Crane and Escalator 3-phase motor protection

The stable operation of three-phase motors is crucial for cranes and escalators. This article will focus on the 3 phase motor protection used in cranes and escalators.

Crane three-phase motor protection solution

Crane motor protection can be divided into two modes: comprehensive three-phase voltage monitoring and single-phase current monitoring.

Comprehensive three-phase voltage monitoring uses a three-phase voltage monitoring relay or a motor protection relay. This 3 phase motor overload protection relay not only monitors voltage but, more importantly, ensures the motor’s operating status. This three-phase motor protection solution effectively detects single-phase power loss due to a blown fuse or other fault, preventing motor stalls caused by undervoltage and overheating caused by voltage imbalance or overvoltage.

The electrical circuitry of the entire system, from left to right, is as follows: the three-phase power first connects to the fuse board, which provides short-circuit protection against abnormal current damage. The power then flows to the three-phase monitoring relay, which monitors the three-phase voltage in real time to ensure it remains within the set range. It also provides protection against phase loss, undervoltage, overvoltage, imbalance, and stall. It also supports phase sequence switching to meet the crane’s ascent and descent control requirements, and uses an adjustable delay to prevent nuisance tripping caused by transient voltage drops.

The 3 phase motor protection relay’s output is connected to a contactor, which controls the motor’s start and stop. The entire system is managed by a control panel, which provides logic and operation. Ultimately, it drives the three-phase motor on the right side, providing stable power for the gantry crane, ensuring safe and reliable operation.

Single-phase current monitoring uses a motor protection relay to monitor the current in one of the three phases. When the voltage is too high or too low, the motor’s single-phase current will be too high or too low. The relay provides protection by detecting this abnormality in the single-phase current.

In a system related to single-phase current monitoring, the three-phase power supply functions in two ways: one is converted to an appropriate voltage by a transformer, providing power or voltage signals to three-phase motor protection relays, etc.; the other uses a current transformer to detect the current, converting the high current into a small current proportionally before transmitting it to the relay. The relay monitors current and other parameters. If it detects an abnormality in the single-phase current, it sends a control signal to the contactor, which then switches the three-phase motor on and off.

Three-Phase Motor Protection Solution for Escalators

One of the most dangerous escalator faults is reverse motor operation due to a reversed phase sequence. To fundamentally eliminate this risk, a three-phase voltage monitoring relay or motor protection relay is essential. This relay monitors the phase sequence and takes action if an anomaly is detected. In addition to phase sequence protection, this three-phase motor protection relay can also simultaneously monitor overvoltage and undervoltage.

This wiring diagram illustrates the protection system for an escalator’s three-phase motor, fundamentally preventing dangerous motor failures such as reverse phase rotation. The three-phase power supply on the left first connects to the fuse board, which blows when excessive current flows, protecting subsequent circuits and equipment. The three-phase power supply then connects to the three-phase motor protection relay, a core protection component. This relay monitors the phase sequence, triggering protection if a phase sequence is reversed, and also simultaneously monitors overvoltage and undervoltage. The relay then connects to the contactor, which is controlled by the relay to open and close the circuit, thereby controlling the operation of the escalator’s three-phase motor.

In addition, the control panel, serving as the system’s “command center,” allows operation and monitoring of the system, ensuring safer and more controllable escalator operation. The actual escalator shown in the circle on the right corresponds to the wiring diagram on the left. This protection system prevents dangerous failures caused by phase sequence errors.

Conclusion

Regardless of the application, a professional motor protection solution should select the most appropriate monitoring method based on its unique operating environment and safety requirements to ensure the safety, reliability and efficiency of the equipment.