Program features 17
Grid monitoring
The inverter monitors grid conditions with internal measurements. The measured
frequency and voltages are compared against the limits set in parameter group135 Grid
monitoring. If the measured values do not stay within the limit for a certain minimum period
of time, the inverter declares the grid as unstable and disconnects from the grid and
inhibits grid connection.
There are two types of grid monitoring limits: normal limit and connection limit.
Normal limit – is always active and can declare the grid unstable at anytime.
Connection limit – is active when the inverter is not connected to the grid. Typically
connection limit is stricter than normal limit.
All grid monitoring limits can be enabled independently. Grid monitoring and fault
ride-through are parallel features. They can both be enabled or disabled separately.
Note:
• All grid monitoring settings are reset when the grid code is changed.
• Depending on the installation grid, an external third party-certified grid monitoring
relay may be needed.
Nominal values
Note: Consider the fault ride-through settings when defining grid monitoring limits.
The inverter monitors the line-to-line voltages. The settings for grid monitoring can be set
in relation to nominal values. The inverter nominal line-to-line voltage on the low voltage
side of the MV transformer can be set with parameter 135.02 Nominal LL voltage and
nominal frequency can be selected to be 50 Hz or 60 Hz with parameter 135.04 Nominal
frequency.
Settings
Parameters:135.02 Nominal LL voltage,135.04 Nominal frequency
Connection delays
Typically, it is required that the grid must be stable for a time period before connection to
the grid is allowed. For this purpose there is a set of delays.
• 135.10 Initial connection delay must expire before the first grid connection attempt can
be made after a power-up.
• 135.11 Reconnection delay defines the delay that must expire after a disconnection
before the following reconnection can be made.
• 135.13 Quick reconnection delay is used if the grid is unstable for less than the time
defined in parameter135.12 Quick disturbance limit. Thus a short unstable grid allows
a faster reconnection. If parameter135.12 is set to 0, quick reconnection is not used.
Settings
Parameters:135.10...135.13
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