Note:
The angle in the table above is the angle between voltages and their respective currents. In state 4 the currents are displaced
180° from their respective voltages.
15.2 PREDICTIVE OST SETTING
1. Clear all alarms.
2. Set the OST timer to zero.
3. To test OST, a 3-state test sequence is required. Based on healthy voltages (VA = VB = VC = 57.8 V) calculate
the currents to generate the impedances as below
State 1 State 2 State 3
Applied current
(all 3 phases)
57.8/(1.1R6) 57.8/(R5+0.5(R6-R5)) 57.8/(0.95R5)
Angle 0° 0° 0°
Duration 500 ms
Longer than 25 ms but shorter than
‘Delta t’ set time
500 ms
Now apply the 3-state sequence, check that all 3-phases have tripped and that an OST alarm is displayed on the
local LCD.
15.3
PREDICTIVE AND OST SETTING
As per Predictive OST
15.4
OST TIMER TEST
1. Repeat the test as for ‘predictive OST’ and observe that the 3-phase tripping comes up after the ‘Tost’ set
delay.
2. Record the operating time in the commissioning record sheet.
P543i/P545i Chapter 25 - Commissioning Instructions
P54x1i-TM-EN-1 681
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