—
Anoop Nanda, Managing Director-S.Asia, S.E.Asia & Japan,
Electrical Sector, Eaton Corporation
Abstract: Electrical system over-current protective devices (OCPDs) dissipate heat during normal operation. Depending on the type, rating
and size of the OCPD (fuses and circuit breakers), the magnitude of energy loss varies. (Note: Throughout this paper it is understood that the
term "fuse" always includes a switching device.) This paper discusses a test program that quantified those losses for several typical fuses and
circuit breakers. The results of this effort show that systems using switches and fuses were found to be less energy-efficient compared with equivalently
sized circuit breakers when carrying the same load currents.
INTRODUCTION
The devices in an electrical
distribution system are a
critical part of a facility's
infrastructure. These
devices include transformers,
conductors and overcurrent
protective devices.
They are selected based on
performance considerations
including cost, reliability
and safety. The selection
of these devices typically
includes inputs from
contractors, facility owners
and engineers. Each of
these stakeholders tends to
focus on these performance
considerations to different
degrees.
Cost is always an important
consideration for a facility.
Everyone understands
that these costs include the
initial purchase price, the
design, installation, start-up
costs, etc., associated with a
facility. However there may
be less obvious costs associated
with the ongoing operation
and maintenance of the
facility. The more energyefficient
a facility is run, the
lower the operating costs
will be.
As mentioned above, electrical
devices contribute in
different degrees to the energy
efficiency of a facility.
Lower-efficiency electrical
devices waste more energy,
and as a result also contribute
to the production of more
greenhouse gas. One of these
common electrical devices
whose energy efficiency
should also be evaluated is
OCPDs, and this is the focus
of this document.
In making the choice of
either circuit breakers or
fuses, the energy efficiency
of these two devices ought
to be considered. Is there a
difference in their energy
efficiency?
To answer that question,
a study was commissioned
to quantify energy efficiency
of several
types of circuit breakers
and fuses. The results of this
study show that switches
and fuses were found to be
less energy-efficient as compared
with equivalently
sized circuit breakers.
These differences in efficiency
result in different levels
of energy savings. While
the absolute magnitude of
savings related to the energy
efficiency of OCPD may be
small compared with other
types of electrical devices,
the relative differences are
very significant. Knowing
this difference, why install
equipment that you know
wastes more energy than
another solution?
STUDY RESULTS
The study was developed
to quantify the energy losses
for several typical fuses and
circuit breakers.
Energy losses in fuses and
circuit breakers are primarily
the direct result of the
I2R resistive loss effect of
the current flowing
through the resistive elements
of these devices.
As its name suggests, resistive
losses are defined as:
Equation 1: Wloss = I2R
Where:
- Wloss = energy loss in
watts
- I = current in amperes
- R = resistance of conductor
in ohms
From Equation 1, we see
that the resistive energy losses
in a device are proportional
to the resistance of the
conductors within a device.
For the same current flowing
in two devices, the device
with the higher internal
resistance will have greater
energy loss, which may
result in a higher device temperature.
However, temperature
rise alone is not a reliable
indicator of losses. Energy
losses are best determined
via the I2R energy loss in
these devices.
Manufacturers of electrical
products must meet
third-party certifications
(Several UL standards specify
temperature limits for
protective devices and
assemblies of protective
devices including UL standards
198, 489, 891, 1558 and
many others). Many of these
certifications specify temperature
rise limits of bus,
terminal lugs, coil windings
and/or conductors.
In order to meet the specified
temperature rise limits,
some manufacturers
use the options of adding
heat sinks or specifying
larger products.
Therefore, although these
devices may have higher
internal energy losses, these
options allow the devices to
still meet the specified temperature
limits.
To ensure that we understood
the actual energy
losses within circuit breakers
and fuses, a test program
was developed to
measure the losses from
each of several types,
brands, sizes and ratings of
circuit breakers, fuses and
switches. The test program
attempted to study
as many combinations of
the various types, brands
and sizes that are currently
available. The test looked at
fuses of types RK-5, J and L,
Molded Case Circuit Breakers
(MCCB) and Air Circuit
Breakers (ACB), and overcurrent
range of 20 to 5000
amperes. Although attempts
were made to be as comprehensive
as possible, it was
not practical to study every
possible combination of
these types and ratings of
devices. Instead, the test
focused on ensuring that an
"apples-to-apples" comparison
was done on equivalent
devices-tests compared
devices of the same rating.
The details of the specific
test methodology and combinations
of devices that
were tested and their test
results can be found in
EatonT Technical Paper
AP08324002E.
As a result of theses tests,
the differences in watts losses
(Wloss) between several
types of circuit breakers and
fuses were noted. These differences
are noted in Table 1.
When the differences
highlighted in Table 1 are
viewed graphically in terms
of absolute watts, the differences
appear as shown in Figures
1 & 2.
CONCLUSION
The energy efficiency
of the electrical distribution
system of a
facility typically contributes
significantly
to the operating costs
of that facility. Different
types of electrical
devices have different
levels of cost impact.
Some devices have a
significant impact,
while others have a
lesser impact. The
more energy-efficient
an electrical device is,
the lower its operating
costs will be. In the
design and implementation
of the system of
over-current protective
devices that are to
be used in a facility,
choices in the types of
these devices must be
made. In making these
choices, in addition to
other performance factors
and commercial
considerations, system
designers and facility owners
should also consider the
energy efficiency of the
two basic options-fuses or
circuit breakers. Is one of
these devices more energyefficient
than the other?
A study was conducted
to evaluate the relative
energy efficiencies of a
range of fuses and circuit
breakers. The data from
this study showed that, on
average, circuit breakers
are appreciably more energy-
efficient than fuses.
With this fact in mind,
designers and facility owners
are able to include this
consideration when looking
at the various other
performance factors for
selecting the type of overcurrent
protective devices
to be used in a facility.
Untitled Document
Table 1: Percentage watts-loss differences between
various types of circuit breakers and fuses |
| Comparison |
Ampere Range |
3-Phase Watts Losses |
| Molded Case Breaker versus
RK-5 fuses |
20600 A |
Fuse dissipated, on average, 121% higher
losses than MCCB
of same size and rating |
| Molded Case Breaker versus
Class J fuses |
20600 A |
Fuse dissipated, on average, 91% higher
losses than MCCB
of same size and rating |
| Molded Case Breaker versus
Class L fuses |
8002500 A |
Fuse dissipated, on average, 226% higher
losses than MCCB
of same size and rating |
| Fixed Mounted Air Circuit
Breaker versus Class L fuses |
8005000 A |
Fuse dissipated, on average, 434% higher
losses than MCCB
of same size and rating |
| Draw-out Air Circuit Breaker
versus Class L fuses |
8005000 A |
Fuse dissipated, on average, 148% higher
losses than MCCB
of same size and rating |