GE Vernova GER-3620 Operating and Maintenance

Page | 025

Doc Name : GER-3620 Rev P Released Date : 2021/03/15 Page 25 of 60
Maintenance Inspections
Maintenance inspection types may be broadly classified
as standby, running, and disassembly inspections. The
standby inspection is performed during off-peak periods
when the unit is not operating and includes routine
servicing of accessory systems and device calibration. The
running inspection is performed by observing key operating
parameters while the turbine is running. The disassembly
inspection requires opening the turbine for inspection of
internal components. Disassembly inspections progress
from the combustion inspection to the hot gas path
inspection to the major inspection as shown in Figure 29.
Details of each of these inspections are described below.
The section ABC Inspections describes the maintenance
inspections for the GE Vernova Annular/Silo Fleet.
Standby Inspections
Standby inspections are performed on all gas turbines but
pertain particularly to gas turbines used in peaking and
intermittent-duty service where starting reliability is of
primary concern. This inspection includes routinely servicing
the battery system, changing filters, checking oil and water
levels, cleaning relays, and checking device calibrations.
Servicing can be performed in off-peak periods without
interrupting the availability of the turbine. A periodic startup
test run is an essential part of the standby inspection.
The O&M Manual, as well as the Service Manual Instruction
Books, contains information and drawings necessary to
perform these periodic checks. Among the most useful
drawings in the Service Manual Instruction Books for
standby maintenance are the control specifications, piping
schematics, and electrical elementaries. These drawings
provide the calibrations, operating limits, operating
characteristics, and sequencing of all control devices. This
information should be used regularly by operating and
maintenance personnel. Careful adherence to minor
standby inspection maintenance can have a significant effect
on reducing overall maintenance costs and maintaining high
turbine reliability. It is essential that a good record be kept
of all inspections and maintenance work in order to ensure a
sound maintenance program.
Running Inspections
Running inspections consist of the general and continued
observations made while a unit is operating. This starts
by establishing baseline operating data during startup of
a new unit and after any major disassembly work. This
baseline then serves as a reference from which subsequent
unit deterioration can be measured.
Data should be taken to establish normal equipment
startup parameters as well as key steady state operating
parameters. Steady state is defined as conditions at
which no more than a 5°F/3°C change in wheelspace
temperature occurs over a 15-minute time period. Data
must be taken at regular intervals and should be recorded
to permit an evaluation of the turbine performance and
maintenance requirements as a function of operating time.
Heavy-Duty Gas Turbine Operating and Maintenance Considerations This operating inspection data, summarized in Figure 30,
includes: load versus exhaust temperature, vibration level,
fuel flow and pressure, bearing metal temperature, lube oil
pressure, exhaust gas temperatures, exhaust temperature
spread variation, startup time, and coast-down time. This
list is only a minimum and other parameters should be used
as necessary. A graph of these parameters will help provide
a basis for judging the conditions of the system. Deviations
from the norm help pinpoint impending issues, changes in
calibration, or damaged components.
A sudden abnormal change in running conditions or a severe
trip event could indicate damage to internal components.
Conditions that may indicate turbine damage include high
vibration, high exhaust temperature spreads, compressor
surge, abnormal changes in health monitoring systems,
and abnormal changes in other monitoring systems. It is
recommended to conduct a borescope inspection after such
events whenever component damage is suspected.
Load vs. Exhaust Temperature
The general relationship between load and exhaust
temperature should be observed and compared to previous
data. Ambient temperature and barometric pressure will
have some effect upon the exhaust temperature. High
exhaust temperature can be an indicator of deterioration of
internal parts, excessive leaks or a fouled air compressor. For
mechanical drive applications, it may also be an indication of
increased power required by the driven equipment.
Vibration Level
The vibration signature of the unit should be observed and
recorded. Minor changes will occur with changes in
operating conditions. However, large changes or a
continuously increasing trend give indications of the need
to apply corrective action.
Fuel Flow and Pressure
The fuel system should be observed for the general fuel
flow versus load relationship. Fuel pressures through the
system should be observed. Changes in fuel pressure can
indicate that the fuel nozzle passages are plugged or that
fuel-metering elements are damaged or out of calibration.
Exhaust Temperature and Spread Variation
The most important control function to be monitored is the
exhaust temperature fuel override system and the back-up
over temperature trip system. Routine verification of the
operation and calibration of these functions will minimize
wear on the hot gas path parts.
Startup Time
Startup time is a reference against which subsequent
operating parameters can be compared and evaluated.
A curve of the starting parameters of speed, fuel signal,
exhaust temperature, and critical sequence bench marks
versus time will provide a good indication of the condition
of the control system. Deviations from normal conditions
21
Non-Public- Class II (Non Critical) - NLR