single bull gear for a total of 800 hp. In operation, each motor at
full power provides approximately half of the required drill string
torque. Since they are mechanically in parallel, they will rotate
at the same speed. In the event that there is an issue with one of
the motors or the electrical system supplying the motor, the drive
can continue to operate – but because both motors are rated at
400 hp, the entire top‑drive will be limited to 50% capacity until
the issue can be resolved, which might require an un‑scheduled
shutdown.
If instead the top‑drive had been upgraded to twin WL12BB
high power density motors, each rated at 600 hp each, several
benefits immediately become apparent:
Ì
Ì
In the event of a single failure, the opposite motor can
provide continuous power up to the rated 600 hp, effectively
improving on the single motor operating limit from the prior
400 hp to a very respectable 600 hp:
a 50% improvement.
Ì
Ì
Since both of the motors are rated
at 600 hp but will normally only
be run at 400 hp, the total heat
production internal to the motor
and overall temperature of the
motor will be much lower. Lower
motor temperatures result in longer
insulation life than would otherwise
be expected if running at full power.
Ì
Ì
Since the machine is externally
identical to the incumbent 400 hp
motor and has around the same
mass, a thorough review of the
torque path components up to
the bull gear is all that is required
mechanically to provide more
robust single motor operation
and longer life from twin motor
operation.
Because a single motor can now
operate at 600 hp, a thorough review of
electrical cabling and VFD capabilities
will be required to ensure that both
the mechanical and electrical systems
will be capable of transmitting the
additional power.
Technologyprimer
In order for any technology to
experience a step change in
capabilities, something within that
technology must have changed. For
example, micro‑processors get faster
because transistors get smaller, cars
get faster and more powerful due
to advanced computerised engine
controls, and home lighting gets more
energy efficient because manufacturers
switch from incandescent bulbs to
CCFL or LED.
2
In each of these cases,
significant improvements have been
made through ingenuity, a thorough
understanding of the science, and
because another new technology or
manufacturing process has enabled the
enhancement.
Perhaps the most significant change to induction motor
performance has occurred over the past 25 years due to
developments in variable frequency drive (VFD) technology and
the associated digital controls. Initially, VFDs were coupled with
existing induction motors in an effort to provide variable speed
but the aggressive switching imposed by VFDs stressed the motor
insulation in many motors beyond the design limits since they had
been designed to operate only on sinusoidal or line power. Motor
models were subsequently released to the market capable of
being driven by a VFD by improving the motor’s insulation system
and making it more resistant to inverter generated voltage spikes.
These newer inverter duty motors are, in most cases, adaptations
from 60 Hz line‑start designs with insulation upgrades that make
them more durable when powered from a VFD. Because of this,
the motor design naturally incorporates certain design features
Houma
985.223.1966
Port Allen
225.421.3300
Houston
713.821.0050
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