Understanding Transformer Processing Centers: Types and Uses
Processing Center
A Transformer Processing Center is a facility that reduces the average voltage of distribution lines to a lower voltage for use in industrial buildings and homes. Processing centers can be classified according to their location:
- Outdoor or External: These processing centers are placed on poles. Lines to switchgear and transformers are placed on concrete or steel supports.
- Interior: Located inside buildings, the placement surface may be semi-buried or underground. Today, these buildings are often prefabricated.
According to their construction, CTs (Current Transformers) installed in the premises may be:
- Open: Enclosures or cells where the CT elements are placed, separated by partitions, and can be open or closed-front.
- Prefabricated Metal Cell: Switchgear is joined with a mechanical envelope.
- Compact: The CT switchgear is in a compact single cell with sulfur hexafluoride insulation, occupying very little space.
CTs can also be classified according to their connection to the MV (Medium Voltage) distribution line:
- Simple Derivation on Air: In an MT line from a substation, the high voltage is directly connected to processing centers, lowering it to medium voltage. This distribution is generally used in rural areas.
- Ring: In a ring network of MT, each CT has two switches: one input and one output. The output switch connects to the input of another CT, and so on, returning to the substation that feeds the line, reducing MT.
- Double-Pass: The CT is connected through two switches to MT lines from two different substations. This allows the CT to function even if there is a fault in one power line.
According to their use, CTs are classified as:
- Distribution Centers: Owned by the energy supply company, they feed low voltage to subscribers.
- Subscriber Center: Customer-owned. Sometimes, the supplier maintains the CT and it becomes their property after a while. They have equipment for measuring energy consumption, which can be located in two ways:
- On the low voltage side, often outdoors on a support.
- On the high voltage side, often indoors, with a measuring cell containing structures and voltage transformers that connect to the power meter equipment.
Neutral Regime in the CT
- TT Scheme: The neutral of the transformer and the masses of equipment are connected to the ground. This is the system used in homes and buildings. A differential switch turns off the installation when there is an earth fault.
- TN Scheme: The neutral of the transformer is connected to the ground, and the masses of the facility are connected to neutral by protective conductors.
- IT Regime: The transformer neutral is isolated or grounded through high impedance (around 2000 ohms), and the masses of the equipment are grounded. Businesses can opt for this arrangement, with a system that controls the installation’s insulation to ground. With a single fault, the controller issues a warning; a second fault turns off the installation. This system allows for better continuity of service but requires maintenance personnel to monitor the installation and quickly eliminate the fault upon the first warning.