Phase loss and phase sequence protection relays are devices used in industrial automation control systems for three-phase circuits.
This phase loss and sequence protection relay incorporates a sampling circuit for three phase lines internally. It is particularly suitable for applications such as overhead cranes or machine tools requiring fixed phase sequence during forward/reverse operation. This protective device provides overvoltage, undervoltage, and phase loss protection in three-phase AC circuits, as well as phase sequence protection for non-reversible drive equipment. It features reliable performance, broad applicability, and ease of use.
When connected to the power control circuit as shown in the diagram, this series of protectors immediately activates its protective function. During normal operation of a three-phase circuit, if any phase fuse opens or a phase break occurs in the low-voltage supply line, the internal relay-controlled by the integrated circuit chip's output signal-will rapidly actuate. This action controls the coil of the AC contactor, causing its contacts to open. This prevents the 3×380V main circuit power from reaching the controlled load motor, thereby achieving phase failure protection for the load through the operation of the main contacts of the AC contactor.
In fact, this phase loss and phase sequence protection relay is a device that integrates phase sequence protection and uses a relay to expand control over the coil of an AC contactor. It is factory-equipped with a status indicator light. Generally, a lit indicator light indicates normal operation. If the indicator light is not illuminated, it indicates a phase loss or a phase sequence problem.
When wiring phase loss protection, note that the three phase lines of standard AC power are designated as L1, L2, and L3. These must be connected to terminals 1, 2, and 3 of the phase loss and sequence relay, respectively. If the indicator light does not illuminate during initial wiring, simply swap any two phase lines. When wired correctly, the indicator light will remain steadily illuminated.
During normal operation, if a phase loss occurs or the line voltage of any phase falls below 85%, the protector shall reliably trip within < 2 seconds.
This phase sequence protector can also detect three-phase voltage imbalance. If the asymmetry between the voltage of any phase and the other two phases satisfies the following equation, the protector shall reliably trip within < 2 seconds.
This phase failure and phase sequence relay features four terminals: 5, 6, 7, and 8. Terminals 5 and 6 form a set of normally open contacts, while terminals 7 and 8 form a set of normally closed contacts. Typically, terminals 5 and 6 are wired to control the coil of an AC contactor, while terminals 7 and 8 are generally used to control a fault alarm horn, serving solely as an audible alert to notify personnel.
