultrasonic testing (UT) with a detachable UT attachment, employing Toshiba-developed dry-coupling technology rather than a liquid contact UT medium, leaving no contamination post-inspection. Both robots are equipped with hammers for checking stator wedge tightness, with automated diagnostics based on acoustic analysis of the hammering sound, and high quality diagnostics are achieved, says Toshiba ESS. Both robots can also be equipped with Chattock coils enabling them to perform ELCID (electromagnetic core imperfection detection). Docking bay stations for the robots are installed on rotor retaining rings. The docking bay station inserts the robot into the air gap and moves it circumferentially. All robot movements, inspections and diagnostics are automated. The quality of inspection that can be achieved by the new robots is said to be equivalent to that achieved by “inspection experts.”


Chattock coil installation for ELCID (Source: Toshiba ESS)


The generator periodic major outage cycle (with rotor removal) can be extended, and preventive maintenance and planned repairs can be carried out based on an assessment of generator condition based on actual inspection data. Toshiba ESS is using the new robots to help strengthen its service offering for fossil-fuelled and nuclear power plants worldwide.


Robot insertion point (Source: Toshiba ESS)


24 | July/August 2023| www.modernpowersystems.com


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93