Three Phase Solid State Relays with ZVS

In electrical and electronic circuits, an electronic component often used to make or break a circuit is called as a switch. Electrical switches are typically used to operate, switch OFF or ON the power supply to the circuits or devices. In general, a switch is used to cut off the current flow in the circuit or deviate it from one conductor to another conductor. There various types of switches such as electronic switches, light switch, reversing switch, foot switch, knife switch, mercury switch, relays, etc.,. In this article, let us discuss about a special type of switch, relay.

What is a Relay?

The relay is a special type of switch that can be operated electrically. In general, a relay switch is used for controlling a circuit or device by a low power signal such that the control and controlled circuits are completely electrically isolated.

In most of the relays, an electromagnet is used to operate a switch mechanically and the other major type of relays is solid state relays. In fact, there are various types of relays such as solid state relays, electromagnetic relays, latching relays, reed relays, vacuum relays, mercury relays, and so on.

Solid State Relays

The solid state relays are termed as electronic switching devices, these solid state relays are turned on or off by applying a small external voltage supply across the control terminals. Even though function of solid state relays and electromechanical relays is same but the solid state relays don’t have any moving parts like electromechanical relays. The three phase solid state relays can be differentiated as single phase solid state relays and three phase solid state relays. The functioning of single solid state relays and three phase solid state relays is similar but the applications are different.

Three individual single phase solid-state relays are combined together in a single housing with common input functioning as three phase solid state relay. The applications of three phase solid state relays significantly vary from single phase solid state relays due to the characteristics of three phase power and demands of three phase loads, especially inductive loads. Here in this article, let us discuss about three phase solid state relay with ZVS.

Three Phase Solid State Relay with ZVS

There are various types of 3 phase solid state relays, let us discuss about three phase solid state relay with ZVS. In this project, the three phase units are incorporated and these single phase units are controlled individually using TRIAC and RC snubber circuit for ZVS (zero voltage switching). The block diagram of 3 phase solid state relays with zero voltage switching is shown in the below figure which consists of different types of blocks such as a power supply block, microcontroller, zero crossing, switches, Opto-isolator, Triacs, etc.,.

The power supply block of the relay circuit diagram shown above consists of various components such as transformer, bridge rectifier, voltage regulator. The power supply required for the project circuit is provided by this power supply block. The transformer is used to step down voltage from 230V AC to 12V AC. This stepped down AC voltage is fed to bridge rectifier which is used to rectify the voltage (convert AC voltage into DC voltage using four diodes connected in the form of bridge). The rectified output DC voltage is fed to voltage regulator IC 7805 which consists of three pins (input, output and ground). The IC 7805 voltage regulator is used to give a constant output voltage of 5V required for the project circuit.

The input required to the microcontroller is given from this power supply block, this microcontroller is one of the 8051 family. The microcontroller is programmed for generating output pulses after zero voltage pulse such that at the zero crossing of supply waveform the load gets switched on.

The zero-crossing feature of an Opto-isolator (TRIAC driver) ensures low noise generation and thus, sudden inrush of current can be avoided on inductive and resistive loads. There are two push buttons in the project used to randomly generate output pulses from the microcontroller such that not coincides with zero voltage supply voltage. We can use a CRO (Cathode Ray Oscilloscope) or a DSO (Digital Storage Oscilloscope) to see the supplied voltage waveform in order to verify the switching of the load at zero voltage point.

For heavy load switching used in industries we can use this project relay circuit by connecting two back to back SCRs (Silicon Controlled Rectifier). To achieve higher reliability, overload protection and short circuit protection can also be incorporated.

Do you know any special type of relays and their applications? Are you interested to develop electronics projects with real time application of relays? Then, please feel free to post your ideas, queries, comments and suggestions in the comments section below.