Compressor Instrument and Control

Compressor control , operation and
maintenance
Control System
1
Field
Control room
front real
COMPRESSOR HAZARD
• MOVING PARTS
• HOT SURFACE
• NOISY
• LEAKS FROM THE GAS SYSTEM
• FLAMMABLE EXPLOSIVE GASES (SPARK PRODUCING
EQUIPMENT SHOULD NEVER BE USED)
ACCESSORIES
• LUBRICATION

• COOLING

• FILTERING
LUBRICATION SYSTEM
• MAIN FUNCTION IS TO REDUCE FRICTION BETWEEN
THE MOVING PARTS

• LUBRICATION HELPS COOLING THE COMPRESSOR
MOVING PARTS AND HELP PREVENT THE LEAKING
GAS OUT OF COMPRESSOR.
DESCRIPTION
• OIL FROM THE COMPRESSOR FLOWS INTO THE OIL PUMP.THE OIL IS
THEN PUMPED THROUGH FILTER WHICH REMOVES ANY SOLID
PARTICLE FROM THE OIL.
• OIL FLOWS THROUGH THE HEAT EXCHANGER WHERE IT IS COOLED
• FROM HEAT EXCHANGER MOST OF THE OIL FLOWS DIRECTLY TO
COMPRESSOR LUBRICATION.
• REST OF THE OIL GOES TO OILER.
• OILER SUPPLIES A SMALL AMOUNT OF OIL TO THE
COMPRESSOR CYLINDER
• THE OIL LUBRICTES THE PISTON RINGS AND HELPS SEAL
THE SPACE BETWEEN THE CYLINDER WALL AND THE RING.
COOLING
• WHEN A GAS IS COMPRESSED HEAT IS PRODUCED THIS
HEAT CAN CAUSE TWO PROBLEM
1. EXCESS HEAT CAN BREAK DOWN OIL CAUSING IT TO
BE LOOSE ITS LUBRICATING CHARECTORSTIC

2. GASED EXPAND WHEN THEY ARE
HEATED SINCE COMPRESSOR IS DESINGED TO
COMPRESS GASES THE EFFECT CREATE ADDITIONAL
FORCE WHICH COMPRESSOR MUST OVERCOME.
HEAT REMOVAL
• AIR COOLING AND WATER COOLING ARE TWO TECHNIQUES
1. AN AIR COOLED COMPRESSOR
EASILY IDENTIFIED BY MEAL FINS
ON ITS CASING THE FINS PROVIDE INCREASED SURFACE
AREA.
2. ANOTHER WAY TO REMOVE THE
EXCESS HEAT IS TO COOL THE GAS AFTER THE
COMPRESSION IS COMPLETE, THE DEVICE THAT
DOES THIS IS AN AFTERCOOLER OR INTERCOOLER
• DEPENDING UPON ITS LOCATION THESE EXCHANGERS
ARE CLASSIFIED AS INTERCOOLER OF AFTER COOLER.
Compressor
INSTRUMENTATION AND CONTROL
Compressor control
‘Compressor controls’’ have different definitions
among users, designers, and suppliers.
These can be, but are not limited to:
1. Machinery protection
a. Simple alarm system for several parameters
b. Simple shutdown system for several parameters
2. Safety shutdown system monitoring multiple parameters for machinery
protection
and safety of personnel
3. Same as 2, with loading/capacity control
4. Same as 3 with communications and remote monitoring. Computer
monitoring
provides enhanced automation and energy management in addition to the
capability
to store and manipulate data for maintenance and diagnostic purposes.
Compressor control cont.
Compressor control cont.2
• 5. Environmental regulations have made the
addition of emissions controls on compressors
and engine drivers necessary for certain
geographical areas.

SYSTEM CONSIDERATIONS
SYSTEM CONSIDERATIONS
The control system must be selected to suit the machine, the operator,
and the application. These considerations include, but are not
limited to:
1. Is this machine part of a critical process?
2. What is the cost/benefit ratio to be provided by controls?
3. What are the personnel hazards?
4. Is this machine in a hazardous area?
5. What codes such as NEC, API, NFPA, OSHA, EPA or other regulatory
agencies apply?

6. What degree of complexity is required for safety shutdown,
capacity control, loading control, remote start-stop capability, and
communications?

7. Should the safety devices be monitored by the
information/operations/capacity
controls system or should safety monitoring be in a
separate stand alone system?
8. Will the system be maintained by:
a. Mechanics and/or operators
b. Instrument technicians
c. Electronics technicians
d. Communications technicians
e. Users or contract personnel
9. Will the system require expansion at a later date?
SYSTEM CONSIDERATIONS
INSTRUMENTATION AND CONTROL
• THE PROPER OPERATION OF COMP. DEPENDS UPON
INSTRUMENTAITON AND CONTROL DEVICES
• THESE DEVICES ALLOWS THE COMPRESSOR TO BE STARTED
AND STOPPED.
• THEY PROVIDE INFORMATION ABOUT THE COMPRESSOR
OPERATING CONDITIONS
• THEY MAINTAIN THE VALUES OF PROCESS VARIABLES
• THEY KEEP THE COMPRESSOR OPERATION STABLE
• THEY CAN SHUT DOWN THE COMPRESSOR IF
UNSAFE CONDTITON OCCURED
• CONTROL PANEL MAY HAVE CONTROL TO REGULATE
THE SPEED

• CONTROL PANEL ME ALSO CONTAIN ALARMS THAT
LET THE PERSONNEL KNOW WHEN ABNORMAL AND
POTENTIAL DAMAGING CONDITION EXISTS
• PRESSURE CONTROLLER CONTROLS THE DISCHARGE
PRESSUR AND IF IT DEVIATES CONTROLLER
MANUPULATE THE INLET FLOW
SURGE CONTROL
• FOR A GIVEN DISCHARGE PRESSURE A COMPRESSOR HAS A
CERTAIN MINIMUM FLOW RATE. BELOW THIS FLOW RATE THE
COMPRESSOR BECOME UNSTABLE. A DECREASE IN FLOW
BELOW THE MINIMUM FLOW CAN CAUSE A SERIES OF
MOMENTARY REVERSAL OF FLOW THROUGH THE
COMPRESSOR. THIS SITUATIION IS CALLED SURGE
• SURGING RESULTS IN VIOLENT FLUCTUATIONS IN
DISCHARGE PRESSURE.
• WHEN AN ELECTRIC MOTOR IS USED AS DRIVER
SURGING CAN CAUSE EXTREME VARIANTION IN MOTOR
CURRENT.
• SYMPTOMS OF SURGING ARE LOW GAS FLOW, EXCESSIVE
VIBRATION AND BANGING SOUND INSIDE COMPRESSOR
• TO PREVENT THE SURGING THE FLOW RATE OF THE
GAS THRU THE COMPRESSOR MUST BE KEPT ABOVE
THE MINIMUM STABLE FLOW RATE OR SURGE POINT
• WHEN THE DEMAND IS LOW FLOW RATE IS
MAINTAINED BY RECIRCULATING THE PORTION
FROM DISCHARGE TO BACK TO COMPRESSOR.
SURGE CURVE
P= p2 /p1
Q 1 FLOW RATE

START UP
• PREPARING THE COMPRESSOR FOR STARTUP
• WARMING UP THE COMPRESSOR
• STARTING THE GAS FLOW THRU COMPRESSOR
• COMPRESSORS GAS SUPPLY IS AVAILABLE, CONTROLS
ARE SET IN POSITIONS.
• VALVE LINE UP MEANS ALL THE VALVE ARE PROPERLY SET.
• START THE COMPRESSOR AUXILARIES AND MAKE SURE
THEY ARE OPERATING PROPERLY.
• OPERATOR MUST CHECK THE COMPRESSOR AND MAKE
SURE THAT NO ABNORMAL CONDITION EXISTS.
• IF THE COMPRESSOR HANDLES THE FLAMMABLE GAS IT MUST BE
PURGE WITH AN INERT GAS LIKE NITORGEN.
• ONCE PURGED IT CAN BE STARTED AND KEPT IN WARMING UP.
• ONCE THE COMPRESSOR AND ITS PARTS RUNS FOR A WHILE AT A
LOW SPEED THE COMPRSSOR CAN BE BROUGHT UP TO NORMAL
SPEED.
• THIS INVOLVES THE INCREASE OF SPEED AT CERTAIN RATE CALLED
RAMP RATE
• CRITICAL SPEED – FOR CETRUFUGAL COMPRSSOR CERTAIN
ROTATIONAL SPEED CAUSE SEVERE VIBRATION, IT IS CALLED
CRITICAL SPEED.
• IT IS DUE TO PHYSICAL CHARECTORSTIC OF MOVING PARTS OF
COMPRESSOR.
• WHEN A CRITICAL SPEED IS REACHED THE RAMP SPEED IS
USUALLY INCREADED TO PASS THROUGH THE CRITICAL SPEED.
OPERATION
• ONCE STARTED COMPRESSOR SHOULD BE CHECKED
ROUTINELY.
• WHILE CHECKING A COMPRSSOR OPERATOR MUST KEEP IN
MIND THAT IT OPERATES AT VERY HIGH SPEED.
• AN IMPORTANT PART OF CHECKING A COMPRSSOR IS TO
LISTEN TO THE ABNORMAL SOUND.
• IT IS IMPORTANT TO CHECK THE COMPRESSOR BEARING FOR
EXCESSIVE VIBRATION AND OVERHEATING IT INDICATE
PROBABLE BEARING FAILURE.
• COMPRESSOR AUXILIARY CHECK IS IMPORTANT DURING
OPERATION OF COMP. LIKE OIL LEVEL IS IN NORMAL
RANGE,OIL IS CLEAR AND NOT MILKY.
• OIL PRESSURE IS IMPORTANT PARAMETER TO CHECK,
INIDCATE MALFUNCTION OF OIL PUMP OR OIL LEAK IN
SYSTEM.
• OIL PARAMETER IS CRITICAL PARAMETER, HIGHER
THAN NORMAL OIL PRESSURE INDICATES THE
CLOGGING OF SOME PART IN OIL LUBRICATION
SYSTEM.
Five Valve Loading Sequence Machine Not Running
Blowdown valve open
Bypass valve open
Suction valve closed
Discharge valve closed
Purge valve closed
Prior to start—
1. Close bypass valve.
2. Open purge valve.
3. After time delay for pressurized purge, open bypass.
Start machine—
1. After warm-up or appropriate time, initiate load sequence.
2. Open purge valve (pressurize compressor and confirm pressure).
3. Close purge valve.
4. Open discharge valve.
5. Open suction valve.
6. Close bypass valve to begin flow through the compressor. (Bypass valve can be
used to control flow through the machine.)
Five Valve Unloading Sequence
1. Open bybass valve.
2. Open blowdown valve (optional)
3. Close suction valve.
4. Close discharge valve.
• RECIPROCATING COMPRESSOR MONITORING
Monitoring systems have progressed to measuring many
parameters beyond those required for basic safety.
These include capacity, pressure, volume, time,
vibration , calculations of gas, rod load, power, fuel
consumption and efficiency.
The industry is also rapidly moving to a ‘‘predictive
maintenance’’ mode as compared to ‘‘preventive
maintenance.’’ Monitoring systems must be more
complex to accomplish predictive maintenance.
Centrifugal/Axial Compressor Monitoring
- Centrifugal and axial compressors are less forgiving than slower speed reciprocating
machines because of the operating speeds.
- The controls for centrifugal machines must have very quick response times in
order to prevent catastrophic failures and are much more complex than the systems
required for reciprocating compressors.
- Real time on-line performance monitoring and trending is now commonplace
because of available high speed computer systems.
- Surge control on axial and centrifugal machines is essential to prevent damage
in the event of rapidly changing flow conditions. Bearing vibration monitoring in
three planes and axial trip sensors, along with bearing trip monitors, are common
practice on centrifugal machinery.
Control Architecture
Enterprise
Control
Plant Control
(Production,
Quality, …)
Cell Controller
(Supervisory Control)
Machine Controller
(Automatic Control)
Device Control
(Sensors/Actuators)
Transformation Process
Raw
Material
Part or
Product
Power
Tools
Machines
Labour
Scrap or
Waste
Level 0
Level 1
Level 2
Level 3
Level 4
Industrial Automation
(Shop Floor)
Business Information
(Business Office)
Coffe break
SUPERVISION STAGES
DIAGNOSTICS
CONTROL
FAILURE DETECTION
RECONFIGURATION
PROCESS
“Inteligencia artificial para la detección y el diagnóstico de fallos”
Joaquín Melémdez / Joan Colomer (Universitat de Girona)
CONDITION MONITORING SYSTEM (CMS)
CONDITION BASED MAINTENANCE (CBM)
Impressions
(human senses)
Vibration monitors
Chemical
analysis
I&C channels
Thermograph
Maintenance
operators
DECISIONS
MAINTENANCE MANAGEMENT
Electrical
consumption
Others
Cumulated
Experience
CONDITION MONITORING SYSTEM
CONDITION BASED MAINTENANCE
COMPUTER MAINTENANCE MANAGEMENT
SYSTEM (CMMS)
CONDITION MONITORING
DECISIONS
MAINTENANCE MANAGEMENT
- Trends
- “Analysis”
- Alerts
- Store data
- Data management
- Experience database
Cumulated
Experience
CMMS
TECHNIQUES INTEGRATION FOR
FAILURE DETECTION & DIAGNOSTICS
...
Physical Process
- Continuous

- Discrete
(event driven)

- Hybrid
User Interfaces
Decision support
Alarm Generation
and management
Monitoring
Uncertainty
treatment
Knowledge
Processing
facilities
Knowledge
Representation
facilities
Modelling
Facilities
Abstraction Tools
Numeric
Processing
DB management
Supervisory
System
Numeric
variables
Qualitative
variables
Models
Data Bases
Knowledge
Bases
Alarm
generation
Fault
detection
Diagnosis
Reconfiguration
Information
ON LINE:
- Data Acquisition System
(Instrumentation,
Measures, Controllers)

OFF LINE:
- Modelling (process
representation, relations,...)
- Experience (expertise,
rules, ...)
- Learning
- History


Actions

“Inteligencia artificial para la detección y el diagnóstico de fallos”
Joaquín Melémdez / Joan Colomer (Universitat de Girona)
Sequence Control

Sequence control uses an automated
system and operating instructions.
The instructions are listed in the order
required to perform a certain task to
reach a desired result.

The sequence may begin with the
operator pushing a button in a
remotely located control room.

( Contd.)

Control System: Components

Control system components and instruments
include the following devices:

· sensing
· monitoring
· protective
· sequencing
· regulating
· optimizing

Information about each component follows.
Sensoring & Monitoring Devices

Sensing devices are the most basic control system
elements. The figure shows a partial list of common
sensing devices.

These devices only provide information to the control
systems. They do not make adjustments.

Sensing devices provide information to the monitoring
devices.

Monitoring devices include gauges, lights, and
distributed control systems. Monitoring devices provide
detailed information about operating conditions
Sensoring & Monitoring
Devices

Protective devices include shutdown and
alarm devices. If operating conditions are
sensed to be at, or in excess of, an
emergency shutdown setpoint, the
equipment is automatically shut down.

Start-up and shutdowns must be done in a
particular order to ensure safety of
personnel and prevent equipment damage.
Sequencing devices perform the necessary
steps to accomplish start-up and shutdown.
Protective & Sequencing
Devices

Regulating devices receive information
from sensing devices and adjust the
process to achieve a certain setpoint.

Regulating devices such as the anti-
surge controller make adjustments
based only on the current
measurement and do not predict
trends, as does an optimizing system,
which is discussed next.
(Contd.)
Optimizing devices are the most complex devices in a control system.
Optimizing systems can look at one variable or can be connected to a computer-
based system that controls the entire process.
The programmable logic computer (PLC) is an optimizing device.
Compressor capacity control is discussed next.

Vibration Monitoring

Several protective systems are used to alert
operators to abnormal operating conditions that
could result in damage to the turbine or other
equipment.

Vibration is one of the critical operating
parameters that is monitored by a protection
system.


A vibration monitoring system is usually a part of the gas turbine's programmable logic
control and operator terminal.

The figure shows typical vibration detector locations in relation to the rotor.
Vibration Monitoring
Vibration Monitoring System:
Purpose (Contd.)

The last topic discussed in this lesson is the
vibration monitoring system. The purpose of
the vibration monitoring system is to help in
preventing abnormal operating conditions.

The rotating shafts of any machine or gearbox
have a tendency to move axially or radially as a
result of speed, loads, worn internal parts,
unbalance, or other reasons.

Vibration Monitoring System: Purpose

Axial and radial shaft movement is called vibration.
Vibration is a continuing periodic change in a
displacement from a fixed reference.

Excessive vibration is an abnormal operating condition
that can result in equipment damage. Excessive
vibration is a symptom of other abnormal conditions.

A bent shaft or improper shaft alignment could be the
source of vibration.

Shaft Movement

Vibration monitoring systems are installed
on gas turbines and driven equipment to
monitor and sometimes record axial and
radial shaft movement.

Shaft movement is monitored in either
displacement (mils), velocity (length/unit-
time), or acceleration (g's).

(Contd.)
One mil equals 0.001 of an inch. A shaft movement of 5 mils could generate an
electrical impulse of one volt. Either of these measurements may be used as
setpoints to initiate an alarm or shutdown.

Vibration Monitoring Probes
(Contd.)

In the gas turbine, vibration probes are
installed in the bearing housings near the
shaft.

The probe tips operate on 24-volt DC
power to establish a magnetic field
between the probe tip and a burnished
area on the shaft.

As the distance between the probe tip and
the shaft changes, the strength of the
magnetic field changes.
The probe senses fluctuations in
the magnetic field, and the
monitoring systems uses this
information.

The figure illustrates a typical
single and double radial probe
installation in a bearing.





Vibration Monitoring Probes:
Function

In the figure, four probes monitor the
radial movement of a gas turbine shaft
and two probes monitor the shaft axial
location.

Axial position probes 1 and 2 monitor
shaft axial movement in two places at
the thrust collar.

Probes 3Y and 4X measure radial
movement at the low pressure end of
the compressor. (Contd.)
Probes 5Y and 6X measure radial movement
at the high pressure end of the compressor.

The probes are placed 90 degrees apart to
monitor relatively both horizontal and vertical
radial movement.

One probe monitors the X axis, and the other
monitors the Y axis.





Lube Oil Instrumentation
Introduction
The preceding lessons in this series discussed
the lube oil system, its operation, and individual
components of the system.

This lesson provides information about lube oil
system pressure and temperature controls,
instruments, and alarms.

Proper lubrication of gas turbine engines is
critical to engine performance and operating
life.

Proper lubrication depends on oil pressure and
oil temperature.

High oil pressure can damage lube oil system
components. Low oil pressure can prevent oil
from reaching internal engine parts.
Introduction
Proper lubrication also depends on oil
viscosity, which is affected by oil
temperature.

Cold oil is more viscous than hot oil.
Cold oil also produces higher oil
pressure at the pump discharge.

Hot oil loses film strength because of
reduced viscosity.

Information about the devices used to
control lube oil pressure and
temperature begins the lesson.
Pressure Control Devices:
Purpose

The purpose of pressure control devices is to
regulate lube oil pressure. Excessive pressure
in the lube oil system is prevented by relief
valves.

The following lube oil system pressure
control devices are discussed:

· pump relief valve

· pressure relief valve

· diaphragm operated control valve

The figure illustrates typical lube oil
system protection devices.
Relief Valves
Lube oil pumps are protected by a relief valve. If
the oil pressure at the pump discharge outlet is
high, the valve is lifted off its seat and some of
the excess oil is returned to the pump inlet. Some
systems return the oil to the reservoir.

A lube oil system pressure relief valve relieves
excessive oil pressure.

Like the pump relief valve, this valve opens when
oil pressure overcomes spring pressure, and
excess oil is returned to the reservoir.
The pressure relief valve can be adjusted by increasing or decreasing spring tension.
Diaphragm Valve

A diaphragm valve regulates lube oil pressure
within a very narrow range. A diaphragm valve
senses lube oil pressure in the bearing header
and opens or closes to maintain the pressure in
the correct operating range.

As mentioned at the beginning of this lesson, oil
pressure and oil temperature are closely related.

Information about temperature control devices is
presented next.

Temperature Control Devices:
Purpose

The purpose of temperature control
devices is to regulate lube oil
temperature.

Such devices include:

· oil cooler

· thermostat

· lube oil regulator assembly (thermal
bypass valve and pressure regulator)
The figure illustrates a typical oil cooler
arrangement. Lube oil always flows
through an oil filter, but it does not
always flow through an oil cooler.

Oil Coolers & Thermostat

The figure illustrates two water-cooled
oil coolers. The oil cooler at the top of
the figure shows the oil temperature
control valve in the cool oil mode. The oil
cooler at the bottom of the figure shows
the oil temperature control valve in the
hot oil mode.

In the cool oil mode the valve is partially
open. Most of the oil flowing through the
valve completely bypasses the cooler.
Contd.
The oil that flows through the oil
cooler is mixed with the bypassed oil
at the control valve outlet.

The lube oil temperature control
valve is an oil temperature
thermostat.

The thermostat uses a heat sensitive
spring to position the valve.




Oil Coolers & Thermostat

In the hot oil mode, the thermostat spring
expands to hold the valve against the valve
seat and stop the flow of oil through the
bypass part of the valve.

When the thermostat is cold, the spring
retracts to lift the valve off its seat.

This position allows the oil to flow through
the valve and bypass the oil cooler.

As the thermostat warms, it begins to close
the temperature control valve to force
more flow through the oil cooler.
Lube Oil Regulator Assembly

A typical lube oil regulator assembly
contains:

· two thermal bypass valves
· a pressure regulating unloading valve

The figure shows these components and
the flow of the oil through the lube oil
regulator assembly.

(Contd.)

The thermal bypass valves located
inside the lube oil regulator assembly
serve two purposes:

· control the lube oil temperature

· protect the oil cooler against high oil
pressure during a cold weather start

If lube oil temperature is below 60°F,
the thermal bypass valves are fully
open and lube oil bypasses the oil
coolers.
Lube Oil Regulator Assembly

When oil temperature exceeds 60°F, the
valves begin to close and are fully closed at
140°F. At that point, all oil flows through the
oil cooler.

This assembly also protects the oil cooler
against high oil pressure during cold weather
starts.

When the differential pressure across the
bypass valves exceeds 50 psig, the valves are
opened wide enough to maintain 50 psig
differential pressure. ( Contd.)

Another component of the lube
oil regulator assembly is the
pressure regulating unloading
valve.

This valve is pilot operated and
spring closed. The valve also has
a center passage with an oil
metering opening.




Lube Oil Regulator Assembly

During operation, pressurized pilot oil flows through the
opening to the back side of the regulating valve and assists
the spring in keeping the valve closed.

Oil pressure is adjusted by means of the externally adjusted
pilot oil pressure relief valve. Pressurized pilot oil comes
from the lube oil filter outlet.

As the engine-driven lube oil pump pressure increases with
engine speed, the unloading valve opens to maintain a
constant lube oil system pressure.

Lube oil system instruments and alarms are discussed next.
Instruments & Alarms
Instruments provide information on the operation
of the lube oil system. They monitor conditions such
as oil level in the reservoir and oil pressure and
temperature throughout the system.

Alarms alert the operator to out-of-limit conditions
that must be corrected to ensure safe operations.

The lube oil system instruments and alarms used by
G.E. and Solar perform the same basic functions.
However, the schematics used by the two
companies are different.

Schematics for both companies are included in this
lesson.
G. E.: Level Indicator

The figure shows a typical G.E. lube oil system
schematic. The devices explained are highlighted. The
letter "L" in a circle represents the lube oil reservoir
level indicator.

As drawn in the schematic, the level indicator is a local
gauge. It also signals lube oil level information to the
gas turbine control panel and to the distributed
control system (DCS).

Various lube oil levels are listed to the right of the
level indicator. When the oil level is 12 inches below
the top of the tank, the lube oil reservoir is considered
full.
G. E.: Level Indicator

When the level is 10 inches or less from the top
of the reservoir, the high lube oil level alarm is
initiated by the high level switch 71QH-1.

The level gauge indicates EMPTY when the oil
level is 16 inches below the top of the tank.

If the oil level is 17 inches below the top of the
tank, level switch 71QL-1 initiates the low lube
oil level alarm and shutdown.

G. E.: Temperature Indicator
& Relief Valve

The temperature indicator gauge is
identified by the letter "T" in a circle.

This gauge indicates the temperature of
the lube oil in the reservoir.

The relief valve VR1 regulates the
discharge pressure of the main engine-
driven lube oil pump, which is discussed
next.
G. E.: Pressure Indicator

In the figure, the main lube oil pump is a shaft-
driven gear pump.

This pump is attached to the accessory gearbox
of the gas turbine.

Following the discharge line from the bottom of
the main lube oil pump, the first instrument
encountered is a pressure indicator identified by
the letters "PI" in a circle.

Follow the pump discharge line almost to the oil
cooler where another pressure indicator is
located.
G. E.: Pressure Indicator &
Switch
Low lube oil pressure switch 63QA-1 is located to
the right of this indicator. During the shutdown
sequence or whenever the main oil supply
pressure decreases to approximately 75 psig, oil
pressure switch 63QA-1 actuates. This action starts
the auxiliary lube oil pump.

The auxiliary lube oil pump, identified as 88QA in
the figure, is a motor-driven pump. A pressure
indicator and another pressure switch are located
between the pump and the check valve.

The pressure switch, identifed as 63QP, signals the
control system when the auxiliary lube oil pump is
operating.
G. E.: Pressure Indicator &
Switch

The emergency lube oil pump is identified as 88QE.

An emergency lube oil pump is started when AC
power is lost or the auxiliary lube oil pump fails.

The emergency lube oil pump is started by actuating a
low lube oil pressure switch located on the gas
turbine bearing header. This pump also has a pressure
indicator and a "run" switch located between the
pump and the check valve.

Pressure switch 63QE sends a "pump running" signal
to the gas turbine control system when the
emergency lube oil pump is operating.
G. E.: Pressure Indicator &
Switch

In the G.E. lube oil system, a pressure
indicator is installed in the discharge of each
pump.

The indicator may be local, it may have a
transmitter to signal the pressure
information to the DCS, or both.

G.E. uses a pressure switch at the discharge
of each motor-operated pump to initiate a
"pump running" signal to the DCS.
G. E.: Differential Pressure
Indicator
In the figure, lube oil flows from the pumps to the oil
coolers, oil filters, and the bearing header.

Lube oil for the generator is discharged from the main
lube oil header.

The differential pressure indicator (PDI) is connected
across the lube oil filter inlet and outlet lines.

The purpose of the differential pressure indicator is to
monitor the pressure drop across the lube oil filter
that is in operation.
The device identified as 63QQ-1 is the main lube oil filter differential pressure alarm switch.

This switch initiates an alarm when the differential pressure reaches the setpoint.
G.E.: Bearing Header
Pressure Regulator

The bearing header pressure regulator
(VPR2) is located between the generator
lube oil line and the gas turbine bearing
header.

A diaphragm in the regulator senses the
oil pressure in the bearing header and
opens or closes the control valve to
maintain set pressure.

G. E.: Emergency Pump Start Switch

To the left of the bearing header is the low lube oil pressure emergency pump start
switch, 63QL.

On the right side of the gas turbine bearing header are three outgoing lines labeled
hydraulic supply.

Lube oil from the bearing header provides oil to the hydraulic pumps which provides
hydraulic pressure for starting, inlet guide vane operation, and fuel gas control valves.
G. E.: Temperature Switches

High lube oil temperature may indicate fouled lube oil
cooler tubes.

A temperature indicator and several switches are located to
the right of the hydraulic supply lines.

The temperature indicator is a local instrument as drawn.
When used with a transmitter, this temperature can be
signaled to the DCS.

The devices identified as 26QT are related temperature
switches. If lube oil temperature in the bearing header
increases to approximately 165°F, a high lube oil
temperature alarm is initiated. If corrective action is not
taken and lube oil temperature increases to 175°F,
temperature switches 26QT-1A and 26QT-1B will trip the
gas turbine.
G. E.: Thermocouples

The device labeled LT-TH-1A,B represents
thermocouples located in the bearing header.

These thermocouples provide high temperature
alarms and trip signals to the control system.

To trip the unit, the trip temperature must be
sensed by at least two thermocouples.

This concludes the information about oil
instruments and alarms in the G.E lube oil system.

The Solar lube oil system will be discussed next.
Thermocouples

The point where the two
dissimilar metals are joined
that will be most exposed
to the heat of a fire is called
the hot junction.

The cold junction,
sometimes called the
reference junction, is
enclosed in dead air space
between insulation blocks.
( Contd. )
Thermocouples

A typical thermocouple is
installed in a protective well
or cage. Other
thermocouple cages have
several passages that allow
air (or gas) to enter the
protective cage and
surround the elements.

A thermocouple fire
detection system has a
different response to the
thermal switch
system.

(Contd.)
Thermistor

A thermistor (thermal resistor) is a
resistive circuit component. When
cool, a thermistor has high resistance
to current flow. As the temperature of
a thermistor increases, its resistance
decreases.

A thermistor fire/rate-of-rise detection
system is a continuous loop system
that usually surrounds the surveillance
area.

(Contd.)
Thermistor

In both systems, the power lead is insulated from
ground. The single-wire system uses an insulator of
ceramic beads that are coated with a substance
called eutectic salt. The two-wire system uses a
thermistor material to insulate the wires.

Each of these materials loses electrical resistance
when heated.

In the fire/rate-of-rise circuit diagram shown in the
figure, 24V DC is supplied to the hot lead through
an alarm relay coil.

When cool, the insulation does not allow current
flow between the hot lead and ground.
Thermistor

When a fire condition heats the
insulator material, it loses electrical
resistance and a path is complete from
the hot lead to ground.

The thermistor system, like the thermal
switch systems, automatically resets
when cooled.

A pneumatic fire detection system is
discussed next.


MM
Maintenance Management Overview

SUPERVISION STAGES
DIAGNOSTICS
CONTROL
FAILURE DETECTION
RECONFIGURATION
PROCESS
“Inteligencia artificial para la detección y el diagnóstico de fallos”
Joaquín Melémdez / Joan Colomer (Universitat de Girona)
CONDITION MONITORING SYSTEM (CMS)
CONDITION BASED MAINTENANCE (CBM)
Impressions
(human senses)
Vibration monitors
Chemical
analysis
I&C channels
Thermograph
Maintenance
operators
DECISIONS
MAINTENANCE MANAGEMENT
Electrical
consumption
Others
Cumulated
Experience
CONDITION MONITORING SYSTEM
CONDITION BASED MAINTENANCE
COMPUTER MAINTENANCE MANAGEMENT
SYSTEM (CMMS)
CONDITION MONITORING
DECISIONS
MAINTENANCE MANAGEMENT
- Trends
- “Analysis”
- Alerts
- Store data
- Data management
- Experience database
Cumulated
Experience
CMMS
Refer to BS3811:2000

Maintenance is the work undertaken in order to keep or
restore a facility to an acceptable standard level.
Work undertaken All activities (information, analysis, repair, etc.)
To keep Planned maintenance (Preventive, Predictive and
proactive) policy for critical equipment
To restore Unplanned maintenance (Corrective or run to failure
policy for non-critical equipment
Facility System level (equipment, unit, plant)
Acceptable standard
level
Acceptable level at certain working condition (HSE,
working hours, etc.)
Cost
PM Cost
Total Maintenance Cost
CM Cost
Best level
Down Time Cost
PM level

Reliability

Total Maintenance cost
= Direct cost + Overhead cost + Downtime cost
or
= PM cost + CM cost + Downtime cost
Company Logo
Criticality Analysis
HSE Effect
Stand By
Availability
Process Effect
Major
(B)
Major
(A)
Without
(C)
With
(D)
Minor
Minor
Centrifugal Pump
(System level)
Criticality
Drain system C
Water system B
Oil system A
Steam system A
Fire-fighting system A
Comparison of different maintenance policies
Policy
Approach
Goals
Reactive
Run to failure (fix-it when
broke).
Minimize maintenance
costs for non-critical
equipment.
Preventive
Use-based maintenance
program.
Minimize equipment
breakdown.
Predictive
Maintenance decision
based on equipment
condition.
Discover hidden failures
and improve reliability for
critical equipment.
Proactive
Detection of sources of
failures.
Minimize the risk of
failures for critical systems.
Global
Integrated approach.
Maximize the system
productivity.
A comparison among proactive maintenance approaches
Policy Approach Goals
RCFA
Identification of root causes of
failures.
Eliminate failures.
FMECA
Identification of criticality of
failures.
Improve equipment
availability.
HAZOP
Identification of hazards and
problems associated with
operations.
Improve HSE effect.
RCM
Determination of best
maintenance requirements for
critical systems.
Preserve system
function & improve
reliability.
RBI
Determination of an optimum
inspection plan for critical
systems.
Improve system HSE
and availability.
Comparison among global maintenance approaches

Policy Approach Goals
OSM
Optimization
approach for the
global maintenance
system.
Maximize reliability
measures and minimize
maintenance cost rates.
TPM
Comprehensive
productive-
maintenance system.
Maximize plant
effectiveness and resource
productivity.
Facility equipment are divided into four major categories:
• Run-to-Failure - Most cost effective to let equipment run
unattended until it fails. Used on lowest priority equipment.

• Preventive Maintenance - Perform maintenance tasks
on a piece of equipment at regular intervals, whether the equipment
needs it or not.

• Predictive Maintenance - Perform maintenance based
upon real-time data collected on a piece of equipment. This data
shows the ‘health’ of the equipment

• Proactive Maintenance - Determine root causes of
failure and implement ‘fixes’ (e.g., redesigning the piece of
equipment so that it does not break down as frequently)

Why PM should be done?

To prevent
equipment failures

To detect
early failures

To discover
hidden failures
Time-Directed
Maintenance (TD)
Condition-Directed
Maintenance (CD)
Failure
Finding (FF)
Preventive Maintenance:
Predictive Maintenance:
Condition based
management
Visual
Inspection
Vibration
analysis
Ultrasonic

Pressure
analysis

Temperature
analysis
Oil
analysis
Efficiency
analysis
Wear
analysis
Atypical machine condition-vibration trend
PdM Planning:
1. Best Method (vibration analysis, .. etc.)
2. Best Frequency (inspection interval)
3. Best Locations
4. Best Tools
5. International Standard (ISO10816, .. etc.)
6. Standard Limits
7. Severity Chart
8. Trouble Shooting Chart
9. Reference Creation
10. Regular Measurements (monthly, .. etc.)
11. Analysis
12. Decision Making
13. Corrective Actions
- Good conditions,
- Routine Maintenance,
- Repair, or
- Replace.
PdM Policy: Vibration analysis:
1- Frequency: Every 300 Running Hours

2- Tool:
Vibration Equipment: accelerometers, charge amplifier and analyser.
Computer program for trend analysis and prediction.

3- International Standard: CDA/MS/NVSH107

4- Method:
Record the vibration spectrum, specify the peaks corresponds to the bearing components
Record each component peak and frequency.
By using the soft ware and the standard limits, determine the trend of each peak.
Determine the bearing state(good –need service –need change)

5- Limits: According to CDA/MS/NVSH107
Pre-failure: vibration level≤5.6 m/s
Failure: vibration level 5.6≥10 m/s
Near catastrophic failure: vibration level >10 m/s

6- Actions:
Bearing is Good
Call for bearing change
Bearing must be changed immediately
Proactive Maintenance:
• Definition: Determine the root causes of repeated failures and address
these rather than just treating the symptom.
– E.g., if seals keep failing on a certain pump, do not just keep rebuilding the
pump, figure out why they keep failing.
• Is the type of pump wrong for the application?
• Is the seal material not compatible with the fluid being pumped?
• Is the pump grossly mis-sized for the duty? etc.

• Some root causes of failure:
– Poor Design/Poor Manufacturing,
– Poor shipping, handling, and storage procedures, equipment becomes
damaged or begins to degrade before it is installed,
– Poor Installation,
– Poor materials,
– Poor working conditions.
What is the Maintenance? How?
1- How to keep or restore the facility at
acceptable standard level in certain
operating conditions?
 System description
 Main parameters
 Main items
 Functional block diagram
 Criticality
 Working conditions
2- How to prevent the failures?
Main failures:
PM:
3- How to discover the hidden failures?
Main failures:
Policy:
4- How to detect the early failures?
Main failures:
Policy:
5- How to minimize the risk of failures?
Main failures:
Risk:
Policy: