Note: Descriptions are shown in the official language in which they were submitted.
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Predictive Landing Failsafe
Cross-Reference to Related Applications
[0001] This application is a non-provisional application which claims priority
from U.S.
provisional application number 61/952,452, filed March 13, 2014, which is
incorporated by
reference herein in its entirety.
Technical Field/Field of the Disclosure
[0002] The present disclosure relates generally to control systems for
electric motors, and
specifically to control systems for permanent magnet AC motor drawworks.
Background of the Disclosure
[0003] While undergoing a drilling operation, a drilling rig utilizes a
drawworks to raise and
lower pieces of oilfield equipment. For example, the drawworks is used to
raise and lower the
interconnected lengths of drill pipe, casing, or the like, herein referred to
as a tubular string, into
and out of the wellbore. The tubular string, as well as additional connected
equipment such as a
top drive, travelling block, tubular elevator, etc., may be very heavy. The
ability to precisely
control movement of the drawworks may be critical to prevent damage to
equipment as well as
maintain a safe work environment for workers on the drilling rig.
[0004] Typical drawworks may be run using electric motors such as alternating
current electric
motors. AC electric motors rely on alternating currents passed through
induction windings within
the stator to cause rotation of the rotor. So-called three phase AC motors
include three matched
sets of windings positioned radially about the stator. By supplying sinusoidal
AC power to each
of the sets of windings such that each set receives an alternating current
offset by 120 degrees, a
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continuously rotating electromagnetic field can be induced by the stator. The
rotation of the
electromagnetic field in turn causes rotation of the rotor.
[0005] In a permanent magnet AC motor, the rotor includes one or more
permanent magnets
which, in response to the rotating electromagnetic field, cause the rotor to
rotate. Alternatively, if
the rotor is rotated and no AC power is supplied to the windings of the
stator, the movement of
the magnetic field of the permanent magnets may induce voltage in the windings
according to
Lenz's Law.
Summary
[0006] The present disclosure provides for a predictive landing failsafe
system. The predictive
landing failsafe system may include an AC motor. The AC motor may be powered
by one or more
phases of AC power supplied through two or more terminals of the AC motor. The
predictive
landing failsafe system may also include a predictive landing failsafe
controller. The predictive
landing failsafe controller may include a contactor, the contactor having a
normal operating
position and a failsafe position, the contactor positioned to supply power to
each phase of the AC
motor when in the normal operating position and to electrically connect at
least two terminals of
the AC motor when in the failsafe position. The contactor may be positioned to
be automatically
transitioned from the normal operating position to the failsafe position in
response to a selected
condition.
[0007] The present disclosure also provides for a hoist. The hoist may include
a drum. The hoist may
also include an AC motor. The AC motor may be powered by one or more phases of
AC power
supplied through two or more terminals of the AC motor. The AC motor may be
positioned to
rotate a shaft, the shaft coupled to the drum. The hoist may also include a
predictive landing
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failsafe controller. The predictive landing failsafe controller may include a
contactor, the
contactor having a normal operating position and a failsafe position, the
contactor positioned to
electrically couple a power source to each phase of the AC motor when in the
normal operating
position and to electrically connect at least two terminals of the AC motor
when in the failsafe
position. The contactor may be positioned to be automatically transitioned
from the normal
operating position to the failsafe position in response to a selected
condition.
Brief Description of the Drawings
[0008] The present disclosure is best understood from the following detailed
description when
read with the accompanying figures. It is emphasized that, in accordance with
the standard
practice in the industry, various features are not drawn to scale. In fact,
the dimensions of the
various features may be arbitrarily increased or reduced for clarity of
discussion.
[0009] FIG. 1 is a block diagram of an oil rig electrical system consistent
with embodiments of
the present disclosure.
[0010] FIGS. 2A-2D depict predictive landing failsafe systems consistent with
embodiments of
the present disclosure coupled to different winding configurations for an
electric motor.
[0011] FIG. 3 depicts a drawworks utilizing a predictive landing failsafe
system consistent with
embodiments of the present disclosure.
[0012] FIG. 4 depicts a detailed view of the drawworks of FIG. 3.
[0013] FIG. 5 depicts a predictive landing failsafe system consistent with
embodiments of the
present disclosure.
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Detailed Description
[0014] It is to be understood that the following disclosure provides many
different embodiments,
or examples, for implementing different features of various embodiments.
Specific examples of
components and arrangements are described below to simplify the present
disclosure. These are,
of course, merely examples and are not intended to be limiting. In addition,
the present
disclosure may repeat reference numerals and/or letters in the various
examples. This repetition
is for the purpose of simplicity and clarity and does not in itself dictate a
relationship between
the various embodiments and/or configurations discussed.
[0015] FIG. 1 depicts a block diagram of a partial oil rig electrical system
100 consistent with
embodiments of the present disclosure. In some embodiments, power may be
supplied to oil rig
electrical system 100 by generator 101. Generator 101 may be driven by engine
103. In some
embodiments, engine 103 may be driven by natural gas. In some embodiments,
power may be
supplied to oil rig electrical system 100 from line power 101'. As understood
in the art, line
power 101' may be sourced from, for example and without limitation, a local
utility power grid.
In some embodiments, line power 101' may be transformed from, for example,
high voltage to a
lower voltage by transformer 103'. In some embodiments, line power 101' and
generator 101
may be coupled to the rest of oil rig electrical system 100 through one or
more circuit breakers
104 as understood in the art. Generator 101 and line power 101' may supply
power through
supply line 105. In some embodiments, the power supplied may be rectified by
one or more
rectifiers 107. Here, rectifiers 107 are depicted as a single diode, but one
having ordinary skill in
the art with the benefit of this disclosure will understand that any suitable
rectifier arrangement
may be used, including without limitation, half bridge, full bridge, single or
multiphase, etc. The
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output electricity, coupled to DC power bus 109, may then be used to power
other electrical
equipment.
[0016] In some embodiments of the present disclosure, the electrical equipment
may include AC
motor 111. AC motor 111 may, in some embodiments, be a permanent magnet AC
motor,
positioned to rotate in response to AC power supplied to AC motor 111. In some
embodiments,
AC power may be supplied using VFD controller 113 to control inverter 115.
Inverter 115 may
be positioned to provide pulse width modulated AC current to AC motor 111 as
controlled by
VFD controller 113. One having ordinary skill in the art with the benefit of
this disclosure will
understand that rectifier 107, VFD controller 113, and inverter 115 need not
be used to power
AC motor 111. Instead, AC power may be supplied directly from generator 101.
Additionally,
one having ordinary skill in the art with the benefit of this disclosure will
understand that AC
power may be supplied to oil rig electrical system 100 by, for example, a
municipal power
supply.
[0017] In some embodiments, AC motor 111 may be a single or multi-phase AC
motor. As
understood in the art, the number of phases of an AC motor corresponds to the
number of
windings or winding phase groups of AC motor. In a single phase AC motor, one
phase of AC
power is supplied to the windings of the AC motor through a single conductor,
with a neutral
conductor electrically coupled to the opposite ends of the windings. In a
three-phase AC motor,
such as depicted in FIG. 1, three phases of AC power are supplied to AC motor
111, each
through a separate conductor 117a-c coupled to a terminal of AC motor 111. In
a three-phase AC
motor, the windings are grouped into three winding phase groups. As depicted
in FIGS. 2A-2D,
terminals A, B, and C may be connected to the winding groups in a Wye
configuration (FIGS.
2A, 2B) or a delta configuration (FIGS. 2C, 2D). In each configuration, each
phase of the AC
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power supplied to the AC motor is supplied to a corresponding terminal A, B,
or C, with a phase
offset 120 degrees to the other two phases.
[0018] As depicted in FIG. 1, oil rig electrical system 100 may further
include a predictive
landing failsafe system 119. Predictive landing failsafe system 119 may, as
depicted in FIG. 1,
include contactor 121. Contactor 121 may be positioned to selectively couple
or decouple each
of conductors 117a-c with terminals A, B, C of AC motor 111. When coupled,
conductors 117a-
c are capable of powering AC motor 111 through terminals A, B, C thereof. When
disconnected,
AC motor 111 is disconnected from the AC power oil rig electrical system 100.
[0019] In some embodiments, when contactor 121 decouples conductors 117a-c
from AC motor
111, contactor 121 is positioned to instead short between at least two
terminals A, B, C of AC
motor 111. If AC power is not supplied to AC motor 111, as the permanent
magnets on the rotor
of AC motor 111 rotate, the electromagnetic flux on each winding group varies
and, according to
Lenz's Law, electricity is induced into the windings. This generated
electricity is known as back
EMF. When at least two terminals A, B, C of AC motor 111 are shorted, the back
EMF of each
winding group creates a short circuit current. The magnetic field of the
permanent magnets of the
rotor of AC motor 111 are opposed by the induced electromagnetic field, and a
resultant braking
or stopping force is imparted on the rotor. This braking or stopping force is
known as dynamic
braking.
[0020] As depicted in FIGS. 2A-2D, contactor 121 may switch between a normal
operating
mode, in which each terminal A, B, C is coupled to a conductor 117a-c
respectively, and a
failsafe mode, in which each terminal A, B, C is disconnected from the
respective conductor
117a-c and at least two of which are connected directly together (dashed
lines). As depicted in
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FIGS. 2A, 2C, terminals A and B are shorted together. As depicted in FIGS. 2B,
2D, all three
terminals A, B, C are shorted together. In the failsafe configurations,
because two or more of the
terminals are shorted together, dynamic braking occurs, thus slowing or
stopping AC motor 111.
In some embodiments, the dynamic braking force may be sufficient to completely
stop the
movement of AC motor 111.
[0021] In some embodiments, the short circuit current previously described
may, for example,
cause an abrupt and immediate stoppage of the rotor of AC motor 111. In some
embodiments, as
depicted in FIG. 5, one or more resistors 122a-c may be included in predictive
landing failsafe
system 119. Resistors 122ac may, for example, be adapted to lower the short
circuit current when
in the failsafe configuration. By lowering the short circuit current, the rate
of deceleration of the
rotor of AC motor 111 may be lowered, thus allowing the rotor to come to a
more smooth stop.
In some embodiments, resistors 122ac may be variable resistors as depicted. By
varying the
resistance of each of the resistors 122ac, the rate of deceleration may be
controlled. In some
embodiments, the selected resistance value for resistors 122ac may be small so
that sufficient
short circuit current remains to completely stop the rotor of AC motor 111
despite any external
load imparted on the rotor. In other embodiments, the selected resistance
value for resistors
122ac may be high enough that the rotor of AC motor 111 is slowed but may be
capable of
turning a desired speed under external load. In some embodiments, the selected
resistance value
for resistors 122ac may be optimized based on, for example, the intended
application of AC
motor 111 and any expected load during normal operation of AC motor 111.
[0022] In some embodiments of the present disclosure, predictive landing
failsafe system 119
may be coupled to oil rig electrical system 100 such that when power is being
supplied, contactor
121 remains in the normal operating mode. In response to a certain condition,
predictive landing
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failsafe system 119 may be positioned to cause contactor 121 to trip into the
failsafe position,
thus halting the rotation of AC motor 111 immediately. In some embodiments,
the certain
condition may be a power outage or blackout on oil rig electrical system 100.
For example, in
some embodiments, contactor 121 may be held in the normal operating position
by a spring-
opposed electromagnet (not shown) powered by oil rig electrical system 100. If
a blackout
occurs, the electromagnetic attraction between the electromagnet and contactor
121 may cease,
allowing the spring to move the contactor into the failsafe position. In some
embodiments, the
condition may be a manual override triggered by an operator, such as in an "E-
stop" condition.
[0023] In some embodiments of the present disclosure, AC motor 111 may be used
as part of a
piece of oilfield equipment. With reference to FIG. 3, AC motor 111 may be
used to drive,
without limitation, drawworks 201, top drive 203, or a rotary table (not
shown). For the purposes
of this disclosure and to clarify the operation of the present disclosure, an
embodiment in which
AC motor 111 is used as part of drawworks 201 will be described. Additionally,
although
described herein as a drawworks, one having ordinary skill in the art with the
benefit of this
disclosure will understand that drawworks 201 may be any hoist apparatus and
is not limited to
lifting or supporting the described equipment.
[0024] FIG. 3 depicts oil rig 205. Oil rig 205 may include derrick 207.
Derrick 207 may be
positioned to support crown block 209. Crown block 209 may be coupled to
travelling block 211
by wireline 213. Wireline 213 may be coupled to drawworks 201. As understood
in the art,
crown block 209 and travelling block 211 may include one or more pulleys
positioned to allow
wireline 213 to lift or lower travelling block 211 relative to crown block 209
as wireline 213 is
paid in or out by drawworks 201. In some embodiments, travelling block 211 may
be coupled to
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top drive 203. Top drive 203 may be used to support a string of interconnected
tubular members
such as tubular string 215 as depicted.
[0025] As depicted in FIG. 4, drawworks 201 may include AC motor 111. AC motor
111 may be
coupled by, for example a shaft (not shown), to drum 217. Wire line 213 may
wrap around drum
217 such that as drum 217 is rotated by AC motor 111, wire line 213 extends or
retracts
depending on the direction of rotation of drum 217.
[0026] As an example, a lowering operation for tubular string 215 will be
described. Once
tubular string 215 is properly coupled to travelling block 211, wireline 213
may be extended by
drawworks 201. As wireline 213 extends, travelling block 211 lowers, causing
tubular string 215
and any other equipment such as top drive 203 to be lowered. During normal
operation,
predictive landing failsafe system 119 may remain in the normal operating
mode. In the event of
a power outage or other condition, predictive landing failsafe system 119 may
trip into the
failsafe mode, causing rotation of AC motor 111, and thus rotation of
drawworks 201 to slow or
stop. As drawworks 201 slows or stops, wireline 213's extension is slowed or
stopped, causing
the descent of tubular string 215 to likewise slow or stop. By automatically
triggering this
slowing or stoppage of tubular string 215 without the need for additional
power or operator
input, damage to, for example, top drive 203, travelling block 211, or tubular
string 215 and any
associated components may be prevented. Additionally, damage to a wellbore or
to the seabed
for offshore drilling operations may likewise be prevented. Furthermore,
safety of rig personnel
may be increased and injuries may be prevented.
[0027] The foregoing outlines features of several embodiments so that a person
of ordinary skill
in the art may better understand the aspects of the present disclosure. Such
features may be
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replaced by any one of numerous equivalent alternatives, only some of which
are disclosed
herein. One of ordinary skill in the art should appreciate that they may
readily use the present
disclosure as a basis for designing or modifying other processes and
structures for carrying out
the same purposes and/or achieving the same advantages of the embodiments
introduced herein.
One of ordinary skill in the art should also realize that such equivalent
constructions do not
depart from the spirit and scope of the present disclosure and that they may
make various
changes, substitutions, and alterations herein without departing from the
spirit and scope of the
present disclosure.
