GE 869 Instruction Manual page 371

CHAPTER 4: SETPOINTS
869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
2. Determine the values of the motor transient reactance (X'
(Z ). The total impedance is given by Z
S
3. Set MHO REVERSE REACH for 0.05 to 0.15 times the motor transient reactance. Set
MHO FORWARD REACH to twice the motor transient reactance in the motor direction.
4. Set BLINDERS RCA to the angle of Z
Using the results of transient stability analysis, find the critical angle δ
5.
motor 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
6. Determine the blinder distance, d, from the following equation:
7. Set RIGHT BLINDER and LEFT BLINDER to d.
8. Using the results of the transient stability analysis, find the PICKUP DELAY, which is
shorter than the time required for the impedance locus to travel between the left and
right blinders during the fastest expected out-of-step.
9. Validate the settings with the transient stability study cases.
Figure 4-91: A Typical Out-of-step Setting
Path: Setpoints > Protection > Group 1(6) > Impedance > Out of Step
FUNCTION
Range: Disabled, Trip, ALarm, Latched Alarm, Configurable
Default: Disabled
), and system impedance
d
= Z + j * X'
total S d
, θ.
total
PROTECTION
between the
c
+10.
c
4–239