SIGMA is a manufacturer of transformers immersed in insulating mineral oil. These transformers are widely used in different appliances, both to power homes in rural and urban areas as well as to supply power to residential or commercial buildings or even to industries and factories of different products.
Our transformers are designed to meet ABNT standards or client specification and electric power concessionaires.
•About the transformer:
Our transformers are built with high-permeability GO (Oriented Grain) silicon steel cores, which provides low power losses for the activation of the transformer. On this core is assembled the winding through which circulate the load currents of the transformer. Usually the low voltage winding is assembled closer to the core, which facilitates the insulation between the conductor, which is powered with voltages between 380 and 220 Volts, and the silicon steel core, which is grounded. After the installation of the BT (Low Voltage) winding, the AT (High Voltage) is placed, which is in direct contact with the high voltage grid of the utility and feeds the transformer, a fact that requires greater care with the insulation since it is where there is a higher chance of failure, which may result in the equipment being burned.
After completing the winding assembly, the windings are connected to the commutator, which is used to adjust the input voltage on the transformer with the voltage of the utility grid at the liaison point, i.e. the commutator has the purpose of adjusting and to reconcile both voltages. Commutators typically have 3 TAPs (choices). For 24,2 kV transformers (transformers that are installed in grids that have 23100 Volts in High Voltage) TAPs are divided in 23100 V, 22000V and 20900V. For 15 kV transformers (high voltage grids that have 13800V) TAPs are divided in 13800V, 13200V and 12600V.
•Receiving the transformer:
Our transformers undergo a series of of tests before being sent to the customer. These are the so-called routine tests, which aim to guarantee the perfect functioning of the transformer, to which it was designed for. For proper functioning of your transformer, you can also follow some tips such as trying to leave the transformer in a clean, dry and sheltered place before installing it, as well as not leaving it in direct contact with the ground.
It is important that before unloading the transformer, you inspect the transformer to identify any possible damage caused during transport. Check tank deformation, oil leakage, paint condition in the bushings and accessories. If you encounter any problem, please contact us immediately so we can make the necessary arrangements.
•Unloading and handling:
The transformer must be unloaded using proper equipment such as a crane or a forklift truck that is compatible with the mass of the transformer, the moving must be made only through the lift loops.
All transformer unloading and moving services must be performed and supervised by qualified personnel in compliance with safety regulations.
Before installation make sure that the board data is compatible with the technical specification of the equipment. Check that the data on the nameplate is consistent with the system in which the transformer will be installed and also the correct position of the commutator.
The installation of the transformer must be carried out by qualified professionals under the supervision of an electrical engineer as, as mentioned previously, there are adjustments and safety regulations that must be respected for proper functioning of the equipment and for the safety of consumers.
•Installation on poles:
Transformers of power up to 300 kVA can be installed directly on poles, for which the customer must mention that the equipment should me prepared for such installation, in this case, it is usually used concrete poles that support the voltage, the designer or engineer responsible for the installation must size the pole according to the mechanical requests to which it will be subjected.
• Installation on the floor:
Check for the proper leveling and strength of the foundations on which the transformers will be installed. Usually transformers rely on two-way wheels for proper movement and positioning. If the installation is on rails, first consult the distances between the wheels for proper positioning of the rails.
When space for installation is reduced, a minimum spacing of 70 cm between transformers and between these and walls or barriers must be ensured, providing easy access for inspection and ventilation.
• Sheltered substations:
The location where the transformer will be placed must be well ventilated so that the heated air can escape freely, being renewed by fresher air. Thus, the air inlet opening should be close to the floor and distributed efficiently. Exit openings should be closer to the cabin ceiling. The number and size of the outputs depend on their distances above the transformer, it is recommended to use inlet and outlet openings of 1m² per 200kVA o installed power.
Connecting the transformer to the grid
The connection of the transformer to the main electrical conductors must be made according to the wiring diagram of your nameplate. The transformer bushings are endowed with a metal alloy suitable for good electrical conductivity, but do not over tighten the connector screws or allow them to be subjected to mechanical stress as this may damage the bushing or even cause oil leaks. The cables of the secondary grid can be quite heavy and in this case a support must provided for them at the liaison point in order to prevent their weight being borne by the bushings.
The tank has specific points for earthing. It i necessary to provide a good grounding system in order to ensure leakage currents discharge and the safety of the installations, because, if there is a possible insulation failure, it will be immediately noticed. The earthing system can be made in the form of a mesh, formed by copper cables connected to copper or galvanized iron rods. The resistance of the grounding system should normally be less than 10 OHMs.