POWER May 2016 - 66

INSTRUMENTATION & CONTROLS
4. Facelift complete. The AutomationDirect C-More human machine interface, visible in
the center cabinet, was installed as an assembly with other control hardware to reduce installation
time and save money. Courtesy: Piedmont Hydro Technologies
5. Smooth startup. Extensive testing
offsite and during commissioning ensured
a quick and on-schedule startup. Courtesy:
Piedmont Hydro Technologies
mize head pressure and corresponding power
output.
The end result is an overall control strategy
using three interdependent PID loops
in series. The first is a water-level loop that
provides a power setpoint. The governor then
uses the power setpoint, applied to another
PID loop to set the wicket gate. The wicket
gate then uses this setpoint along with the
current position of the gate to provide PID
control of the gate proportional valve.
To control power output, the plant can operate
in two modes. One is based on water
level, as just discussed, where water flow is
the constraint. In the other, the operator can
order a fixed, constant power level. This is
useful when there is more than enough water
flow to supply power demand.
The PAC and its ancillary equipment can
be run by an onsite generator to allow black
starting, which is restarting the plant without
relying on the external transmission network.
Although a hydroelectric generator requires
only a small amount of external power to
start up, it does require the PAC to control
field flashing sequencing to inject current
into the rotor.
Starting on Schedule
PHT designed, built, and tested the control
system at its facility in North Carolina and
then shipped everything to the Maggotty site.
Technicians Carter Combs and Josh Knight
and other PHT personnel traveled to the site
to install and commission the new automation
system. JPS personnel assisting PHT
with the install included Peter Baker, Shane
Montaque, Renwick Brown, and Horace
66
Fuller. This collaborative effort made installation
much faster while providing training
for the JPS staff.
Because the retail cost of electricity on the
island is high-roughly $0.33/kWh-minimizing
downtime was important. The existing
control cabinets were reused, but a new
backplane was installed, with the new PAC
and supporting hardware already in place.
The existing door equipment was removed
and a large rectangular hole was cut. A new
laser-cut door blank was attached, with the
HMI, switches, and protection relays already
installed and tested (Figure 4).
Most of the input/output (I/O) points from
the connection blocks on the reverse side of
the main control cabinet were reused, so it
was a simple matter to connect to the terminal
strip on the new backplane. Some sensors
were added, including vibration monitors, an
ultrasonic flowmeter, and pressure transducers.
The existing exciter was replaced with a
new Payne static exciter, which is essentially
a DC voltage source controlled by the PAC.
After the wiring was completed, all I/O
points were tested. Following that, functional
checks of all the equipment were performed.
This included hydraulic pumps, numerous
valves (including a 1.25-m-diameter butterfly
valve), the wicket gate operator, exciter,
and more. Finally, the generator electrical
protection relay settings were confirmed.
Once the systems were checked out, the
unit was started. This included testing synchronization
of the generator with the grid
and producing power. Hundreds of settings,
all easily available through the HMI, were
adjusted to ensure safe, smooth, and reliwww.powermag.com
able
operation (Figure 5). PHT remained for
the first few days of commercial operation,
making minor adjustments and watching for
problems. Startup went very well and finished
on schedule.
Improved Control
The new control system has worked as advertised
during its first year of operation
and overall plant uptime has been excellent.
Maintenance technicians appreciate having
spares available again, and operation has
been greatly simplified for the plant's staff.
The new governor and excitation controls
greatly improve plant usability by replacing
the difficult-to-use " black boxes " with easily
monitored and adjusted subsystems via
the HMI. The new exciter and controller are
much easier to tune, resulting in better voltage
stability.
JPS has four other hydroelectric plants
still controlled by old automation systems,
similar to what Maggotty Unit A used before
its upgrade. Management expects to
replace one of these every few years until
all are modernized. JPS has been technically
competent and easy to work with during the
upgrade as their personnel know the plant
and have an intimate knowledge of its operation.
Their technical, engineering, and
management assistance was invaluable and
greatly helped speed installation, startup,
and commissioning. ■
-Kevin Edwards is owner and lead engineer
at Piedmont Hydro Technologies.
POWER | May 2016

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POWER May 2016

Table of Contents for the Digital Edition of POWER May 2016