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Abstract

Content

Introduction

Today, electricity occupies a special position. Its exceptional qualities, such as the possibility of transformation and easy conversion to other forms of energy: thermal, mechanical, led to the current widespread development of electric power systems (EPS). Today, the production, delivery and distribution of electric energy is carried out by many services: energy production, operational services, dispatch services of distribution networks, electrical equipment repairmen and others. It should be noted that the delivery and distribution of electric energy has a number of distinctive features that are not characteristic of other industries. For example, the instantaneous propagation of electric current, as well as the possibility of transmitting huge amounts of energy (at high voltage) can lead to extreme consequences in the event of an accident. That is why EES has a special place to provide protection.

Today, many concepts have been developed to protect lines, devices and network sections from the occurrence of abnormal modes, the most dangerous of which are Short Circuits (CC). In addition to security systems, the monitoring of network parameters at individual sites, as well as the on-line remote control of switching equipment is also of particular importance. Telemechanics and measurements, along with protection against abnormal modes, are usually also the area of responsibility of the relay protection service, commonly referred to as the Relay Protection, Automation and Measurement Service (RDA) [2].

Basic requirements for relay protection

Each electrical installation must be equipment relay protection devices designed to:

  1. automatic shutdown of the damaged element from the rest of the intact part of the electrical system (electrical installation) using switches; if the damage directly disrupts the operation of the electrical system, relay protection is allowed only on the signal;
  2. response to dangerous, abnormal modes of operation of the elements of the electrical system; depending on the operating mode and electrical installation operating conditions, the relay protection must be performed with an effect on the signal or on the deviation of those elements, which in work may lead to damage [6].

Relay protection devices should provide the shortest possible time to disable short circuits in order to preserve the uninterrupted operation of the intact part of the system and limit the area and extent of damage to the element. Relay protection acting on the outage must ensure the selectivity of action, so that if an electrical component is damaged, only that damaged element is disconnected.

Nonselective action of protection is allowed (corrected by the subsequent action of AR or AVR):

  • to ensure acceleration of short circuit shutdown;
  • when using simplified main electric circuits with separators in circuits or transformers that disconnect a damaged element into an empty pause [4, 6].

Reliability of relay protection implies reliable operation of the device when conditions for operation occur and reliable failure of the device in their absence. The reliability of the relay protection should be provided by devices that correspond in their parameters and performance to the purpose and conditions of use.

Requirements for tire protection:

  1. Selectivity – turning off only damaged elements that are included in its zone of action, limited by current transformers, leaving the main equipment in operation;
  2. Sensitivity, which assumes the protection of equipment against long-range short circuits, which allows to maintain the reliability of the power supply to consumers even at small values of short–circuit currents;
  3. High–speed performance, which allows almost instantaneous disconnection of damaged areas, which is achieved by the correct choice of current relay settings. This property of the relay protection to disable damage with the shortest possible time lag, since a quick disconnection of damaged equipment or an electrical installation section prevents or reduces damage, maintains normal operation of consumers in the intact part of the installation, prevents disruption of parallel operation of generators.
  4. Reliability – this property of protection is guaranteed to perform its functions throughout the entire period of operation. The protection must correctly and reliably act on the opening of the switches for all damages and disturbances of the normal mode of operation and not act in normal conditions.

Methods of protection busbar

Consider busbar protection methods:

  • Arc protection;
  • Differential protection;
  • Overcurrent protection.

1) Arc busbar protection or protection against arc faults is used to protect busbars and busbar elements of switchgear 6–10 kV located in closed compartments . The work of protection is based mainly on the physical principle. It can react to two factors: a flash of light in the switchgear compartments and the mechanical effect of the arc. In this regard, it can be used only in switchgear and control gear assemblies, where all current carrying parts are placed in closed compartments. Arc protection is a special type of high–speed protection against short circuits, based on the recording of the light spectrum of an open electric arc.

The work of protection is based mainly on the physical principle. It can react to two factors: a flash of light in the switchgear compartments and the mechanical effect of the arc. In this regard, it can be used only in switchgear and control gear assemblies, where all current carrying parts are placed in closed compartments. The current protection of power supply connections has been blocked [8].

There are two main types of arc protection:

  • mechanical arc protection is adjusted to increase the pressure inside the cell volume as a result of the arc burning – valve, frame.
  • the electronic arc protection is tuned to the luminous flux appearing at the moment of arcing of the arc circuit - photo thyristor, photodiode, optical fiber [9].

2) Differential protection is one of the types of relay protection, distinguished by absolute selectivity and performed by high–speed (without artificial time delay). Differential current protection of tires is designed for fastdisabling electrical circuits included on busbars, with short circuits on busbars or on any other equipment included in the protection zone [7]. The main advantages of differential protection are: speed combined with selectivity; fundamental ease of implementation, the action for all types of short circuits.

One of the drawbacks of the differential principle is the possibility of false positives in case of a break in the connecting wires. To eliminate this drawback, the pickup current is chosen somewhat higher than the operating current of the most powerful connection [10].

3) Overcurrent protection. In case reactive lines leave the partitioned busbars of the substation with the included sectional switch, bus protection can be performed in the form of a current instantaneous cut–off. The protection actuation current is chosen greater than the short–circuit current behind the reactor. The protection acts on the disconnection of the sectional switch without time delay. The protection response time is chosen longer than the consumer protection response time.

The protections act on the disconnection of the section switch. Transformer disconnection occurs under the action of its backup protection. Overcurrent protection or distance protection. These protections can be both basic and single, if the substation buses are powered from the same source and non–sectioned. Basically, this solution is used in low-power substations. If several sources are connected to the tires, or there are two busbar systems, or the busbars are partitioned by a sectional switch, the short–circuit protection shutdown is obtained by non–selective protection.

Current Protection

In case reactive lines leave the partitioned busbars of the substation with the included sectional switch, bus protection can be performed in the form of a current instantaneous cut–off. The protection actuation current is chosen greater than the short-circuit current behind the reactor. The protection acts on the disconnection of the sectional switch without time delay. In the presence of unreacted lines, time cutoffs with time delay and MTZ are used. The tripping current and time delay are selected from the condition of detuning from the tripping current and time delay of consumer protection, for example, outgoing line protection.

One of the signs of short circuit is an increase in current in the line. This symptom is used to perform protections called current. Current protections come into effect when the current increases in the phases of the line above a certain value. The maximum current relays are used as relays to increase current. Current protection is divided into maximum current protection and current cutoff. The main difference between these protections lies in the way selectivity is achieved. The selectivity of the maximum protection is achieved using a time delay. The selectivity of the action of the current cut–off is provided by the appropriate choice of the response current.

References

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