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What is the role and importance of relays in power systems?

Author: Tanssion Date: 2023-07-24 Hits: 0

Ⅰ. The importance of relays in power systems
Ⅱ. The role of relays in power systems
Ⅲ.Common relay types
Ⅳ. Application of relays in household appliances
Ⅴ. Relay socket
Ⅵ. Action characteristics and release characteristics of relays
Ⅶ. The difference between relays and solid state relays
Ⅷ. The role of relays in automatic control systems

Ⅰ. The importance of relays in power systems

1. Guarantee the safe operation of the power system: the function of the relay is to prevent abnormal conditions in the power system, such as short circuit, overload, ground fault, etc. of power equipment. Through timely fault detection and cutting off the fault circuit, the relay ensures that the power system operates within a safe range, prevents the expansion of accidents, and maintains the stability and reliability of the system.

What is the role and importance of relays in power systems

2. Protection of power equipment and systems: Relays are one of the main protection devices in power systems. It can detect faults in the power system in time, such as over-current, over-voltage, under-voltage, ground fault, etc. Once a fault is detected, the relay will act quickly to cut off the fault circuit or take corresponding protection measures to protect power equipment and systems from damage.

3. Improve the operating efficiency of the power system: the automatic control function of the relay can realize the precise control of power equipment, such as voltage regulation and load distribution, so as to optimize the operating efficiency of the power system and reduce energy loss and cost.

4. Improve the reliability of the power system: relays play a fast and accurate monitoring and protection role in the power system. Through the precise action of the relay, the fault can be removed in time, the damage to the power equipment can be prevented, and the power failure time can be reduced, thereby improving the reliability and availability of the power system.

5. Remote monitoring and control: Some modern relays are equipped with communication interfaces, which can realize remote monitoring and control. Through remote monitoring, operation and maintenance personnel can keep abreast of the status of the power system and make corresponding adjustments and processing. At the same time, the remote control function makes the operation of the power system more convenient and flexible.

Ⅱ. The role of relays in power systems

1. Differential protection: Relays are used for differential protection to detect faults in power equipment and lines by monitoring current differences. The differential relay can detect the current imbalance inside the equipment in time, so as to cut off the faulty equipment accurately.

2. Over-current protection: Relays are used to detect over-current conditions in power systems. When an overcurrent occurs in the system, the relay will act quickly to cut off the faulty part to prevent the fault from expanding and protect the safe operation of power equipment and lines.

3. Undervoltage protection: The relay is used to detect undervoltage conditions in the power system. When the system voltage drops to an abnormally low value, the relay will perform corresponding actions to prevent the equipment from operating under low voltage and avoid equipment damage.

4. Overvoltage protection: Relays are used to detect overvoltage conditions in power systems. Overvoltages can be caused by lightning strikes, transformer failures, etc. When the relay detects overvoltage, it will cut off the power supply or connect the protective equipment in time to protect the system equipment from damage.

5. Voltage regulation and control: Relays are used for voltage regulation and control, monitor the voltage level of the power system, and switch or adjust equipment such as transformers as needed to maintain a stable voltage supply.

6. Frequency protection: Relays are used to detect frequency anomalies in power systems. Frequency protection can prevent equipment failure caused by frequency deviation and ensure the stable operation of the power system.

7. Ground protection: Relays are used to detect ground faults in power systems. When a ground fault occurs, the relay will act quickly to isolate the faulty circuit from the power supply to avoid personal safety and equipment damage.

What is the role and importance of relays in power systems

Ⅲ.Common relay types

1. Signal relay

It is a relay specially used for low power and signal circuits. Different from power relays used to control high current and high voltage electrical equipment, by controlling small current or low voltage signals, it can control the on and off of large current or high voltage circuits. Signal relays are mainly used to control the transmission of low current and low voltage signals or control signals. The signal relay has the advantages of fast action, stable operation, long service life and small size. Widely used in power protection, automation, motion, remote control, measurement and communication devices.

The signal relay is generally composed of iron core, coil, armature, contact reed and so on. As long as a certain voltage is applied to both ends of the coil, a certain current will flow through the coil, thereby generating an electromagnetic effect, and the armature will overcome the pull force of the return spring to attract the iron core under the action of electromagnetic force, thereby driving the moving contact of the armature to pull in the static contact (normally open contact).

2. Safety relay

The safety relay is composed of several relays and circuits in order to complement each other's abnormal defects and achieve the complete function of the correct and low-malfunction relay. The lower the error and failure value, the higher the safety factor. Therefore, it is necessary to design a variety of safety relays to protect different levels of machinery. The main goal is to protect the mechanical operators exposed to different levels of danger.

Safety relays can monitor the status of various safety circuits such as emergency stops, safety door switches, light barrier sensors, etc. It periodically checks the status of these safety circuits to ensure they are within normal operating range. In order to improve safety, many safety relays adopt a dual-channel monitoring design, that is, simultaneously monitor two independent safety circuits to ensure that when one channel fails, the other channel can still effectively carry out safety control.

The outputs of safety relays are usually force-guided, which means that in any case, the output will forcefully cut off the power supply or perform other safety control actions without interference from external signals. The safety relay can identify faults in the safety circuit, such as disconnection, short circuit, etc. Once a fault is found, it will take corresponding safety measures, usually cutting off the power supply or stopping the operation of the equipment to protect the safety of personnel and equipment.

3. I/O relay module

A module for connecting input and output signals. It is usually used to connect external input signals (such as switches, sensor signals, etc.) and output signals (such as relay control signals) with computers, PLCs (programmable logic controllers) or other automated control systems.

The input terminal of the I/O relay module is used to receive external input signals. Input signals can come from various sensors, switches, buttons or other control devices. These input signals will be converted into digital signals by the module for logic operation and judgment by the control system.

The I/O relay module contains signal processing circuits for converting external input signals into digital signals, and converting the digital signals of the control system into signals suitable for controlling external devices.

The output terminal of the I/O relay module is used to control external equipment, usually a relay output. By controlling the output signal, the module can control the switching status of various devices such as actuators, motors, lights, and valves.

The I/O relay module has the characteristics of scalability, flexibility, and automatic control.

4. Power relay

It is a relay used in high power circuits. They are usually used to control electrical equipment with high current and high voltage, such as motors, solenoid valves, heaters, lights, transformers, etc. The main feature of the power relay is its high rated current and rated voltage.

The characteristics of power relays are: power relays have a wide range of rated voltages and can handle high-voltage loads, usually ranging from hundreds of volts to thousands of volts; power relays have good input and output electrical isolation to protect circuits and equipment; power relays have a large rated current and can handle high-power loads, usually ranging from tens of amperes to hundreds of amperes; power relays have good anti-interference ability against electromagnetic interference and surge interference to ensure stable work.

5. High frequency (RF) relays

High-frequency relays are used to switch high-frequency circuit relays, and high-frequency signal relays with a switching frequency below 100MHz are called high-frequency relays. The low-profile components made of ceramic base perfectly match the thermal expansion coefficient between the reed switch and the pins, and can reduce any thermal stress generated inside the package, and the switching life can reach billions of times.

For high-frequency relays, in addition to the small distributed capacitance of the contact system, the matching of the characteristic impedance must also be considered in the structure. The structural size should avoid or be much smaller than 1/4 wavelength of the working frequency to reduce signal reflection. The structural size here refers to the parts with distributed capacitance between the contact reeds and the size and assembly size of the parts connected to it.

6. Solid state relay

It is an optocoupler made by using a light-emitting device such as a light-emitting diode (LED) and a light-receiving device such as a phototransistor to trigger a silicon controlled rectifier (SCR) or a bidirectional thyristor (TRIAC). Therefore, it can accept low-voltage (DC or AC) signal input and drive high-voltage output. It has the effect of isolating input and output and controlling high-power output. The advantages are fast switching speed, high operating frequency, long service life, low noise and reliable operation. It is used in explosion-proof places, but it also has many disadvantages, such as: high resistance (heat) when closed, increasing electrical noise. Low resistance, reverse leakage current (typically in the µA range) when disconnected. It can be used to replace conventional electromagnetic relays and is widely used in digital program-controlled devices.

Solid state relays can be divided into AC type and DC type according to the type of load power supply. According to the switch type, it can be divided into normally open type and normally closed type. According to the isolation type, it can be divided into hybrid type, transformer isolation type and photoelectric isolation type, and the photoelectric isolation type is the most.

The characteristics of high-frequency (RF) relays are: high-frequency relays are suitable for high-frequency signal transmission, including applications such as wireless communication, radar, and radio frequency testing; high-frequency relays need to have low intermodulation distortion to prevent spurious signals during high-frequency signal transmission; In high-frequency applications, relays need to have high isolation to prevent interference between signals; high-frequency relays need to have high reliability in wireless communication and radio frequency applications to ensure long-term stable operation.

AC type relay: It is a relay used in AC circuits. Corresponding to the DC type relay, the AC type relay is specially designed for AC power system. AC type relays are suitable for industrial frequency AC power, usually operating at a frequency of 50Hz or 60Hz. AC relays are widely used in the control and protection of AC circuits, such as motor control, lighting control, heating control, communication equipment, power system protection, etc.

DC relay: It is a relay used in DC circuits. Corresponding to the AC type relay, the DC type relay is specially designed for DC power supply system. DC type relays are suitable for DC power systems and usually work at specific DC voltages, such as 12V, 24V, 48V, etc. : DC relays usually have good electrical isolation between input and output to protect circuits and equipment.

Normally open relay: It is a classification of relay contact state. In a normally open relay, when the relay coil is not energized, the contacts are closed, allowing current to flow. When the relay coil is energized by current, the contacts open, cutting off the current path. Normally open relays are often used in situations where a circuit needs to be broken under certain conditions, such as safety controls and emergency stops.

Normally closed relay: It is a classification of relay contact state. In a normally closed relay, when the relay coil is not energized, the contacts are closed, preventing the flow of current. When the relay coil is energized by current, the contacts open, allowing the passage of current. In some applications, when the relay loses the excitation current, the contacts will automatically close, which can keep the circuit disconnected, which is often used for power failure protection.

Hybrid relay: It combines the characteristics of normally open and normally closed relays, and its contacts include normally open contacts and normally closed contacts. When the relay coil receives excitation current, the state of the contacts will act according to the design configuration of the relay, some contacts may be closed, some contacts may be opened, or all contacts may switch states. Hybrid relays can be flexibly used in circuits and systems that require complex control, especially for those occasions that need to realize on and off, off and on and off functions at the same time.

Photoelectric isolation relay: It is a special type of relay. It uses photoelectric isolation technology to isolate the input signal from the output signal through an optical coupling device to achieve electrical isolation between input and output. The basic structure of the photoelectric isolation relay includes a photocoupler and an output relay. The photoelectric isolation relay has good electrical isolation performance, which can realize complete isolation of the input terminal and the output terminal, and effectively prevent the input signal from interfering with the output signal and the system. The photoelectric isolation relay has a high insulation withstand voltage capability between the input terminal and the output terminal, and can withstand a large insulation voltage.

Transformer-isolated relay: is a special type of relay that uses a transformer for electrical isolation between input and output. The basic structure of a transformer-isolated relay includes a control circuit on the input side and a relay section on the output side. The input signal is transmitted to the output side through the coupling of the transformer to realize the electrical isolation between the input and output. Transformer-isolated relays use transformers for electrical isolation between input and output, to achieve complete isolation of input signals and output signals, and effectively prevent input signals from interfering with output signals and the system.

Ⅳ. Application of relays in household appliances

1. Smart home: In the smart home system, relays are used to control various household appliances and equipment, such as smart sockets, smart switches, etc.

2. Air conditioner: In the air conditioner, relays are used to control the compressor, fan and refrigeration cycle to achieve temperature regulation and cooling or heating functions.

3. Lighting control: The lighting control system in the home uses relays to control the switch and brightness of the lights to realize intelligent lighting control.

4. Refrigerator: A relay is used in the refrigerator to control the compressor and defrost function to maintain the correct temperature and prevent frosting.

5. Audio equipment: Relays are used in audio equipment to control switches, volume and audio output.

6. Oven: Relays are used in the oven to control the heating element and temperature adjustment to achieve cooking and baking functions.

7. Water heater: A relay is used in the water heater to control the heating element to maintain the water temperature or to heat the water.

 Ⅴ. Relay socket

A relay socket is a socket-type device equipped with a relay, which allows the user to control the circuit by plugging and unplugging the relay.

The basic structure and working principle of the relay socket:

Circuit protection: Relay sockets usually have overload protection, short circuit protection, etc. to protect the socket and connected equipment.

Socket Housing: The housing of a relay socket is usually made of a heat-resistant and durable material to protect the internal circuitry and relay.

Relay: One or more relays are installed inside the socket. The relay is a switching device used to control the circuit, which can control the on-off of a large current through a small current.

Ⅵ. Action characteristics and release characteristics of relays

The action characteristics and release characteristics of the relay refer to the process of the relay acting when receiving the control signal and the process of returning to the original state after the control signal stops.

Action characteristics:

Action current: refers to the control current required by the relay during the action process. This is the lowest current value to activate the relay.

Action time: refers to the time required for the relay to completely close the contacts from receiving the control signal. Usually in ms.

Release characteristics:

Release current: refers to the current required by the relay during the release process. This is the highest current value that the relay will release.

Release time: refers to the time required for the relay to fully open from the stop of the control signal to the contact. Usually in ms.

Ⅶ. The difference between relays and solid state relays

1. Durability and longevity

Relay: Due to the mechanical movement inside the relay, the contacts will wear when they are opened and closed. Therefore, the life of the relay is limited by the life of the contacts, usually hundreds of thousands to millions of times.

Solid state relay: Solid state relay has no mechanical movement, so there is no contact wear, and it has a long service life, usually more than millions of times.

2. Working principle:

Relays: Traditional relays use electromagnetic coils and mechanical contacts to control circuits. When the electromagnetic coil receives the control current, a magnetic field is generated to attract the contacts to close, thereby controlling the on-off of the high-power circuit.

Solid State Relays: Solid state relays implement circuit control through semiconductor devices such as optocouplers, transistors, or three-terminal devices. It has no mechanical contacts, and uses the switching characteristics of semiconductor devices to realize electrical isolation and signal transmission between input and output.

3. Electrical isolation

Relays: Relays generally have good electrical isolation between input and output, but isolation is affected by the contacts.

Solid state relay: Solid state relays usually have better electrical isolation performance, can provide higher isolation voltage, and better protect control circuits and controlled equipment.

4. Noise and vibration resistance

Relay: When the relay operates and releases, it will generate noise of mechanical contact opening and closing, and is more sensitive to vibration.

Solid State Relays: Solid state relays have no mechanical parts, no contact noise, and are less sensitive to vibration.

5. Response time

Relay: The action and release process of the relay takes a certain amount of time, usually between a few milliseconds and tens of milliseconds, and the response time is relatively long.

Solid State Relays: Solid state relays have no mechanical parts and respond quickly, usually between microseconds and milliseconds.

What is the role and importance of relays in power systems

Ⅷ. The role of relays in automatic control systems

1. Safety protection: In the automation control system, the relay can be used to realize the safety protection function. For example, by connecting sensors and relays, the monitoring and protection of abnormal conditions such as overload, overcurrent, and overvoltage of equipment or systems can be realized.

2. Circuit control: As an electronic switch device, the relay can control the on and off of various circuits. By controlling the action state of the relay, operations such as starting, stopping and switching of equipment, machines or systems can be realized.

3. Electrical isolation: The relay has good electrical isolation performance, can effectively isolate the control signal from the controlled equipment, and protect the control system and equipment from external electrical interference and failure.

4. Multi-channel control: The relay can realize multi-channel control through multiple input control signals. This allows one relay to control multiple circuits or devices, enabling parallel operation in automated control systems.

5. Signal conversion: The relay can convert low-power control signals into high-power control signals, thereby realizing the control of high-power loads. This signal conversion protects the control system and isolates it from high power loads, preventing overload and damage.


Frequently Asked Questions

1、What is the contact type of a relay?
The contact type of the relay refers to the connection status and opening and closing mode of the contacts during the working process of the relay. The contact types of relays are mainly divided into hybrid contacts, normally open contacts, and normally closed contacts.
2、What is the response time and life of the relay?
Relay response time and life depend on factors such as relay type, brand, manufacturing quality, and application environment. Different types of relays have different response times and life spans. Relay response times typically range from a few milliseconds to tens of milliseconds, depending on the type and build quality of the relay. Solid state relays typically have faster response times, usually between a few microseconds and a few milliseconds. The lifetime of the relay also varies by type. The contacts of traditional electromagnetic relays usually have a short lifespan, about hundreds of thousands to millions of opening and closing times. The solid-state relay has a longer life, usually more than millions of times.

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