Due to the increased use of temporary power solutions, container ports are experiencing issues with ‘regenerative power’, so how can the risks be mitigated?
The container shipping industry is an ever-growing, fast-paced environment, and power infrastructure cannot always grow in line with power requirements. For this reason, many container ports are choosing to expand their power capacity by using stand-alone temporary power solutions, such as diesel generators, rather than waiting for additional power infrastructure.
This is a quick fix, and the best way to secure additional crane power, thereby increasing the number of containers that can be moved simultaneously. Due to the increase in temporary power usage, Crestchic is witnessing an increased demand from container ports for a solution to the issue of ‘regenerative power’.
Power generation vs power regeneration
Generally, in power generation a variable frequency drive controls the motor by supplying it with energy, which then powers the crane to lift its load. In some applications the energy flow will be in reverse, that is, from the load, through the motor, back to the drive. This will occur if the load is giving up energy, such as when a crane is lowering its load, or a cable car is travelling downhill. If this ‘regeneration power’ is significant, the energy will return to the initial power source. In most grid connected situations this regenerative power will be absorbed by the grid without any issues.
If power regeneration happens in an ‘island mode’ application with a stand-alone power source, ie where a crane or cable car is being powered by a dedicated generator, it can have catastrophic effects on the asset.
The continued operation of the drive will maintain a voltage on the motor, so a magnetic flux will be present, but the phase of the currents will reverse, so energy – that is current – will flow into the drive from the motor, motorising the alternator and causing it to turn the opposite and incorrect direction.
This reversal can twist the shaft and cause alignment problems, both of which are irreversible problems and will damage the generator alternator and engine. The reverse power will make the voltage swell, which will result in an unstable system and may cause damage to other loads, especially critical ones.
Introducing a resistive loadbank into the circuit allows for the dissipation of the regenerated power. This means that the power coming from the crane load back towards the motor is stopped before it can reach the drive, therefore negating the risk to generation equipment. The loadbank can rapidly respond and follow the returning regenerative load and ensure the genset sees only ‘good’ load from the system.
A simple, yet rapid and robust system based on CT signals, the Crestchic Regen system (pictured) can operate constantly while also continuously varying the load to the generator at low (380-690V) or medium (3-36kV) voltages.