Three-phase motor voltage loss protection (phase failure protection) - Solutions - Huaqiang Electronic Network

LC03-3.3 SOP8 TVS Static Protection 3.3V

Single chip microcomputer STM32L151CCU6

When a phase failure occurs in a three-phase power supply, the system automatically cuts off the power to protect the motor from damage. This is known as phase failure protection. The working mechanism is illustrated in Figure 5-11. In a standard self-locking control circuit, an additional circuit is integrated to detect and respond to phase loss using zero-sequence voltage.

Figure 5-11: Schematic of the Voltage Loss Protection Circuit

When the power switch Q is turned on and the start button SBT is pressed, the contactor KM is energized and latches in place. This closes the main contacts, allowing the motor to operate normally. However, if one of the phases is lost, the three-phase winding in the motor becomes unbalanced. This imbalance generates a zero-sequence voltage that is reflected on the neutral line. This voltage triggers the relay KA to activate. As a result, the normally closed contact of the relay, which is connected in series with the contactor KM, opens. This action de-energizes the contactor, causing it to release and cutting off the motor’s power supply instantly.

It is important to note that to enhance the sensitivity of the protection system, different motors should be paired with relays that have appropriate operating voltages based on their specifications. This ensures reliable and accurate detection of phase failure under varying load conditions.