What Are Monitoring Relays and How Do They Work?

A monitoring relay is a type of electrical switch that is used to monitor and protect electrical systems. More specifically, it is a switch that is triggered when a certain preset condition is met. For this reason, they are commonly employed in a wide range of electrical circuits where the switch can protect the system by switching it off in case of an abnormal circumstance. Knowing the role of these useful devices can become very helpful when working with the aerospace, IT hardware, and industrial systems in which they are commonly found. Additionally, there are several types to be aware of, including those that monitor voltage, phase, current, frequency, temperature, and level.

What Are Monitoring Relays?

As the name suggests, monitoring relays are a type of electrical switch that provides protection to a system by monitoring various conditions. While many variations exist, a typical monitoring relay is essentially the combination of two main components: a sensing circuit and a trip element. The sensing circuit is involved with sensing the parameter that is being monitored, such as voltage or temperature. Conversely, the trip element is used to provide the switching action, reacting to an abnormal condition by altering or shutting down the circuit. In addition to these two parts, most monitoring relays have adjustable set points, meaning that the user can easily program the system to suit the needs of their application. The adjustable functions of a monitoring relay often include important features like time delay, manual/auto reset, remote reset, alarm contacts, and visual indicators.

Monitoring Relay Categories

Monitoring relays fall into different categories based on the parameter that they are designed to monitor. The most common types of monitoring relays are as follows:

Voltage Monitoring Relay: Voltage monitoring relays are designed to protect electrical systems against voltage surges which exceed the levels they are designed to handle. They are triggered when voltage exceeds or drops below the preset level, acting accordingly either by tripping or opening the circuit.

Phase Monitoring Relay: Phase monitoring relays are designed to monitor and protect against phase reversal, phase loss, and phase unbalance. They work by constantly checking the phase difference between two or more phases and tripping or opening the circuit when a phase anomaly is detected.

Current Monitoring Relay: These relays protect the equipment in an electrical system against overcurrent or undercurrent events. Just like the voltage monitoring type, current relays are triggered when the current exceeds or drops below a preset level. When this occurs, the relay will immediately trip and disconnect the equipment from the power supply.

Frequency Monitoring Relay: Designed to protect against frequency anomalies, this form of relay is used mainly in alternating current (AC) systems where monitoring power frequency is crucial. When an abnormal frequency is detected due to a sudden change in load or a system malfunction, the device will disconnect the circuit.

Temperature Monitoring Relay: A temperature monitoring relay is designed to protect against overheating. It accomplishes this by constantly monitoring the temperature of a system and that of the equipment it is meant to protect.

Level Monitoring Relay: As the name suggests, level monitoring relays are used to constantly monitor liquid levels in tanks, reservoirs, and other similar applications. A level monitoring relay may be used to prevent pumps from running dry and getting damaged or to prevent leaks.

Conclusion

Monitoring relays are key devices for protecting electrical systems against damage resulting from operating in abnormal conditions. By shorting or opening a circuit in the case of unexpected changes, monitoring relays safeguard a system from potentially dangerous or irreparable malfunction. As such, it is important to source high-quality monitoring relays that will stay effective across their service lifetime. For access to monitoring relays that have been sourced from accredited manufacturers, you can rely on Integrated Automation Parts for all your procurement needs. Hosting a vast inventory of electrical and other aerospace components from a widespread network of trusted manufacturers, we are well equipped to offer premium service as your sourcing partner. Get started today when you browse our online catalog of available parts or send an RFQ form with details about your operational needs. Our dedicated team of experts are available 24/7x365 to answer customer inquiries and requests, so you can expect a response within just 15 minutes of sending a completed RFQ form.