Stealing routines for low-cost transformers (coils, silicon steel sheets, fuel tanks)
In transformer procurement, quotations that are much lower than the average market price are often not "concessions", but vicious cost control achieved by manufacturers through material downgrades. For people in the industry, seeing through these hidden means of stealing materials is a compulsory course to ensure the safe operation of the power system.
Common Situations
Copper loss and number of turns trap of coil link
The coil is the heart of the transformer, and it is also the hardest-hit area for stealing materials. Some non-standard manufacturers use "half-copper and half-aluminum" or all-aluminum coils to pretend to be copper coils, and only a small amount of copper is used at the lead terminals for welding camouflage. In addition to material replacement, reducing the number of turns of the winding is a more concealed technique. For example, in 10kV grade products, if the number of turns of the high-voltage winding is lower than the design value, the magnetic flux density will increase and the no-load current will increase. Although it can barely operate in the short term, long-term overload can easily cause a short circuit between turns and burn down the whole machine.
The iron loss of silicon steel sheet is tricky
The quality of the iron core directly determines the energy efficiency. Regular products mostly use cold-rolled oriented silicon steel sheets with high magnetic conductivity and low loss.Low-cost transformers often use hot-rolled sheets or recycled old silicon steel sheets to piece together, and even doped with amorphous alloy scraps. Such materials have poor magnetic permeability and large seam gaps, which directly cause no-load loss (iron loss) to soar by more than 30%.Users not only have to bear long-term invalid electricity bills, but also accelerate the aging of insulation due to severe heating of the iron core.
Structural shrinkage of the fuel tank
As the last line of defense for explosion-proof and heat dissipation, fuel tanks are often overlooked. National standard products require that the thickness of the steel plate of the box body is up to standard, and it needs to undergo strict sealing tests. However, low-cost products often use inferior plates with a thickness of less than 2mm, and the welding process is rough, and only external spray paint is used to cover up the weld bubbles and rust. The mechanical strength of such fuel tanks is extremely low, and they are prone to oil leakage during transportation vibration or operation. Once the internal insulating oil level drops, it will cause a high-temperature explosion of the winding.
The essence of low-cost competition is the stripping of security redundancy.If the purchaser only relies on the price to set the price, it will often pay a higher price in the later operation and maintenance costs and accident risks. Strictly checking the conductor material inspection report, verifying the grade of silicon steel sheet and the thickness of the fuel tank sheet are the only ways to avoid risks.
