Powering Europe - European Wind Energy Association

2.2 An overview of the present
grid code requirements for wind
power
Essential requirements
Technical grid code requirements and related documents
vary from one electricity system to another.
However, for simplicity, the typical requirements for
generators can be grouped as follows:
• Tolerance - that is, the range of conditions on the
electricity system for which wind power plants must
continue to operate
• Control of reactive power: this often includes requirements
to contribute to the control of voltage
in the network
• Control of active power and frequency response
• Protective devices
• Power quality
• Visibility of the power plant in the network
It is important to note that these requirements are
often specified at the Point of Connection (POC) of
the wind power plant to the electricity network. In
this case, the requirements are placed on the wind
power plant. To achieve them the requirements for
wind turbines may have to be different. Often wind
turbine manufacturers will only specify the performance
of their wind turbines, not the entire wind power
plant. EWEA recommends that for transparency and
inter-comparability, all grid codes should specify the
requirements to apply at POC. It is also possible to
meet some of the requirements by providing additional
equipment separate from wind turbines. This is noted
below where relevant.
tolerance
The wind power plant must continue to operate between
minimum and maximum limits of voltage. Usually
this is stated as steady-state quantities, though a
wider range may apply for a limited duration.
chApTEr 2 Windgenerationandwindplants:theessentials
The wind power plant must also continue to operate
between minimum and maximum limits of frequency.
Usually there is a range which is continuously applied,
and several further more extreme short-term ranges.
Early generation wind turbines (type A) 13 are generally
not capable of meeting wider operational frequency
ranges as stipulated in several grid codes. However,
the operation of a wind turbine in a wider frequency
range is not really a complicated task as it mainly involves
the thermal overloading of equipment, which
has short thermal time-constants, in particular by using
power electronic components. A possible solution
for short-term overload capability consists of oversizing
the converters, which in general can be done
at reasonable cost. Increased operating temperature
may also result in a reduced insulation lifetime. However,
since operation at deviating frequency occurs
rarely, the effect is negligible and can be reduced by
limiting power output at the extremities of the frequency
range. Therefore – in general - wind turbines can be
made to operate in wider frequency ranges.
In systems with relatively high wind penetration, it is
common that wind power plants are required to continue
to operate during severe system disturbances,
during which the voltage can drop to very low levels for
very short periods. This is termed fault ride-through
(FRT) or low voltage ride-through. A decade back, the
TSOs required all wind turbines to disconnect during
faults. Today they demand that wind turbines stay on
the grid through these disturbances. Faults are inevitable
on any electrical system and can be due to natural
causes (e.g. lightning), equipment failure or third
party damage. With relatively low transmission circuit
impedances, such fault conditions can cause a large
transient voltage depression across wide network areas.
Conventional large synchronous generators are –
in general - expected to trip only if a permanent fault
occurs in the circuit to which they are directly connected
14 . Other generators that are connected to adjacent
healthy circuits should remain connected and stable
after the faulty circuits are disconnected, otherwise
too much generation will be lost in addition to that
13 Wind turbine electrical concept types as previously defined.
14 The actual fulfilment of the FrT requirement is not always the case with large conventional generators such as some new ccGT’s in
Europe and nuclear power plants in the USA.
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