GE MiCOM P40 Agile Technical Manual page 325

P543i/P545i
disabled on all others. To detect the Out-of-Step conditions, the OST Z5', OST Z5, OST Z6', and OST Z6 settings must
be set to comfortably encompass the total system impedance Z
OST Z5 = OST Z5' = Z
The OST Z6 and OST Z6' settings are not of great importance and could be set to 1.1 x OST Z5.
4.4.1.3 SETTING OST R5, OST R6 AND DELTA T
The R5min and R6max settings determined above represent limit values. The actual OST R5 and OST R6 values
need to be determined in relation to the Delta T timer.
Predictive OST setting
For the Pred. OST Trip setting, it is important to:
● Set OST R6 equal to R6max
Set OST R5 as close as practical to R6max
●
The aim of pushing the OST R5 setting to the right is to detect fast oscillations as soon as possible, in order to gain
sufficient time to operate the breaker before the two source voltages are in opposite directions. The only restriction
is the limitation of the Delta T minimum time delay of 30ms and the speed of oscillation.
You should set Delta T such that it does not expire after the positive sequence impedance has passed the OST R6
– OST R5 region.
For this setting, you need to know the rate-of-change of swing impedance when crossing the OST R6 – OST R5
region. This must therefore be based on system studies.
Note:
You cannot assume that the rate-of-change of positive sequence impedance while crossing the OST R6 – OST R5 region is the
same as the average rate-of-change of positive sequence impedance for the whole swing cycle. A false assumumption could
lead to incorrect predictive OST operation.
Note:
For a fault, the OST R6 – OST R5 region will be crossed faster than 25ms, therefore even very fast oscillations up to 7Hz will
not be mistaken as a fault condition and predictive OST will not operate.
OST setting
For the OST Trip setting option, such a precise setting of the blinders and Delta T is not necessary. This is
because for a wide ∆R region and a short Delta T setting, any oscillation will be successfully detected. However,
the fault impedance must pass through the ∆R region faster than the Delta T setting.
Therefore, for the OST Trip setting, assume that θ = 120° and set:
● OST R5 = OST R5' = R5min = Z
OST R6 = OST R6' = R6max
●
● Delta T = 30 ms
Delta T always expires. Therefore, the setting value given above will secure the detection of a wide range of
oscillations, starting from very slow oscillations (caused by recoverable swings) up to a fastest oscillation limit of
7Hz. Note that any fault impedance will pass the OST R6 – OST R5 region faster than the minimum settable Delta T
time of 30ms.
Predictive and OST setting
The recommendations for Pred. & OST Trip are the same as for Pred. OST Trip.
P54x1i-TM-EN-1
T
/3.46
T
Chapter 10 - Power Swing Functions
. A typical setting could be:
T
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