High voltage technology in electricity, types of plant insulation and insulation coordination

High voltage technique

High voltage engineering is one of the main disciplines in a number of electrical, electrical and electrophysical specialties.

It is widely used in many sectors of the national economy. With regard to high-voltage power systems, this discipline studies electrical insulation and the processes occurring in the insulation when exposed to rated (operating) voltages and overvoltages.

High-voltage installations, based on the characteristics of processes in electrical insulation, include installations with a nominal voltage above 1000 V.

The high voltage technique course is usually divided into two parts. The first part addresses issues related to design, technology, testing and operation. insulation of electrical installations… The second part examines the occurrence of overvoltages in electrical networks and methods for their limitation.

Both parts of high-voltage technology are closely related to each other, and the overall solution to the problems of one or the other part must be carried out in a mutual relationship.

The range of issues addressed by high voltage technology includes:

• electric field at high voltage;

• electric discharge and surfing in dielectrics;

• electrical insulation and insulating structures;

• surge and surge protection methods;

• issues related to the equipment of high-voltage laboratories, high-voltage measurements, methods of preventive testing of insulation and insulation structures, ground currents and grounding devices.

Each of these questions has its own characteristics and independent importance. However, all of them are aimed at solving the main problem of high voltage technology — creation and provision of reliably working electrical insulation of high-voltage installations (creation of insulation structures with technically and economically rational levels of insulation).

For example, gas leaks are of great independent importance, but in high-voltage technologies they are considered in terms of insulation properties, since gases, especially air, are present in all insulation structures.

This scientific discipline arose simultaneously with the appearance of the first high-voltage installations, when electrical insulation began to determine the reliability of their operation.

As you grow nominal voltage of the installations insulation requirements are increasing.These requirements are largely determined by those transients that occur in various parts of electrical installations during circuit switching, ground faults, etc. (internal surges) and lightning discharges (atmospheric surges).

In connection with solving the problems of high-voltage technology, special high-voltage laboratories were needed for obtaining high voltages of various types and forms, as well as high-voltage measuring devices.

Therefore, high-voltage engineering considers the main equipment of modern high-voltage laboratories and high-voltage measurements.

In addition, the flow of currents in the ground (industrial frequency and pulse) is considered from the point of view of the arrangement of working and protective earthings, necessary to ensure the modes of operation of high-voltage installations and the safety of their maintenance.

High-voltage engineering is the only academic discipline that comprehensively examines the performance of insulation structures in electrical systems, which is why it is one of the core disciplines for all electrical engineering and electrical engineering majors.

Types of insulation for high voltage electrical installations

Modern power systems, consisting of a number of power plants (NPP, HPP, GRES, TPP), substations, overhead and cable power lines, contain three main types of high voltage insulation: station, substation and line insulation.

To gas insulation include the insulation of electrical equipment intended for internal installation, that is, the insulation of rotating machines (generators, motors and compensators), electrical devices (switches, limiters, reactors, etc.). power transformers and autotransformers, as well as electrical insulating structures for internal installation (sockets and support insulators, etc.).

For substation isolation include insulation of electrical equipment intended for external installation (in the open part of the substation), i.e. insulation of power transformers and autotransformers, external electrical devices, as well as electrical isolation structures for external installation.

For line isolation include overhead line insulation and cable line insulation.

Electrical insulation of high-voltage installations is divided into external and internal. To external insulation include electrical insulating devices and structures in the air, and to internal insulation — devices and structures in a liquid or semi-liquid medium.

High-voltage insulation determines the reliability of the operation of power systems, and therefore it is subject to requirements for electrical strength when exposed to high voltages and overvoltages, mechanical strength, resistance to environmental influences, etc.

The insulation must withstand the operating voltage for a long time as well as the impact different types of overvoltage.

External insulation intended for external installation must work reliably in rain, snow, ice, various pollutants, etc. Internal insulation, compared to external insulation, usually has better working conditions.In mountainous areas, external insulation must work reliably at reduced air pressure.

Many types of electrical insulation structures must have increased mechanical strength. For example, support and sleeve insulators, sleeves, etc. must repeatedly withstand the impact of large electrodynamic forces during short circuits, line insulators (garlands) and high-support electrical insulating structures — wind loading, since wind can create high pressure.

Limitation of overvoltages dangerous for insulation in different operating modes is carried out using the help special protective devices.

The main protective devices are arresters, surge arresters, protective capacitances, arc suppression and reactive coils, lightning arresters (rope and rod), high-speed circuit breakers with automatic closing devices (AR).

Reasonable operating measures help to ensure reliable operation of the insulation when using limiters and other protective devices. They include coordination of the insulation, organization of periodic preventive insulation tests (in order to identify and remove weakened insulation), grounding of neutrals of transformers and etc.

Isolation coordination

One of the main problems that arise in the design of insulation in high voltage technologies is the definition of the so-called "Insulation level", that is, the voltage it can withstand without being damaged.

The insulation of electrical installations must be carried out with such a limit of electrical strength that there will be no overlap (destruction) at any possible overvoltage.However, this insulation is too cumbersome and expensive.

Therefore, when choosing insulation, it is advisable not to go along the line of creating a limit to its electrical strength, but along the line of applying such protective measures that, on the one hand, prevent the appearance of overvoltage waves dangerous for insulation, and on the other hand, it protects the insulation from occurring surge waves...

Therefore, the insulation is selected at a certain level, ie. specified value for discharge and breakdown voltage, taking into account protective measures.

Isolation level and protective measures must be selected in such a way that the insulation does not collapse under the influence of various forms of overvoltage occurring in a given installation, and at the same time has a minimum size and cost.

Reconciliation of the adopted level of insulation and protective measures with overvoltages affecting the insulation is called isolation coordination.

Insulation levels for installations with a voltage of 220 kV inclusive are mainly determined by the values ​​of atmospheric overvoltages, i.e. they are significantly higher than the values ​​of internal overvoltages, and the insulation coordination in them is based on impulse characteristics.

The insulation levels of installations of 330 kV and higher are mainly determined by internal overvoltages, and the coordination of insulation in them is based on consideration of the possible magnitudes of these overvoltages.

Insulation coordination is highly dependent on the neutral point of the installation. Installations with an isolated neutral require a higher level of insulation than installations with a hard earthed neutral.