Today, single phase AC solid state relays have found wide application in industry. These devices are small in size and highly reliable. Solid State Relays (SSRs) are easy to connect, and even a novice electrician can handle the job. The only factor holding back the widespread use of these devices in everyday life is the higher cost in comparison with classical electromechanical devices.
Content
- Principle of operation
- Applications and benefits
- Main types
- Connection features
Principle of operation
A solid state relay is designed to control electrical circuits. Unlike classic relays, they do not have moving contacts, and switching occurs using semiconductor devices. Most of the SSR models have a similar circuitry, and the changes made by the manufacturers practically do not affect the principle of their operation.
The device structure contains:
- Entrance.
- Optical isolation.
- Trigger chains.
- Protection and switching circuits.
The role of the input is performed by a primary electrical circuit containing a series-connected resistance on a permanent insulator. The input circuit receives the signal and transmits commands to the switching circuit.
Optical isolation required to isolate the input and output circuits. It is on this structural element that the type of SSR and the principle of operation of the device depend.The task of the trigger circuit is to process the input signal and then switch the output. It can be part of the optical isolation or is a separate structural element.
To supply the supply voltage to the load, a switching circuit is present in the device. It includes semiconductor devices - triac, transistor and diode.
The principle of operation of a solid state relay is to control the contacts that transmit voltage to the relay. An activator is required to activate the contacts. If the device is intended to operate in a three-phase circuit, then its role is played by a thyristor or triac. A DC solid state relay uses a transistor as an activator.
Applications and benefits
Compared to classic relays, SSRs have many advantages. If not the relatively high cost of these devices, they would be much more widely used in everyday life. Among their main advantages are:
- Low power consumption.
- They are characterized by high performance.
- Lack of noise during operation.
- Once connected to the circuit, SSRs do not generate electromagnetic interference.
- Long service life.
These devices are widely used in industry. They are used to control electric motors, control lighting levels, etc.
Main types
These devices are usually classified according to several indicators. First of all, we are talking about the type of control voltage - DC and AC. DC devices are designed to operate in electrical circuits with a voltage of 3-32 V. They are highly reliable, are equipped with LED indication, and the operating temperature range is from -30 to 60 degrees. There are also manual devices that can be adjusted to the desired type of operation.
In accordance with the type of load, SSRs are single-phase and three-phase. Devices designed for three-phase circuits are capable of monitoring current in the range of 10-120 A at once on all phases. Among these devices, a special place is occupied by reversing relays, which are distinguished by contactless switching. They are often used in combination with special devices to provide reliable protection against false alarms.
The solid-state single-phase relay allows switching the electric current when it crosses the zero mark, and the operating current range is 10-500 A.
Connection features
Almost every home craftsman can handle this job. For the device to start functioning, it is enough to apply the supply voltage to the input terminals, observing the polarity. As an example, consider connecting a solid state relay to a lighting system:
- At the point where the SSR is mounted, you need to make a break in the phase conductor.
- The device is connected in a gap with terminals for commutation.
- The supply voltage is applied to the control contacts in accordance with the polarity.
Please note that the control circuit is connected via the start button. A short-time supply of voltage is enough to open the semiconductor element of the structure and then close the circuit. Most often, solid state relays are mounted on a DIN rail.
When choosing a device, it is necessary to be guided by the technical characteristics of the power circuit, as well as the operating conditions of the relay. Connecting the SSR to the circuit should not cause major problems.
