design flexibility and safety are
becoming increasingly important to
controlling costs.
While market conditions continue
to cycle, the power management
technologies that will enable the
mines of the future are available now.
This article explores three product
trends that streamline power
management solutions, while
achieving greater levels of energy
efficiency, power reliability and
personnel safety.
Reduce energy costs
and enhance process
control
In the mining industry, optimal
power management is directly related
to how precisely reactive power is
managed. With its large motors,
mining can create large inductive
loads that may have large-scale
effects on both the grid and the
equipment in the overall power
infrastructure. This makes reliable
power quality – sometimes described
as voltage stability – essential to the
interconnected ecosystem of any
large industrial mine site and its
utility provider.
Adjustable frequency drives
(AFDs) are advanced motor control
systems that can save dramatic
amounts of energy in variable torque
applications. They function by
converting the AC line power to DC,
supporting the DC energy via
capacitors then using an inverter to
convert back to AC power at a
desired voltage and frequency. In
general, whenever frequency (and
thus motor speed) can be varied, the
system’s load requirements can be
better met.
As a standalone drive or as a
component of an Eaton integrated
control gear configuration, the
SC9000™ EP delivers when it comes
to reliability, system flexibility, ease of
use and reduced equipment costs.
Eaton’s medium voltage AFDs
feature an encapsulated powerpole
inverter with advanced heat pipe
technology that may be of special
interest to coal mining applications.
Heat pipe technology
affords highly efficient and fast
transfer of heat using a
self‑contained, constant flow of fluid,
vapourised from heat‑generating
elements. The fluid vapourises and
flows into the fin stacks, condenses
and is then forced back to the
heat-generating devices by capillary
pressure.
This heat pipe cooling method is
the most efficient air-cooled thermal
management system available today
– up to ten times more efficient than
conventional air-cooled methods.
Consequently, less airflow is
necessary, reducing audible noise and
levels of contaminants pulled into
electrical cabinets.
Superior protection from dust and
debris is ready-built into the design,
with the sensitive electronic
components encapsulated within the
powerpole. This provides increased
reliability, while maintaining the
integrity of the inverter in harsh
environments.
Another benefit of the powerpole
is its ability to maximise modularity
and choice by sectionalising the
inverter into separate encapsulated
phase sections. In the event of an
insulated gate bipolar transistor
(IGBT) failure, the powerpole’s
design lends flexibility and speed of
replacement, lowering the overall
time of lost production. The
replaceable powerpole modules can
be exchanged in less than two hours;
field replacement of gate drivers and
power supplies can also be completed
in less than 30 min.
However, with a count of 46 active
components in the topology of the
SC9000 EP drive’s inverter, the mean
time to failure (MTTF) extends to
12.7 yr, versus 2.8 yr for competing
products built with H-bridge
multi-level topology with
192 active components. This enhances
system reliability and reduces the
possibility of downtime.
With its integral contactor design,
the footprint for the SC9000 EP is
small; the need to run additional
cables is eliminated, along with the
potential for failure at connection
points. A high‑voltage input option
(up to 15 kV) also eliminates the need
for a separate power transformer. The
result is reduced cost, smaller overall
footprint (ideal for electrical houses
and smaller control rooms) and
simplified installation.
Overall, the SC9000 EP drive
delivers energy savings from
10 – 50% by providing precise control
for variable torque fan and pump
loads, resulting in significant
advantages, such as reduced
maintenance and repair time,
improved energy efficiency and better
long-term return on investment.
Case study: Canada coal
preparation plant
AFDs have the potential for very
tangible and rapid payback. The
potential impact on a site’s bottom
line can be readily observed in the
application of a medium-voltage AFD
at a coal preparation plant in British
Columbia, Canada, following an
energy efficiency study there in 2012.
The site’s energy efficiency study was
fully funded by the local utility
company serving the mine. In this
case, the shared goals were to assure
that both energy and operational
costs would be reduced, while the
coal preparation plant continued to
deliver a superior end product.
Following a comprehensive
feasibility study, the coal processing
plant was advised to install an AFD
on the main dryer exhaust fan to
control and vary the rotations per
minute (rpm) of the motor. A second
AFD was suggested to control the
speed of the dryer’s combustion air
fan motor. These recommendations
had the same basic effect of opening
and closing the inlet dampers to the
fan to vary the air flow– but with
higher energy efficiency using speed
control.
The amount of electrical energy
used was reduced; power factor was
improved; and several other
non‑electrical and process-oriented
savings were also realised. The
project’s total savings are
summarised in Table 1.
Finally, reliable, user-friendly
software helps make programming
the SC9000 EP very easy, thereby
drastically cutting startup time. Users
can monitor and compare drive
60
|
World Coal
|
August 2015
