Lifting machines modernization
One of the directions of our company’s activity is lifting machines electric equipment modernization. It is not a secret for anyone, that power operated anisochronous motor controller of gantry cranes, overhead gantry cranes and bridge cranes were installed in the last century and begun to malfunctioning due to long period of operation. It is not a serious problem to repair such equipment, but spare parts and time necessary for that – all constitutes time and financial expenditures, that, certainly, causes cautious attitude of industrial enterprises managers, managers of sea and river ports, scrap metal companies and merely crane owners.
Recently specialists developed a suitable solution permitting to exclude that problem known as modernization of electric equipment. Performing modernization of crane electric equipment you benefit in the following:
- In efficiency of costs for spare parts of crane electric equipment;
- In energy saving;
- In crane’s driving gear smoothness control;
- In essential prolongation of service life.
Service engineers of LLC «Gantry cranes Service» performed modernization of more than 20 gantry cranes, overhead gantry cranes and bridge cranes. Modernization was performed according to agreed with a Customer time-frames and still none of these systems is malfunctioning.
For more clear understanding we provide your attention detailed information concerning thyristor system of crane electric drive control.
SPECIFICATIONS OF THYRISTOR DRIVE
- Supply voltage ~380 V 50 Hz
- Permissible deviations of supply voltage +10% …-15%
- Power of an engine 1…150 kW
- Range of operating temperatures -40°С …+40°С
- Control limits of an engine RPM
(in percents from synchronous speed) 8…100%
- Changes in set velocity in case of load
changing from zero to maximum permissible £ 5 %
- Changes in set velocity in case of voltage
supply changing in permissible limits £ 5 %
The system is designed to control crane engines of different types. Depending on crane type, content of control system also changes. Structurally system is performed as a complex of four Rittal cabinets, protection class IP55 in accordance with standard EN6059/IEC529, electrical safety CLASS1 according to IEC536 and NFC20-30 and control panel.
- Drive cabinet (gantry) 800 х 1200 х 300 mm
- Control cabinet 1000 х 1200 х 300 mm
- Switchgear cabinet 800 х 1200 х 300 mm
- Crane operator cabinet 500 х 600 х 210 mm
Crane operator cabinet consists of two racks (600х350х200). Columns are used for command controllers and control buttons (from Telemecanique) installation, as well as for mode select switch and indicator unit installation.
Lead-in cabinet contains crane power electronics: main circuit breaker, transformers, protection circuit breakers, circuit breaker of lighting circuits of gantry and electronics of movement drives.
Control cabinet contains electronics boards and thyistor bridges units for all drives revolving portion of crane.
Switchgear cabinet contains contractors of drive stages.
Crane operator cabinet contains crane lighting switch lighting switches.
COMPOSITION OF ELECTRONIC PART OF THE SYSTEM (6 drives)
- Synchronization and control board (SCB) 2 pcs.
- Supply board (SS) 2 pcs.
- Engine controller (EC) 6 pcs.
- Data acquisition board (DAB) 3 pcs.
- Board of filters 6 pcs.
- Thyristor units 6 pcs.
- Engine speed sensor (SS) 4 pcs.
- Kit of connecting cables 6 pcs.
THE SYSTEM STRUCTURE
Block diagram of the system is presented at figure 1. The system is a net of specialized microcontrollers, connected by four-core shielded cable. These cables transmit information and provide power supply for microcontrollers.
Central net device is sermonizing and controlling board (SCB). It controls information flow in the net and provides protection against overloading through a secondary power supply, tripping faulty boards.
Five engine controllers (EC) are connected with SCB. EC1 and EC2 are controlling winchs operation, EC3 – crane movements, EC4 – crane rotations, EC5 - turret traversing. Besides, SCB is connected with two boards performing data acquisition (BDA). One of these boards is servicing crane operator panel, the other – current sensors and limit switches of drives.
SCB possesses additional electrically isolated channel, compatible with standard interface RS-232C. With the help of portable computer, connected with this channel, it is possible to configure the system during manufacturing and repair works, as well as to monitoring tests results at commissioning the system.
FUNCTIONAL DESCRIPTION OF SEPARATE ASSEMBLIES OF THE SYSTEM
Supply board provides the system with voltage supply 24 V and generates sync pulses consistent with supply phase transitions through zero.
Data acquisition board
Data acquisition board includes 8-channel analog-to-digital converter, 16 digital input lines and 8 digital output lines. The system uses two identical DAB.
First DAB services control panel. Its functions include reception of information concerning positions of command controller handles, interrogation of crane operation mode select switch, displaying information of crane operation at control panel.
Second DAB receipts and processes signals from current transformers and monitors status of the crane contacts sensors, notably: limit switches, thermal relays, monitor sensors of fan performing thyristors units cooling operability, winch engines, signals from overload limiter (OL) and lifting devices limiter (LDL) and etc.
Both boards are connected with SCB via shielded four-core cables.
Sync and control board
SCB is a central element of the system. It arranges data exchange between system’s nodes via serial interface and provides all the boards with power supply.
SCB continuously receives information, incoming from control panel (DAB-1), from current transformers and limit switches (DAB-2) and transfer required commands to engine controller.
SCB performs accounting and indication of motor hours of crane drives.
Engine controller (EC) performs managing of the engine Thyristor Bridge, of rotor resistors contactor, of mechanical brakes contactor (if any).
EC processes signals incoming from rpm sensor, transforms them into the data of direction and engine shaft rotation speed and length of winch cable.
Drive structure is presented at figure 2.
SCB transfers information concerning faulty state of any of the system’s units at indicator, as well as status of limit switches (information may be modified by Customer’s request). In test mode of control panel operation, data acquisition board transfers information concerning status of buttons and sensors to indicator, connected with DAB.
Electronic clamshell automat
In the system, in SCB board and in winch’s engine controller electronic clam-shell automat is implemented at software level, permitting in automatic mode to perform scooping and lifting of closed clamshell. Closure points and complete opening of clamshell are entered from control panel with the help of special knob. Manual operating mode of clamshell is also provided with possibility to drop and to pick-up cable of supporting winch.
BENEFITS OF THE PROPOSED SYSTEM
1. Reduction of hardware amount
Due to the fact, that mechanical characteristics of engine are determined not only by switching operations of rotor resistors, but also by change of stator voltage, amount of rotor resistors is significantly reduces. Thus, for engine with power less than 11 kW, rotor circuit may not switches at all, and for current restriction is sufficient to install small fixed resistor. Total amount of rotor resistors installed at crane is reduces in three times.
Due to possibility provided by electronic drive to adjust continuously slowdown of winch up to very small velocities in automatic mode, it becomes unnecessary to use asynchronous tensioner, step-down transformer and rectifier bridge (used by cranes of Condor type).
All above listed considerably simplifies monitoring of power circuits. Especially significant (in ten times) number of control circuits in reduced. Commonly there are several tens of high voltage cables are conducted from operator’s cabin into control cabinet.
In this system all of them are substituted by a single low voltage 3-core cable, connecting control panel with control cabinet.
Shielded two-core cable is employed for connecting rpm sensors. Connections in control circuits of the system are performed with the help of connectors and not at terminal blocks that significantly simplifies maintenance cables portion of the system
2. Reduction of power consumption
At slowdown using electronic drive it is possible to reduce considerably power loss in rotor resistors due to application of highly efficient dynamic braking with controlled sharpness of resonant curve with subsequent 20% reduction of total power consumption by.
Application of modified double-winch mode (described further) leads to additional saving of power consumption by winch drives equaling 10%.
3. Improvementof ergonomical characteristics
Due to continuous control of stator’s voltage it is possible to considerably improve acceleration and slowdown characteristics of the drive. Crane operator using handle of controller, may set any velocity – from minimum to synchronous (16 values in both sides). Deviation of the handle sets the required velocity, independently from load weight and other external impacts, e.g., lateral wind at turning, mains voltage fluctuations etc.
Shock loads at supporting structures were considerably reduced due to performance of acceleration and slowdown with continuous change of moment in all the modes of operation, and for drives with possible gear play (at turn, in motion) a special program of play selection excluding strikes at the beginning of movement is used, permitting to prolong service live of gears.
Considerable contribution in operation live extension of winch mechanisms (including engines) is provided by modification of double-winch mode of operation. Its peculiarity is that for handling of small loads only one winch is operated. Velocity of loads handling remains the same. In case of high velocities being selected both winches are started automatically with time interval 0.5 s, that considerable decreases value of total starting current.
Advanced indication and diagnostics permit to display from SCB and EC the values of selected drive velocity, current velocity of any engine rotation, developed thrust of engine, length and difference in lengths of winch cables etc.
Possibility of winch cables length monitoring permits to maintain automatically the distance between hoisting swivels during crane operation.
Electronic clamshell automat permits to automatize cycle of scooping-lifting. Clamshell weight is distributed between winches in the ratio 60% to 40%.
4. Reliability and maintainability of hardware
Reliability and maintainability of the system is of special importance for the regions with adverse climatic conditions and severe applications. For the reason that troubleshooting in contactor systems are carried out directly at the crane, crane repair at low ambient temperatures and high level of humidity is rather complicated. This is accentuated due to bulkiness of all the elements of contractor system which possess large quantity of terminal connections of non-regular character. For replacement of faulty assembles it is necessary to address warehouse, and at performing mounting to observe especial thoroughness due to non-regularity of incoming wires and variety of replacing assemblies. Lack of standard procedures of repair (repair is mainly carried out using trial-and-error method), with all the above mentioned, lead to crane repair procedure that require several hours.
Low ambient temperatures lead to loosening of contactors connections of power and control circuits as well. Degradation of plastic insulation of connecting wires and contractor coils is considerably increases. Thus, due to all the wires are under the mains voltage danger of short-circuit and fires increases and considerably decreases electric safety.
Contractors require periodical maintenance inspections of their contacts and movable mechanical parts. In case of violation of the required order of the contractors turn on there are appears a risk of the engines failure as well as the other expensive equipment.
All the listed shortcomings are absent in the proposed system. Low nomenclature of assemblies, used in the system, small number of connections, application of connectors instead of terminal connections, low supply voltage of the bards used (=24 V), simplicity of boards replacements, availability of multilevel integrated self-diagnostic, application of modern elementary base make repair simple and operational. The same is the reason for reduction in requirement of qualified servicing personnel.
Contractors used in the rotor circuit of winch engine are tune off at removed stator voltage, and actually does not wear due to absence of electric arc at contacts.
Engine currents are controlled.
Engine controller boards are interchangeable. Similarly SBC boards are interchangeable. These unification simplifiers repair and reduces required amount of spare parts.
Application of described control will significantly reduce operating costs, will considerably improve crane specifications and will increase service life of metallic structures.
Permit for production and application № РРС-19-00538
Certificate of conformity (PB 10-382-00) № РОСС RU.МБ02.Н00579
Certificate of conformity GOST № РОСС RU.АЮ40.В18380
Any advisory assistance on the given system you may obtain from our specialists, contacting with our organization by phone with numbers indicated at «Main page» of LLC «Gantry-crane Service».
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