4.5.7.5 Application
Distributed generation, mainly wind and solar farms, are rapidly increasing due to
liberalized markets (deregulation) and the global trend to use more renewable sources of
energy. These farms are directly connected to grids, and due to their large size may
influence the behavior of the grid. These farms are now required to comply with stringent
grid connection requirement, which was previously mandatory only for high capacity
power plants. These requirements include helping grid in maintaining system stability,
reactive power support, transient recovery and voltage-frequency regulation. These
requirements make it necessary for the wind and solar farms to remain in operation in the
event of network disturbances.
Many grid codes now demand that the distributed generation connected to HV grids must
withstand voltage dips to a certain percentage of nominal voltage (down to 0% in some
cases) and for a specific duration. Such requirements are known as Low-Voltage Ride-
Through (LVRT) or Fault-Ride-Through (FRT) and are described by a voltage versus
time characteristics.
Typical LVRT behavior of a distributed generation can be divided into three areas
according to the variation in voltage over time.
• At the time of system faults, the magnitude of the voltage may dip to Voltage level 1
for time defined by Recovery time 1. The generating unit has to remain connected to
the network during such condition. This boundary defines area A.
• Area B defines the linear growth recovery voltage level from Voltage level 1 to
Voltage level 2 in a time period from Recovery time 1 to Recovery time 2.
• Area C is the zone where voltage stabilizes. Voltage level 3 is defined to same value as
Voltage level 2. The system should remain above this voltage in a time period from
Recovery time 2 to Recovery time 3.
The system restores to a normal state and function resets when the voltage is equal or
greater than Voltage level 4 after Recovery time 4 time period.
When the voltage at the point of common coupling is above the LVRT curve, the
generation unit must remain connected, and must be disconnected only if the voltage takes
values below the curve.
1MAC059074-MB A Section 4
Protection functions
615 series ANSI 663
Technical Manual
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