Drives augment hydropower scheme

In the remote southwestern province of Yunnan, 2000km from Beijing and Shanghai, Sinohydro is constructing a vitally important piece of China?s renewable energy programme. The Xiang Jia Ba dam and hydropower scheme is China?s third largest hydropower system and a major step forward in China?s sustainable energy and water resource management strategies.

To build this dam, Sinohydro chose Baldor?s Controlled Start Transmission (CST) as the best drives solution, installing 13 CST drives and two Controlled Stop Braking (CSB) units to deliver some 60 million tonnes of gravel over 31km on five conveyor flights, laid through 29km of tunnels.

When completed in 2015, the 30.7 billion kW per hour per year of electricity that will be generated by the Xiang Jia Ba hydro scheme will replace the equivalent of burning 14 million tonnes of coal per year. The upshot of this renewable energy is also a significant reduction in emissions, equivalent to 25 million tonnes per year of carbon dioxide, 170,000 tonnes per year of nitrogen dioxide and 300,000 tonnes per year of sulfur dioxide.

Xiang Jia Ba will come on-line in 2012 and the power will be transported by high tension power lines to China?s central and eastern provinces. In addition to providing power, the 900 million-plus cubic metre long reservoir on the Jin Sha Jiang River will help cities like Chongqing, Zhouzhou, Yibin, Shuifu and others to achieve national flood prevention standards. It will also provide water to irrigate approximately 2.5 million square metres of land in 14 downstream regions.

Sinohydro Corporation is the largest, most successful Chinese construction company in the field of hydraulic and hydropower engineering, and is managed internationally as a state-owned enterprise. It is ranked as one of the world?s top technology companies in terms of hydropower construction experience, having completed 70 per cent of all hydro projects in China, including the world-renowned Three Gorges Project. China?s total installed hydropower generation capacity has reached 100,000 megawatts.

The scale, rugged topography and sheer isolation of the Sinohydro Xiang Jia Ba project created numerous technological and logistical hurdles. Designing, developing, manufacturing, installing and supporting a reliable conveyor system on this scale presented an enormous challenge. Baldor and its proven CST technology were entrusted with this task.

Baldor?s CST patented two-in-one drive combines a planetary gear reducer and a hydro-viscous clutch engineered to deliver and synchronise power from multiple drives, and to control acceleration of high inertia loads such as long-haul conveyors.
There are over 2000 CST units operating around the world, 1452 of which are in China. A further 250 will be installed in China in 2010. CSTs have a proven track record on conveyors of up to 30km in length, in coal, gold, iron ore, copper and gravel mining operations, cement and power generation, as well as bulk-handling port facilities.

Planning for the Xiang Jia Ba project began in 2000, and presented a series of unique challenges. How to deliver gravel through such rugged mountains with very few opportunities to locate head/tail drives at surface locations meant that a five-stage conveyor network was the preferred design. Sinohydro began construction of the infrastructure in 2005 and finished boring the nine tunnels in two and a half years. After signing the contract, Baldor set about preparing designs, including extensive static and dynamic analysis of all five conveyors to ensure safe operation under all foreseeable start up, shutdown, part-load conditions and power-out situations.

During the design stage, a number of issues were detected, and Baldor met with other OEM suppliers and Sinohydro to ensure that these issues were overcome, including the downhill grade of conveyor #1. Baldor is well experienced in this area, and by integrating two CSB clutch only units and one CST drive in the design, it was able to ensure excellent control over the downhill acceleration profile.

Also during the dynamic analysis stage, a possible issue was discovered between conveyors #2, #3 and #4. The concern was that flywheels might be required on the head drives to balance the belt drift timing. Baldor?s analysis determined that a more economical solution was to use very high inertia motor rotors on conveyors #3 and #4 to allow more drift time for these conveyor belts, otherwise they would spill excess material if the preceding belt stopped too rapidly during a power outage scenario.

The design was completed in 12 months, and during this time Baldor also provided extensive data to other OEM suppliers so that equipment such as winches and take-ups could be manufactured and installed to the required specifications.

Although China has an extensive and modern network of highways and toll roads, it is inevitable that to get equipment into these mountainous regions there are many small, steep and winding roads to negotiate. There are also issues of isolation and language, and it is here where suppliers without suitable experience in China find the going very tough. Baldor, however, had developed an extensive network of regional sales and service centres, and had trained a highly capable team of Chinese born staff. This ensured that there was excellent communication with the client?s engineers and technicians, and a good knowledge of regional logistical issues.

In the case of the Xiang Jia Ba installation, most of the drives were assembled on skids and tested at Baldor?s Shanghai factory, then transported by road to the various installation locations. However, one of the most challenging installation issues occurred when dynamic analysis showed that a tripper drive should be located near midway on conveyor #3, in a totally inaccessible valley. This would provide substantial cost savings for the client by reducing costs for both the structure and belting. To overcome the lack of access to the valley, Baldor engineers decided the best solution was to split the frame into two pieces so that it could be delivered through the tunnel. Baldor engineers then reassembled the unit on-site.

The final and most critical step in a successful installation is tuning and commissioning, an area in which Baldor has enormous expertise. One of the biggest advantages of the CST technology is the inherent speed and accuracy at which the hydro-viscous clutch is able to absorb and smooth shock loads during start-up, and during continuous operation. Shock loads and surges are always present in a conveyor system and are a major cause of conveyor failure. By incorporating the hydro-viscous clutch on the output side instead of the input side of the gear reduction, the CST unit delivers superior reliability and tuning features compared to VFD and fluid drives.

Some of the advantages with this configuration include:
? Faster and more accurate reaction to conveyor load changes as the CST clutch is directly coupled to the drive pulley.
? Low-speed clutch for less wear and higher reliability.
? Shock absorption after torque multiplication protects gear train and motor.
? Shock absorption via slippage reduces load on all components.
? Load monitoring and tuning is delivered at the clutch unit and shocks are not amplified through the gearbox to the motor.
? Motors are started under no load, reducing electrical delivery problems and mechanical stress on all components.

Control of such a complex network of drives is also critical to the successful implementation of the design. Baldor has unparalleled experience in the deployment and integration of appropriate control strategies into a client?s network. Due to the extent of the Xiang Jia Ba project, multiple layers of control were used. As depicted in the Xiang Jia Ba overview diagram (Figure 1), a Programmable Logic Controller (PLC) is installed to command each cluster of CST/CSB drives. These units can be based on either AB-RSLogix, AB-Contrologix or Siemens? platforms and can synchronise up to four drives. For this project, a mixture of DH+ data highway, ControlNet and Ethernet communications was implemented. The PLCs are used to provide an appropriate S-curve start-up ramp via managed hydraulic pressure to the clutch pack of each drive. Feedback information is processed continuously and programmed adjustments are made automatically on the run. Baldor also installed load-cell data measurement units at three locations to provide accurate belt tension information.

Baldor?s worldwide experience in installing and commissioning of conveyor systems over the past 20 years has provided a huge database of information on all scenarios. Combined with the detailed dynamic analysis for this project, it was a straightforward process to formulate an optimum starting sequence that would give good control under all load conditions, while limiting the maximum belt tension at the lowest level possible.

CST hydro-viscous clutch technology also makes it possible to:
? Reduce belt peak stress by up to 15 per cent.
? Reduce peak motor torque demand.
? Reduce potential belt slip.
? Reduce jerk and belt tensile stress wave impulse on all non-drive pulleys and structures.
? Reduce take-up travel.
? Improve load-sharing action and control of multiple pulley drives.
Baldor completed the commissioning of all five conveyor flights over a six-month period, and handed over to Sinohydro on 15 June, 2007.

Baldor continues to supply Sinohydro with technical support. On a recent visit to the installation, Baldor engineers met with project managers Gong Zhi Guo, vice director, and Wan Zhong Hua, vice manager of Sinohydro?s Eighth Division, China Water and Electricity Engineering Group. They discussed current operations and were very satisfied with the reliability and operation of the CSTs and the conveyor network. They explained that since production began, they had achieved their targets and at times had operated for periods of up to 18 days non-stop. The client was also appreciative of Baldor?s continued support, with regular visits from CST engineers. Baldor was also pleased to be able to arrange training in Shanghai for Sinohydro engineers so that they would be more confident in the future maintenance requirements of the drives.

Source: Baldor Australia Pty Limited

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