HIMALAYAL - SHANGHAI - CHINA
1. Unload the power transformer (PT) and get it in place
Level and tamp the work site; build unloading platform and transport track well; inspect the power transformer again before being transported to installation site.
Check the high voltage and low voltage side of PT to determine the unloading direction; ground the transformer reliably prior to subsequent operation.
2. Inspect the power transformer body
There are two options available: hanging up the bell jar or entering the body directly for inspection. The method adoption depends on actual conditions as well as manufacturer & customer’s requirements.
No matter which method is selected, inspection should be carried out in good weather and big efforts need to be made not to expose the body in air for a long time. In addition, it shall meet the following three requirements. First of all, body temperature shall not be lower than ambient temperature, which must be higher than 0℃; secondly, relative humidity should be lower than 75; lastly, work site shall be clean and free from dust.
3. Hang up the bell jar for inspection
Raise the bell jar in a balanced and slow manner; included angle between sling and plumb line ≤ 30°; no collision between body and tank surface.
Expose the power transformer filled with nitrogen in transit in air for above 15min; conduct the inspection only after the nitrogen diffuses.
4. Enter the body for inspection
Before inspecting the power transformer body filled with nitrogen in transit, qualified insulation oil shall be injected to expel the nitrogen. Prior to nitrogen expulsion, residual oil must be drained away from oil tank . The oil level needs to be above 100mm higher than upper iron core. The oil can be drained only after stewing for 12 hours.
5. Install the accessories
How to install HV bushing is described as follows: remove the wiring board and conductive head; get nylon rope (20m long & 8-10mm diameter) penetrate into bushing; the upper part of rope passing though the pulley is held by staff; use crane to lift the bushing slowly and move to ascending base; Connect the other end of rope with wire joint of power transformer by means of ring screws; place bushing hoisting in the right place, pull the wire joint beyond the top of bushing and screw off to fix the bushing firmly.
6. Inject the oil at the vacuum state
Start to vacuum upon the completion of accessories installation; separate accessories which cannot bear mechanical strength from oil tank during vacuuming according to manufacturer’s requirements; keep an eye on deformation of tank wall during vacuuming.
First of all, vacuum the oil tank into 0.02Mpa and then increase by 0.0067Mpa per hour to 0.101Mpa (or manufacturer’s requirement). Inject the oil from the bottom butterfly valve. The oil temperature must be higher than body temperature and tank surface.
Inject the oil steadily and the speed ≤ 100L/min; keep vacuum during the whole process of oil injection; continue to keep vacuum more than 4 hours after oil injection.
7. Hot-oil circulation
Do perform hot-oil circulation after oil injection in order to remove moisture and residual gas thoroughly; perform the hot-oil circulation when reaching rated oil level of oil conservator at full condition, which is recommended or when the oil is 200mm away from the top cover of body.
Determine hot-oil circulation technologies based on user manual; deflate on a regular basis during the circulation.
HIMALAYAL provides innovative products that comprise high voltage test equipment, full-set high voltage test instruments, on-site test systems and on-line monitoring systems, and services regarding tests, diagnostics and asset monitoring for clients in power industry. We help to ensure safety and reliability in the power generation, transmission and distribution.