School for an electrician: everything about electrical engineering and electronics. Adjusting the rear axle gearbox

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In accordance with the requirements of the rules of technical operation of electrical installations (abbreviated PTE), power equipment of electrical networks, substations and power plants themselves must be protected from short-circuit currents and failures of normal operation. Special devices are used as protective equipment, the main element of which is a relay. Actually, that’s why they are called that – relay protection and electrical automation devices (RPA). Today, there are many devices that can quickly prevent an accident in the serviced section of the power grid or, in extreme cases, warn personnel about a violation of the operating mode. In this article we will look at the purpose of relay protection, as well as its types and design.

What is it for?

First of all, we’ll tell you why you need to use relay protection. The fact is that there is such a danger as in a chain. As a result of a short circuit, conductive parts, insulators and the equipment itself are very quickly destroyed, which entails not only the occurrence of an accident, but also an industrial accident.

In addition to a short circuit, gas evolution may occur when the oil decomposes inside the transformer, etc. In order to promptly detect danger and prevent it, special relays are used that signal (if equipment failure does not pose a threat) or instantly turn off the power in the faulty area. This is the main purpose of relay protection and automation.

Basic requirements for protective devices

So, in relation to relay protection and automation the following requirements are imposed:

1. . In the event of an emergency, only the area in which an abnormal operating mode is detected should be switched off. All other electrical equipment must work.
2. Sensitivity. Relay protection must respond even to the most minimal values ​​of emergency parameters (set by the response setting).
3. Performance. An equally important requirement for relay protection and automation, because The faster the relay operates, the less chance there is of damage to electrical equipment, as well as danger.
4. Reliability. Of course, the devices must perform their protective functions under the given operating conditions.

In simple words, the purpose of relay protection and the requirements for it are that the devices must monitor the operation of electrical equipment, respond in a timely manner to changes in the operating mode, instantly disconnect the damaged section of the network and alert personnel about an accident.

Relay classification

When considering this topic, one cannot help but dwell on the types of relay protection. Relay classification is presented as follows:

• Connection method: primary (connected directly to the equipment circuit) and secondary (connected through transformers).
• Execution options: electromechanical (a system of moving contacts disconnects the circuit) and electronic (disconnection occurs using electronics).
• Purpose: measuring (measure voltage, current, temperature and other parameters) and logical (transmit commands to other devices, carry out time delay, etc.).
• Method of influence: relay protection of direct influence (mechanically connected to the disconnecting device) and indirect influence (control the electromagnet circuit that turns off the power).

As for the types of relay protection systems themselves, there are many of them. Let’s immediately look at what types of relays there are and what they are used for.

1. Overcurrent protection (overcurrent protection) is triggered if the current reaches the setting specified by the manufacturer.
2. Directional overcurrent protection, in addition to the setting, the direction of power is controlled.
3. Gas protection (GZ) is used to cut off power to the transformer as a result of gas release.
4. Differential, scope of application - protection of busbars, transformers, and generators by comparing the values ​​of currents at the input and output. If the difference is greater than the specified setting, the relay protection is activated.
5. Remote (RD), turns off the power if it detects a decrease in resistance in the circuit, which occurs if a short-circuit current occurs.
6. Distance protection with high-frequency blocking, used to disconnect overhead lines when a short circuit is detected.
7. Remote with blocking via an optical channel, a more reliable version of the previous type of protection, because the influence of electrical noise on the optical channel is not so significant.
8. Logical bus protection (LBP) is also used to detect short circuits, only in this case on buses and (supply lines extending from substation buses).
9. Dugovaya. Purpose – protection of complete switchgears (KRU) and complete transformer substations (CTS) from fire. The operating principle is based on the activation of optical sensors as a result of increased illumination, as well as pressure sensors when pressure increases.
10. Differential phase (DPZ). Used to control phases at two ends of the supply line. If the current exceeds the setting, the relay is activated.

Separately, I would also like to consider the types of electrical automation, the purpose of which, unlike relay protection, is, on the contrary, to turn the power back on. So, in modern relay and automation systems they use the following type of automation:

1. Automatic transfer of reserve (ATS). Such automation is often used as a backup source of power supply.
2. Automatic reclosing (AR). Area of ​​application: power lines with voltages of 1 kV and higher, as well as busbars of substations, electric motors and transformers.
3. Automatic frequency unloading, which turns off third-party devices when the frequency in the network decreases.

In addition, there are the following types of automation:

So we looked at the purpose and areas of application of relay protection. The last thing I would like to talk about is what the relay protection consists of.

Relay protection and automation design

The relay protection device is a circuit consisting of the following parts:

1. Starting elements - current, power. Designed to monitor the operating mode of electrical equipment, as well as detect violations in the circuit.
2. Measuring elements - can also be located in starting elements (current and voltage relays). The main purpose is to launch other devices, send a signal as a result of detecting an abnormal operating mode, as well as instantly turn off devices or with a time delay.
3. Logical part. Represented by timers, as well as .
4. Executive part. Responsible directly for turning off or turning on switching devices.
5. Transmitting part. Can be used in phase differential protection.

This question may seem strange to some, because the answer is hidden in their name - the position relay is on/off. But if you think that these relays report the current position of the switch, then read on. Because the answer is wrong.

To correctly answer this question, you need to consider the standard connection diagram for the power circuit breaker drive, for example, 35 kV. Relays RPV (KQC) and RPV (KQT) are highlighted in red.

Fig.1. Connection diagram for 35 kV vacuum circuit breaker drive (example)

And here is another diagram, this time for a 110 kV switch

Fig.2. Connection diagram for 110 kV SF6 gas circuit breaker drive (example)

As you can see, power is supplied to the coils of these relays (especially RPO) through fairly long chains, including other contacts and on/off electromagnets.

Naturally, these chains contain switch block contacts, but they are not the only ones. In general, this may include the spring charging control limit switch, contacts of the SF6 gas pressure control relay (blocking stage), etc. That is why the RPV and RPO relays cannot signal the current position of the switch.

What then do RPO and RPV “show”?

They indicate that the drive is ready for operation:

RPO – readiness for switching operation,

RPV – readiness for shutdown operation.

Let's look at the switching circuit on Fig.1, which includes RPO. In addition to the block contact of switch Q1 and the closing coil YAC, it includes the following elements:

— Switch SA1 in the drive cabinet, which switches the drive to remote or local (repair) control. To power the RPO input, the switch must be in the remote position, otherwise the signal will not pass through.

— Contacts for monitoring the state of the drive spring SQM1 and SQM2, which close when the spring is charged, i.e. when the switch is ready for closing operation. After each switch-on, the drive spring is discharged and the SQM contacts open, blocking the passage of the switch-on command until the spring is charged.

— SQF contact, which breaks the switching circuit if there is a parallel command to open the circuit breaker so that there is no effect of repeated closing.

If at least one of these elements is in the open state, then the RPO circuit will not assemble, even if the switch is in the off position (Q1 is closed). The combination of all these elements indicates the switch’s readiness/unreadiness for the switching operation.

If the switch is SF6, then contacts of a SF6 pressure switch are added to the on and off circuit, which completely blocks the controls when the pressure drops critically. This prevents the circuit breaker from failing during a short circuit due to the inability to extinguish the arc (no SF6 gas - no extinguishing medium). Such a relay can be seen on Fig.2 (+K9)

Also, the relays/inputs of the RPO or RPV will not be energized when the on-off circuits are broken or the power supply is turned off. When both RPV and RPO signals disappear, the relay protection device issues a warning signal to the duty officer at the substation or in the automated control system.

Initially, these relays were used precisely to monitor the integrity of the switch control circuits.

Features of the use of RPV and RPO signals in logic circuits

RPO and RPV signals must be processed taking into account the logic of their formation.

For example, the RPO signal may disappear during the charging of the spring, especially in the cycle of unsuccessful automatic reclosure (O-tapv-VO operation), when a stable short circuit is switched off again, but the closing spring has not yet had time to charge.

The spring winding time can reach 15 s (VVU-SESH-P-10) or more, especially at reduced operating voltage.

This means that it is necessary to signal a broken drive circuit (simultaneous disappearance of the RPO and RPV) with a time delay of no less than the spring charging time.

RPV signals are also widely used in protection and automation algorithms. For example, RPV is usually used when starting automatic reclosure, and RPO when accelerating protection.

Rice. 3. Use of RPV and RPO in MP RPA algorithms (using the example of BMRZ-152-KL, taken from the website http://mtrele.ru)

In addition, you need to understand that even if all auxiliary contacts are closed, it is still incorrect to judge the position of the switch by RPO and RPV because in this case the RPO and RPV signals disappear faster than the complete on/off operation occurs.

For example, the RPV signal ( Fig.1) will disappear at the discrete input of terminal A1 as soon as a shutdown command is issued by the KCT1 relay contact. Those. the switch has not yet turned off (it is still on), and the RPV signal has already disappeared (the RPV input is bypassed by the KCT1 relay contact).

The difference here is of course small (tens of milliseconds), but for systems such as RAS and ACS it can be significant. Therefore, for them, the switch position must be “taken away” through the “dry” block contacts of the switch, when powered from the opercurrent of the corresponding system.

It is the block contact of the switch c that shows its current position, and RPV and RPO are relays for monitoring the readiness of the switch for the corresponding operation.

Well, and finally, a little observation

Recently, designers and manufacturers of switches have been trying to move the RPO circuit as far as possible to the switching electromagnet, bypassing the entire complex chain of auxiliary contacts.

On Rice. 4 two diagrams are shown for drives of the same type of VVU-SESH-P switches with a difference of 3 years. On the left you see a diagram from 2010, and on the right a more modern one. Pay attention to the RPO chain - this is what I was talking about. In the first case, you control almost the entire switching circuit, and in the second, only the Q1-YAC section.