Tower crane design - DBE, Drawings

4.2 Maintenance of tower crane electrical equipment

Maintenance of electrical equipment is divided into daily, conduct-my crane driver before the start of operation, and periodic, carried out by the driver together with the electrician servicing the crane.

Maintenance of electric motors. During daily maintenance, the outer surface of the electric motor is cleaned from dust and dirt and checked whether there are no external damages, in particular, damage or breakage of cable entries, loosening of the bolt attachment.

During periodic maintenance, it is controlled whether the cover of the terminal box of the stator winding, the cover of the hatch of the bearing shield adjoins tightly, what is the condition of the contact rings.

During operation of the mechanism, the driver must listen to the operation of the electric motor, and in case of technological interruptions in the crane operation, check the engine heating for a touch two to three times per shift. Strong humming or knocking in the operating electric motor, as well as increased heating of its housing or bearing boards, indicate a failure of the electric motor.

During engine operation, as a result of abrasion of contact rings and brushes, fine metal dust accumulates, which settles on the insulation surface of the contact rings and the brush holder. It can lead to a short circuit. Therefore, during inspection, the contact rings and brush holders are cleaned with a dry clean rag. Dirt and fat on the surface of the contact rings are removed with a rag slightly wetted with gasoline. The surface of the contact rings must be clean and smooth. The carbon brushes shall have a shiny surface over the entire contact area with the contact rings. During rotation, the engine must operate silently and without sparking.

Traces of burning on contact rings are cleaned with glass paper No. 100-120, attached to a wooden block. Surface of block is cut in compliance with contact ring circumference. Its girth angle must be made at least 30 °. Contact rings are cleaned at idling of electric motor. During grinding, precautions are observed: they use dielectric gloves, work standing on a rubber mat or in dielectric pebbles. Grinding is carried out in several steps, periodically disconnecting the engine from the mains and wiping brushes and rings with dry rags. After grinding the rings, the electric motor is cleaned from copper sawdust and coal dust. It is not allowed to clean rings without a block. One of the reasons for sparking brushes is that the brush holder sticks in the hinges. By lifting the brush with your hand and lowering it to its place, they check whether there is a jamming. The lapping of the brushes and heavily worn brushes are replaced by the clocking rings of the electric motor: The newly installed brushes are pre-processed along the radius of the contact ring, and then finally lapped to the contact ring using glass paper No. 00. For this purpose paper is passed between brush and contact rings (rough side to brush) and pulled in one direction by pressing spring on brush. The paper is pressed tightly against the contact ring so as not to round the edges of the brush. In the reverse direction, the paper is moved when the brush is raised. Contact rings are lapped on the engine disconnected from the mains. Coal dust formed after lapping is removed by blowing the surface with compressed air. Only M-1 brushes are used for replacement.

Maintenance of crane electrical equipment. During daily maintenance performed before the start of the shift, the driver must ensure that there are no external damages to the contactors, relays, automata, controllers, command controllers, resistances and brake electromagnets. During operation, threaded connections of contactors, relays and magnetic, starters can be loosened, with unscrewed screws or nuts falling to the bottom of the control cabinet or protective panel. Therefore, during inspection, make sure that there are no lost fasteners at the bottom of the cabinet. Controllers and command controllers check the lightness of the handle or steering wheel and the clarity of their fixation in positions. The operator checks the serviceability of the limit switches, including the valve at idle, and the operation of the limit switch - load limiter, lifting the test load. Maintenance of brake electromagnets and electrohydraulic pushers is carried out by the driver simultaneously with inspection of the mechanical part of the brake. It is checked whether armature of electromagnet or rod of electrohydraulic pusher runs easily and if there are no damages on coils of electromagnets and terminals of motors of electrohydraulic pusher.

During periodic maintenance contacts of contactors, relays, controllers and magnetic starters are inspected, electrical equipment is cleaned from dust and dirt and brake electromagnets, time relays and maximum relays are adjusted if necessary. All threaded connections of electrical wiring contacts and attachments of the devices themselves are tightened. Contactors, relays and magnetic starters are checked whether they are easy to walk and whether the movable part is jammed. For this purpose, a movable part of a contactor, a starter or a relay is manually actuated by a quick movement until the armature is fully adjacent to the yoke and then the movable part is released, slowly and gradually withdrawing the arm. During jamming, the movable part does not return to its original position. Jamming must be eliminated by bending the corresponding parts of the apparatus or changing their position.

The coils of contactors, starters and relays must not have a play and traces of armature touch: a loosely fixed coil experiences shocks when the device is turned on, its insulation is violated and the coil burns. Heavily buried contacts must be wiped with a dry clean rag. Metal ceramic contacts of contactors and circuit breakers, as well as silver contacts of starters, limit switches and relays should not be cleaned even when their surface becomes uneven, with small metal strains. The oxide film on their surface has very low resistance (almost the same as the metal itself), so the desire to grind the con-tacts to shine leads to their premature wear.

Clean, contact surfaces should be cleaned only when they are significantly burnt or melted. For cleaning, filers with small notches are used. Silver contacts are recommended to be cleaned with velvet filler or suede. It is strictly forbidden to clean the contacts with sandpaper or glass paper, since at the same time intrusions of non-conductive particles remain in the contact surface, the resistance of the contacts increases sharply and they quickly fail.

The command controllers (Figure 4.1) check the solution and failure of the test cycles. When the contact solution is reduced in comparison with Figure 4.1, and, usually caused by loosening of the fastening tightness of the cam element, the position of the cam element should be adjusted and the threaded attachment to the rack should be tightened. The value of the dip determines the limit wear of the contacts. If the dip is less than that shown in Figure 4.1, b, replace the contact bridge or fixed contacts or replace the cam element completely.

When checking the selenium rectifier with a soft cloth, the washers of selenium elements are cleaned from dust and it is made sure that there are no visible external damages, in particular, the connecting bridges are not broken and there are no traces of the washers breaking. Dust settling on the washers of selenium elements worsens their cooling, as a result of which the elements overheat and can fail. During one of the periodic services, but at least once every two months, the heating of the selenium rectifier is checked using a thermometer. The temperature of the rectifier in steady state operation shall not exceed 75 ° С.

During inspection of the ballast rheostats, the attachment of contacts is tightened, it is ensured that the elements are not broken and do not touch the steel structure of the crane.

The wiring at the point of approach to the resistors shall be arranged in such a way that there is no possibility of wire insulation overheating.

All maintenance of electrical equipment during daily and periodic maintenance is carried out in compliance with safety measures. When checking, cleaning and regulating electrical equipment, the crane electrical equipment must be disconnected from the external network.

Maintenance of wiring. During daily maintenance, the driver inspects the external insulation of the wiring, especially at the places where it approaches the electric motors and electrical equipment, checks the condition of the supply cable and its attachment to the crane structure.

During periodic maintenance, density and reliability of contact of wires on terminal sets are controlled and terminal sets are cleaned from dust and dirt. As a rule; wires must have tips, only single-wire wires with a cross section of up to 10 mm2 and multi-wire wires with a cross section of up to 2.5 mm2 can be connected without tips, but necessarily with twisting and cutting of the ends. The wire is fixed on the apparatus or terminal set using a screw, a flat and necessarily spring washer.

During periodic inspection, insulation resistance of wiring and electrical equipment is measured. For this purpose, a megohmmeter is used. Previously, the crane is disconnected from the external network and measures are taken to prevent a person from falling under the voltage created by the meg-meter inductor. Insulation resistance of a separate wire conductor must be at least 1000 ohms per 1 V of operating voltage.