8 Protection Measures For Metallurgical Cranes - Electrical Equipment

8 Protection Measures for Metallurgical Cranes - Electrical Equipment

 

In order to protect the safety of metallurgical bridge crane electrical equipment and staff, the metallurgical bridge crane electrical control system should be equipped with the following necessary electrical protection measures:

 

1. Main disconnect switch.
 

The maintenance and inspection of electrical equipment should generally be carried out under the condition of power failure. Therefore, there should be an isolating switch or other isolation measures between the electrical equipment and the power supply grid. When the isolating switch is in the disconnected state, there must be an effective disconnecting distance and a clearly visible disconnecting point, so that the maintenance personnel can visually confirm that the main power circuit has been disconnected.
 

In particular, it should be pointed out that when the air switch and iron shell switch are in the off position, there is no obvious break point, so they cannot be used as isolating switches.

 

2. Short circuit protection of the main power supply.
 

When the insulation of the electrical equipment on the metallurgical bridge crane is damaged, and when there is a shell collision or a phase-to-phase short circuit, the short-circuit protection device of the main power supply should act quickly to cut off the faulty power supply. The main power short-circuit protection device should be completed by a fuse circuit breaker.

 

 

3. Loss of voltage protection for the total power supply.
 

The loss of voltage protection of the main power supply means that the main power circuit can be automatically disconnected after the power supply is interrupted; when the power supply is restored, the main power circuit cannot be connected without manual operation.
 

Generally, the automatic reset button is connected to the main power contactor coil or the voltage-loss tripping coil circuit of the automatic circuit breaker to realize the loss-of-voltage protection of the main power supply.

 

4. Zero position protection.
 

The motor of the mechanism is controlled by a controller that cannot be automatically reset. In order to prevent that when the controller handle is not at the zero position, the power supply of the metallurgical bridge crane will be restored after losing voltage, causing the motor to start by mistake, and the crane is equipped with zero position protection.

 

Inspection method of zero position protection:
 

① The motor of the mechanism is directly controlled by the cam controller; turn off the main power supply, and pull one of the controller handles away from the zero position, and then turn on the main power supply. The main power supply should not be connected, and put all the controller handles at the zero position , the total power supply can be connected.
 

② If the motor of the mechanism is controlled by the master controller and contactor, turn off the main power supply, pull the master controller away from the zero position, and turn on the main power supply. When the main power supply is turned on, the motors of the mechanism cannot be started at the same time.

 

 

5. Motor overload protection.
 

If the rated power of the motor on the metallurgical bridge crane is greater than 1KW, overload protection should be set separately.

Overcurrent protection is the motor overload protection method commonly used in metallurgical bridge cranes at present.

 

6. Emergency power off switch.
 

The metallurgical bridge crane must be equipped with an emergency power-off switch that can quickly disconnect the main power supply in an emergency, and it should be located at a place where the driver can easily operate. Emergency power-off shall not be automatically reset.

 

There are two ways to judge whether the emergency power off switch is qualified:
 

① Check whether there is a main power contactor on the crane. The metallurgical bridge crane must be equipped with a main power contactor, and the power supply lines of all mechanisms must be led from the outlet end of the power contactor.

② Pull the emergency power-off switch, the main power contactor or the circuit breaker with a voltage loss tripping coil will act, cut off the main power supply of all institutions, and stop the operation of all institutions.
 

At the same time, meeting the above conditions can determine that the emergency power-off switch is qualified.

 

 

7. Safety interlock protection at the passage opening.
 

The metallurgical bridge crane should be equipped with an interlock switch of the passage opening, which is used to cut off the main power supply when the passage opening is opened. The trolley of the bridge crane is powered by a bare slide wire, which can prevent accidental electric shocks to the staff on the walking platform, and also prevent crushing and falling accidents caused by the sudden start of the mechanism.

 

8. Limit protection.
 

In order to prevent accidents in which the sling is lifted to the upper support structure due to negligence and mistakes in work, the steel wire rope is broken and the sling falls, a stopper for the limit position of the dagger lift should be installed.
 

There are two common types: hammer type and screw (or worm gear) type.
 

In addition, electrical protection includes stroke protection and grounding protection.