Static relay

The static relay's name implies that it has no moving parts. In 1960, the solid-state relay, sometimes known as the static relay, was introduced. This relay has a longer lifespan and responds more quickly than an electromechanical relay. These relays were created as semiconductor devices, such as capacitors, integrated circuits, transistors, and tiny microprocessors. Thus, nearly every function that was performed by an electromechanical relay is replaced by these kinds of relays.

Table of Contents

• What is a Static Relay?
• Static Relay Block Diagram
• Static Relay Working Principle
• Static Relay Types
• Advantages of Static Relay
• Limitations of Static Relay
• Conclusion

What is a Static Relay?

Static relays are electrically operated switches without any moving parts. The output of this kind of relay is easily obtained by means of stationary parts like electrical and magnetic circuits. Because electromechanical type relays require moving parts to carry out a switching function, they are compared to static relays. However, both relays use a switch that is either open or closed in response to an electrical input to control electrical circuits. These relays are primarily made to carry out comparable tasks utilizing electronic circuit control, just as an electromechanical relay does through the use of components or moving parts. The designs of digital logic circuits, analog solid-state circuits, and microprocessors are the primary determinants of a static relay.

Static Relay Block Diagram

The diagram of the static relay block is displayed below. The rectifier, amplifier, o/p unit, and relay measurement circuit are the primary static relay components in this block diagram.

Static Relay Block Diagram
Image used courtesy of elprocus

In this case, the relay's measuring circuit consists of comparators such as amplitude and phase, logic gates, and level detectors. The transmission line is merely linked to the potential transformer (PT) or current transformer (CT) in the block diagram above so that the transmission line supplies the input to the CT/PT. The rectifier, which converts the incoming AC signal into a DC signal, receives the output of the current transformer as an input. A relay's measurement device receives this DC signal. By sensing the input signal level using level detectors and assessing the signal's magnitude and phase using comparators to carry out logic gate operations, the measurement unit relay completes the most important task required inside the static relay system. Amplitude and phase comparators are the two types of comparators employed in this relay. While the phase comparator is used to compare the phase change of the input quantity, the amplitude comparator's primary purpose is to compare the size of the input signal. The amplifier receives the relay measuring unit o/p in order to boost the signal's magnitude and send it to the o/p device. In order to trip the circuit breaker (CB), this device will strengthen the trip coil.

Static Relay Working Principle

The static relay operates by first receiving the input voltage/current signal from the transmission line and sending it to the rectifier via the current transformer or potential transformer. The AC signal is then converted to DC by this rectifier and sent to the relay's measurement unit. After determining the input signal level, this measurement device compares the signal's magnitude and phase using its built-in comparator. To determine if the transmission is flawed or not, this comparator compares the i/p signal. The signal is then amplified by this amplifier and sent to the o/p device, where it activates the trip coil and trips the circuit breaker. At a glance:

1. Input Signal: The relay receives an electrical parameter (voltage, current, etc.).
2. Signal processing: The input is examined by the control circuit, which then compares it to predetermined thresholds.
3. Switching Decision: The control circuit transmits a signal to the output stage based on the comparison.
4. Output Action: The electronic switch controls the associated circuit by turning it on or off.

Static Relay Types

1. Electronic relays: One type of electronic switch that opens and closes circuit contacts without the need for mechanical action is an electronic relay.
2. Transductor relays: Transductor relays, also referred to as magnetic amplifier relays, are extremely straightforward mechanically. Although some of them may be somewhat complex electrically, this does not affect their dependability.
3. Transistor relays: The most popular type of static relay is a transistor relay, which overcomes the constraints imposed by electronic valves by acting as a triode.
4. Rectifier bridge relays: The introduction of semiconductor diodes has made rectifier bridge relays extremely well-known. This type of relay consists of two rectifier bridges, a polarized moving iron relay, and a moving coil.
5. Gauss effect relays: When certain metals and semiconductors are exposed to a magnetic field in relays, their resistance decreases at lower temperatures; this phenomenon is referred to as the Gauss effect relay. This effect is primarily dependent on the depth to breadth ratio and rises as this ratio grows.

Advantages of Static Relay

• The static relay uses relatively little power, which lessens the strain on the measurement devices and improves their accuracy.
• Static relays are shockproof, have a long lifespan, high precision, and dependability.
• The relay has a very short reset time.
• There are no issues with thermal storage.
• Their sensitivity is increased by the relay's amplification of the incoming signal.
• This relay has a lower risk of unintentional tripping.
• Because static relays have a high shock tolerance, they can function with ease in active places.

Limitations of Static Relay

• The static relay's components are extremely vulnerable to electrostatic discharges. Electrostatic discharges are abrupt electron fluxes between charged objects. In order to prevent electrostatic discharges from affecting the components, extra maintenance is given.
• The strong voltage spikes might easily affect the relay. Therefore, care should be made to prevent damage from voltage spikes.
• The electrical components are necessary for the relay to function.
• The relay is less capable of overloaded.
• When compared to electromagnetic relays, static relays are more expensive.
• The surrounding interference easily affects the relay's construction.

Conclusion

This concludes our discussion of a static relay's operation with applications. When an external voltage source is applied across the device's input terminals, these relays—also known as solid state switches—turn ON and OFF to control the load. These relays are semiconductor devices that carry out input and output switching functions using solid-state semiconductor electrical characteristics like MOSFET, transistors, and TRIAC. Though static relay throw some drawbacks, invention of it has brought s revolutionary advancement indeed.