Prisma Plus - error

Slick changeover
keeps fish fresh
When the mains switchboard at one of
the world’s largest tuna-processing
plants began feeling its age, Schneider
Electric NZ and Napier’s Electrotech
Controls Ltd teamed up to design, build
and supply a more efficient replacement.
The COS Samoa Packing Company in
Pago Pago, American Samoa, processes
some 300 tonnes of tuna a day and in
global terms is second in size only to the
neighboring StarKist plant.
COS runs a 24-hour operation, and its
major electrical demand is for refrigeration,
water pumps and generating steam. In
recent years power reliability had become
an issue as a result of an increasingly
fragile mains switchboard. After a tendering
process, the plant’s management
appointed Electrotech to design, build and
supply a replacement, and Schneider
Electric supplied much of the hardware.
“A major problem with the equipment,”
says Electrotech project manager Steve
Pardoe, “was the environment in which it
operated. There were a few leaks in the
roof of the building, and that had caused
quite a bit of corrosion. As a result,
the local crews were replacing the
switchboard’s ACBs on a regular basis –
as a kind of preventative maintenance.”
Electrotech’s design of the new switchboard
was governed by the power feed into the
plant – delivered from two 2MVA
transformers.That was complemented by
three 940kW standby, diesel-generating
sets. Designed as standby units, in practice
the generating sets ran continuously, in
parallel with the electricity supply.
“Essentially,” says Pardoe, “we were dealing
with three separate switchboards mounted
side by side.The generator board – for the
three standby generators – and two for the
main distribution board.The two main
switchboards were linked by power cables.
“Because of the potential fault current
associated with paralleling two 2MVA
transformers, we had to keep our design
similar: two switchboards that would be
kept totally separate – but interconnected
– for the transformers, and one for the
generating sets.”
DESIGN
Optimising and monitoring the
performance of the new switchboards
was one of the project’s major drivers.
“The old control system was fraught with
difficulties,” says Pardoe. “It was totally
manual and there was no monitoring. Even
synchronizing the three generators was a
manual operation. Operators had no way
of tracking power consumption.”
The new Prisma switchboards were
designed and built at Electrotech’s Napier
plant. The design team from Electrotech
specified a full distribution and automation
system complete with SCADA and power
factor correction.
Among the challenges the team faced was
designing and specifying equipment that
complied with US regulations. “We had to
take virtually everything we needed with
us, because the US system still uses
imperial measurements.”
In addition, the team had to factor different
voltage system into their design – 110
volts, a 240-volt system as well as a 24-volt
DC system for all controls.
Schneider-Electric’s Bruce Morrison says
highly specialised Merlin Gerin breakers
were fitted to the Prisma switchboards.
“As a standard feature, all source breakers
were equipped with ammeters to facilitate
easier power monitoring.This included full
modbus communication with energy
management and preventative
maintenance monitoring achieved. In
addition, all 24 x 800A feeder breakers
were supplied with PM500 power monitors.”
INSTALLATION
The project ran over a five-week period
in April and May this year, and installing
the two switchboards was by far the most
difficult part of the project because of the
very tight time limit. “The fish is kept in
freezers and the factory can only survive
for about 24 hours – tops – without
electricity,” says Pardoe. “And that’s what
we were given for the changeover.”
As it happened, the installation crew
only needed 21 hours. “Apart from the
success of meeting the time-limit, it was
particularly gratifying to witness the
improved efficiency of the switchboards.
Tests conducted after the installation
showed the boards were running at a
significantly lower load than the previous
equipment. We believe a lot of the
‘excess’ load on the old boards was
attributable to heat losses and
poor connections.”
Control is also much easier. It’s entirely
automatic, and operators now monitor
the switchboards’ performance on a PC
screen. Being able to monitor load in real
time, Pardoe points out, “also allows
operators to consider strategies such
as peak load sharing for the first time –
and improve the plant’s overall
energy efficiency.”
THE HARDWARE
Schneider-Electric supplied the majority of the components used in the two
switchboards. Below is a selection of the Merlin Gerin items:
2 x 3200A 3P 85kA Masterpact NW ACB Mains Breakers
2 x 3200A 3P ACB Masterpact NW Generator Feeders
3 x 2000A ACB Masterpact NW Generator Breakers
2 x 3200A ACB Masterpact NW Bus Ties
24 x 800A MCCB Compact NS Sub Circuit Feeders
24 x PM 500 Powerlogic power meters
5 x PM 850 Powerlogic power meters
For more information contact your
local Sales Engineer