Electrical Switchgear and Protection Equipment in Transformer Centers

Posted on Dec 10, 2024 in Electronics

Transformer Center Switchgear and Elements

1. CT Switchgear and Elements

It’s called electrical facing any equipment or apparatus for controlling the electrical system at will. The cladding, which has indoor or outdoor CT, has the following functions:

  • Maneuvers of the circuit.
  • Transformation of energy.
  • Protection of persons and goods.

To achieve these goals, the enclosure where the switchgear is placed requires additional facilities such as:

  • Ground Installation
  • Fire Installation
  • Ventilation
  • Lighting Installation for CT

The elements of the CT are:

  • Insulators: Pieces of insulating material are used to support or hold conductors and switchgear. The materials used in insulators for indoor switchgear CT are steatite and epoxy-resin because of their great capacity to withstand large mechanical stresses that occur when performing the opening and closing of the switchgear.
  • Busbar: Consists of copper strips. Its calculation is performed with great simplicity, and its length is reduced by current density:
    d = I / S = S = I / d = mm2
    However, the mechanical calculation is due to electrodynamic forces that occur in bars in short circuit conditions, causing bending forces.
  • Conductors: The entrance to the CT is done through insulated conductors as a function of line voltage input to the cell by connecting to switch terminals or connectors.
  • Switch: The device is equipped with cutting power to perform the opening and closing of the load circuit, i.e., the nominal current of the line may close but not open a short-circuit. The court is given power by the arc-extinguishing system, which has the switch that is used for classification, and there are the following:
    • Areas spark off or horns.
    • In magnetic blow.
    • In oil bath (most commonly) called small volume of oil
    • Of gas SF6 = sulfur hexafluoride (it is best to cut more)
    These devices, in addition to their electrical properties and voltage rating, it is essential to know their cutting power and closing.
    • Breaking: Current value that the device is capable of breaking under stress and under prescribed conditions of operation, expressed in MVA KA and cutting power.
    • Making capacity: Intensity value close or reset.
  • Circuit breaker or circuit breaker: The switch is able to establish, maintain, and disrupt the service rated as well as interrupting automatically or set abnormally high currents such as short circuit current. It is used to protect facilities and transformers. The operation of these devices, as well as automatic and manual, are driven by the order of overcurrent relay coils, undervoltage trip. One of the most important features is its cutting power, which is based on the place or point where it is installed in accordance with the existing short-circuit power.
  • Disconnecting grounding: Switchgear used for grounding, part of a circuit or installation.

2. Equipment Protection

These are devices that detect anomalies in the line, such as overload or short circuit, giving the order to disconnect the circuit breaker. They are used as follows:

  • Direct-Relay: Excited by the phase current feeding the transformer, when the intensity is higher than it has regulated the relay, causing the tripping of the circuit associated with it.
  • Indirect relay: Is excited by a low intensity, the image of the primary current transformer feeding power transformers using intensity ratio In / SA.

In the processor, the following protective devices are used:

  • Thermometer: To check the temperature of the oil medium voltage transformers MT, thermometers are used, and any anomaly produces heat and the action of temperature above the nominal. There are two types: column and field.
    • T. Columna: Placed on top of a reduced power transformer, it consists of a glass ampoule within which alcohol is colored red with divisions on a scale where the temperature reading is.
    • T. Esfera: In addition to pointing out the direct temperature of the transformer, it is equipped with two contacts, triggering the alarm, allowing a given temperature T-1, and ordering the disconnection of the transformer when it reaches a temperature T-2.
  • Buchholz-Relay: Electrical incidents or anomalies that may affect the transformer windings immersed in oil, resulting in the detachment of gases whose composition varies depending on the type of problem. Gas can be extracted from the relay for consideration.
    • 1st Level: Home of damage: in the case of local heating, contact between coils, phase loss, triggering the alarm.
    • 2nd Level: Due to pressure waves by the jet of gas emitted in the case of a short circuit.
    It is installed in the tube that connects the Cuba of the transformer with the expansion tank between 2 valves, sight glasses includes operational control and measurement of gases. For the first level, the float acts superior, localized heating causes a release of bubbles that accumulate in the top of the relay, causing a lowering of oil that float moves, activating the alarm contact.