Cranes – Design, Practice, and Maintenance phần 3 potx

Cranes – Design, Practice, and Maintenance50 Fig. 3.1.2 Fluid coupling fluid coupling is an excellent type of drive as it gives smooth accelera- tion of the complete belt system. The slipring motor The slipring motor is a drive which is now little used but it is still worth mentioning. The alternating current slipring motor is speed-controlled by resistances. These resistance-steps can be switched on or off by the controller. If torque is required: the more resistance, the lower the speed. ‘No resistance’ gives the speed curve of the normal squirrel cage motor. The brushes of the motor need regular maintenance; the resist- ances can burn out and rust. Therefore resistances made of stainless steel have preference. Fig. 3.1.3 Slipring motor: resistance controlled Drives; Calculating Motor Powers 51 The Ward–Leonard drive The Ward–Leonard (WL) drive can be considered as a ‘better DC dri- ve’. (The DC drive with resistance control is not further described.) The more complicated WL drive has great advantages compared to drives with slipring motors or DC motors with resistance control. The main motor, which is a squirrel cage motor, runs at a constant speed during the workshift on the crane. It drives a Ward–Leonard generator for each mechanism. The generator is directly coupled to the main motor and gives a regulated voltage and current to the respective motor which forms the drive-element of the crane mechanism. The speed control of this drive-element can be stepless. With a three-field generator like the Ward–Leonard–Kra ¨ mer the maximum torque can be fixed exactly at the desired level. This gives excellent drives for the hoisting mechanisms of grabbing cranes which dredge under water and for the drives of cutter-dredgers and similar devices. Cosphi compensation is not necessary. The Ward–Leonard– Fig. 3.1.4 Ward–Leonard–Kra ¨ mer (hoist motion) Cranes – Design, Practice, and Maintenance52 Kra ¨ mer drive has advantages when the current-supply delivery net is weak or when the main drive element is a diesel engine. A factor, which must be carefully monitored, is the average accelerating torque. Knowl- edge of how to design and manufacture these powerful Ward–Leonard drives has unfortunately been largely lost. Direct current full-thyristor systems In the last twenty years the direct current full-thyristor drive has become the successor to the resistance-controlled AC drives and DC drives and the Ward–Leonard drives. The stepless controlled full-thyristor direct current motor is available for all mechanisms and all capacities. It can be regarded as fool proof. Regular maintenance is needed to attend to the brushes, and collectors in the motors. Dust caused by wear and tear of the brushes has to be removed from time-to-time and the brushes have to be adjusted, checked, and replaced to prevent breakdown and loss of efficiency. These motors can be totally enclosed or drip-watertight, self-ventilated or ventilated by an external, continously running ventilator (force-venti- lated). Field weakening can occur, normally to a level of approximately 1500 to 2000 rev͞min depending on the power range and field compen- sation. The normal voltage is 400 V or 500 V. Cosphi compensation is needed to achieve a cosphi of approximately 0,9. Alternating current drives with frequency control To reduce maintenance on the motors as much as possible, the manu- facturers of electrical systems have developed and now use AC motors with frequency control. Since 1995 a good working system has been achieved. AC frequency control is also available for hoisting mechan- isms using large amounts of power. The motors are of a simple design. However these are special squirrel cage motors. The electrical control is somewhat more complicated than that of the full-thyristor systems, and forced ventilation is not normally required. Control of these motors is always stepless. Field weakening, up to 2000 to 2200 rev͞min – based on a four-pole motor, is possible by increasing the frequency. Torque–speed curves can be adjusted within a limited range. It is safe to assume that the research and development of the design of motors will continue and that further advances will be made. How- ever, this drive offers the most appropriate and suitable answer for the next ten years. Cosphi compensation may be necessary to achieve a cosphi level of approximately 0,9 depending on the type of the drive. Drives; Calculating Motor Powers 53 Fig. 3.1.5 DC full thyristor In low speed crane-travelling mechanisms, the option of using one drive for all the motors under the two sill-beams of the cranes is poss- ible. Because all the motors will receive the same frequency, synchroniz- ation between the motors is not absolutely necessary providing that the wheel loads and the wind loads on each sill-beam of the crane do not differ significantly. However, it is preferable to use one drive for each sill-beam and also to make ‘cross-over’ connections between the motors on the two sill-beams. This ensures exact synchronization. Warning Especially with AC frequency control, but often also with DC-Full-Thyristor Control the Electromagnetic Compat- ability (EMC) due to the Higher Harmonics plays an important role. To prevent disturbances by this Electro Magnetic Inter- ference (EMI) special double-shielded cables must be used. These screens or shields consist of a copper foil wrapping and optimized copper wire braiding. On both ends of the cable special EMC glands must be used. These must be well-earthed and connected to steel boxes. In the bigger motors insulated bearings should also be used. Cranes – Design, Practice, and Maintenance54 Fig. 3.1.6 AC frequency control: torque–speed diagram for hoisting/lowering Fig. 3.1.7 2B800 kW Holec AC frequency control motors in the hoisting winch of a grab-unloader Drives; Calculating Motor Powers 55 Hydraulic drives We now concentrate on the Ha ¨ gglunds hydraulic drive, which consists of a control system; an electric motor; an oil tank; a pump; and a hydraulic motor. The pump is driven by an electric motor, which runs with a fixed speed. The oil flow from the pump is controlled by either a Squashplate or a tilting cylinder block, the angle of which can be changed by a signal from the control system. The motor pumps the oil which flows into the motor cylinders and presses the pistons radially out towards the camring. The speed of the motor is stepless variable. This system has a low moment of inertia and a high starting torque (200 to 300 percent of a nominal rated torque). A brake system can also be provided on these drives. Fig. 3.1.8 Winches with Ha ¨ gglunds hydraulic drives Cranes – Design, Practice, and Maintenance56 3.2 Numbers of wire rope sheaves in the hoisting mechanisms of different reeving systems As already mentioned in Wire Rope Reeving Systems (Section 2.1), there are quite a number of reeving systems for hoisting mechanisms. The main types are considered in Figs 3.2.1(a) to 3.2.1(e). Fig. 3.2.1(a) Container cranes with machinery trolley. (Hoisting winch on the trolley.) Number of rope sheaves: minimum Fig. 3.2.1(b) Container cranes with rope trolley. (Hoisting winch fixed on the bridge.) Number of rope sheaves: depending on wire rope layout Drives; Calculating Motor Powers 57 Fig. 3.2.1(c) Grab unloader with main and auxiliary trolley. Number of rope sheaves: see Fig. 2.1.2 Fig. 3.2.1(d) Level luffing crane. Number of rope sheaves: see sketch Cranes – Design, Practice, and Maintenance58 Fig. 3.2.1(e) Stacking crane with ‘rope tower’. Number of sheaves: depends on rope system in trolley 3.3 Calculating the requisite power of the hoisting motors For calculating the requisite motor power the following items must be considered: (a) the resistance due to normal (nominal) hoisting; (b) the resistance due to acceleration of the rotating masses; (c) the resistance due to acceleration of the linear moving masses; (d) for the hoisting mechanism shown in Fig. 3.2.1(e) the influence of the angles α have to be taken into account, as the forces and the motor power are multiplied in this wire rope system with fG 1 cos α where α is then half of the biggest angle between the wire ropes when the load is in the highest position. Drives; Calculating Motor Powers 59 Example 1 The example, shown here, is related to a container crane with a rope trolley, as in Fig. 3.2.1(b). Main Characteristics Example Weight of load: spreader and container or grab and contents or hook and load Q kg QG66 000 kg kN QG660 kN Maximum speed of the load: û m͞min ûG60 m͞min m͞sec ûG1m͞sec Efficiency of all gearings and rope sheaves: η t η t G0,90 Motor speed: rev͞min nG783 rev͞min Inertia moment on motorshaft from motor(s); break sheave(s); and gearbox: J rot GJ m CJ b CJ gb kg m 2 J rot G24C16C6 G46 kg m 2 Acceleration time: sec t a G2 sec Acceleration of the mass Q: aG û t m͞sec 2 aG 1 2 G0,5 m͞sec 2 [...]... Transfer ΂ JG JG 30 û 2 Q · · π n η ΂π ΃ 30 · 2 · 7 83 1 66 000 0,9 G10,92 kgm2 ωG 2·π ·n 60 rad͞sec 66 Cranes – Design, Practice, and Maintenance Fig 3. 3.2 4000 ton floating crane ‘Asian Hercules’ Acceleration of linear moving masses N3 G 33 ,6 · 1 0,9 G37 ,33 kW N3 · 9550 M3 G Nm n 33 , 73 · 9550 M 3G 7 83 G455 Nm Transfer ωG 2 · π · 7 83 60 J·ω Nm ta 10,92 · 82 M3 G M3G G82 rad͞sec 2 G448 Nm 3. 4 Calculating... N2G 7 83 · 1885 9550 G154,5 kW 3 Resistance due to accelerating the linear masses: Q·û F3 G g · ta kN F3G 660 · 1 9,81 · 2 G 33, 6 kN N3 G F3 · û η kW N3G 33 ,6 · 1 0,9 kW G37 ,33 kW M3 G N3 · 9550 n Nm M3G 37 ,33 · 9550 7 83 G455 Nm Drives; Calculating Motor Powers 61 Torque (Nm) kiloWatts (kW) 1 Nominal hoisting M1 G8940 Nm N1 G 733 kW 2 Acceleration of the rotating masses M2 G1885 Nm N2 G154,5 kW 3 Acceleration... due to accelerating the linear masses: Q·û F3 G g · ta N3 G F3 · û M3 G η N3 · 9550 n kW Nm N1G M1G 847 · 9550 7 83 G10 33 0 Nm 7 83 · 2 · π 60 G81,95 rad͞sec 46 · 81,95 M2G 2 G1885 Nm kW N2G 7 83 · 1885 9550 G154,5 kW kN F3G 36 0 · 2 9,81 · 2 G36,7 kN 36 ,7 · 2 N3G 0,85 G86 ,35 kW kW Nm 36 0 · 2 0,85 G847 kW rad͞sec ω G Nm kiloWatts (kW) M3G 86 ,35 · 9550 7 83 G10 53 Nm Drives; Calculating Motor Powers 65 Torque... G3,05 kN N1 G F1 · û η kW N1G 3, 05 · 4 ,33 0,85 G15, 53 kW 2 Resistance due to nominal travelling of the auxiliary trolley: F2 GW3 · f kN F2 G 13 · 0,05 G0,65 kN N2 G F2 · 0,5 · û η kW N2G 0,65 · 0,5 · 4 ,33 0,85 G1,65 kW 78 Cranes – Design, Practice, and Maintenance Drive forces in the wire ropes (kN) Calculation: 3 Resistance due to the wind: F3 GFw kN F3 · û N3 G kW η Needed motor power (kW) F3 G6 ,3. .. kW 73 kW F1 G90 · 0,06 G5,4 kN N1G 5,4 · 3, 5 0,85 G22,2 kW (For full-supported hoist-wire ropes it can be necessary to calculate approximately twice as much for F1 and N1) 74 Cranes – Design, Practice, and Maintenance kN 2 Resistance due to the festoon system: kN F2 F2 · û N2 G kW η 3 Resistance due to wind: F3 GFw kN F3 · û N3 G kW η kW F2 G1,5 kN N2G 1,5 · 3, 5 0,85 G6,2 kW F3 G12 kN N3G 12 · 3, 5... Resistance due to nominal travelling: F1 GWt · f N1 G F1 · û η kN F1G 130 · 0,05 G6,5 kN kW 2 Resistance due to the festoon system: F2 kN F2 · û N2 G kW η kW N1G 6,5 · 2,5 0,9 G18,05 kW F2 G3 kN N 2G 3 · 2,5 0,9 G8 ,3 kW 70 Cranes – Design, Practice, and Maintenance kN kW 3 Resistance due to wind: kN F3GFw F3 · û N3G η F3 G18 kN kW N3 G 18 · 2,5 0,9 G50 kW 4 Resistance due to the accelerating of the rotating... F7G45 · 10 · 0,285 G128,25 kN kW N7G 128,25 · 4 ,33 0,85 G6 53, 3 kW (Fa Gm · aG 450 4 ,33 · G64,95 kN 10 3 sin α 1 G64,95͞450G0,14 43 α 1 G8 ,3 degrees Take α G2B8 ,3 degreesG16,6 degrees in order to calculate the swing of the grab Taking this great swing into account is necessary The motor must be able to develop a great torque!) 80 Cranes – Design, Practice, and Maintenance Addition: (bulk unloader) Drive... Fig 3. 4.2 Drives; Calculating Motor Powers Fig 3. 4 .3 The swinging grab of an unloader Fig 3. 4.4 Grab of a floating unloader 81 82 Cranes – Design, Practice, and Maintenance 3. 5 Hoisting the boom; calculating the power needed for the boom hoist motor Make a schematic diagram (as Fig 3. 5.1) and estimate the weight of the boom and it’s centre of gravity Fig 3. 5.1 For an example we use the following: – Centre... kiloWatts (kW) M1 G2707 Nm N1 G444 kW M2 G1885 Nm N2 G309 kW M3 G 138 Nm N3 G22,6 kW ΣMG 437 0 Nm ΣNG775,6 kW Addition: 1 Nominal hoisting 2 Acceleration of the rotating masses 3 Acceleration of the linear moving masses Total Take motors: NG 733 kW (2 · 36 6 kW) nG7 83 1566 rev͞min S3 – 60 percent rating (see Section 3. 7) fa G160 percent Fig 3. 3.1 DC FT torque–speed diagram For grabbing winches Follow the same calculation... G1 63, 9 rad͞sec 46 · 1 63, 9 M2G 4 Jrot · ω ta G1885 Nm N2 G n · M2 9550 kW N2G 1566 · 1885 9550 G309 kW 3 Resistance due to accelerating the linear masses: Q·û F3 G g · ta N3 G F3 · û ηt kN F 3G 200 · 2 9,81 · 4 G10,19 kN 10,19 · 2 N3G 0,9 kW G22,6 kW M3 G N3 · 9550 n Nm M3G 22,6 · 9550 1566 G 138 Nm Drives; Calculating Motor Powers 63 Torque (Nm) kiloWatts (kW) M1 G2707 Nm N1 G444 kW M2 G1885 Nm N2 G309 . N 2 G 7 83 · 1885 9550 G154,5 kW 3. Resistance due to accelerating the linear masses: F 3 G Q · û g · t a kN F 3 G 660 · 1 9,81 · 2 G 33, 6 kN N 3 G F 3 · û η kW N 3 G 33 ,6 · 1 0,9 kW G37 ,33 kW M 3 G N 3 ·. N 2 G 7 83 · 1885 9550 G154,5 kW 3. Resistance due to accelerating the linear masses: F 3 G Q · û g · t a kN F 3 G 36 0 · 2 9,81 · 2 G36,7 kN N 3 G F 3 · û η kW N 3 G 36 ,7 · 2 0,85 G86 ,35 kW M 3 G N 3 ·. Transfer F 3 G Q · û g · t a kN JG ΂ 30 π · û n ΃ 2 · Q η F 3 G 660 · 1 9,81 · 2 JG ΂ 30 π · 1 7 83 ΃ 2 · 66 000 0,9 G 33, 6 kN G10,92 kgm 2 N 3 G F 3 · û η kW ω G 2 · π · n 60 rad͞sec Cranes – Design, Practice,