31 Jul Oil and vacuum high voltage circuit breakers and their operation.
High-voltage equipment in Yekaterinburg implies a wide range of products that perform different purposes and tasks. So, for switching electrical circuits, switches are used that turn on and off short-circuit load currents, magnetization of transformers and charging currents of buses and lines.
In whatever modes the switch works, certain requirements are imposed on it. So, it must reliably turn off any currents within the rated values, extinguish the arc in the shortest possible time, easy to maintain. It must be explosion and fire safe and suitable for automatic switching on
The most difficult mode is considered to be the shutdown of short-circuit currents, which, passing through the switch, affect it not only with significant electrodynamic forces, but also with high temperatures. In addition, if the current is re-applied manually or automatically when the short circuit is not cleared, the gap between the contacts may break down, and the pressure on the contact is insufficient, which can lead to premature wear of the equipment. That is why the main material for contacts today is cermet. The switches themselves come in different designs and types, of which the most common are oil tank, low-oil and vacuum switches.
Tank oil circuit breakers use a large volume of oil, which quenches the arc and isolates conductive parts from grounded structures.
Oil is an arc extinguishing medium, and during extinguishing, strong heating, oil decomposition and gas formation are observed. The high arc-quenching ability of the oil is determined by the 70% oxygen content in the resulting gas mixture. Successful arc quenching and intense gas formation directly depend on the value of the current to be switched off.
The speed with which the contacts diverge plays an important role. The high speed at which the contacts move ensures that the critical length is reached quickly. In this case, the recovering voltage may not be enough to break through the gap between the arc contacts. Speed is negatively affected by oil viscosity, low temperatures, as well as contamination and thickening of the lubrication of parts of the transmission mechanism and drives. All this can lead not only to a decrease in speed, but also to a complete cessation of the movement of contacts.
Vacuum circuit breakers used in electrical installations with a voltage of more than 10 kV are characterized by a simple design, high reliability and economical maintenance. The main part of such a switch is a vacuum chamber with a cylindrical body. This case has two sections of hollow ceramic insulators, which are connected with a metal gasket and closed with flanges at the ends. In the chamber itself there is a contact system and electrostatic screens designed to protect the insulating surfaces from metallization and contribute to the intra-chamber distribution of potentials. A fixed contact is attached to the lower flange of the chamber, which is connected by a stainless steel bellows to a moving contact passing through the upper flange of the chamber. Pole chambers are fixed with support insulators on a metal frame.
Throughout the entire period of operation, a deep vacuum is maintained in the chambers. Such a medium does not conduct electric current, so the electric arc is extinguished and the insulation of the interelectrode gap is restored as soon as the current passes zero. During the service life of the circuit breaker, it is necessary to check the condition of the insulators and surfaces for defects and contamination, and also to ensure that no traces of corona discharges appear.