Abstract: This paper focuses on the 250t bridge crane at the Kariba South Bank Hydropower Station in Zimbabwe. Through hardware and software design, a PROFIBUS-DP bus control system for the bridge crane was developed, which simplifies the entire electrical system, improves the reliability of system operation, and serves as a starting point for the future development of electrical technology for lifting machinery.
1 Introduction
The Kariba South Bank Hydropower Station in Zimbabwe requires the design and manufacture of two 250t/50t/10t single-trolley bridge cranes (hereinafter referred to as bridge cranes) for the installation and maintenance of the turbine generator stator and rotor, as well as other equipment within the powerhouse. The heaviest component to be lifted is the rotor with its lifting shaft. The rotor assembly (including the lifting shaft) weighs approximately 403.5t and requires synchronous lifting by two bridge cranes (see Figure 1 below). During lifting, the hoisting and trolley operation of both bridge cranes must be synchronized, making the system control quite complex. Therefore, by developing a PROFIBUS-DP bus control system for the bridge cranes, the wiring of the entire electrical system can be greatly simplified, thereby ensuring the accuracy of control and the stability of system operation.
Figure 1250t/50t/10t bridge crane lifting 3D diagram
2. Electrical System Design
The bridge crane's electrical system adopts the internationally advanced three-level control method of "HMI + PLC + frequency converter". The HMI (Human-Machine Interface) primarily facilitates operators and maintenance personnel in understanding the overall machine's operating status and quickly diagnosing equipment faults, providing a user-friendly interface and high-quality information processing capabilities. The PLC, as the core of the bridge crane's control system, collects various signals and uses its internal virtual contacts to implement the timing logic control of each mechanism, significantly reducing hardware failures and improving system reliability. The frequency converter ensures smooth starting and braking of all transmission mechanisms, reducing impact on the steel structure. The entire electrical system (see Figure 2 below) is divided into several parts: power supply system, hoisting system, trolley system, main trolley system, communication and lighting system, etc. The hoisting and trolley/main trolley systems use Yaskawa H1000 and A1000 frequency converters respectively, and communicate with the Siemens PLC via PROFIBUS-DP fieldbus.
Figure 2. Electrical system diagram of the bridge crane
2.1 Power Supply System
The bridge crane is powered by a safety sliding contact line, with a three-phase four-wire AC 380V, 50Hz power supply. The control power supply is provided by control transformer T2, supplying AC 220V. The trolley power supply uses a cable trolley. The main power supply is equipped with a main isolating knife switch QS100, which can cut off all power to the bridge crane, providing a clear disconnect point for safe maintenance. A circuit breaker QF100 is also provided for short-circuit protection. Under normal circumstances, QF100 does not operate; the power circuit is opened and closed by the main contactor KM10. QF100 includes a shunt trip coil, controlled by the emergency stop button on the operator's cab control panel, power control cabinet, and remote control. The shunt trip device is only used occasionally in emergency situations where the main contactor fails to disconnect the power circuit for some reason.
2.2 Lifting Mechanism
The hoisting mechanism consists of two sets of mechanisms: a main hoist and an auxiliary hoist. Each is driven by a YZPFM315M2-8C, 55kW and a YZPFM315S2-8C, 30kW variable frequency motor, respectively. The speed is regulated by Yaskawa H1000 frequency converters CIMR-HB4A0260 and CIMR-HB4A0150 with vector control technology, and closed-loop control is used.
Main hoisting speed:
When 80t < Q ≤ 250t, the flow rate is 0.1–1.0 m/min.
When Q≤80t, the flow rate is 0.1～3.5m/min
Auxiliary lifting speed:
When 15t < Q ≤ 50t, the flow rate is 0.3–3.0 m/min.
When Q≤15t, the speed is 0.3～10m/min
Both the main and auxiliary hoists are controlled by a master controller, with a stepless speed regulation mode. There are five speeds for each working condition, and the speed corresponding to each speed can be set arbitrarily in the PLC.
2.3 Trolley running mechanism
The trolley's running mechanism is driven by two YZPFE132M-4 7.5kW variable frequency motors, using Yaskawa A1000 frequency converter CIMR-AB4A0072 with vector control technology for transmission and closed-loop control.
Operating speed: 0.3～20m/min, controlled by a master controller, with stepless speed regulation in gears, five speeds in front and five speeds behind, and the speed corresponding to each gear can be set arbitrarily in the PLC.
2.4 Trolley traveling mechanism
The trolley traveling mechanism is driven by four YZPFE132M-4 7.5kW variable frequency motors, using Yaskawa A1000 frequency converter CIMR-AB4A0165 with vector control technology for transmission and closed-loop control.
Operating speed: 0.5～25m/min, controlled by a master controller, with stepless speed regulation in gears, five speeds on each side, and the speed corresponding to each gear can be arbitrarily set in the PLC.
2.5 Communication System
2.5.1 Hardware System Design
PROFIBUS is a fieldbus standard for industrial control systems developed by Siemens, primarily used for distributed process control. The PROFIBUS family includes PROFIBUS-DP, PROFIBUS-PA, and PROFIBUS-FMS. PROFIBUS-DP utilizes Layer 1 and Layer 2 of the interconnect network; this streamlined structure ensures high-speed data transmission, with a transmission rate of 9.6kbps to 12Mbps, making it particularly suitable for communication between PLCs and field I/O devices. Therefore, this bridge crane adopts the PROFIBUS-DP network control method, as shown in Figure 3. The entire PROFIBUS-DP communication system consists of one master station and seven slave stations. The master station is a Siemens S7-300 PLC (CPU-2DP) in the machine room, which has a built-in DP interface. It is connected to the main hoisting inverter, auxiliary hoisting inverter, trolley inverter, crane inverter, trolley position detection encoder, hoisting position detection encoder, and the driver's cab PLC via the PROFIBUS-DP bus. The CPU of the master station PLC is 6ES7315-2AH14-0AB0. The inverter is connected to the PROFIBUS-DP communication network through a built-in SI-P3 interface card. The encoder is a P+F product PVM58 with DP interface and protocol. The driver's cab PLC slave stations are connected to the DP bus through an ET200M communication module.
Figure 3. PROFIBUS-DP hardware system diagram of the bridge crane
2.5.2 Software Design
Since this bridge crane's PLC system uses a Siemens S7-300, the programming software STEP7 V5.5 was used. Before hardware configuration, the file named YASKOACF.GSD must be downloaded from the Yaskawa Corporation website and successfully installed in STEP7. Similarly, the GSD file for the P+F encoder PVM58 also needs to be installed. After installing the GSD file, in the hardware directory on the right, PROFIBUS-DP—AdditionalFieldDevices—Drives—SI-P3PROFIBUS-DPINTERFACECARD and PROFIBUS-DP—AdditionalFieldDevices—Encoders—PEPPERL+FUCHS—P+FEncoder, the Yaskawa inverter and P+F encoder are connected to the DP network. This completes the hardware configuration of the bridge crane's PROFIBUS-DP network, as shown in Figure 4 below.
Figure 4. Hardware configuration of the bridge crane's PROFIBUS-DP network
The Yaskawa SI-P3 DP communication card for frequency converters offers three commonly available input/output data lengths: Extendeddata1 (32 bytes), Extendeddata2 (12 bytes), and Basicdata (6 bytes). This programming uses the Basicdata method, transmitting the frequency converter's speed and current to the main PLC in the control room via the DP bus. The main PLC then transmits this data to the driver's cab PLC via the bus. The driver's cab touchscreen retrieves data from the PLC, enabling real-time reading of the operating data of each mechanism. Conversely, the driver's cab's operating commands are read from the main PLC via the bus, and then the main PLC sends the commands to each frequency converter. See Figure 5 below for details.
Figure 5. Speed setting of main hoisting inverter
3. Conclusion
After factory debugging, the system successfully realized data exchange of the bridge crane communication system, and all mechanisms operated stably (see Figure 6). It also well met the requirements for parallel lifting and hoisting, and all indicators met the requirements, which was well received by users.
Figure 6 Factory commissioning
