2020-02 Tank opening report
Date
2020/02/17 00:00to 2020/02/19 00:00
Attendees
Goals
- Repair the failed GVM system
Discussion items
Time | Item | Who | Notes |
|---|---|---|---|
5 min | Problem symptoms | Pietari |
|
10-30 min | Checking the electronics | Harri, Mikko |
Action items
Balancing the pressures between EGP tank and S1/S2 2020/02/17 00:00
Pumping EGP tank to NTP pressure 2020/02/17 00:00
Removing the GVM assy. and blanking the flange opening at tank wall 2020/02/17 00:00
Disassembly of the GVM mechanics (rotor/stator + driver motor) to find the faulty parts 2020/02/17 00:00
Test the motor operation, found to be stuck 2020/02/17 00:00
Front bearing found faulty due to abrasive dust, back bearing OK, get a new one of type 626-2Z (standard 6x19x6 mm bearing, Laakeri-Center Oy, Laippatie 7, Helsinki) 2020/02/18 00:00
Install new bearings, polish the GVM rotor vane axis contact surface (scratches from dust generated by the graphite/silver slider) 2020/02/18 00:00
Check the proper operation of the GVM system (mechanics and electronics) 2020/02/18 00:00
Install the GVM assembly and electronics back 2020/02/18 00:00
Balance the pressures EGP and either S1 or S2 tank and dry the gas for about three hours with belt running2020/02/18 00:00
Check that the GVM shows some realistic voltages with belt running. @httyrvai@helsinki_fi 2020/02/18 00:00
Pump the rest of the insulating gas back to EGP tank through the absorption dryer. 2020/02/19 00:00
Start running the tandem@piekie@helsinki_fi 2020/02/19 00:00
First experiments at 5 MV high voltage performed successfully. One spark only. The GVM was observed to show about +20 kV higher that it used to. 2020/02/20 00:00
Note on the GVM system
The original Russian GVM system was replaced with a NEC version in 2011. The reason was mainly that the original electronics was too unreliable and was not possible to repair or replace with a modernized system. Sticking to the old mechanical parts (GVM rotor/stator system) would have needed too much of design work for the control electronics etc. that it was then decided to buy a complete system from NEC. The old GVM mechanism still exists, if somebody is interested. In fact it's very well done.
The NEC GVM has been working well for about 8 years, the only failure was one worn-out bearing. In the future, it would be useful to pay some attention to the GVM let's say every third or fourth year. At least blow the generated dust away and perhaps install new graphite/silver slider and rotor axis! Unfortunately that requires that the big flange is unbolted from the tank wall and that the mechanism taken to the workshop.
There was some uncertainty of how the NEC GVM is installed on the old housing. No drawings were found, but it turned out that there was an adapter plate that fits on the NEC assy nicely. The back flange was adapted for the cable feedthroughs.
In case the GVM device needs to be modified in the future, the drawings of the housing are in the Black folder "Kiihdytinpaineastia A-54048". In practice, you only need to design an adapter flange of stainless steel (eg. 316L), with thickness of 5 to 6 mm, outer diameter ø151.9 mm, equidistant holes at ø140 for fixing (4 x M4 and 4 x ø5), and threads/holes for the GVM device.
Note on the GVM driver motor
The motor is a synchronous 115 VAC motor (Bodine Electric Company model 0710, 1/900 Hp, 3600 Rpm, .31 oz-in., KYC-24, 115 Vac.,Capacitor Start 494 00051, Permanent Split Capacitor, Synchronous.). If a corresponding 230 VAC motor were easily available, such could be used instead. Perhaps easier to stick to existing solution.
New motor, axis, and silver-graphite brush were ordered from NEC and arrived on February 24th. Ask Pietari. Installation instructions below.
Note on calibration of the GVM
After replacing the motor or motor bearings, the geometry of the GVM assembly may have changed slightly. You adjusted the gap between rotor vanes and stator to 1/32", didn't you? Even if you did, the high voltage shown may differ from the old value. If that is the case, please follow the calibration instructions in the NEC documentation. The manuals are in pdf-form under the group folder,
.../klobeam/Documents/SCAN/NEC/MANUAL NO.2HT065790/ for the Terminal potential stabilizer and
../klobeam/Documents/SCAN/NEC/MANUAL NO.2HT072920/ for the GVM amplifier
../klobeam/Documents/SCAN/NEC/MANUAL NO.2BT059040/ for the GVM assembly.
Note that you may need to calibrate the GVM amplifier first (if you suspect the device drifted from the factory settings!)