Page 361 - Practical Power System and Protective Relays Commissioning

356 Practical Power System and Protective Relays Commissioning

FIGURE 20.7.1 Checking the synchronizing and system check operations.

System synchronizing limits:
ΔF 5 125 mHz
ɸ 5 10 degrees
When the two systems are connected outside the permissible limit the
following can happen:
Vibration for generating units;
Sudden load for nearby generating stations;
A sudden change in the power system transmission line impedance;
Live voltage: the limit of voltage at which we can consider the line to be
on (energized);
Dead voltage: the limit of voltage at which we can consider the line to be
switched off.
System synchronizing is sometimes called autosynchronizing.
The old system applied manual synchronizing by synchroscope or lamp
method, but the new one applies synchronizing relay for automatic synchro-
nizing operation of a CB between the two electrical parts or systems.