Operation Principle - ABB 615 series Technical Manual

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1MAC059074-MB A

615 series ANSI

Technical Manual

protection 27 by allowing the grid operators to define its own Low-Voltage Ride-Through

(LVRT) curve for generators, as defined by local or national grid codes. The LVRT curve

can be defined accurately according to the requirements by setting the appropriate time-

voltage coordinates.

The function contains a blocking functionality. 27RT can be blocked with the BLOCK

input. Blocking resets timers and outputs.

Operation principle

The function can be enabled and disabled with the Operation setting. The corresponding

parameter values are "Enable" and "Disable".

The operation of 27RT is described using a module diagram. All modules in the diagram

are explained in the next sections.

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Functional module diagram

LVRT curve monitoring

LVRT curve monitoring starts with detection of undervoltage. Undervoltage detection

depends on Voltage selection setting. All selectable options are based on fundamental

frequency components.

Function uses phase-to-ground voltages when Voltage selection is set to "Highest Ph-to-

E" or "Lowest Ph-to-E" and phase-to-phase voltages when Voltage selection is set to

"Highest Ph-to-Ph" or "Lowest Ph-to-Ph".

When the Voltage selection setting is set to "Highest Ph-to-E", "Lowest Ph-to-E",

"Highest Ph-to-Ph" or "Lowest Ph-to-Ph", the measured three-phase voltages are

compared phase-wise to the set Voltage pickup value. If the measured value is lower than

the set Voltage pickup value setting in number of phases equal to that set Num of pickup

phases, the PICKUP output is activated.

The setting options available for Num of pickup phases are "Exactly 1 of 3", "Exactly 2 of

3", and "Exactly 3 of 3", which are different from conventional setting options available

in other functions. For example, Num of pickup phases is set to "Exactly 2 of 3", any two

voltages should drop below Voltage pickup value within one cycle network for the

Protection functions

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