The availability of shore power is both a blessing and a curse. It is convenient to supplement systems when in a marina or harbor. At the same time, the plethora of voltages, frequencies, and capacities is confusing. Vanguard is built to cruise worldwide and should encompass the flexibility to maximize what is achievable, but that's easier said than done. Have you ever started a project then wished you had not? That was us and "shore power", so many false dawns along the way.
The illustration below is the our shore power system, there follows the story of how we understood the issues and how we arrive at this solution.
Yacht power electrical system including single and three phase shore power connections with galvanic isolation. Fully independent of frequency or input voltage worldwide.
The Short Version
Accept shore power from anywhere in single or three phase at any voltage or frequency. Convert everything to DC, charge your batteries. Accept some inevitable transmission losses along the way and move on. Feed solar direct to 24VDC consumers to minimize transmission losses when at sea.
The Problem
Our XPM-78 explorer yacht, Vanguard, has some unique machinery. A diesel electric hybrid drive and huge power batteries. To summarize:*
230 VAC 50Hz Single phase
400 VAC 50Hz Three-phase plus neutral
24VDC (with the occasional 12VDC for Comms and Nav gear)
These feed into systems containing:
20 kWh of LiFePO house batteries at 24 VDC
120 kWh of LiFePO power batteries at nominally 600 VDC
In turn, the available power sources are:
6.5 kW of solar panels at peak capacity
Two by 90kW 50Hz alternators (hybrid drives operated decoupled from the propellers and at full engine speed)
Shore power vis:
Single Phase: 120 VAC 60 HZ 30 amps approx
240 VAC 60HZ split phase (2 phase and floating neutral) 50 amps
230 VAC 50 HZ 50/100 amps
Three-phase: 208 VAC 60 HZ Three-phase 100 amps (combined)
400 VAC 50 HZ Three-phase 100 amps (combined)
One last complication in the mix is that we need galvanic protection for our aluminum hull utilizing an Isolation Transformer. The device prevents earth currents from circulating between ship and shore (for safety and to limit corrosion).
Have you ever seen a circus trick known as "plate spinning"? Lots of moving pieces in the air at the same time? Well, that is how this felt at the time!
Solving for Single Phase Systems. With a multifaceted problem, start by simplifying the issues. The supply frequency 50 and 60 Hz systems that are incompatible at the AC level. Also, an isolation transformer will not change the frequency. All single-phase power input runs through the same dual frequency Victron isolation transformer and charging system to feed the house batteries. A slight increase in conversion losses results, but we felt it worthwhile to pursue simplicity. 6.5 kW peak of Solar in-feed also charges the house batteries and powers the 24VDC system whenever the sun shines.
Victron 3600kW Isolation Transformer.
Solving for our Three Phase System
The problem remained of how to cope with three-phase supplies? I refer you here to the circuit diagram on the top of the page. We wanted to maximize the advantage of a beefed-up power source to charge two by 60kWh power batteries.
We have three choices here -
Install a universal shore power supply that will produce clean three-phase power, voltage stabilized with input from both single and three-phase shore power, 50 or 60Hz. These are available from several suppliers, Magnus Marine, ASEA, and ANG just three of them. We found all the vendors helpful but again ran into issues. The physical size was the first problem as we have a cramped engine room. We solved this by reducing the capacity from 25 KVA to 12KVA. Still a powerful charger but at a much smaller physical size. We also needed to limit the in-feed current so as not to trip the shore power breaker when the batteries are partially discharged. That feature was not (yet) available in the size we needed and that was a deal breaker.
To create a hybrid solution with 50Hz supply dropping to the three-phase bus bars and 60Hz supply is converted to 600VDC and charges batteries (Power Batteries and when they charge, following on to House Batteries).
The hybrid drive installation uses large, 25KVA, three-phase transformers and powerful AC/DC High Power inverters. Inverters are bi-direction in that you can feed AC and DC to receive the opposite at the outlet end. They also have their own controllers to monitor, limit and report on the process.
Power Management Controllers are ordinarily used to control and switch AC generators so have useful functions such as recognizing input frequency and triggering breakers. Notice in the diagram above that the shore power 50 & 60Hz options are controlled by this means (SHK1,2,3). This prevents inadvertent frequency contention of 60Hz being fed to a 50Hz system and the loss of a nice evening in the marina bar or worse.
Two 25KVA 3 phase inverters were used to convert 400V AC 50Hz and 280VAC 60HZ to 600 VDC to charge the power batteries.
This controller also limits the in-feed current so as to achieve a soft start to the connection and limiting the maximum current draw to prevent tripping the shore power breaker.
Praxis Power Management Controllers (SHK-I,2,3 in the drawing) monitor shore power input and frequency, automatically setting and controlling input current.
In Conclusion
There is no simple, all-encompassing answer to shore power connection. (Sorry!)
Relying on a single frequency is viable if your cruising area is limited.
You should always fit an isolation transformer for safety, to protect your hull and machinery from corrosion and any swimmers in the marine from worse.
Things become more complicated if you have a high power requirement and a worldwide cruising scope.
Converting incoming AC to DC avoids this frequency issue at some penalty in transmission losses.
Charging requirements for hybrid battery systems complicate the situation.
For larger installations, consider an automatic shore power converter or convert everything to DC if you have the battery capacity. However, these have a cost and size penalty compared to more simplistic systems.
(*) - all voltages quoted are approximate and may vary.
Chris Leigh-Jones
Acknowledgement also to Praxis Automation for their design assistance.
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