The two basic parameters when choosing a transformer are the load and the type of application. One has to evaluate all associated factors carefully before buying the transformer to ensure that it meets the required criteria. You have to consider whether the transformer has sufficient capacity not only to handle the expected load, but also some provision for marginal overload.
The life expectancy of the unit is important and this aspect must be gone into. Further, one should work out the initial, installation, operational, and maintenance costs.
Transformer requirements will seriously vary depending on the application it is put to. In some industries, a large amount of uninterrupted power is critical for carrying out different processes. Thus, load losses should be low and a particular type of transformer construction that minimizes copper losses is the one to be favored.
In some industries, output power will swing to extremes at different instances and thus the transformers used here should be able to withstand surges. In smelting industries, uninterrupted and correct power supply is crucial. Industries that use motors of various voltage specifications will need intermittent or tap-changing transformers.
Thus the type of load - amplitude, duration, and the extent of non-linear and linear loads –should be the key considerations. If transformers to suit your specific application is not readily available, then you will have to opt for a customized transformer. There are several manufacturers who regularly build custom transformers for unique applications.
Experts say that liquid-filled transformers can be preferred because they are more efficient, provide for greater overload and are generally long-lasting. The downside is liquid-filled transformers have higher risk of flammability than dry types. Besides, liquid-filled transformers sometimes require containment troughs to guard against fluid leaks. So, one has to study the safety aspect before buying liquid-filled transformers.
Transformers generally come with either copper or aluminum windings. It is reported that aluminum-wound units, by comparison, are more cost-effective. Copper-wound transformers are the favorite with some because copper is a better conductor and copper contributes to greater mechanical strength of the coil.
Core choice is another factor that merits consideration. Core losses occur due to hysteresis and eddy currents. High quality magnetic steel minimizes hysteresis losses and laminated cores are chosen to reduce eddy current losses.
Dry-type transformers normally use insulators made from fiberglass-reinforced polyester molding compounds. Liquid-filled transformers, on the other hand, use insulators made of porcelain. Porcelain insulators are track resistant, suitable for outdoor use, and easy to clean. Please bear in mind that power factor tests must be performed at specific intervals to verify the condition of these insulators. It is commonly held that the life of a transformer is the life of the insulation system.
Operating conditions can sometimes entail overloading of a transformer; and one should know to what extent the unit can withstand overloading without developing problems. A primary issue in this regard is heat and its dissipation.
You must take into account the cost of additional accessories that you may require. Stainless steel tanks and cabinets for extra corrosion protection, weather shields for outdoor units, and protective provisions for humid environments, device to guard against rodents, temperature monitors, and space heaters are some of the accessories people usually buy.