What Are The Main Electrical Protections For Cranes?

1. Protection of the motor

The motor shall have one or more of the following protection functions, and the specific method shall be determined according to the motor and its control method:

1.1 For transient or inverse-time action overcurrent protection, the instantaneous action current setting should be approximately 2.5 times the rated operating current of the motor or 1.25 times the maximum starting current.

1.2 Install a thermal sensor in the motor.

1.3 Thermal overload protection.

2. Line protection

All external circuits shall have the function of overcurrent protection caused by short-circuit or grounding, and the protection device shall instantaneously break the circuit when the circuit is short-circuited or grounded. For control or auxiliary circuits with small conductor cross-sections and long external circuits, when the expected ground current does not reach the instantaneous trip current value, a thermal trip function should be added to ensure that the conductor does not cause insulation burnout due to grounding.

3. Loss of phase and wrong phase protection

Make sure that the phase sequence is correct when starting the motor. When the lack of phase may cause danger, the lack of phase protection is required.

4. Zero protection

Each transmission mechanism of the crane must be equipped with zero protection. If the operation is stopped due to a failure or loss of voltage during operation, the mechanism shall not automatically move when the power supply is restored. The mechanism must be reset to the zero position before the mechanism can be restarted.

5. Loss of pressure protection

When the power supply of the crane is interrupted and the power supply is restored, all electrical equipment that involves safety or that is not suitable for automatic opening should be in a power-off state. Avoid the automatic operation of the electrical equipment after the power supply is restored.

6. Overspeed protection

An overspeed switch should be provided for the lifting mechanism that causes danger or potential safety hazards when the load is overspeed. When the lifting mechanism is driven by a planetary reducer, each (or each group) motor should be equipped with an overspeed switch. The setting value of the overspeed switch depends on the performance of the control system and the reduced rated speed, usually 1.25 to 1.4 times of the reduced rated speed.

7. Grounding protection

7.1 The metal structure of the crane body should be reliably connected to the ground slider of the power supply line. The wheels between the cart and the trolley, any other rollers, or the hinge used in the end beam connection, all cannot replace the necessary conductive connection. Instead, use special grounding wires to connect the grounding points on each part of the structure; The driver's cab and the grounding point of the crane body must also be connected with a grounding wire to ensure that all parts of the crane are reliably grounded.

7.2 All electrical equipment, conduits and trunkings of the crane should be reliably grounded. It is advisable to use a specially set grounding wire to ensure the reliable grounding of electrical equipment.

7.3 The conductance of the grounding wire and the grounding facility shall generally not be less than 1/2 of the largest phase conductance in the line, but the maximum cross-section of the grounding wire shall not be greater than 50mm2 copper wire.

7.4 It is strictly forbidden to use the grounding wire as the current-carrying zero line.

8. Lightning protection

For cranes installed in the field and at a higher position relative to the surrounding ground, consideration must be given to avoiding lightning strikes that may cause damage and injury to their high-mounted components and personnel, especially:

8.1 Structural parts that are vulnerable to lightning strikes (for example: support cables of booms);

8.2 Connect rolling bearings and wheels between large parts (for example: supporting slewing large bearings, running wheel bearings);

8.3 Personal safety (for this reason, the crane track should be reliably grounded).

9. Other protection

9.1 An interlocking door switch should be installed on the door of the crane from the outside of the crane or from the crane driver's cab. When the personnel get on and off the crane, the power supply of the operating mechanism should be disconnected.

9.2 The live exposed parts of the electrical control equipment on the crane that may be touched shall have protective measures to prevent electric shock to ensure personal safety.

9.3 When the protruding end of the crane may hinder air or water transportation, obstruction lights should be installed at its end.

9.4 Safety protection of lighting circuit

9.5 The crane should be equipped with a separate lighting transformer, one end of the 220V AC lighting power supply should be grounded. The main power switch of the lighting circuit should be equipped with a circuit breaker and a leakage protection switch.

9.6 One end of the secondary side of the 36V safety lighting transformer should be grounded.

10. Indicator

According to the needs of use, an indicator can be set to facilitate the driver to complete the lifting operation. Indicators mainly include lifting height indicator, boom inclination indicator, tower crane radius indicator, loose rope indicator and so on.