54 Planning the electrical installation
Checking the compatibility of the generator and the
converter
The converter is compatible with induction generators and permanent magnet generators.
1. Select the generator according to the ratings table in chapter Technical data on
page 107.
2. Check that the generator and the converter have the same voltage rating. Check also
that the voltage ratings match the voltage to be connected to the grid-side converter.
Note: You can rise the converter DC link voltage 10% of its natural level (by a
parameter setting). The effect is equivalent to a 10% voltage rise at the generator
terminals. Before you use this feature, make sure that the generator insulation can
withstand the higher voltage level.
3. Make sure that the generator is suitable for the converter use, ie, it can withstand the
voltage peaks at of the converter:
• Use insulated N end (non-driven end) bearing in the generator.
• Make sure that the generator insulation meets the requirements in the table below.
• Select the cables according to the instruction in this manual.
• Install the converter and its cabling as instructed in this manual.
Protecting the generator insulation and bearings
The generator-side converter output of the wind turbine converter comprises – regardless
of output frequency – pulses of approximately the converter DC bus voltage with a very
short rise time. This is the case with all converters employing modern IGBT technology.
The voltage of the pulses can be almost double at the generator terminals, depending on
the attenuation and reflection properties of the generator cable and the terminals. This in
turn can cause additional stress on the generator and generator cable insulation.
Modern variable speed converters with their fast rising voltage pulses and high switching
frequencies can cause current pulses that flow through the generator bearings, which can
gradually erode the bearing races and rolling elements.
You can avoid the stress on generator insulation by using ABB du/dt filters. du/dt filters
also reduce bearing currents. The converter is equipped with the following output filters:
• du/dt filter protects generator insulation system and reduces bearing currents
• common mode filter mainly reduces bearing currents.
When the generator voltage rating
should be
DC bus voltage is not increased from nominal (default) U
N
DC bus voltage is increased from nominal by parameter setting U
ACeq
U
N
rated grid-side voltage of the converter
U
ACeq
equivalent grid-side voltage of the converter in V AC, U
ACeq
= U
DC
/ 1.41
U
DC
maximum DC bus voltage of the converter in V DC. You can set the voltage reference with
parameter in grid-side converter control program for 1.1 · 1.41 · U
N
at maximum. You can set the
reference to a lower value but the program restricts it to a value of at least 1.41 · U
N
.
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