Demag Cranes was one of the first companies in the world to produce the first steam-powered crane. With the time today these are known as EOT cranes
EOT Cranes Means (Electric Overhead Travelling Crane).They are also known as bridge Cranes. Most of the industries use EOT cranes for Material Handling in the Plant. EOT cranes are rated in terms of Tonnage (e.g. 2T, 5T. 50T, 100T, etc ) They are mainly Classified in Single Girder and double girder Cranes. This crane has a Parallel runway with a Travelling Girder. (Either Single Girder or Double Girder). On this girder Main part is Hoisting trolley. Hoist consists of Motor, Gear Box and Wire roping with Special engineering Design. Hoisting will Lift the Material to Desired height and Hold it till destination. After Lifting material Crane has to reach the destination, this is done by two movements Cross Travel and Long travel. This will move the Hoisting material like in X-Y axis to reach its destination.
Some of the Cranes have Dual Tonnage rating with two Hoist for energy saving Purpose. They are called as Main Hoist and Auxiliary Hoist.
Before introduction to VFD in Cranes, slip-ring Dual Speed motors were used to drive Crane. But with the introduction of VFD, It has become main part of Crane.
How to use ac Drive/VFD in EOT Crane Application?
EOT Crane is one of the critical Applications of VFD.
When you see a name plate of a crane’s motor, current ratings will be on higher size than a normal HP-Current Ratio. Choose the VFD / AC drives rating according to output current rating. VFD current rating should be more than Motor current ratings. Motors used for Crane are heavy Duty motors so drives used in this application should be heavy Duty. Drive should be able to generate high torque around 180% at 0.5Hz, so that hoist can lift heavy load. With V/F control it is difficult to generate such high torque at Low speed. So VFD should be Sensor less Vector control.
Brake is important feature of Crane. VFD generates set Percentage of toque at a selected frequency in motor before it releases brake. VFD has such function inbuilt to control Motor Brake. Same thing happens while stopping the motor.
In cranes Ramp up time (acceleration) and Ramp Down Time (deceleration) are very Small. Also load of crane is too High. No of start stop can be 15-20 times per minutes when operator is inching to adjust the crane position. Due to this reasons There is huge amount of regeneration. To dissipate this energy when need to connect Braking resistors to Braking chopper (Braking Transistor). If not connected Drive may go into Overvoltage error and you won’t get proper braking and performance.
Another way to utilize this energy is to connect Regenerative convertor and feedback that energy back to mains. We will learn more about regenerative convertor seperately
Features Required in VFD / Ac Drive
- High starting Torque : Starting torque should be minimum 180% for a sec and 150% for 60 Sec
- Sensorless Vector Control : For High torque at Low speed of 0.5Hz
- Braking Chopper: To connect Braking Resistor to dissipate back emf over voltage.
- Brake Logic: Brake Logic as mentioned above should be standard Feature
- Two Relay Output: For Brake Signal and fault Output. If only one relay output, you can use transistor output to drive a external 24VDC relay. This relay you can use as second output relay.
Fuji Electric, Siemens, Yasakawa, Schneider Electric (Altivar) and Hitachi
If you have any issues regarding using ac drives or VFD in EOT Cranes you can write us to email@example.com