Regen Drives for Cranes and Hoists

A crane hoist exemplifies a prime application where the motor frequently transitions between motoring and generating modes. During lifting, the motor operates in ‘motoring mode,’ drawing electrical energy from the utility to overcome gravity and lift the load. This process converts electrical energy into mechanical work, increasing the potential energy stored within the system proportional to the load’s mass and height.

Conversely, when the load is lowered, the motor enters ‘generating mode.’ In this state, the potential energy of the descending load drives the motor, which acts as a generator, converting mechanical energy back into electrical energy. This regenerated energy flows back into the Variable Frequency Drive (VFD) as electrical current, offering potential benefits such as energy efficiency and reduced mechanical braking requirements.
 

The problem is that most VFDs have input rectifiers that act as a one-way street. They allow energy to be delivered from the source to the motor, but not the other way. This excess regen energy is dissipated as heat across a power braking resistor. However, some applications make the use of braking resistors very difficult due to the environment, duty cycle, and heat generation.

Regen units provide a compelling alternative to traditional braking resistors in a wide range of crane and hoist applications, including critical deployments within material handling and the defense sector. This post has outlined several key considerations for their use in both commercial and military crane and hoist systems.

See the video below to gain a foundational understanding of regen drives and four-quadrant operation.

 

Hazardous Environment Cranes

Cranes operating in hazardous environments face stringent safety regulations, presenting unique engineering challenges. A traditional hurdle has been the implementation of braking resistors with Crane VFDs.

In typical crane applications, the VFD is housed within an electrical enclosure, and the braking resistor, which dissipates excess energy as heat during regenerative braking, is mounted externally to facilitate heat dissipation.

However, in explosion-proof environments, this conventional approach is problematic. Mounting the braking resistor outside the explosion-proof enclosure creates a significant safety hazard, as the heat generated by the resistor could potentially ignite flammable gases or dust present in the atmosphere, negating the explosion-proof rating of the system.

 
What often happens is the resistor must be mounted outside the hazardous area which leads to an extremely long conductor and conduit run. The additional cost for this can add up quickly.

As a safer and more efficient alternative to traditional braking resistors in hazardous environments, a KEB R6 regenerative drive offers a compelling solution. The R6 unit is mounted within the explosion-proof enclosure and connects directly to the DC bus of the crane’s VFD.

Unlike braking resistors that dissipate regenerated energy as heat – a potential ignition source – the R6 unit actively returns this energy to the building’s power supply. This regenerated energy can then be utilized by other electrical loads within the facility, significantly improving energy efficiency and eliminating the safety concerns associated with external heat dissipation in hazardous locations.

 
The R6 unit uses innovative power hardware, allowing for a very compact size, up to 49% smaller than competitor units. This real estate becomes valuable when considering the cost of explosion-proof enclosures.

Go Green – Less consumption, save $$

Beyond the safety advantages in hazardous environments, cost savings represent another significant driver for implementing a regenerative unit like the KEB R6. By returning energy to the building’s power supply instead of dissipating it as heat, the R6 unit directly reduces power consumption and associated electrical energy costs. The actual amount of energy recovered will depend on several factors, including the efficiency of the hoist mechanism, its size and capacity, and the frequency and duration of loaded crane operation.

To illustrate the potential energy recovery, consider a typical application where system losses occur during both the energy delivery (motoring) and energy regeneration phases. These losses, inherent in the mechanical and electrical components, effectively reduce the amount of energy that can be returned. Therefore, when evaluating the overall energy savings, it’s crucial to account for these system inefficiencies.

Let’s examine a sample application to quantify the potential energy return, keeping in mind the impact of these system losses:

 
In this theoretical example, 10Hp of input power equates to 6.6Hp at the hoist drum after transmission losses. As the load is lowered, this power must pass through the transmission components again, and there are additional losses. So, the 10Hp of system input actually results in 4.4Hp of regenerated energy.

 
It’s important to remember that the previous figures represent a specific example; larger crane systems with higher duty cycles will naturally generate significantly more regenerated energy. Furthermore, the efficiency of the crane’s components plays a crucial role in maximizing energy return and improving the overall return on investment (ROI).

For instance, upgrading from a less efficient right-angle worm gear to a more efficient right-angle helical bevel gear can dramatically increase regenerative power – in some cases, by as much as 40%. This substantial increase in regenerated energy directly translates to more significant cost savings and a faster payback period for the regenerative drive system.

KEB’s Regenerative Drives for Cranes and Hoists

In conclusion, the adoption of regenerative drives for overhead cranes offers significant advantages beyond simple energy savings and reduced electrical costs. For customers facing challenges with traditional braking resistors, particularly in hazardous environments, regenerative drives provide a robust and safe alternative. By eliminating the need for external heat dissipation, systems utilizing KEB’s R6 Regen units enhance safety and efficiency.

Interested in learning more about how KEB’s R6 Line Regen units can benefit your overhead crane application? Connect with a KEB engineer today for a personalized consultation.