Types of Protective Relays: Protective relays are categorized by their mechanism (electromagnetic, static, mechanical) and function (time-based, current, voltage). Eng, IEEE Life Fellow IEEE/IAS/I&CPSD Protection & Coordination WG Chair Jacobs Canada, Calgary, AB rasheek. Static Relays: Use electronic components without moving parts. The rectangular devices are test connection blocks, used for testing and isolation of instrument transformer circuits.