Protection Functions
86 PRS-7367
59_Str_Ph_Num shows the number of phases required for operate activation.
 Timer element
The timer mode is determined by IDMT curves for over quantity protection.
The operation is activated after the operation timer has reached the calculated value. If
59_Alm_Ena = 0, the 59_Op output is activated, the corresponding output for the respective
phases (59_Op_A/B/C) is also activated, when 59_Alm_Ena = 1, the 59_Alm output is activated.
However, 59_Min_Op_T defines the minimum desired operate time for IDMT. If a drop-off situation
occurs, that is, a fault suddenly disappears before the operation delay is exceeded, the reset state
is activated. If the drop-off situation exceeds the set 59_Reset_T, the timer is reset and the 59_Str
output is deactivated.
NOTICE!
The 59_Min_Op_T setting should be used with care because the operation time is
according to the IDMT curve but always at least the value of the 59_Min_Op_T setting.
The binary input 59_Blk can be used to block the function. The activation of the 59_Blk input
deactivates all outputs and resets the internal timers. The binary input 59_Blk_Str can be used to
block the start signals. The binary input 59_Blk_Op can be used to block the operating signals.
3.11.3 59 Application Scope
Overvoltage in a network occurs either due to the transient surges on the network or due to
prolonged power frequency overvoltage. Surge arresters are used to protect the network against
the transient overvoltage, but the IED protection function is used to protect against power
frequency overvoltage.
The power frequency overvoltage may occur in the network due to contingencies such as:
• Defective operation of the automatic voltage regulator when the generator is in isolated
operation.
• Operation under manual control with the voltage regulator out of service. A sudden variation
of load, in particular the reactive power component, gives rise to a substantial change in voltage
because of the large voltage regulation inherent in a typical alternator.
• Sudden loss of load due to the tripping of outgoing feeders, leaving the generator isolated or
feeding a very small load, can cause a sudden rise in the terminal voltage due to the trapped field
flux and over speed.
59 is not usually applied to the attended generators but can be required for the unattended
automatic hydro-stations. If a load sensitive to overvoltage remains connected, it leads to
equipment damage.
Therefore, it is essential to provide power frequency overvoltage protection in the form of time
delayed element, either IDMT or DT.
3.11.4 59 Settings
In the following table, i is the protection stage number, it can be set according to the requirements.
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