User guide

FRAX 150
Sweep Frequency Response Analyzer
Considerations When Performing
SFRA Measurements
SFRA measurements are compared over time or between
different test objects. This accentuates the need to perform
the test with the highest repeatability and eliminates
the influence from external parameters such as cables,
connections and instrument performance. FRAX offers
all the necessary tools to ensure that the measured curve
represents the internal condition of the transformer.
Good Connections
Bad connections can compromise the test results which
is why FRAX offers a rugged test clamp that ensures good
connection to the bushings and solid connections to the
instrument.
Import and Export
The FRAX software can import data files from other FRA
instruments making it possible to compare data obtained
using another FRA unit. FRAX can import and export data
according to the international XFRA standard format as well
as standard CSV and TXT formats.
Optimized Sweep Setting
The software offers the user an unmatched feature that
allows for fast and efficient testing. Traditional SFRA
systems use a logarithmic spacing of measurement points.
This results in as many test points between 20Hz and
200Hz as between 200KHz and 2MHz and a relatively long
measurement time.
The frequency response from the transformer contains a
few resonances in the low frequency range but a lot of
resonances at higher frequencies. FRAX allows the user to
specify less measurement points at lower frequencies and
high measurement point density at higher frequencies. The
result is a much faster sweep with greater detail where it is
needed.
Variable Voltage
The applied test voltage may affect the response at lower
frequencies. Some FRA instruments do not use the 10 V
peak-to-peak used by major manufacturers and this may
complicate comparisons between tests. FRAX standard
voltage is 10 V peak-to-peak but FRAX also allows the user
to adjust the applied voltage to match the voltage used in a
different test.
FTB 101
Several international FRA guides recommends to verify the
integrity of cables and instrument before and after a test
using a test circuit with a known FRA response supplied by
the equipment manufacturer. FRAX comes with a field test
box FTB101 as a standard accessory and allows the user to
perform this important validation in the field at any time
and secure measurement quality.
FRAX 150 has a built-in computer with high contrast
and powerful backlit screen suitable for use in direct
sunlight.
Solid connections using the C-clamps and the
shortest braid method to connect the shield to
ground makes it possible to eliminate connection
problems and cable loops that otherwise affect the
measurement.
Contacts made with the C-clamp guarantee good connections
Shortest Braid Concept
The connection from the cable shield to ground has to be
the same for every measurement on a given transformer.
Traditional ground connections techniques have issues
when it comes to providing repeatable conditions. This
causes unwanted variations in the measured response for the
highest frequencies that makes analysis difficult.
The FRAX braid drops down from the connection clamp next
to the insulating discs to the ground connection at
the base of the bushing. This creates near identical
conditions every time you connect to a bushing whether it is
tall or short.
FRAX 150 with Built-in PC
FRAX 150 has a built-in PC with a high contrast, powerful
backlit screen suitable for work in direct sunlight. The cursor
is controlled via the built-in joystick or using an external USB
mouse and the built-in keyboard makes data entry easy.
All data is stored on the built-in hard drive. The data can be
moved to any other computer using a USB memory stick.
FTB 101 Field Test Box