A Comprehensive Guide to Solid State Relays: How They Work and Where They're Used

In the present day, electrical and electronic systems control of circuits is impossible without using relays. In the case of the Relay, the Solid State Relay (SSR) has gained much attention in the market because of its high power, high reliability, and long service life. So, what is a solid state relay, and how does it differ from electromagnetic relays that people are used to seeing? This article covers all the aspects of using and understanding solid state relays, including primary and advanced concepts such as their working principles, types, and uses. If you want to know about these complex technological gadgets and other information, you must continue reading below.

What is a Solid State Relay?

A solid-state relay is an electrical controller that regulates electric power supplied to a load without the convection of mechanical rotary contacts, as is the case with electromagnetic relays. Compared to mechanical Relays, solid state relays use semiconductor devices like transistors, thyristors, or triacs to control current switching.

Compared with mechanical relays, solid-state relays possess significant advantages, such as short operating time, low noise, and service life. Also, they are less prone to shock and vibration and, therefore, can be used in harsh conditions.

How do Solid State Relays Work?

Here's a simple breakdown of the solid state relay working principle:

• Input Circuit: In simple terms, when a signal from outside is introduced at the input terminals of the SSR, it activates the internal circuits. This signal could be from a Programmable Logic Controller, microcontroller or any other control source.
• Control Circuit: Inside the SSR is a control circuit that takes the input signal and turns on the switching components, which may be transistors or triacs.
• Output Circuit: To provide the required control signal to the load, the output circuit switches the load current in or out once the control circuit is activated. Since it does not contain moving parts, the transition process is swift and produces no noise.

Since the switching function of a relay is performed through semiconductors, the lifetime of the Relay is increased, the heat generated is dissipated well, and its response time is faster. However, it is essential to note that SSRs can be used to control AC and DC loads, subject to their configuration.

Read Also - Differential Relay: Working, Types, Advantage & Its Applications

Types of Solid-State Relays 

You can find diverse types of solid state relay in the market depending on the application needed. The main distinction between such types is determined by how they control AC or DC loads. Let's take a closer look at some of the most common types of solid state relays:

• AC Output Solid State Relay: Controlled for AC loads, this type of SSR incorporates electronic components such as triacs or thyristors to regulate the currents of the line.
• DC Output Solid State Relay: The desired SSRs for DC loads are typically explicitly built for direct current control, usually with MOSFETs or transistors.
• Three-Phase Solid State Relay: These SSRs are widely used for controlling power loads in industrial applications, and the loads may extend up to the three phases of AC supply before being used in the operation of large machines.
• Zero Crossing Solid State Relay: This type of SSR waits for the AC voltage to go to zero before switching; thus, it cuts out electrical noise and counter-emf spikes.

Use of Solid State Relay

Solid state relay is used widely in many industries due to its features and benefits. These relays are extensively used in all types of applications where high switching speeds and/or power frequency are required along with the long life of the Relay. Some typical application of solid state relay include:

• Industrial Automation: Due to the low current flowing through them, SSRs are suitable for regulating motor drives, heaters, and pumps in an automated environment. They are capable of controlling high currents and voltages while at the same time exercising excellent control over the functions of the equipment.
• HVAC Systems: In heating, ventilation, and air conditioning systems, the application of SSRs aids in controlling the compressor, fans, and other accessories with less noise and a faster response.
• Home Appliances: Motor control and heating elements in washing machines, ovens, refrigerators and other home appliances use SSRs for effective and noiseless operation.
• Lighting Control: Zero-crossing SSRs are used in lighting applications to minimise electromagnetic interference and guarantee a smooth operating device, especially in applications that contain dimming circuits.
• Medical Equipment: In the medical field, SSRs are applied in all the devices that require high levels of reliability and meagre amounts of noise, such as MRI machines and diagnostic equipment, among others, that support patients' lives.

Advantages of Solid State Relays

Solid state relays have many benefits that make them more suitable for use than mechanical relays in various applications. Some of the critical advantages of Solid State Relays include:

• Long Lifespan: Due to this, SSRs rely on electricity to operate, and they do not undergo mechanical stress, just like the standard mechanical relays; this means that SSRs can have a much longer lifespan than regular mechanical relays.
• High Switching Speed: Solid state relays can turn on and off at the rate of mS or ms and hence are well suited for their usage in applications that demand prompt actions.
• Quiet Operation: Unlike electromagnetic relays that produce audible clicking sounds when switching, SSRs operate silently, which is a significant advantage in noise-sensitive environments.
• Vibration and Shock Resistance: The lack of mechanical components makes SSRs resistant to vibrations and mechanical shocks, making them suitable for harsh environments.
• Low Power Consumption: Solid state relays require less power to operate, reducing overall energy consumption in systems where they are deployed.
• Arc-Free Switching: Traditional relays can create electrical arcs when switching, which can wear down the contacts over time. SSRs, however, switch without generating any arcs, making them safer and more reliable.

Read Also - A Guide to Choosing the Best Relay for Your Needs

In the End

In conclusion, solid state relays are critical in modern electrical systems due to their efficiency, reliability, and wide range of applications. Whether you need SSRs for industrial automation or home appliances, Schneider Electric eShop offers a variety of high-quality options to suit your requirements.

Frequently Asked Questions

Q1. What is a solid state relay, and how does it differ from mechanical relays?

Ans: A solid state relay (SSR) is an electronic switching device that controls electrical power without mechanical components. Unlike mechanical relays, SSRs use semiconductors such as transistors and triacs to switch the electrical load. The absence of moving parts in SSRs leads to longer life, faster switching, and quieter operation.

Q2. How do solid state relays work in controlling electrical loads?

Ans: Solid state relays use semiconductor devices to switch electrical loads on and off. When an input control signal is applied, the SSR activates its internal electronics, triggering the output circuit to control the load. This process is silent, fast, and free from mechanical wear and tear.

Q3. What are the advantages of using solid state relays in industrial applications?

Ans: Some key advantages of using solid state relays include their long lifespan, high switching speed, resistance to vibration and shock, quiet operation, and low power consumption. These features make SSRs ideal for industrial automation, HVAC systems, and many other applications.