Table of Contents
CHAPTER 4: SETPOINTS
Impedance Elements
Setpoints
Level 1
Out-of-step (78)
889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
Figure 4-95: Impedance Elements Display Hierarchy
Device
System
Inputs
Group 1
Outputs
Group 2
Data Capture
Protection
Group 3
Monitoring
Group 4
Control
Group 5
FlexLogic
Group 6
RTD Temperature
Level 2
The Out-of-step element provides an out-of-step (loss-of-synchronism or pole slip) tripping
function for generators. The element measures the positive-sequence apparent
impedance, and traces its locus with respect to a single blinder operating characteristic
with an offset mho supervisory. The purpose of the supervisory mho is to permit tripping
for swings that pass through the generator or step-up transformer and a limited portion of
the system, but to prevent operation on stable swings that pass through both blinders and
outside the mho characteristic.
The out-of-step tripping feature operates as follows: The trip sequence identifies unstable
power swings by determining whether the impedance locus enters one blinder, spends a
finite time between the left and right blinder characteristics, and then exits the opposite
blinder. The out-of-step trip process is supervised by a mho characteristic. If the locus
enters the left blinder, right blinder and mho characteristic (indicated by the AND operation
of OOS LFT BLD PKP and OOS RGT BLD PKP FlexLogic operands) for an interval longer than
PICKUP DELAY, the timing out signal (OOS TIMER PKP FlexLogic operand) is established.
After the PICKUP DELAY timer times out, latch 1 is set as long as the impedance stays
within the mho characteristic. If afterwards, at any time (given the impedance stays
between the two blinders characteristic), the locus exits from the opposite blinder, latch 2
is set as long as the impedance stays inside the mho characteristic. The element is now
ready to trip. If the "BLINDER EXIT" trip mode is selected, the OOS OP operand is set
immediately and sealed-in for the interval set by the SEAL-IN DELAY. If the "MHO EXIT" trip
mode is selected, the element waits until the impedance locus leaves the mho
characteristic, and then the OOS OP operand is set and sealed-in.
Generator
Current
Voltage
Data Capture
Impedance
Power
Frequency
Level 3
Level 4
PROTECTION
Out-of-step
Level 5
4–245
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- Protection
- Typical Wiring Diagrams
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