To some this question may seem strange, 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 incorrect.
In order to correctly answer this question, you need to consider the standard wiring diagram of the circuit breaker drive, for example, at 35 kV. Relays RPV (KQC) and RPV (KQT) are highlighted in red.
Fig. 1. Connection diagram of the 35 kV vacuum circuit breaker drive (example)
And here is another circuit, this time for a 110 kV circuit breaker
Fig. 2. Connection diagram for 110 kV SF6 circuit breaker drive (example)
As you can see, the power to the coils of these relays (especially RPO) is supplied along fairly long chains, including other contacts and shutdown electromagnets.
Naturally, in these chains there are block contacts of the switch, but not only they. In the general case, the spring cock control limit switch, the contacts of the gas pressure monitoring relay (blocking stage), etc. can be included here. That is why the RPV and RPO relays cannot signal the current position of the circuit breaker.
What then "show" RPO and RPV?
They indicate the readiness of the drive for operation:
RPO - readiness for the inclusion operation,
RPV - readiness for the shutdown operation.
Let's look at the inclusion circuit on Fig. 1which includes RPO. In addition to the block contact of the Q1 switch and the YAC switching coil, it includes the following elements:
- Switch SA1 in the drive cabinet, which transfers the drive to remote or local (repair) control. To power the RPO input, the switch must be in the remote control position, otherwise the signal will not pass.
- Contacts for monitoring the state of the actuator spring SQM1 and SQM2, which close when the spring is cocked, i.e. when the switch is ready for the 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.
- An SQF contact that breaks the closing circuit if there is a parallel circuit breaker command so that there is no multiple switching effect.
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 readiness / unavailability of the switch for the operation of inclusion.
If the circuit breaker is SF6 gas, then the contacts of the SF6 gas pressure switch are added to the on and off circuit, which completely blocks the control during a critical pressure drop. This prevents the circuit breaker from failing due to a failure to extinguish the arc (no SF6 - no extinguishing medium). Such a relay can be seen on Fig. 2 (+ K9)
Also, the relay / RPO or RPV inputs will not be powered when the on and off circuits are broken or the power circuit breaker is turned off. In the event of the disappearance of both RPV and RPO signals, the relay protection and control device gives a warning signal to the duty officer at the substation or in the automatic control system.
Initially, these relays were used precisely to control the integrity of the control circuit of the circuit breaker.
Features of the use of RPV and RPO signals in logic circuits
Signal processing RPO, RPV must be done taking into account the logic of their formation.
For example, the RPO signal may disappear during the spring charging time, especially in the cycle of unsuccessful automatic reclosure (operation O-tapv-VO), when a stable short-circuit occurs again, but the switch-on spring has not yet been charged.
Spring winding time can reach 15 s (VVU-SEShch-P-10) and more, especially at low operating current voltage.
This means that it is necessary to carry out the signaling of the open circuit of the drive (the simultaneous disappearance of RPO and RPV) with a time delay of at least the spring cocking time.
RPV signals are also widely used in protection and automation algorithms. For example, RPV is usually used when starting an automatic reclosure, and RPO when accelerating protection.
Fig. 3. The use of RPV and RPO in the algorithms of MP RPA (for example, BMRZ-152-KL, taken from the site http://mtrele.ru)
In addition, it must be understood 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.
For example, the RPV signal ( Fig. 1) will disappear at the discrete input of terminal A1 as soon as a command to disconnect the relay contact KCT1 is issued. Those. the switch has not yet had time to open (still on), and the RPV signal has already disappeared (the RPV input is bridged by relay contact KCT1).
The difference here is certainly small (tens of milliseconds), but for systems such as RAS and ACS can be significant. Therefore, for them, the position of the circuit breaker must be "taken" through the "dry" block contacts of the circuit breaker, when powered from the tracer of the corresponding system.
It is the contact block of the circuit breaker with which shows its current position, and the RPV and RPO are the relay monitoring the readiness of the switch for the corresponding operation.
Well, finally, a little observation
Recently, designers and manufacturers of circuit breakers have been trying to take the RPO circuit as far as possible to the switching electromagnet, bypassing the entire complex chain of auxiliary contacts.
On the Fig. 4 shows two schemes for drives of the same type of circuit breakers VVU-SESH-P 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.
Synchronous electrical machines belong to AC machines, usually three-phase. Like most electromechanical converters, they can operate in both generator mode and engine mode. A special mode of operation of a synchronous machine is the reactive power compensation mode. Special machines designed for this purpose are called synchronous compensators. Despite the fundamental reversibility of synchronous motors and generators, they usually have design features ...
Power oil transformers are the most expensive components of distribution substation equipment. Transformers are designed for a long service life, but provided that they will operate in normal mode and will not be subjected to unacceptable current overloads, overvoltages and other undesirable operating modes. To prevent damage to the transformer, extend its service life and ensure its operation, various protection and automation devices are needed ...
|
|
Electricity in the energy sector is produced at generator stations, transmitted over long distances through power lines. Aerial and cable power lines are located between transformer substations and consumers, supply electricity to the latter. At all technological stages of production, transmission and distribution of electrical capacities, emergency situations can occur that can destroy technical equipment or lead to the death of service personnel in a very short time ...
All consumers of electricity are connected to the generator end by a circuit breaker. When the load corresponds to the nominal value or less than it, there are no reasons for disconnection, and current protection scans the circuit in a constant mode. The circuit breaker can be disconnected from current protection when: the load due to a short circuit sharply exceeded the nominal value and short-circuit currents were created that could burn the equipment. Disabling such an accident must be done ...
When operating electrical equipment, it can be damaged not only from short circuits, but also from lightning discharges into its circuitry, the penetration of a higher voltage from other equipment, or a significant decrease in the level of the supply circuit. According to the value of the operating voltage, the protection is divided into two types: minimum and maximum. In the event of emergency situations associated with short circuits, large energy losses occur when the applied power is spent on the development of damage ...
Purpose: protection of electrical objects from accident currents arising inside the controlled area with an absolute degree of selectivity without time delay. The measuring unit is a differential organ consisting of current transformers and relays that constantly monitor the direction of currents in different sections and operate when they change.In nominal, operating mode, the load current flows from the generator end to consumers and has one direction along the entire line. It is tracked and taken into account by measuring relays ...
In the article describing the operation of automatic reclosure devices, cases of power failure for various reasons and methods for its recovery by the automation of power lines in the case where the causes of the emergency situations have self-removed and ceased to work are considered. A bird flying between the wires of an overhead power line can create a short circuit through its wings. This will entail the removal of voltage from the overhead line by disconnecting from the protection of the power switch at the power substation. Automatic reclosure devices will restore power after a few seconds ...
The main requirements for power supply to consumers are the reliability and uninterrupted supply of electricity. Transport energy flows of electric networks occupy hundreds and thousands of kilometers. At such distances, various natural and physical processes that damage equipment, create leakage currents or short circuits can affect power lines. To prevent the spread of accidents, any power lines are equipped with protections that are constantly in real time ...
Zero-sequence directional current protection (TNZNP) is used when it is necessary to protect high-voltage power lines from single-phase short circuits - ground faults of one of the phase wires in the power grid. This protection is used as a backup protection for power lines of voltage class 110 kV. Below we give the principle of operation of this protection, consider how and with what devices TNZNP is implemented in 110 kV electric networks. In electrical engineering there is a concept of symmetrical ...
Remote protection (DZ) in electric networks of voltage class 110 kV performs the function of backup protection of high voltage lines, it reserves the differential-phase protection of the line, which is used as the main protection in electric networks of 110 kV. DZ protects the overhead line from interphase short circuits. Consider the principle of operation and devices that operate distance protection in electrical networks of 110 kV. The principle of operation of distance protection is based on the calculation of distance ...
In accordance with the requirements of the rules for the technical operation of electrical installations (abbreviated as PTE), the power equipment of electric networks, substations and the electric stations themselves must be protected from short-circuit currents and failures of normal operation. As protection equipment, special devices are used, the main element of which is a relay. Actually, that's why they are called so - relay protection devices and electroautomatics (RPA). To date, there are many devices that can as soon as possible prevent an accident on a serviced section of the power grid or, in extreme cases, alert personnel about a violation of the operating mode. In this article we will consider the purpose of relay protection, as well as its types and device.
What is it for?
First of all, we will talk about why you need to use RPA. The fact is that there is such a danger as in a chain. As a result of the 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 during the decomposition of oil inside the transformer, etc. In order to detect danger in a timely manner and prevent it, special relays are used that signal (if a malfunction of the equipment 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 RPA the following requirements are presented:
- . In the event of an emergency, only that section in which an abnormal operating mode is detected should be turned off. All other electrical equipment should work.
- Sensitivity. Relay protection must respond even to the smallest values \u200b\u200bof the alarm parameters (set by the trip setting).
- Performance. No less important requirement for relay protection, as the faster the relay operates, the less chance of damage to electrical equipment, as well as the occurrence of danger.
- Reliability. Of course, the devices must perform their protective functions in 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 signal personnel about the accident.
Relay classification
When considering this topic, one can not stop at the types of relay protection. The relay classification is as follows:
- Connection method: primary (connected directly to the equipment circuit) and secondary (connected via transformers).
- Variant of execution: electromechanical (the system of movable contacts disengages the circuit) and electronic (disconnection is done using electronics).
- Appointment: measuring (carry out the measurement of voltage, current, temperature and other parameters) and logical (transmit commands to other devices, carry out time delay, etc.).
- Way of action: relay protection of direct action (mechanically connected to the disconnecting device) and indirect effect (control the circuit of the electromagnet, which turns off the power).
As for the types of RPA themselves, there are many of them. Immediately consider what types of relays are and what they are used for.
- Overcurrent protection (MTZ), triggered if the current reaches the setpoint set by the manufacturer.
- Directional overcurrent protection, in addition to the setting, the direction of power is monitored.
- Gas protection (GZ), is used to turn off the power to the transformer as a result of gas evolution.
- Differential, scope - protection of busbars, transformers, as well as generators by comparing the values \u200b\u200bof currents at the input and output. If the difference is greater than the set point, the relay protection is activated.
- Remote (DZ), turns off the power if it detects a decrease in resistance in the circuit, which occurs if a short-circuit current occurs.
- Remote protection with high-frequency interlock, is used to turn off the overhead line when a short circuit is detected.
- Remote with optical channel locking, a more reliable version of the previous type of protection, as the effect of electrical noise on the optical channel is not so significant.
- Logical bus protection (LZS) is also used to detect faults, only in this case on buses and (supply lines extending from substation buses).
- Arc. Purpose - protection of complete switchgears (switchgear) and complete transformer substations (KTP) from fire. The principle of operation is based on the operation of optical sensors as a result of increased illumination, as well as pressure sensors with increasing pressure.
- Differential phase (DFZ). They are used for phase control at two ends of the supply line. If the current exceeds the setpoint, the relay trips.
Separately, I would also like to consider the types of electroautomatics, the purpose of which, in contrast to relay protection, on the contrary, is to turn on the power back. So, in modern relay protection and automation use the following type of automation:
- Automatic reserve input (ABP). Such automation is often used when, as a backup source of power supply.
- Automatic reclosing (AR). Scope - power lines of 1 kV and above, as well as busbars of substations, electric motors and transformers.
- Automatic frequency unloading, which turns off third-party devices when lowering the frequency in the network.
In addition, there are the following types of automation:
So we examined the purpose and scope of relay protection. The last thing I would like to talk about is what the RPA consists of.
Relay Design
The relay protection device is a diagram of the following parts:
- Starting organs -, current, power. Designed to control the operating mode of electrical equipment, as well as detect violations in the circuit.
- Measuring organs - can also be located in the starting organs (current, voltage relays). The main purpose is to start other devices, signaling as a result of detecting an abnormal operating mode, as well as instantly turning off the devices or with a time delay.
- The logical part. Presented by timers as well.
- Executive part. Responsible directly for turning off or on switching devices.
- The transmitting part. It can be used in differential phase protection.
