As a top manufacturer of this pad mounted transformer in China since 2010, we think it is necessary to do a full analysis of this transformer to our customers, and can help them to select a right type product for their real applications.
Due to the high electricity consumption in United States, and the absence of high-voltage measurement methods, these pad mounted transformers generally do not have high-voltage measurement, and various instruments and distribution circuit breakers are not installed in low-voltage intervals.
Pad mounted transformers are divided into two types: those with operating corridors (for workers to operate inside the box) and those without operating corridors (for workers to operate outside the box). A pad mounted transformer can be an integral box shell, or a split box shell composed of two, three, or more boxes. The box should have sufficient mechanical strength and should not deform during transportation and installation. We should strive for aesthetic appearance, color coordination with the environment. The high and low voltage rooms of the casing should be equipped with lighting fixtures, and measures should be taken to prevent dust and condensation. The humidity in the high and low voltage rooms should not exceed 90% (25 ℃), and the transformer room should be well ventilated. The box shell should have measures or devices such as sun protection, rain protection, rust prevention, and prevention of small animals from entering.
Main Technical Features of a pad mounted transformer
Strong overload capacity, allowing for 2 times 2 hours of overload and 1.6 times 7 hours of overload without affecting the lifespan of the transformer.
By using elbow type connectors, it is very convenient to connect high-voltage incoming cables and can be used as a load switch in emergency situations, allowing for live plugging and unplugging.
Adopting dual fuse protection, the plug-in fuse (BAY-o-net) is a dual sensitive fuse (temperature, current) that protects the secondary side of the transformer box from short circuit faults. The backup current limiting protection fuse (ELSP) is used to protect the high-voltage side from faults that occur inside the transformer box.
Transformers generally use high ignition point oil (FR3).
All components such as fuses for high-voltage load switch protection are placed in the same oil tank as the transformer core and winding.
Product Features of a pad mounted transformer
1. Compact structure, small size, convenient installation, and flexibility;
2. Fully insulated, fully sealed structure, safe and reliable, maintenance free, reliable protection of personal safety;
The high-voltage side adopts dual fuse protection, with the plug-in fuse being a dual sensitive fuse (temperature and current) and the backup fuse being a current limiting fuse, reducing operating costs;
The high-voltage incoming line adopts a cable connector structure, which is fully insulated, safe and reliable, and easy to operate;
5 can be used for both ring networks and terminals, making conversion very convenient and improving power supply reliability
The transformer adopts a three-phase three column or three-phase five column structure, and the iron core adopts a stepped seam process or a rolled iron core process, which has low noise, low loss, strong resistance to short circuits and overload.
7 adopts a special process of vacuum drying and vacuum oil injection. Our company will extend this process used in 110kV products to 10kV products, providing strong guarantees for improving product quality.
The 8 boxes can adopt anti-corrosion design and special paint treatment according to the requirements of the operating environment, and have the “three prevention” functions, namely anti condensation, anti salt spray, and anti mold, and can meet the anti-corrosion requirements in high temperature and high humidity environments.
Applications of these pad mounted transformers
Integrated the transformer body, high-voltage load switch, fuse and other components together in the transformer oil tank. Due to being immersed in oil, the volume of the components is greatly reduced, the structure is more compact, and installation is convenient and flexible. Fully insulated, fully sealed structure, safe and reliable, easy to operate, and maintenance free. Widely used in residential communities, high-tech centers, factories and mining enterprises, airports, stations, schools and other places.
Advantages and disadvantages of a pad mounted transformer
Small size and compact structure; Fully sealed oil tank, fully insulated design, safe and reliable operation; Both the ring network and terminal power supply can be used, with convenient operation and reliable power supply; Strong overload capacity and superior resistance to sudden short circuits; Good impact resistance; Energy saving, low loss, not higher than the loss value of the new S9; The cable head can operate a load current of 200A, with long mechanical and electrical life.
Disadvantages: Low power supply reliability; Without electric mechanisms, it is not possible to install distribution automation devices; No capacitor device, which is not conducive to reducing line loss; The noise is higher than that of Type III and Type V stations, because Type III and Type V stations place transformers indoors to provide sound insulation; In addition, decompose the concentrated electromagnetic radiation of Type III and Type V stations into multi-point radiation; Due to the different civil foundations of different capacity box transformers, it is inconvenient to increase their capacity; When the transformer is overloaded or when the user increases capacity, the civil engineering needs to be rebuilt, which will result in a longer power outage time and increase the difficulty of the project.
Corrosion prevention and protection for a pad mounted transformer
According to COOPER’s data, the pad mounted transformer adopts anti-corrosion design and special paint treatment, which can be suitable for various harsh environments, such as stormy and high pollution areas. The box undergoes eight pre-treatment processes before painting, followed by seven painting and baking processes to complete, indicating its cautious attitude towards corrosion prevention. The pad mounted transformer housing produced domestically hardly undergoes any special treatment, and is basically treated with acid washing and electrostatic spraying. Some companies even do not carry out acid washing treatment, and some even only spray paint treatment on the outer surface. It can be imagined how strong the anti-corrosion ability of the housing is. Even with electrostatic spraying treatment, there are often blind spots on the bottom surface during treatment, and electrostatic spraying is difficult to spray powder on these poorly treated areas, which inevitably leaves a risk of rust. Due to the fact that the transformer box needs to work in outdoor environments with wind, rain, and sunlight for many years, if the surface treatment is not good, corrosion will be very serious. This issue is very important and has been a topic of great concern, attention, and research in China for decades. Therefore, many manufacturers have adopted other technologies to solve this problem. Regarding protection issues, the transformer oil tank and heat sink of American style box transformers are partially exposed to the outside, with the aim of improving heat dissipation conditions. However, due to its direct exposure to sunlight, will it affect temperature rise under the thermal radiation of sunlight. In addition, the exposed parts are easily damaged by external collisions and impacts. If damaged, a large amount of transformer oil will be lost, and the consequences are unimaginable. Therefore, some domestic manufacturers have added a layer of steel plate to the heat sink to increase protection capabilities.
High voltage load switch
The load switch of the pad mounted transformer is placed inside the transformer oil tank. The oil immersed three-phase linkage switch can be divided into two positions (terminal type) and four positions (ring network type). As this load switch is placed in the transformer oil tank, its closing position can only be determined based on the instructions of the external operation panel, and its operation needs to be carried out through a dedicated insulated operating rod, so its operation is relatively complex. From this point of view, its operation is very inconvenient. In addition, due to the inability to see the breaking contact of the load switch (i.e. the obvious breaking point), it gives people a feeling of unease after disconnection. In addition, once the load switch malfunctions, replacement and maintenance will be very difficult. Load switches generally use vacuum circuit breakers.
Maintenance methods for a pad mounted transformer
After the installation and use of pad mounted transformers, there is basically no need for maintenance, but the maintenance work of box transformers is indispensable for products produced in China due to various reasons.
Due to technical issues with surface treatment of the casing, it is necessary to strengthen the inspection of its corrosion condition;
The oil filled in the tank of pad mounted transformer is generally FR3 insulation oil, which has a ignition point of 312 ℃, excellent electric heating characteristics, high insulation strength, good lubrication, strong arc extinguishing ability, non-toxic, and can be biodegraded, thus minimizing the harm to the environment and health. FR3 insulation oil does not form sediment like traditional mineral oil, and the vast majority of domestically produced American style transformer boxes are filled with 25 # ordinary mineral oil. In addition, in general, the upper part of the oil tank of American style box transformers is filled with inert gas to prevent the exchange of water from the air into the oil. However, domestic American style box transformers may not have been carried out by enterprises for this work yet. Over time, the performance of the oil will decrease, and its sealing performance cannot meet the requirement of 7 Psig, so it is necessary to change the oil regularly.
The pad mounted transformer has no oil temperature protection, only a thermometer to display the oil temperature. When the oil temperature is too high, it relies on a plug-in fuse for protection, and there is also a pressure relief valve to release too much pressure in the tank. Therefore, it is necessary to regularly check whether the fuse operates normally in these two situations and whether there is oil leakage in the casing.
Due to the exposed oil tank of the pad mounted transformer, regular inspections should be carried out to prevent oil leakage caused by external impact.
When using new equipment such as fully sealed transformers and SF6 switchgear, the maintenance cycle of the equipment can be extended, and even maintenance free requirements can be achieved. The appearance is novel and beautiful, and can coordinate with the environment around the substation. The urban power supply department stipulates that high-voltage metering must be used for self maintenance box transformers (250kVA or 315kVA or above), and in some cases, there are many distribution circuits, including setting up backup circuits.
Conclusion,
The pad mounted transformer mainly consists of a base, side panels, partitions, doors, and a top cover. The box is divided into high pressure chamber, transformer chamber, and low pressure chamber. The high-voltage chamber adopts a perfect and reliable compact design, with comprehensive anti misoperation interlocking function, high reliability, and convenient maintenance. The high-voltage switchgear can use terminal load switches, ring network switchgear, etc. The transformer room can be equipped with oil immersed or dry type transformers with a capacity of 1600Kvar or less and a voltage of 12/0.4KV, and is equipped with isolation protection nets. The transformer room can adopt natural ventilation or forced ventilation, and automatic temperature controllers, room temperature monitoring, and automatic opening and closing ventilation devices can be installed as needed. The low-voltage room is equipped with standard schemes for distribution, metering, reactive power compensation, etc., and secondary control circuits and output lines can be designed according to your specific needs.
PowerTel and his dedicated engineering team are able to provide you a custom design of this pad mounted transformer for your various applications. if you still have any technical questions or delivery time for these pad mounted transfomers, please feel free to let us know.