4–246
889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
PROTECTION
CHAPTER 4: SETPOINTS
The element is set to use the single blinder characteristic with a supervisory mho as
illustrated below.
The FlexLogic output operands for the out-of-step element are described as follows:
•
The OOS Lft Bld PKP, OOS Rgt Bld PKP, and OOS Timer PKP FlexLogic operands are
auxiliary operands that can be used to facilitate testing and special applications.
•
The OOS OP FlexLogic operand can be used to trip the circuit breaker to isolate the
loss-of-synchronism generator.
Follow these steps for a typical setting procedure of the out-of-step element:
1.
Carry out detailed transient stability studies for the overall system.
2.
Determine the values of generator transient reactance (X'
d
), step-up transformer
reactance (X
T
), and system impedance under maximum generation (Z
maxS
). The total
impedance is given by:
3.
Set MHO FORWARD REACH to 1.5 times the transformer impedance in the system
direction. Set MHO REVERSE REACH to twice the generator transient reactance in the
generator direction.
4.
Set BLINDERS RCA to the angle of Z
total
,
θ
.
5.
Using the results of transient stability analysis, find the critical angle
δ
c
between the
generator and the system, beyond which the system begins to become unstable. If a
stability study is not available, this angle is typically set at 120°. Then, 10 degrees are
normally added in order to increase relay operation security,
δ
=
δ
c
+10.
6.
Determine the blinder distance, d, from the following equation:
7.
Set RIGHT BLINDER and LEFT BLINDER to
d
.
