Electrical networks on yachts are categorized as ‘weak networks’ or ‘weak grids’. This type of network is self-sufficient while sailing, but very vulnerable as a result of Power Quality problems.
Designing a cost-effective weak grid is complicated by inrush currents: short bursts of current required to start a device such as a motor. Guidelines exist to limit the inrush current of motors, but not for other types of increasingly popular electronic devices.
An electrical installation needs to be engineered in such a way no Power Quality issues can occur. However, there is always the possibility of unexpected events taking place. Furthermore, a soft starter is not always installed in small loads. This soft starter might not be considered cost-effective, as it would only be used on highly specific occasions. The result may be flicker, as the breaker is not likely to trip.
Negative effects of inrush current
- Voltage drop in the rest of the installation
- High instantaneous load on the generator
- High losses in cables
- Excessive wear on switching equipment
- Visible flicker of lights
Big loads are generally equipped with a soft starter. In most cases, bow thrusters cause some voltage drops, which are reduced due to the presence of a soft starter. On a yacht, dangerous inrush currents are unlikely to occur thanks to careful planning. Any occurring inrush currents will be limited to a few volts. They may, at most, cause an annoying flicker that needs to be fixed, but will not interfere with normal operation of the yacht.
Inrush currents in Hybrid vessels
Hybrid vessels in which the main propulsion is tied to the main busbar can draw enormous currents. A synchronous increase of generator power is necessary to maintain grid balance. If this balance is not maintained, voltage levels will fluctuate, causing brown outs and over-voltages.
Inrush current due to many small loads: electronics
Besides the familiar inrush current produced by motors, inrush currents may also be caused by electronics. Electronics have a shorter inrush current than traditional equipment, however, their peak current can be far higher. Since electronics often present a smaller load, the effects are less noticeable. However, when a large number of electronic devices are switched on at the same time (LED lights, for example), the inrush currents add up. The inrush current caused by restarting IT equipment following a blackout is often underestimated, for example. In such cases, proper sequencing is more important than ever.
We call this the ‘The small loads effect’: a group of small loads, randomly distributed over the three phases, presents an inrush when simultaneously switched on, even if the load is minimal. If equipment is not distributed evenly among the phases, the inrush current can induce current unbalance and, therefore, voltage unbalance for a short duration, too. This increases wear on the generator.
In the past, motors mainly caused inrushes, but the effect is always the same. What’s more, LEDs have a significantly faster inrush with a higher peak in relation to the nominal current. In short: power electronics make everything far more complex.
Flicker caused by inrush currents
Visible flickering of lights can be perceived by visitors as well as crew on board of your yacht. Flicker is a known source of annoyance, causing eye strain, and is associated with an increase in headaches and decreased visual task performance. This has serious implications for your crew working onboard, particularly in rooms without windows.
Inrush currents are especially complex to model and simulate. Normally, the problem can be solved by finding the load (or resonance) causing the inrush. It is advisable to install a soft starter / inrush limiter on that load. Finding the root cause is always important.
HyTEPS helps you avoid inrush currents on yachts
We have the knowledge, experience and high-quality products to reduce your inrush current. Through measurements we gain insight into the situation within your specific installation. This gives us tools to dimension and advise the most suitable solution. When the inrush current issue cannot be solved, several solutions are available to isolate the affected equipment.