Out Of Step (78Oos) Protection; Element Operation - Basler BE1-11g Instruction Manual

9424200994 Rev U 151

Out of Step (78OOS) Protection

The Out of Step (78OOS) element detects out-of-step conditions by monitoring the rate of impedance
change as viewed at the generator terminals.
Element logic connections are made on the BESTlogic™Plus screen in BESTCOMSPlus® and element
operational settings are configured on the Out of Step (78OOS) settings screen in BESTCOMSPlus. A
summary of the logic inputs and outputs and operational settings appears at the end of this chapter.
BESTCOMSPlus Navigation Path: Settings Explorer, Protection, Impedance, Out of Step (78OOS)
HMI Navigation Path: Settings Explorer, Protection, Settings Group x (where x = 0 to 3), Impedance
Protection, Out of Step 78OOS

Element Operation

When a fault occurs on the power system, a synchronous generator can begin to accelerate due to
differences in the mechanical power into the generator and the electrical power at the generator
terminals. If the power system fault is not cleared quickly enough, this acceleration will result in the
generator rotor voltage advancing beyond 90 degrees with respect to the generator terminal voltage. At
this point, power will flow into the generator and the rotor angle will continue to advance until it is aligned
with the next pole. This condition is known as slipping a pole or loss of synchronism.
The out of step element uses a single blinder scheme as shown in Figure 94 to detect an out-of-step
condition and protect against pole slip. The blinder units allow the BE1-11g to trip for a region of
impedances that are supervised or enabled by a mho unit which is set to permit tripping only for
impedance swings appearing in the generator or unit transformer and a limited portion of the system.
Figure 94. Single Blinder Scheme
BE1-11g Out of Step (78OOS) Protection