Reverse Power Resistor

He is correct, you either fit resistors to the set or alternatively you may regenerate power back in to a power grid (if you are connected to a grid)

Both are not that simple. For the regenartion back you need all sorts of relays, sinchronizing etc.

For the resistors you need to know the ohmic value required to maintain the voltage on a acceptable level. You also need to know the duty cycle for the resistor as this will determine the size of the resisitor. The more the resistor is required to absorb the power, the higher the rating (in kW) of the resistor will be. You will also require a brake chopper with controls to introduce the resistor to the circuit as and when required (when the voltage on the DG start rising above a certain level)

Thanks for your kind reply.

And I think my question is insufficient.

We are now on a design stage. But we can't change the crane maker and the capacity of D/G. so; actually the only way to solve this problem is using resistor if the reverse power is really occurred.

To be brief, we use two sets of generator (total 1200 kw) when using deck crane (total 528kw).

And we assume that the reverse power doesn't occur from both cranes together.

So we consider the capacity of reverse power as 200kw.

And 200kw is the maximum capacity of reverse power when the hoist lowering with fastest speed and heavy load.

So, in your experience, I wonder whether the reverse power (200kw) is really occurring.

I desire our D/G (1200kw) could endure the reverse power(200kw)

Actually, I can't understand why the reverse power is occurring in spite of the crane is hydraulic pneumatic type.

Thank you for having interest on my question.

Regards

Glition

I believe the crane uses power to lift and they want you to either use dynamic braking of the DC motor used to make power into a resistor to control the downwards travel of the load. They can use common friction brakes, but these wear out and turning it into heat is a waste. I could suggest a battery bank to both power and act to receive the reverse power. That would allow you to use less power from the DG set and help you with a faster lift by running from battery power in excess of the DG rating. Such design aspects need the involvement of the makers/installers of the crane system.

The concept would allow you to save power which comes from diesel by use of the battery and depending on your situation and diesel usage could save you some amount of money. You need to study this. In adition, with all cranes with their own battery pack, you might have speedier operation since the battert will average things and allow all cranes to run at full lift/load at the same time.

Thank you for having interest on my question.

And the maker said to me as below.

If the crane lowering, the motor has to braking (else the load is very fast at the bottom), torque and current in negative direction. The current flow is from crane motor to the vessel generator.

I wonder how the Liebherr crane could compensate the power by itself....

Regards

Glition

Hi Glition.

If you do not like to buy a 200 Kw Resistor bank, you may use salt water tank as a resistor.

We use them for the load test purposes for medium range generators.

Make a good earthed metal (or fiber) water tank. Fill inside with salt water.

Get three copper busbars (similar with the ones used in the switchboards), of which the length is smaller than the tank length.

Fix the copper busbars on a strong insulator from one end to form a triangle. Hang the insulator over the tank. Connect your reverse power cables to the busbars.

When you submerse the copper into the salt water, it becomes a resistor bank. You can adjust the value of resistance by hoisting or lowering the Copper busbars into the tank.

It may warm or even boil in often use cases, but I am sure this method simply solves your problem, if you do not want to pay for a resistor bank.

Kindest Regards

Dear all,

Before operating the crane, find a load of 260kW in your vessel, for instance HVAC and all lighting loads. With 200kW of reverse power from your crane, your D/G still supply 60kW of power. Actually, your HVAC is used as a resistance.

Regards

this reverse power is not a known precise source. It is variable power DC, drop faster = more power, drop heavier = more power, so few application loads will tolerate this, lights brighter/dimmer etc.

A resistor is a convenient way to waste this power.

It can be wasted in a use where this power is used, and that is in a hot water tank for shipboard use to save the conventional heater needed, and space heat in colder climates.

Usually resistors are so cheap they just use them and waste the power.

But if you have 200 KW x 1 hour =$20 worth of power, more or less . Of course, this power comes in bits and pieces. How long does it take to lower a load? how much time until the next one is lowered?

I don't know how to post a link to this forum, but try to visit the following web site.

www.vyconenergy.com

It talks about a flywheel based energy storage mechanism which will help solve your problem and put the wasted energy to good use.

Hope this helps,

Glition,

Your problem is not unique. We faced it on an oil drilling platform. Our original contract was to install a fast power factor controller but had to add a resistor bank to absorb the surplus regenerative energy and generator over production when the load (hoist, drill motor) would stop or reverse suddenly.

Our power controller would detects the high voltage condition and bring in the resistor banks until the generators had time to reduce their production (1-2 seconds). Since this protection is over-voltage activated, it will not dump power in the resistors if other loads consume the excess power.

The detection process is a very fast. The detection and switching of the resistor bank(s) is done within one line cycle. The controller can also commands tuned capacitor banks to improve power factor and reduce the harmonics generated by the motor drives.

Send me a mail by clicking on my user name if you want more details.