Phase sensitivity prevents sensitive equipment from being damaged by phase imbalances or reversals. These relays are oftentimes found protecting electrical equipment—such as motors, compressors and pumps—that need to operate within certain limits or risk being burned out completely.
Electrical power is delivered from the power generation facility in three phases. These phases are offset from one another by 120 degrees and this arrangement ensures that there is a consistent delivery of voltage. A change in the load on a circuit and events such as lightning strikes can interrupt this phase. In some cases, it can reverse the phase.
Phase sensitive relays react to these changes in phase. They can be set up so that a certain phase variance shuts down the circuit, protecting the equipment on the circuit from being destroyed. Phase sensitive relays are adjustable, in some cases, allowing for a wider variety of applications.