GE 869 - Page 420

4–288 869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
MONITORING CHAPTER 4: SETPOINTS
• Transients in supply voltage due to power system faults, VFDs, operation of breakers
leading to turn-turn or turn-ground fault
• Thermal stress due to overcurrent flowing due to sustained overload or fault, higher
ambient temperature, obstructed ventilation, unbalanced supply voltage etc.
increases winding temperature and reduces insulation life.
• Environment stress based on ambient temperature
The 869 relay detects stator faults using ESA based on fault frequencies computed as:
CF ± Supply frequency sidebands and CF ± Supply frequency ± Rotational frequency
sidebands
where,
CF = Center Frequency = Rotational frequency (rps) * Number of stator slots
Rotational frequency = Running speed in rpm/60
Sideband represents the upper and lower frequency region for the stated frequency at the
center.
For example, in figure 2a ‘fc’ represents the center frequency and ‘fc+fm’ or ‘fc-fm’
represents sidebands of ‘fc’.
Figure 4-121: Center frequency with sidebands
The algorithm for detection of Bearing, Mechanical and Stator fault consists of two
sections named the Baseline mode and Operation mode.
Baseline Mode
This mode runs once during the commissioning/installation for a given setup of CTs, PTs
and machine rating, for a default 48 hours (baseline period - configurable) of motor
operational time. All dB computations (highest normalized peak magnitude and energy at
peak magnitude) with baseline data are computed and captured for each load bin. During
the baseline period, dB computations are averaged continuously for each load bin and
stored as averaged normalized dBs. Thereafter the device enters into this mode whenever
there is a need to capture baseline data for a particular load bin or if the baseline data is
not captured for that particular bin during the initial 48 hours period (default) after
installation, and enters back to operational or monitoring mode instantly once baseline
data is captured and stored. FFT is run on baseline data samples to capture peak
magnitude or energy for each possible harmonic factor (k = 1,2,3) related to bearing,
mechanical and stator faults and the averaged values are stored in an internal file for each
load bin. Both data quality check and ESA accuracy checks are performed prior to
recording data. Baseline data is considered the data of a healthy motor. Users can clear
baseline data using the ‘Clear ESA baseline data’ command and capture data again by
enabling baseline mode and configuring the baseline period.
Monitoring mode