What is a relay protection device and what are its basic tasks?

Relay is a kind of electrical control device, which is an electrical appliance that makes a predetermined step change of the controlled quantity in the electrical output circuit when the change of the input quantity (excitation quantity) reaches the specified requirements. It has an interactive relationship between the control system (also known as the input loop) and the controlled system (also known as the output loop). Usually used in the control circuit of automation, it is actually a kind of "automatic switch" that uses a small current to control the operation of a large current.

Therefore, it plays the role of automatic adjustment, safety protection, and conversion circuit in the circuit. Main role.

The relay is an automatic switching element with isolation function, which is widely used in remote control, telemetry, communication, automatic control, mechatronics and power electronic equipment, and is one of the most important control components.

relays (Figure 3).

Relays generally have an induction mechanism (input part) that can reflect certain input variables (such as current, voltage, power, impedance, frequency, temperature, pressure, speed, light, etc.); There is an actuator (output part) that can realize "on" and "off" control of the controlled circuit; Between the input and output parts of the relay, there is also an intermediate mechanism (drive part) that couples and isolates the input quantity, processes the function, and drives the output part.

As a control element, in summary, the relay has the following functions:

1) Expand the control range: for example, when the control signal of the multi-contact relay reaches a certain value, it can be changed, interrupted and connected to multiple circuits at the same time according to the different forms of the contact group. [3]

2) Amplification: For example, sensitive relays, intermediate relays, etc., can control very high-power circuits with a very small control quantity.

3) Comprehensive signal: For example, when a plurality of control signals are input into a multi-winding relay in the prescribed form, the predetermined control effect is achieved after comparative synthesis.

4) Automatic, remote control, monitoring: For example, the relay on the automatic device, together with other electrical appliances, can form a program control circuit, so as to achieve automatic operation.

In recent years, relay protection has become an indispensable part of the development of ultra-high voltage power grids, which is directly related to the safe and stable operation of the power system. Therefore, by being familiar with and understanding the characteristics of relay protection, you can better play the role of relay protection and escort the safe operation of the power system.

Meaning of relay protection:

The so-called relay protection refers to the study of the fault of the power system and the situation and hidden danger that may cause harm to the normal operation, and put forward the corresponding solution after analysis. It is called relay protection because relays with contacts were used to protect the power system and its components from loss in operation.

Basic tasks of relay protection:

When the power system fails or abnormal working conditions, the faulty equipment is automatically removed from the system in the shortest time and the smallest area that can be realized, or a signal is sent out by the personnel on duty to eliminate the root cause of the abnormal working conditions, so as to reduce or avoid the damage to the equipment and the impact on the power supply in adjacent areas.

The earliest protective relay devices were fuses. Later, electromagnetic relay protection devices acting on circuit breakers, electronic static relays, and digital relay protection using computers appeared.

Relay Protection Classification:

1. According to the classification of protected objects, there are transmission line protection and main equipment protection (such as generator, transformer, busbar, reactor, capacitor, etc.).

2. According to the classification of protection functions, there are short-circuit fault protection and abnormal operation protection. The former can be divided into primary protection, backup protection and auxiliary protection; The latter can be divided into overload protection, loss of magnetism protection, loss of step protection, low-frequency protection, non-full-phase operation protection, etc.

3. According to the semaphore of the protection device for comparison and calculation processing, there are analog protection and digital protection. All electromechanical, rectifier, transistor and integrated circuit (operational amplifier) protection devices, which directly reflect the continuous analog quantity of the input signal, are analog protection; The protection device of microprocessor and microcomputer is adopted, which reflects the discrete digital quantity after sampling and modular-to-digital conversion of analog quantity, which is digital protection.

4. According to the principle of protection action, there is overcurrent protection, low voltage protection, overvoltage protection, power direction protection, distance protection, differential protection, longitudinal protection, gas protection, etc.

Relay protection device refers to an automatic device that can reflect the failure or abnormal operation of equipment in the power system, and act on the circuit breaker tripping or sending out signals. Its roles include:

1) The power system does not operate during normal operation;

2) When the power system is not operating normally, an alarm signal will be sent to notify the personnel on duty to deal with it, so that the power system can resume normal operation as soon as possible;

3) When the power system fails, identify the faulty power equipment, and send a trip instruction to the circuit breaker closest to the fault point between the fault point and the power point, so as to isolate the fault part from other parts of the power grid.

Basic principle. Relay protection is mainly the principle of relay protection action by using the change of electrical quantity (current, voltage, power, frequency, etc.) when the components in the power system are short-circuited or abnormal, and there are other physical quantities, such as the increase of a large amount of gas and oil flow velocity or the increase of oil pressure strength when the transformer oil tank is faulty. In most cases, regardless of the physical quantity reacted, the protective relay device consists of a measurement part (and a value adjustment part), a logic part, and an execution part.

The basic tasks are as follows:

1. Monitor the normal operation of the power system. When the protected power system element fails, the relay protection device of the element should quickly and accurately send a trip command to the nearest circuit breaker that is separated from the fault element, so that the fault element is disconnected from the power system in time, so as to minimize the damage to the power system component itself and reduce the impact on the safe power supply of the power system. When the failure of the system and equipment is enough to damage the equipment or endanger the safety of the power grid, the relay base electrical protection device can minimize the damage to the power system components themselves and reduce the impact on the safe power supply of the power system.

2. Respond to the abnormal working conditions of electrical equipment, and send a letter with a letter according to the abnormal working conditions and different conditions of equipment operation and maintenance, prompting the attendant to take measures quickly to restore it to normal as soon as possible, or automatically adjust it by the device, or cut off the electrical equipment that will cause accidents if it continues to run. Relay protection devices that respond to abnormal working conditions allow for a certain delay in operation.

3. Realize the automation and remote operation of the power system, as well as the automatic control of industrial production.

1. Automatically, quickly and selectively, the non-faulty element grinding parts are removed from the power system, so that the faulty components are not further damaged, and the other fault-free parts are quickly restored to normal operation.

2. React to the abnormal operation of electrical components, and act on the signal according to the conditions of operation and maintenance, so that the attendant can deal with it in time, or automatically adjust it by the device, or cut off the electrical equipment that will cause damage or develop into an accident if it continues to operate. At this time, it is generally not required to protect the rapid action, but to stipulate a certain delay according to the degree of harm to the power system and its components, so as to avoid the misoperation caused by unnecessary action and interference caused by short-term operation fluctuations.

3. The relay protection device can also be integrated with other automation devices in the power system, and when conditions permit, predetermined measures are taken to shorten the time of the accident power outage and restore the power supply as soon as possible, so as to improve the reliability of the power system operation.

Relay protection device:

When the power components in the power system (such as generators, lines, etc.) or the power system itself fail and endanger the safe operation of the power system, it can send a warning signal to the operation duty personnel in time, or directly send a trip command to the controlled circuit breaker to terminate the development of these automatic measures and equipment. The complete set of equipment that realizes this kind of automation measure is generally referred to as relay protection device.

Relay protection device composition:

The relay protection device consists of a measurement part, a logic part and an execution part.

Purpose:1The measurement part is to determine whether the protection should be activated or not.

2.The logic part is based on the size, nature, and logical state of the output of the measurement part, the order of occurrence or their combination, so that the protection device works according to a certain logical relationship, and finally determines whether it should trip or send a signal, and transmits the relevant commands to the actuator.

3.The execution part is based on the signals transmitted by the logic elements and finally completes the task of the protection device.

Relay protection. Composition of the device Generally speaking, the whole set of relay protection device is composed of three parts: measurement and comparison elements, logic judgment links and execution output elements.

When the power system.

When the power components (such as generators, lines, etc.) or the power system itself fail and endanger the safe operation of the power system, it can send a warning signal to the operation duty personnel in time, or directly issue a trip command to the controlled circuit breaker to finally dissipate the development of these events. The complete set of equipment to realize this kind of automation measures is generally referred to as relay protection device.

Relay protection device is an electrical device used to protect various equipment and lines in the power system, by monitoring the parameters of the power system, such as current, voltage, frequency, phase sequence, etc., to detect the abnormal situation of the system, the town is timely for signal processing and judgment, send out protection signals, control circuit breakers or other switching devices, in order to avoid the power system due to failure caused by equipment damage or even system collapse.

The relay is the core component of the relay protection device, which can judge whether the power system is in a fault state according to the set relay characteristics. Relay characteristics refer to the response characteristics of the relay, that is, the response law of the output signal under certain input signal conditions. Relays usually have many different characteristic curves, such as overcurrent protection, trip time, reclosing time, etc.

These characteristic curves can be configured and selected according to the different requirements of the power system to achieve different protection functions for the power system.