Delta offers energy-saving harbor crane solutions that are ideal for harbor transportation, especially the popular rubber tyred gantry crane (RTG crane) and bridge crane.
Transportation and communication play an important role in the economy, government policies, our livelihoods, and our daily lives. Delta Industrial Automation is focused on providing innovative automation solutions for transportation and communication to create a more energy-saving and safer environment. As one of the leading automation solution providers in the China market, Delta Industrial Automation is currently dedicated to providing the electro-mechanical facilities for harbors, ship manufacturers, and related fields.
Rubber Tyred Gantry (RTG) Crane
Background and Current System Issues: Traditionally, diesel generators have provided the power for RTG cranes. Diesel generators offer flexible operation, but have several major issues: low power conversion efficiency, high power consumption, high cost, as well as severe pollution, noise and vibration.
With the trend toward environmental protection, energy saving, and CO2 emission reduction and faced with high oil prices, many RTG crane users have started to look for more power efficient solutions or to modify their current RTG crane systems. They tend to replace diesel power with electric power to address the issues of current RTG crane systems; however, without an active front end, the new electrical RTG crane systems still have several problems:
Regenerative Power Wasted: During RTG crane operation heat is constantly generated and dissipated through brake modules. Besides energy wasted, users have to spend extra for the maintenance of brake modules.
Harmonic Pollution: Other equipment, such as inverters, in the RTG crane system may produce nonlinear loads, causing severe harmonic pollution. The system voltage is unstable and can affect normal operation.
Low Power Efficiency (Power Factor or PF): The RTG crane work load constantly changes which may cause low PF, and the user may be fined by the local electric company.
Delta's Solution: Delta Industrial Automation has introduced Delta's AFE2000 Series active front end to RTG crane systems, which has helped to improve the PF while collecting regenerative power. In the original system, power is provided to the DC BUS through a power factor correction rectifier. Delta's solution adds an AFE2000 Series to the original system. The AFE2000 Series conducts a self-diagnosis every time the system starts operation. If the diagnosis result is normal, it automatically transfers power to the DC BUS via the AFE2000 Series instead of the power factor correction rectifier.
During RTG crane system operation, the AFE2000 Series will detect and transform the heat generated into power, conduct reactive power compensation and then return the regenerated power to the grid system for reuse. This is how it replaces a brake resistor. When the AFE2000 needs troubleshooting or maintenance, it sends commands for the system to operate in the original way with power provided to the DC BUS through the power factor correction rectifier.
Delta's Solution greatly increases the energy efficiency and safety of RTG crane systems with the AFE2000 Series active front end, which features:
◆Power regeneration efficiency up to 95%
◆Total harmonic distortion (THD) ≦5% and PF up to 0.99 under full-load operation
◆Realizes AC motor drive four-quadrant operation – the motor generates power through motor inversion recovery or deceleration during braking, and the power regenerated goes from motor to AC motor drive with negative speed/positive torque.
◆Maintains a stable DC BUS under unstable power supply from the grid system
Benefits:
Delta's solution offers substantial benefits for customers:
Regenerative power usage for electricity consumption reduction:
The AFE2000 Series replaces traditional brakes to collect and transform the heat generated during RTG crane operation into regenerative power. The generated power is returned to the grid system for reuse, saving costs for energy and the brake resistor. (Refer to Figure 1)
Reduces harmonic pollution and improves PF:
Delta's energy-saving crane solution effectively reduces THD (≦5%) and improves PF (up to 0.99), reducing power consumption and electricity fees for users. (Refer to Figure 2)
Gantry Crane Background and Current System Issues: A gantry crane is composed of cranes and hoists, and the power supply for its AC motor drive usually comes from the DC BUS to increase the power usage efficiency. During operation the speed of the cranes and hoists changes rapidly and constantly, and so does the power usage. The unstable electricity may cause a large amount of harmonics, resulting in severe damage to the reactive compensation capacity. Once the reactive compensation capacity is damaged, it may fail to compensate current normally, and the power voltage would fluctuate severely as well. With unstable power and harmonic pollution, the gantry crane system may easily breakdown, threatening the power system and safety of the harbor.
Delta's Solution: Delta's gantry crane solution adopts Delta's SVG2000 Series static var generator to perform highly efficient power compensation and to decrease harmonics. The SVG2000 Series is able to effectively solve the power issues and increase the stability and safety of the gantry crane system.
The features of the SVG2000 Series include:
◆Compensates both leading and lagging reactive current and improves PF to 0.99
◆Adopts Delta's power supply module, power voltage range 200-480 V, 525-690 V
◆Modular design includes fan module, power module, drive module, control module and power resistor module
◆Adopts 7” TFT LCD 65536 full color HMI
◆Power capacity: 300kVAR/500kVAR
Benefits: After introducing Delta's SVG2000 Series, the gantry crane system's THD remains ≦5%, and the PF improves up to 0.95. The power issues of the gantry crane system are solved, and the system can last up to ten years.
According to field tests, the PF in the original gantry crane system is only 0.34 (far from the standard of 0.9); the system's power efficiency is low, whereas power consumption is high, meaning the company is likely to be fined by the electric company, which in China is usually 5% of the total electricity fee for every 0.1 below the standard PF of 0.9. What's more, the THD of the gantry crane system may reach 117.5%, showing severe harmonics pollution in this system, which may possibly cause abnormal equipment operation, or even an electrical fire. (Refer to Picture 3)
Delta's SVG2000 Series solution successfully raises the gantry crane systems' PF to 0.99, which is higher than the standard PF 0.9, and the THD dramatically drops to only 4.9%, which is much lower than the original system's 117.5%. Delta's gantry crane solution effectively improves power efficiency and power quality, reduces power consumption and avoids harmonic pollution, helping customers create an energy-saving and safe working environment and avoid electric company fines.
Success Story Background: With an import/export volume of 62.7 million tons and 13 million twenty-two foot equivalent unit (TEU) containers exported in 2010, the Harbor is one of the biggest harbors for coal transportation in China and is now the biggest transportation harbor in the world. The gantry crane system adopted by the Harbor requires highly stable and energy-saving operation.
Delta's Solution: To fulfill the Harbor's gantry cranes' requirements, Delta's product development team and professional system integrators studied and developed a specific solution for the customer in 2013 using the AFE Series high-voltage power active front end. The AFE Series has been successfully applied to the Harbor's gantry crane system with 280kW regenerative power converted and supplied—higher than the standard 200kW.
Benefits: For Delta's gantry crane solution, Delta's AFE Series adopts an LCL filter to reduce harmonics and to assure the power regeneration rate reaches over 30%. The AFE Series has regeneration braking and resistance braking functions and can switch to either mode according to real usage. It also adds a DC contactor at the connection point with the DC BUS; both ensure the system operates stably and safely.
After months of operation, Delta's solution continues to offer outstanding power regeneration and power quality improvement, providing a highly efficient, energy-saving and stable system for the customer. The satisfied customer demanded that more of Delta's gantry crane solutions be applied to the Harbor's gantry cranes.