Installation Instructions
23.3.18
Kapitel/Chapter 5: Installation Instructions - Seite/Page 67
5.12 Instructions on prevention of galvanic corrosion
Galvanic corrosion
If several machines are connected by a common electrical potential (e.g. mass) and the system is also still in contact
with other metal parts (e.g. the hull of a neighbour ship), always assume that the different components proceed
different electrical voltage, which affect the entire system and the components. DC voltage causes an electric
current, if in the environment of these parts electrically leading liquids (electrolyte) are available. This is called
„galvanic process“. The electrical charge of the negatively charged fields (anode) is led to the positively charged field
(cathode). The negatively charged part (anode) „is sacrificed“ thereby, i. e. that the electrical particles at the surface
of the material caus decomposition with this chemical process. Since aluminium is an electrically negatively charged
metal, aluminium will play the role of the anode compared with most remaining metals. This applies in particular to
copper, brass, and also steel and stainless steel etc. These metals are positively charged.
5.12.1 Instructions and measures on prevention of galvanic corrosion
Several measures must be considered when making the installation so that galvanic corrosion can be avoided as
much as possible:
• Separation of the water column (between raw water and generator) after shutdown. This can either be a stop vlave
turned by hand (Attention! The valve must be closed after each operation) or by the installation of an automatic
ventilation valve. In this case the valve opens and closes automatically.
• Connecting all components (hull outlet, generator, heat exchanger etc.) to a common potential. For this all elements
of the installation are connected by a cable (earthed).
• Strict separation of the generator from the 12 V on-board power supply, that means potential free installation of the
12 V system (generator installation und general on-board power supply).
5.13 Checking and filling of the oil circuit
Check oil and fill the oil circuit as described in the service chapter.
5.14 Isolation test
ATTENTION!
After installation, before bringing into service and
handover of the generator to the customer, an isolation
test has to be accomplished as follows:
1. Switch off all electrical load.
2. Start the generator.
3. Measure the AC-voltage with a voltmeter (adjust to Volt/AC) between:
a) generator housing and AC-Control box
b) generator housing and ground.
The measured voltage must not exceed 50 mV (millivolt).
4. Once the safety systems have been installed, they must be checked. If a leakage current relay (RCD) has been
installed, it also has to be tested in order to ensure that all contacts are connected properly. The individual
phases have to be checked against each other, and between phase and ground. An additional 4th phase (L1’)
also needs to be checked at generators with DVS winding.
5. If the generator is protected by a ground connection, it has to be ensured that ALL electrical devices must also be
connected to this „common“ ground (usually ground contacts are attached to the device’s metallic housing).
The electrical system installation must also comply with the hook-up requirements of the shore current grid.
