POWER May 2020 - 17

FOCUS ON O&M
2. This graphic illustrates the magnitude of
non-critical and critical load versus generator
capacity. Courtesy: Stanley Consultants
tion wiring and conduit is required to add
remote operation. This adds cost.
Once it's determined where the load
will be shed (Figure 2), it must be determined
how this shedding will take place.
There is a wide range of sophistication
that can be implemented. In the most
advanced cases, the control system can
continuously monitor load levels on individual
loads and sources. Some systems
can even continuously update an estimated
system inertia value.
Advanced systems can execute predictive
contingency-based algorithms
that use data to continuously update the
list of actions that the system will perform
in the event of a disturbance. The
less advanced systems retroactively
shed predefined loads.
One Solution
In the case of this factory, the following
solution was implemented. To determine
how much load needed to be
shed, the control system continually
metered the power flowing into the
facility and out of the generator. This
was done with communication connections
to the main breaker and generator
breaker's protective relaying. The difference
between these two values was
the target amount of load to be shed in
the case of a decoupling.
In the interest of balancing cost and
load-shed accuracy, individual low-voltage
switchgear feeder breakers were
used for the load-shed location. Some
of these breakers already had remote
control capability; where they didn't,
the breakers were retrofitted with
shunt-trip devices.
Next, individual loads did not have
devices capable of providing metering
information to the network. Instead of
May 2020 | POWER
adding this capability, which would increase
cost, typical load values for each
feeder capable of shedding were hardcoded
into the system. Also, these loads
were assigned priority levels that told the
system which loads were most critical.
Finally, the system was programmed
with a curve that told it how much of a
step change the generator could tolerate
under varying output levels. All this
information was used in a contingency
scheme that decided which loads would
be quickly shed if the protective relaying
decoupled the plant from the grid.
Once the control system placed the
plant into an islanded configuration, it
communicated with the engine control
system to switch the generation mode
to one appropriate for the islanding situation.
Again, to minimize capital cost,
the owner chose to return to the utilityconnected
state manually, rather than
automating this function.
With careful planning and engineering,
this facility was able to leverage
existing assets to increase reliability, executing
only modest capital investment.
As distributed generation becomes
more prolific, so does the opportunity
to magnify installed equipment utility
via modern controls.
-Joe Thornam is a principal electrical
engineer with Stanley Consultants Inc.
in Denver, Colorado.
HVTS Stops Alloy 625 Weld
Overlay Corrosion in Wasteto-Energy
Boiler
A boiler at the Renergia waste incineration
plant in Perlen, Switzerland, was
experiencing fireside corrosion.
The
shop-applied Alloy 625 weld overlay was
showing signs of premature accelerated
degradation.
The operators of the waste-to-energy
(WtE) boiler were looking for a solution
to stop the corrosion and ensure
the reliable and safe operation of the
boiler, and looked at several options.
Maintaining operation of the facility
was critical, because the Renergia
Zentralschweiz AG plant (Figure 3)-a
joint effort of all waste disposal associations
from central Switzerland and
Perlen Papier AG-is responsible for
more than just recycling waste. The
plant, in operation since 2015, supplies
Perlen Papier AG with process steam.
It also supplies the district heating networks
Rontal and Emmen with hot water,
and provides electricity for about
44,000 homes.
www.powermag.com
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anzeige_drittel_Seite_power_international_circulation.indd 102.04.2020 10:16:35
17
http://www.auma.com http://www.powermag.com

POWER May 2020

Table of Contents for the Digital Edition of POWER May 2020

Contents
POWER May 2020 - Cover1
POWER May 2020 - Cover2
POWER May 2020 - Contents
POWER May 2020 - 2
POWER May 2020 - 3
POWER May 2020 - 4
POWER May 2020 - 5
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POWER May 2020 - Cover3
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