Automatic Winding Machines
In a core type power transformer, one of the most common types of windings are continuous and disc for HV and helical for LV.
Extremely skilled and experienced winders are required for this process. At VT-GT we have made significant investments in automating winding machines to eliminate human errors.
VT-GT has multiple automated horizontal and vertical winding machines where:
- The online computer keeps track of the number of turns in each disc section and also the total turns wound at a given time
- It maintains the proper tension of the incoming conductor wires
- It puts brakes on the lathe at the precise point of transposition
- It has the capability and die mechanism to make a perfect transposition. All the winder does is tape the conductor on horizontal winding.
Power transformers experience numerous short circuit faults both simple phase and three phase during it lifetime. The winding assembly “vibrates” during the short circuit due to a combination of axial and radial forces resulting in either loosening of insulating spacers or insulation tear resulting in turn-turn failure that could lead to a full three phase fault causing total transformer failure. For this reason, the winding assembly needs to be “sized” under pressure to stabilize the windings.
Isostatic Winding Mushroom (ICM) was specifically developed in-house to achieve flawless sizing and uses a hydraulic stainless steel cylinder piston system for this purpose. The pressure is uniformly distributed using a circular steel plate that locks into the grooves of the stainless-steel piston. The hydraulic pressure is applied to one winding assembly via top piston plate and the bottom cylinder base plate. The pressure is continuously monitored and controlled by the computer based hydraulic mechanism while the winding assembly is being processed in the VPD chamber. This digital control is integrated into the Vapor Phase Process control system.
We use state-of-the-art “Astronics” core cutting / assembly unit. Astronics automated core cutting equipment allows precise cutting of single and multi-leg transformer cores. Integrated with the core cutter is an automated E-stacker that stacks the core steel in its final position as it is cut. That practically eliminates human errors and the result is higher reliability, lower losses and of course higher efficiency.
In addition to oil & insulating paper, there is other insulating material in power transformers in the form of spacers, cleats & leads assembly, winding support structures, winding cylinders, locking ribs, etc. Our design practice is to develop a custom-design for each unit that is optimized for maximum reliability and efficiency. This requires customized insulating parts that are specifically sized and milled for the given application. We use ONSRUD five-axis milling machine for this – all we do is input 3-D drawings into the on-line computer and the machine does the rest.
Digital Test Lab
The validation of a flawless execution of a robust, high-voltage power transformer design comes from IEEE standard testing of the unit in a test lab. VT-GT has the most modern digital test lab that will give you the most accurate & reliable test results.
State of the art impulse Generators made by High Voltage Company based in Germany uses remote digital controls that are fully operated from a console located in a sealed control cabin. (12) 200 kV sections give this generator capability to test up to 2400 kV, BIL with 365 kJ of energy. We have already tested 1650 kV BIL transformers using this equipment. For Hi-Pot we use a resonance test set as opposed to using an old fashioned inductive transformer. We use two redundant power sources for Power measurement and induced voltage tests.
The control cabin has consoles from where the actual tests are conducted. After the initial configuration of transformer unit, all the external doors are locked. Any unlocked door will automatically prevent the console buttons from operating. The entire circuit configuration and the controls are on the GUI screens. The test engineer simply sits at the console and pushes the buttons while the test diagnostics are built into the software.