8/3/2019 Catterpillar Gens Set Requirment
1/28
8/3/2019 Catterpillar Gens Set Requirment
2/28
8/3/2019 Catterpillar Gens Set Requirment
3/28
Contents
Petroleum Applications ......................................................... 1Petroleum Equipment & Terminology................................... 2
Drilling Rig................................................................... 2Conventional or Compound Rig................................... 4Split Rigs................................................................. 5
Service Rigs................................................................. 6Workover Rig ...........................................................6Technical Well.......................................................... 6Additional Service Rig Terms...................................... 7
Mobile Rigs.................................................................. 8Carrier Designations.................................................. 8Mobile Rig Drivetrain Configurations.......................... 10
Production Pumping.................................................... 10Piston Pumps......................................................... 10Centrifugal Pumps .................................................. 10Horizontal Pumps.................................................... 10Rating Review for Pumps......................................... 11
Fire Pump.................................................................. 11Offshore Crane........................................................... 11Auxiliary Power.......................................................... 11
Electric Power Generation................................................ 12DC Generators ........................................................... 12
8/3/2019 Catterpillar Gens Set Requirment
4/28
AC Generators with SCR ............................................. 13Silicon Controlled Rectifier (SCR) Drives..................... 14
Variable Frequency Drive (VFD) Systems ....................... 14Other Petroleum Power Application Considerations ............. 16
Loading Considerations ............................................... 16Transient Response..................................................... 16
Sizing Criterion....................................................... 16ISO Classification ................................................... 17Equipment Selection................................................ 17
Off Shore Requirements .............................................. 18Island Mode............................................................... 18Motor Loads .............................................................. 18Motor Starting ........................................................... 19Regenerative Power .................................................... 20
8/3/2019 Catterpillar Gens Set Requirment
5/28
2006 Caterpillar
All rights reserved.
Information contained in this publication may be considered confidential.
Discretion is recommended when distributing. Materials and specificationsare subject to change without notice.
CAT, CATERPILLAR, their respective logos and Caterpillar Yellow, as well
as corporate and product identity used herein, are trademarks of Caterpillar
and may not be used without permission.
ForewordThis section of the Application and Installation Guide generally describes
Petroleum Applications for Caterpillar engines. Additional engine systems,
components and dynamics are addressed in other sections of this Application
and Installation Guide.Engine-specific information and data are available from a variety of
sources. Refer to the Introduction section of this guide for additional
references.
8/3/2019 Catterpillar Gens Set Requirment
6/28
8/3/2019 Catterpillar Gens Set Requirment
7/28
Application and Installation Guide Petroleum Applications
2006 Caterpillar
All rights reserved. Page 1
Petroleum ApplicationsThe use of Caterpillar engines in petroleum applications requires specific
considerations for engine selection and installation to ensure dependable
performance and a long, trouble-free life.
Petroleum applications for diesel engines include drilling, well servicing,production power, offshore emergency or essential services power, and
pumping applications. Natural gas engines are often used in petroleum
applications for gas compression drive, production power and production
pumping.
The information presented in this guide will aid in planning, installation and
customer acceptance phases of a project. While this application and
installation guide summarizes many aspects of installation, Caterpillar dealers
stand ready to assist you.
It is the installers responsibility to consider and avoid possibly hazardous
conditions which could develop from the systems involved in the specificengine installation. The suggestions provided in this guide regarding
avoidance of hazardous conditions apply to all applications and are
necessarily of a general nature since only the installer is familiar with the
details of a particular installation. Consider the suggestions provided in this
guide as general examples only and are in no way intended to cover every
possible hazard in all installations.
SECTION CONTENTS
Petroleum Equipment &
Terminology........................ 2
Drilling Rigs Service Rigs Mobile Rigs Production Pump Fire Pump Offshore Crane Auxiliary PowerElectric Power Generation....12
DC Generator AC Generator with SCR
Variable Frequency Drive(VFD) Systems
Generator Set EngineRequirements
Other Petroleum Power
Application Considerations...16
Loading Considerations Transient Response Offshore Requirements Island Mode Motor Loads Motor Starting Regenerative Power
8/3/2019 Catterpillar Gens Set Requirment
8/28
Petroleum Applications Application and Installation Guide
2006 Caterpillar
Page 2 All rights reserved.
Petroleum Equipment & Terminology
Before selecting an engine, a
general understanding of the driven
equipment is necessary. Since
nomenclature in the petroleumindustry is not completely standard,
the terminology used in this guide
should be considered representative.
Below are the terms this guide uses
for equipment and systems used in
the petroleum industry.
Drilling RigDue to the fact that oil and gas are
often located far beneath the earth's
surface, it can take a lot of work to
tap into reservoirs containing these
resources.
A drilling rig creates a borehole, or
well, where oil and natural gas can
be extracted for the production of
fuels and other petroleum-based
products. An example of a land
based drilling rig is shown in Figure
1. While all drilling rigs move from
site to site, some rigs requireconsiderable effort and up to 70
semi trucks to change location,
while others can fit on just one
truck. These easily portable rigs will
be referred to as mobile rigs and are
discussed later in this section.
Drilling rigs may be described as
mechanical or electric. These terms
refer to the method in which power
is supplied to the larger equipmenton the rig.
On mechanical rigs, power from
the engine(s) drives the rig
equipment either directly, through a
clutch or through a torque converter.
Electric rigs use engine power to
drive one or more generators. The
generated electricity is then used to
operate motors for the largerequipment on the rig. There are
three types of electric rigs: DC, SCR,
and VFD. DC, or direct current
indicates that a DC generator
supplies power to DC motors. These
are the oldest type. SCR, or Silicon
Control Rectifier, indicates that AC
power from the generators is
changed to DC by switchgear to
power DC motors. This allows for
more power to be generated by
smaller generators and is the most
common type. VFD, or variable
frequency drive, is the newest kind
of rig which utilizes variable rpm AC
motors allowing for even more
power out of the same sized
equipment. The details of these
applications are discussed later in
this guide.
Typical rig equipment, for both
mechanical and electric, include a
drawworks, a rotary table and mud
pumps. These equipment items are
among the larger equipment on the
rig and will have the most significant
and important power requirements.
Some applications also run
compressors which can have any
variety of power requirements.
Drawworks
The drawworks is the cable reel
and controls that hoist the drilling
string into place.
The drawworks also has accessory
drives which assist the crew to
8/3/2019 Catterpillar Gens Set Requirment
9/28
Application and Installation Guide Petroleum Applications
2006 Caterpillar
All rights reserved. Page 3
make up and break out the
joints to and from the drill string.
The power rating of the rig refers
to the power rating of the
drawworks. However, the total
power on the rig will be more. Forexample, a rig referred to as a
3000 hp rig will be equipped with
more than 3000 hp (likely 4500 hp,)
but is equipped with a 3000 hp
drawworks.
Drilling String
A drilling string is a length of pipe
made from separate pieces on which
a drill bit or other borehole tools are
mounted. A portion of the rotarytable turns, which turns the drill
string, which turns the bit attached
to the bottom of the drill string.
Electric rigs might also use a top
drive instead of a rotary table. In this
case, an electric motor in a piece of
equipment attached to the traveling
block on the hoist connects to the
top of the drill string and serves to
turn the bit.
Rotary Table
The rotary table provides the rotary
movement to the drilling string. The
table clamps to the kelly, a special
length of rectangular pipe at the top
end of the drilling string and a
portion of the table turns, providing
a clockwise rotation to the drill
string.
Mud Pumps
Drilling fluid, or mud, is a slurry of
fluid, chemicals and suspended
solids. Mud pumps circulate the mud
down the drill string and up the
outside of the bore hole (also called
the annulus). Mud pumps are usually
piston style, high pressure pumps.
To meet industry demands, mud
pumps are being designed for deeper
wells, requiring higher horsepower.
Mud is absolutely crucial to a
successful drilling operation, makingreliable power to these pumps
equally crucial.
Various mud formulas serve as a
coolant for the drill bit, a medium for
removing drilled rock (or cuttings)
from the hole, and as weight to
stabilize drill-casing pressures and
reduce the possibility of blowouts.
Mud pumps also supply other
fluids and chemicals to the borehole
that stimulate well production.
Gas Compressors
Unlike crude oil, natural gas cannot
be easily pumped into tanks and
shipped. To achieve enough volume
for economical transportation,
natural gas must be compressed and
either loaded as a liquid into
specially designed tank vehicles, or
compressed into a pipeline. Enginedriven compressors are commonly
used for this purpose.
Compressor plants, consisting of
many individual compressors,
pressurize natural gas so it will flow
over long distances through
pipelines. The pipelines are used to
carry gas from the field, to auxiliary
treatment processes and to market.
AC Auxiliary Generators
Although mechanical rigs are
driven directly by engine power, AC
electricity is needed for lighting,
switches and smaller electric
equipment. AC auxiliary generators
8/3/2019 Catterpillar Gens Set Requirment
10/28
Petroleum Applications Application and Installation Guide
2006 Caterpillar
Page 4 All rights reserved.
provide the electricity needed on
mechanical rigs.
Conventional or Compound Rig
Conventional rigs use a mechanical
drive system, known as a
compound, to transmit engine power
to the rigs hoisting, drilling and mud
pump systems.
Various configurations of engines,
compounds and equipment are
possible; for instance, a compound
may be used along with additional
independent drives, as shown in
Figure 1 and Figure 2.
Clutches are used to transfer the
power from the engines to the
compound and the equipment.
Power transfer from the engines can
be direct drive (usually through an
air clutch from the flywheel) or
torque converter drive. Caterpillar
engines work well with both,
however a torque converter is more
forgiving, and acts as a shock
absorber which can reduce wear on
the engine and compound
components. The torque converter
does require cooling however
(usually a 30% increase in heat
rejection requirements) which must
be taken into consideration whensizing the radiator.
Other conventional rig details can
be seen in Figure 1.
The drawworks and rotarytable are on an elevated
structure to provide clearance
for drilling safety valves.
The engines are also elevatedto simplify power transmission
to the drawworks.
Engine outputs are connectedtogether with the compound.
A number of clutches control
power distribution. Normally,
engines operate in compound
while hoisting and separately
when running the rotary table
and mud pumps.
Conventional Rig
Figure 1
8/3/2019 Catterpillar Gens Set Requirment
11/28
Application and Installation Guide Petroleum Applications
2006 Caterpillar
All rights reserved. Page 5
Typical Conventional Rig
Figure 2
Typical Split Rig
Figure 3
Split Rigs
Split rigs utilize independent drivesto power the various pieces of
drilling machinery. Figure 3 shows
two engines driving the drawworks
and rotary table through a
compound and two independent
engines driving separate mud
pumps. Split rig applications allow
for numerous combinations ofequipment, compounds and drives.
This can include the use of electric
motors for a portion of the rigs
power requirement.
8/3/2019 Catterpillar Gens Set Requirment
12/28
Petroleum Applications Application and Installation Guide
2006 Caterpillar
Page 6 All rights reserved.
Service RigsSimilar to drilling rigs, service rigs
can be mechanical or electric.
Service rigs perform well servicing
after the primary drilling is
completed. This broad categorygenerally includes oilfield activities
that provide underground repair or
alteration of an existing well. They
help prolong the useful life of the
well.
Service rigs that utilize large
engines are used to perform three
distinct services: cementing,
acidizing and fracturing.
Workover and technical well aretwo types of service rigs.
Workover Rig
Workover rigs provide maintenance
support for an existing well. This
can include the removal and
replacement of the drill-string, the
repair of casings and cementing. A
workover rig may be called a pulling
unit when there is no provision of
rotating the tubing string.
Cementing
Cementing is the process of
pumping cement down a well bore
to anchor the casing. Cementing can
be required several times during the
drilling and workover of a well.
Cementing units normally carry
mixing equipment not found on
acidizing/fracturing units.
Cementing a well requires less
power, 75-373 kW (100-500 hp)
than fracturing or acidizing [500-
10000 hp (373-7460 kW)].
Cementing is thus usually done with
trucks with two engines of
approximately 400 hp (300 kW)
each.
Additionally, some rigs include a
limited rotary table capacity for use
during well bore cleanout, while
drilling out plugs (packers), or limitedredrilling in an existing well.
Technical Well
Technical well service rigs are not
equipped to do mechanical work on
a well. Technical well services
provide support functions to improve
production. One capability is to
provide means to change
productivity of underground
formations. This is usually done byacidizing and fracturing. Multiple
mobile units are used for high power
acidizing and fracturing operations.
Acidizing
Acidizing is the process of
pumping an acid down the casing of
a completed well into the desired
producing formation. Certain types
of rock can be dissolved by acid,
and this dissolving process createschannels by which hydrocarbons can
more readily flow to the well bore.
Fracturing
Fracturing is the process of
applying an ultra-high pressure,
13783 to 103448 kPa (2,000 to
15,000 psi), down the casing of a
completed well to a desired
producing formation. This pressure
fractures the rock and createschannels by which hydrocarbons can
more readily flow to the well bore.
The same service rig may be used
to acidize or fracture. This does
however require changing the fluid
8/3/2019 Catterpillar Gens Set Requirment
13/28
Application and Installation Guide Petroleum Applications
2006 Caterpillar
All rights reserved. Page 7
end of the pump to match various
pressure and flow requirements.
An acidizing and fracturing unit
consists of an engine, transmission,
and piston-type pump. This
equipment is usually mounted on acommercial truck chassis or may be
trailer-mounted. Mobil rigs will be
discussed in more detail later in this
section. Figure 4 shows a mobile
acidizing/fracturing unit.
Fracturing and acidizing are usually
performed by trucks that have a
1250-2250 hp (930-1575 kW)
engine.
A cement unit is similar but uses
smaller engines; cementing units are
not normally used for fracturing and
acidizing.
Figure 4
Nitrogen Pumping
Nitrogen pumpers can be used
with fracturing units. Nitrogen is
used for foam-fracturing in
formations that would be damagedby a large volume of fracturing fluid.
Nitrogen can also be used to remove
the fracturing fluid from a well after
the fracturing operation; the nitrogen
expands on removal of pump
pressure.
Additional Service Rig Terms
Coil Tubing
Coil tubing is a long, continuous
length of pipe wound on a spool.
The pipe is straightened prior to
pushing into a well bore and recoiled
to spool the pipe back onto the
transport and storage spool.
Depending on the pipe diameter,
typically 25.4 to 114.3 mm (1 to 4-
1/2 in.), and the spool size, coiled
tubing can range from 610 to 4570
m (2000 to 15,000 ft) or greater
length.
Well Workover and Intervention
Well workover and intervention is a
generic term relating to the use of a
coiled tubing string and associated
equipment. As a well-intervention
method, coiled tubing techniques
offer several key benefits over
alternative well-intervention
technologies. The ability to work
safely under live well conditions,
with a continuous string, enables
fluids to be pumped at any timeregardless of the position or
direction of travel. This is a
significant advantage in many
applications. Installing an electrical
conductor or hydraulic conduit
further enhances the capability of a
coiled tubing string and enables
relatively complex intervention
techniques to be applied safely.
BlendersBlenders are the equipment used to
prepare the slurries and gels
commonly used in stimulation
treatments. The blender should be
capable of providing a supply of
adequately mixed ingredients at the
desired treatment rate. Modern
http://www.glossary.oilfield.slb.com/Display.cfm?Term=wellborehttp://www.glossary.oilfield.slb.com/Display.cfm?Term=fthttp://www.glossary.oilfield.slb.com/Display.cfm?Term=slurrieshttp://www.glossary.oilfield.slb.com/Display.cfm?Term=gelshttp://www.glossary.oilfield.slb.com/Display.cfm?Term=stimulationhttp://www.glossary.oilfield.slb.com/Display.cfm?Term=stimulationhttp://www.glossary.oilfield.slb.com/Display.cfm?Term=gelshttp://www.glossary.oilfield.slb.com/Display.cfm?Term=slurrieshttp://www.glossary.oilfield.slb.com/Display.cfm?Term=fthttp://www.glossary.oilfield.slb.com/Display.cfm?Term=wellbore8/3/2019 Catterpillar Gens Set Requirment
14/28
Petroleum Applications Application and Installation Guide
2006 Caterpillar
Page 8 All rights reserved.
blenders are computer controlled,
enabling the flow of chemicals and
ingredients to be efficiently metered
and requiring a relatively small
residence volume to achieve good
control over the blend quality anddelivery rate.
Hydraulic Pump
The hydraulic pump is an artificial-
lift system that utilizes an
underground, or down-hole, pump. A
surface hydraulic pump pressurizes
crude oil called power oil, which
drives the down-hole pump. When a
single production string is used, the
power oil is pumped down thetubing and a mixture of the
formation crude oil and power oil are
produced in the space between the
casing and tubing; this space is also
known as the annulus. If two
production strings are used, the
power oil is pumped through one of
the pipes, and the mixture of
formation crude oil and power oil are
produced in the other parallel pipe.
Mobile RigsMobile units are defined as oil field
drilling or workover units that are
permanently mounted on wheels.
They are frequently called chassis or
carrier units, self-propelled or trailer
mounted. They are a version of the
split rig.
Carrier Designations
Figure 5 shows a back-in workoverrig. It is representative of the
workover rig carrier designation. A
drive-in carrier has the drivers cab
located at the hinge point of the
derrick.
These rigs may also be trailer-
mounted.
Figure 5
Mobile Drilling Rig
A truck or trailer-mounted unit
used to drill a well is known as a
mobile drill rig. The unit consists of
an engine, transmission, drawworks
and a rotary table. In regard to
mobile drilling rigs, mud pumps are
normally independent units.
A mobile drilling rig may even be
used for both drilling and workover,
or the basic unit can be sold into
either application. In such cases, the
major difference is depth capacity. Adrawworks and derrick used for
drilling (where heavy casing is
handled) has a smaller depth
capacity than when used for work-
over (where lighter tubing or rods
are handled).
Manufacturers sales specifications
will state both drilling and workover
depth capacities. Depending upon
power and derrick capacity, dual-purpose rigs (workover/drilling) can
drill to more than 12,000 ft. (3600
m) and workover to more than
20,000 ft. (6000 m).
http://www.glossary.oilfield.slb.com/Display.cfm?Term=productionhttp://www.glossary.oilfield.slb.com/Display.cfm?Term=formationhttp://www.glossary.oilfield.slb.com/Display.cfm?Term=productionhttp://www.glossary.oilfield.slb.com/Display.cfm?Term=formationhttp://www.glossary.oilfield.slb.com/Display.cfm?Term=formationhttp://www.glossary.oilfield.slb.com/Display.cfm?Term=productionhttp://www.glossary.oilfield.slb.com/Display.cfm?Term=formationhttp://www.glossary.oilfield.slb.com/Display.cfm?Term=production8/3/2019 Catterpillar Gens Set Requirment
15/28
Application and Installation Guide Petroleum Applications
2006 Caterpillar
All rights reserved. Page 9
Mobil Workover Rig
A truck or trailer-mounted unit
used to pull rod and tubing from a
producing well describes a mobile
workover rig. The unit consists of an
engine, transmission anddrawworks. Occasionally, a mobile
workover rig includes a chassis-
mounted mud pump. This is required
to kill a flowing well, provide
circulation during cleanout and while
drilling out plugs, etc. Normally, a
mobile workover rig will use an
independent mud pump kill unit.
Mobile Rig Drivetrain Configurations
Figure 6
8/3/2019 Catterpillar Gens Set Requirment
16/28
Petroleum Applications Application and Installation Guide
2006 Caterpillar
Page 10 All rights reserved.
Mobile Rig Drivetrain Configurations
Figure 6 shows a few mobile rig
drivetrain configurations. There are
many other possible combinations of
equipment and configurations.
If the unit is a trailer unit, the
power system drop-box (K) and drive
axle (J) are eliminated.
On the twin engine in-line setup,
the two engines may also be offset
or the rear engine elevated to
eliminate the dropbox (C).
Rigs using only a torque converter
behind the engine may have a
drawworks with either a two-or
three-speed transmission or high-low
drum clutches.
Production PumpingPetroleum applications require a
wide range of pumps to move fluid
(either crude oil, processed products,
or salt water brine) in and out of the
well, to and from processing plants,
and on and off transport vehicles.
Production pumps can be driven byelectric motors or mechanically by
direct engine power. In the case of
electric motor drive, an engine and
generator, or genset, is required to
provide power in remote locations.
This varies on a site-by-site basis
and could include anywhere from
one genset per pump site, to a large
centrally located power house for an
entire field.
Several types of pumps are used
for this application.
Piston Pumps
Piston pumps are low rpm,
reciprocating, positive displacement
pumps that are very similar to mud
pumps for drill rigs. These pumps
are typically used to gather fluids
from the wellheads as well as
loading and unloading fluids to and
from tanks and transportation. These
pumps have high pressure ratios,and will demand a variable speed
engine rating. Piston pumps will
almost always require a speed
reducer.
Centrifugal Pumps
Centrifugal pumps work best for
steady state type pumping
applications such as pipeline
transmission. These pumps in
constant flow applications will havemoderate pressure ratios and may or
may not have a speed increaser.
Horizontal Pumps
Horizontal pumps are an adaptation
of a down-hole pump to a surface
mechanical drive or VFD electric
drive. The electric versions consist
of three parts: a gas or diesel engine
and generator, variable frequency
control, and an electric variablefrequency down hole pump. Properly
configuring the generator to be
compatible with the VFDs is crucial,
because of the complex harmonics
produced by the VFD. They are used
primarily for gathering and waste
disposal. These can have very high
pressure ratios and are used in a
manner similar to piston pumps.
These are becoming more common
in the oil field because they require
less maintenance than traditional
piston pumps.
Note: Most mechanical drive pumps
require a speed increaser or reducer.
To eliminate the chance of torsional
resonance in the system a torsional
8/3/2019 Catterpillar Gens Set Requirment
17/28
Application and Installation Guide Petroleum Applications
2006 Caterpillar
All rights reserved. Page 11
vibration analysis (TVA) will be
required to properly select the
coupling between the engine and the
gearbox and/or load.
Rating Review for Pumps
Mainline transmission / Highhour steady load A rating
Gathering and processing anddisposal B rating
Unloading and loading pumpsC rating
Fire Pump
Another piece of equipment thatrequires power is the fire pump. Fire
pumps are used to pump water for
fire emergencies.
Fire pumps are usually driven by an
independent engine and are common
in locations where access to an
adequate supply or pressure of
municipal water is limited; this
includes offshore and remote
applications. Figure 7 shows a
Caterpillar 3126 engine configured
for a fire pump application.
Figure 7
Offshore CraneOffshore cranes are used for
moving supplies on, off and around
the platform. Electric and hydraulic
systems for these cranes are usually
driven by an independent engine.Figure 8 shows a typical offshore
crane and a 3406 engine configured
to power a crane or other auxiliary
marine application.
Figure 8
Auxiliary Power
In addition to the powerrequirements of the petroleum
equipment already mentioned, many
smaller systems and components
also require power. These include
mud mix pumps, supercharger
pumps and air compressors. These
must be considered when selecting
an engine for petroleum applications.
Mobile applications, especially
single engine configurations, haveadditional auxiliary power concerns
because the engine cooling fan,
alternator, steering pump, air
compressor and hydraulic pump can
represent a significant proportion of
total engine power available.
8/3/2019 Catterpillar Gens Set Requirment
18/28
Petroleum Applications Application and Installation Guide
2006 Caterpillar
Page 12 All rights reserved.
Electric Power Generation
Many petroleum applications use
engine power to drive electric
generators instead of gears, belts
and chains associated withmechanical compounds. Electric
motors power the drawworks, rotary
table, pumps and other systems
with electricity from the generator.
These applications are called electric
drilling rigs or electric rigs.
The electric motors used for
hoisting, drilling and pumping require
high torque at zero rpm and variable
speed characteristics for efficientoperation. These characteristics are
possible using the following
methods.
Direct Current (DC)Generators
Alternating Current (AC)Generators with Silicon
Controlled Rectifiers (SCR)
AC Generators with VariableFrequency Drive (VFD) Motors
DC GeneratorsDC generators, shown in Figure 9,
supply electricity to DC motors. A
control panel regulates the power
and provides means to connect the
generators to various motors or a
motor assignment. Figure 9 also
shows that different motor
assignments are used when hoisting
or pumping and drilling.
Figure 9 is representative of diesel
engine power modules for DC
generators. It is common for these
rigs to have some AC generation
capability. The DC generator is at
the rear of the engine and utilizes a
blower, powered by a separate AC
generator, for forced ventilation of
the generator.
Many of the older DC rigs are
being converted to use the more
common AC generators.
Electric Rig with DC Generator
Figure 9
8/3/2019 Catterpillar Gens Set Requirment
19/28
Application and Installation Guide Petroleum Applications
2006 Caterpillar
All rights reserved. Page 13
Electric Rig with AC Generator & SCR
Figure 10
AC Generators with SCRDistribution of AC current is much
more efficient than DC current; this
makes AC generators an attractiveselection for power generation.
Unfortunately, the majority of
electric motors used in the
petroleum industry are DC-powered.
DC motors provide the high torque
at low rpm and variable speed
characteristics required for hoisting,
drilling and pumping. To take
advantage of AC power and DC
motors, Silicon Controlled Rectifiers(SCR) are used to convert AC power
to DC power.
The AC generators, as shown in
Figure 10, supply power to a
switchgear. The switchgear is
essentially a control panel that
regulates the AC power. The AC
power is then fed to SCR modules
where it is rectified to DC. An
integral DC control panel connects
the SCR modules to various DCmotors or a motor assignment.
Figure 10 also shows that different
motor assignments are used when
hoisting or pumping and drilling.
Figure 10 is representative of
diesel engine power modules for
SCR drives.
Auxiliary AC power, for smaller
equipment and services, is normally
supplied from the same generators;however, the 600V AC power must
be transformed to a lower voltage.
In many SCR applications, separate
main and spare AC generators are
also required for auxiliary power.
8/3/2019 Catterpillar Gens Set Requirment
20/28
Petroleum Applications Application and Installation Guide
2006 Caterpillar
Page 14 All rights reserved.
Silicon Controlled Rectifier (SCR)
Drives
Most electric drilling rigs use SCR
systems to convert AC generator
power to DC. The rated generator
voltage is usually 600V AC for both50 and 60 Hz; when rectified, this
voltage provides an ideal 800V DC
to the motors.
SCR drives require special
generators to compensate for
varying Power Factor (PF) levels and
surges relating to SCR operation.
Operating DC motors at variable
speeds causes the generator Power
Factor (PF) to fluctuate. Forexample, the drawworks transition
from 0 PF to 1.0 PF every hoisting
cycle. This is expected but the
generator must work harder to
maintain an appropriate PF.
Operation of the mud pumps at low
strokes also causes a low PF. To
overcome these fluctuations, AC
generators in drilling applications are
oversized to 0.6 or 0.7 PF and ahigher KVA rating to provide more
generator ampere capacity. The
actual power output of a generator
set with an oversize generator is
limited to the engines rated power
capacity even if the oversized
generator has a higher KVA rating.
Actual power output capacity of the
generator set is given by the
equation:
EkW = (bhp - rad fan hp) x Gen eff x 0.746
Simply oversizing the generator
will not be enough. The generator
must be form wound to provide
additional mechanical bracing of the
generator winding. This bracing
resists the forces caused by current
surges resulting from operation of
the SCR controllers. The design limit
for the generator windingtemperature rise is also lowered to
compensate for additional heating
caused by the SCR load.
Undersized generators may cause
circuit breaker tripping, slower
drawworks acceleration and
unacceptably short generator life.
Variable Frequency Drive (VFD)
SystemsThe newest technology for electricdrill rig power utilizes variable
frequency drive or VFD. The same
engine and generator that are used
for the SCR system will suit the VFD
system perfectly. The VFD
applications generate at 600 or
690VAC to the rigs buss. A portion
of the 600VAC is transformed to
480 VAC for hotel loads and non-
variable speed loads. The majority ofthe power is rectified to 800VDC
and is made available to a VFD
control system for variable speed
750 and 1500 hp AC motors. New
technology has also improved the
efficiency of the VAC motors. VFDs
use of front end diode technology,
which smoothes the conversion from
AC to DC, removes much of the
stress that the older SCR systemsplaced on the generator, and creates
load characteristics similar to a large
UPS load. However, harmonics
remain a concern, and the need to
use the same type of generator as in
the SCR application still exists.
Control of the engine and generator
8/3/2019 Catterpillar Gens Set Requirment
21/28
Application and Installation Guide Petroleum Applications
2006 Caterpillar
All rights reserved. Page 15
is usually left to the engine governor
and generator voltage regulator. The
VFD controller controls the load
application rate. Drilling contractors
should see significantly increased
generator life when comparing the
same generator in VFD rig service to
older SCR rig service.
Some drill rigs could have a
combination of both SCR and VFD
loads.
8/3/2019 Catterpillar Gens Set Requirment
22/28
Petroleum Applications Application and Installation Guide
2006 Caterpillar
Page 16 All rights reserved.
Other Petroleum Power Application Considerations
This section describes some key
factors to consider when sizing
generator equipment for common
petroleum applications. Refer tothe Petroleum Diesel Engine
Selection, Ratings and
Configuration sections of this
Application & Installation Guide for
a detailed discussion of engine
sizing and selection. Additional
guidance can be found in the
Electric Power Applications &
Generator Sizing section of this
Application & Installation Guide.
Loading ConsiderationsLoad acceptance, stability and
response play a major role in
making an installation successful.
Before selecting equipment, the
load requirements and starting
characteristics of all the systems
to be powered by the generator
must be identified, and the stability
and response requirements mustbe specified.
Transient ResponseWhen a load is applied to or
removed from a generator set, the
engine speed, voltage and
frequency are temporarily changed
from its steady-state condition.
This temporary change is called
transient response.
When a significant load is
applied, the engine speed
temporarily reduces (generally
referred to as frequency or voltage
dip) and then returns to its steady
state condition. On removal of
load, the engine speed increases
momentarily (generally referred to
as overshoot), then returns to its
steady-state condition. The time
required for the generator set toreturn to its normal steady-state
speed is called recovery time. This
is illustrated in Figure 11.
Figure 11
The degree of voltage dip or
overshoot depends on:
The amount of active power(kW) and reactive power
(kVAR) changes
The voltage regulatorsettings
The total capacity anddynamic characteristics of
the generator set
The electrical inertia of theother loads in the system
Sizing Criterion
Three primary criteria need to beprovided to accurately size a
generator set:
The acceptable percent ofvoltage & frequency dip
8/3/2019 Catterpillar Gens Set Requirment
23/28
Application and Installation Guide Petroleum Applications
2006 Caterpillar
All rights reserved. Page 17
The acceptable duration ofthe voltage & frequency dip
recovery time
The percent of a load stepand type of load to be
connected
The larger the voltage dip a
generator set can tolerate, the
smaller and perhaps more
economical the generator set can
be. Typical permissible voltage dip
for oil field applications is 25%-
30%. By comparison, a sensitive
application, such as a hospital or a
hotel where loading is light and
equipment is sensitive or flickeringof lights would be highly
objectionable, the permissible
voltage dip might be only 2%.
ISO Classification
ISO Class 1 and 2 are
international standards for
generator set response criteria.
Note that there are two separate
and different sets of Class 1 and 2
standards for diesel engines andnatural gas engines. The ISO
requirements for gas engines are
not as stringent as they are for
diesel engines.
Equipment Selection
The transient response and
steady state stability of generator
set engines can vary with a
number of factors:
Engine Model Engine Speed Aspiration Power Factor Carburetion Governor
It is important to review the
response capability of the specific
generator set against the
application requirements.
Carburetion
To match changing load
requirements, the engine must
adjust is the amount of fuel
available for combustion. Due to
the differences in the fuel delivery
systems, natural gas and diesel
fuel engines will have very
different transient response
capability.
Diesel Engine Transient Response
Caterpillar diesel engines utilize
direct injectors for each cylinder
(unit injectors), which deliver a
precisely controlled amount of fuel
to each cylinder. These injectors
can be either mechanically
controlled (MUI) or electronically
controlled (EUI), however,
pertaining to transient response,
their basic operation is the same. A
certain amount of fuel is allowedinto the injector, and then at the
right time for combustion, a
plunger forces the fuel through
very small nozzles, and into the
combustion chamber. Each injector
acts as an exclusive fuel system
for each cylinder, which delivers
fuel directly to the cylinder. When
the governor or ECM signals to
change the amount of fuel needed
in the cylinder, the amount of fuel
available for combustion is
adjusted and available almost
instantly. This almost
instantaneous power adjustment
ability allows the diesel engine to
8/3/2019 Catterpillar Gens Set Requirment
24/28
Petroleum Applications Application and Installation Guide
2006 Caterpillar
Page 18 All rights reserved.
respond to transient loads very
effectively.
Gas Engine Transient Response
Caterpillar gas engines have
either a carbureted fuel system or
a gas admission valve system.
There are many variations of these
fuel systems, however for this
topic their basic operation is the
same. Similar to the diesel
system, a governor or ECM signals
to a valve to adjust the amount of
fuel allowed into the combustion
chamber, however this is the only
similarity. After the valve, the fuel
gas is not directly delivered to thecylinder, but is mixed in with the
inlet air. Regardless of how the
fuel system delivers this air fuel
mixture to the cylinder, the
distance (and volume) between the
fuel control valve and the
combustion chamber creates a lag
between when the cylinder needs
fuel and when it gets fuel. It is this
property of gas engines that
reduces their ability to respond to a
transient load relative to diesel
engines. Some regulations are
adjusted accordingly; however,
marine society regulations are not
as flexible.
Off Shore RequirementsGenerator sets on offshore rigs
have to meet the transient
response requirements of thevarious Marine Classification
Society (MCS) rules (e.g. ABS,
DNV, etc). This is true for the main
drilling units as well as emergency
or essential services gensets. MCS
requirements are demonstrated on
a resistive load bank with various
step load changes.
MCS transient response
requirements are typically more
stringent than can be met with a
natural gas engine. A solution thatmay be accepted is to use a load
management system to control the
loading of the genset.Island Mode
Many petroleum gas engine
generator sets operate in Island
Mode or independent of the utility
grid. It is especially important in
these applications to have athorough understanding of the
electrical load and transient
response demands and ensure that
the gas genset can meet the
requirements.
Motor LoadsMotors draw more than their
rated power during starting and
acceleration. Motors connected
directly to high inertia centrifugaldevices or loaded reciprocating
compressors cause severe
frequency excursions and lengthy
motor start up. Comparing starting
currents between loaded and
unloaded motors, Figure 12 shows
the extended time that loaded
motors demand high current.
Motors generally exhibit low power
factors (pf) of 0.3 to 0.4 when
starting. Engine load is calculated
by:
kW = Starting kVA x Starting pf
8/3/2019 Catterpillar Gens Set Requirment
25/28
Application and Installation Guide Petroleum Applications
2006 Caterpillar
All rights reserved. Page 19
Figure 12
As shown in Figure 12, the
starting kVA can be as much as 6
times the running kVA. This results
in an engine load of 1.8 to 2.4 times
the normal load required to run the
motor. This must be accounted for
in the load analysis if there are any
large motors that must be started
when the generator initially closes,especially if the motor is started
while loaded.
Jackup drill rigs can impose large
AC motor block loads with their leg
jacking systems. Typically, other AC
motors on land or offshore rigs do
not present significant transient
response challenges due to the size
of these motors in comparison to the
engine and generator capacity.The DC motors, powered through
the SCR control system, are
considered to be soft-start. The
severest transient DC load (but of
short duration) on a drill rig is
applied by the drawworks when
lifting empty blocks.
Motor StartingThe gensets ability to start large
motors without large frequency or
voltage dips depends on the entire
system. System factors include:
Available engine power Capacity of the generator Energy stored in the rotating
inertia of the genset
Acceleration of the motor andits load (motor characteristics)
Electrical componentsbetween the genset and
motor.
A properly sized generator willsupport the high starting kVA (skVA)
required and sustain adequate
output voltage for the motor so it
can produce the needed torque to
accelerate its load to rated speed.
8/3/2019 Catterpillar Gens Set Requirment
26/28
Petroleum Applications Application and Installation Guide
2006 Caterpillar
Page 20 All rights reserved.
After the initial voltage dip, it is
important that the generator restore
voltage to at least 90% to develop
adequate torque to accelerate its
load to rated speed. Full voltage
starting causes the largest voltagedip.
Regenerative PowerSome motor applications, such as
hoisting, depend on motors for
braking. Motors then act as
generators and feed power back to
the generator set. The rating on the
motor is greater when used as a
brake, if no other loads are
connected to absorb thisregenerative energy, only engine
frictional horsepower is used for
braking. Exceeding frictional
horsepower causes generator set
overspeed.
Regenerative potential for a
common application, elevators, is
estimated by:
Regeneration kW = Hoist Motor hp x Full Load Brake Rating Factor x hp to kW Conversion x Motor Efficiency
Where:
Full Load Brake
Rating Factor = 1.8
hp to kW
Conversion = 0.746
Motor Efficiency = 0.9
Load banks activated by directionalpower relays must be installed to
prevent engine/generator damage
when combinations of connected
load and engine frictional
horsepower are not sufficient to
restrain regenerative energy.
8/3/2019 Catterpillar Gens Set Requirment
27/28
8/3/2019 Catterpillar Gens Set Requirment
28/28