Figure 3.13-2 Functional module diagram
The measured or calculated residual voltage U0 is compared with the set 59G_Vol_Str. If the value
exceeds the set start value and no block signal is activated, the timer and 59G_Str signal are
activated.
Where:
59G_Vol_Str is the residual overvoltage start value.
59G_Op_T is operating delay time for 59G.
The time characteristic is according to DT. When the operation timer has reached the value set by
59G_Op_T and 59G_Alm_Ena=0, the 59G_Op output is activated; When the operation timer has
reached the value set by 59G_Op_T and 59G_Alm_Ena=1, the 59G_Alm output is activated. If the
fault disappears before the module operates, the operation will reset with a time delay of 30ms.
The binary input 59G_Blk can be used to block the function. The activation of the 59G_Blk input
deactivates all outputs and resets internal timers. The binary input 59G_Blk_Str can be used to
block the start signals. The binary input 59G_Blk_Op can be used to block the operation signals.
3.13.3 59G Application Scope
59G is designed to be used for earth-fault protection in isolated neutral, resistance earthed or
reactance earthed systems. In compensated and isolated neutral systems, the system neutral
voltage, that is, the residual voltage, increases in case of any fault connected to earth. In
compensated networks, starting of the function can be used to control the switching device of the
neutral resistor.
Therefore, this function is often used as a backup protection or as a release signal for the feeder
earth-fault protection.
The protection can also be used for the earth-fault protection of generators and motors and for the
unbalance protection of capacitor banks.
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