Atec frax150 User Manual
Sweep Frequency Response Analyzer
FRAX 150
Sweep Frequency Response Analyzer
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Highest dynamic range and accuracy
in the industry
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Built-in PC with powerful backlit screen
for use in direct sunlight
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Highest possible repeatability by
using reliable cable practice and
high-performance instrumentation
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Fulfills all international standards
for SFRA measurements
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Advanced analysis and decision support
built into the software
FRAX 150
DESCRIPTION
Power transformers are some of the most vital components
in today’s transmission and distribution infrastructure.
Transformer failures cost enormous amounts of money
in unexpected outages and unscheduled maintenance. It
is important to avoid these failures and make testing and
diagnostics reliable and efficient.
The FRAX 150 Sweep Frequency Response Analyzer
(SFRA) detects potential mechanical and electrical
problems that other methods are unable to detect. Major
utilities and service companies have used the FRA method
for more than a decade. The measurement is easy to
perform and will capture a unique “fingerprint” of the
transformer. The measurement is compared to a reference
“fingerprint” and gives a direct answer if the mechanical
parts of the transformer are unchanged or not. Deviations
indicate geometrical and/or electrical changes within the
transformer.
FRAX 150 detects problems such as:
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Winding deformations and displacements
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Shorted turns and open windings
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Loosened clamping structures
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Broken clamping structures
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Core connection problems
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Partial winding collapse
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Faulty core grounds
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Core movements
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Imports data from other FRA test sets
Collecting fingerprint data using Frequency Response Analysis (FRA) is an
easy way to detect electro-mechanical problems in power transformers
and an investment that will save time and money.
APPLICATION
Power transformers are specified to withstand mechanical
forces from both transportation and in-service events, such
as faults and lightning. However, mechanical forces may
exceed specified limits during severe incidents or when
the insulation’s mechanical strength has weakened due to
aging. A relatively quick test where the fingerprint response
is compared to a post event response allows for a reliable
decision on whether the transformer safely can be put back
into service or if further diagnostics is required.
FRAX 150
Sweep Frequency Response Analyzer
Method Basics
A transformer consists of multiple capacitances, inductances
and resistors, a very complex circuit that generates a unique
fingerprint or signature when test signals are injected at
discrete frequencies and responses are plotted as a curve.
Capacitance is affected by the distance between conductors.
Movements in the winding will consequently affect
capacitances and change the shape of the curve.
The SFRA method is based
on comparisons between
measured curves where
variations are detected. One
SFRA test consists of multiple
sweeps and reveals if the
transformer’s mechanical or
electrical integrity has been
jeopardized.
Practical Application
In its standard application, a
“finger print” reference curve
for each winding is captured
when the transformer is new
or when it is in a known good condition. These curves
can later be used as reference during maintenance tests or
when there is reason to suspect a problem.
The most reliable method is the time based comparison
where curves are compared over time on measurements
from the same transformer. Another method utilizes type
based comparisons between “sister transformers” with
the same design. Lastly, a construction based comparison
can, under certain conditions, be used when comparing
measurements between windings in the same transformer.
These comparative tests can be performed 1) before and
after transportation, 2) after severe through faults 3) before
and after overhaul and 4) as diagnostic test if you suspect
potential problems. One SFRA test can detect winding
problems that requires multiple tests with different kinds of
test equipment or problems that cannot be detected with
other techniques at all. The SFRA test presents a quick and
cost effective way to assess if damages have occurred or if
the transformer can safely be energized again. If there is a
problem, the test result provides valuable information that
can be used as decision support when determining further
action.
Having a reference measurement on a mission critical
transformer when an incident has occurred is, therefore, a
valuable investment as it will allow for an easier and more
reliable analysis.
Analysis and Software
As a general guideline, shorted turns, magnetization and
other problems related to the core alter the shape of the
curve in the lowest frequencies. Medium frequencies
represent axial or radial movements in the windings and
high frequencies indicate problems involving the cables
from the windings, to bushings and tap changers.
An example of low, medium and high frequencies
The FRAX Software provides numerous features to allow
for efficient data analysis. Unlimited tests can be open
at the same time and the user has full control on which
sweeps to compare. The response can be viewed in
traditional Magnitude vs. Frequency and/or Phase vs.
Frequency view. The user can also choose to present the
data in an Impedance or Admittance vs. Frequency view
for powerful analysis on certain transformer types.
The figure above shows a single phase transformer after a service
The figure above shows a single phase transformer after a service
overhaul where, by mistake, the core ground never got connected (red),
overhaul where, by mistake, the core ground never got connected (red),
and after the core ground was properly connected (green). This potential
and after the core ground was properly connected (green). This potential
problem clearly showed up at frequencies between 1 kHz and 10 kHz and
problem clearly showed up at frequencies between 1 kHz and 10 kHz and
a noticeable change is also visible in the 10 kHz - 200 kHz range.
a noticeable change is also visible in the 10 kHz - 200 kHz range.
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