An impulse voltage surge occurring in the event of line overlap or switching is one of the most dangerous emergency situations in electric networks. Against this value, standard circuit breakers and other protection devices that respond to fluctuations in the rated current become useless, because it exceeds the increase in the pulse current and affects the insulation of the equipment.

Overvoltage can be many times higher than the permissible operating value, which jeopardizes all equipment and power supply elements. To avoid losses, special overvoltage limiters are used in electrical installations .

The use of limiters

Limiters are high-voltage devices that are widely used in various industrial sectors in medium and high class AC voltage networks. They protect the following equipment:

• Electric motors;
• Transformers;
• Traction substations;
• Other electrical installations.

Limiter design and principle of operation

A varistor with non-linear resistance is installed in the design of the device. In the presence of a normal voltage, the resistance of this semiconductor resistor remains high, so it will not conduct current. Then, in the event of voltage fluctuations, the varistor immediately switches to a conductive mode, thereby protecting the equipment from dangerous voltage. As a rule, in the design of each limiter, one or several chains of varistors is laid.

Varistors are most often made of zinc oxide, and then coated with a special paint to improve conductivity. In the manufacturing process, various alloys are added to zinc oxide, thereby forming pn junctions, which ensure the non-linearity of the current-voltage characteristics of the semiconductor resistor.

The surge protector has the following principle of operation: at standard voltage, it passes the rated current in fractions of a milliampere, and in the case of surge surges, the current passing through the device increases, thereby limiting the high voltage.

Varieties of limiters

In industrial conditions, the following types of surge arresters are widely used:

• Polymer. In these devices, the varistor column is located in a housing made of high molecular weight rubber. They are distinguished by explosion safety, tightness, low weight, and smooth operation in dusty conditions.
• Porcelain. Such devices consist of a column of semiconductor elements, which is pressed against a fiberglass tube in the inner part of the porcelain tire. They tolerate temperature changes in the best way, have good mechanical characteristics.

Equipment purchase

The MEGATRONIKA company is a supplier of new and used high-quality equipment from world-famous manufacturers. For our customers, we can offer the most optimal conditions for the purchase of equipment:

• Reasonable prices;
• Guarantee;
• Delivery in Russian cities and CIS countries.