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Applications
The proper operation of a transformer relies almost entirely on the
electrical properties of its windings. To ensure continued proper
operation, transformers are tested to verify that their electrical
properties have not changed from design specifications. A TTR is an
extremely useful instrument for testing transformer windings because
it can locate several types of problems within a single - or a
three-phase transformer. It is also ideal to use for testing in
meter shops for the inspection of CTs and PTs. It can determine the
no-load accuracy of CTs and PTs and also determine the need to
further test faulty CTs and PTs.
The TTR100 applies voltage,
with voltage ratio being directly proportional to turns ratio, to
the high-voltage winding of a transformer and accurately measures
the resulting voltage from the low voltage winding. In addition to
turns ratio, the unit measures excitation current, phase angle
deviation between the high and low voltage windings, percent ratio
error, dc winding resistance and polarity.
Transformer
Turns Ratio
Transformer Turns Ratio is the
ratio of the number of turns in the high voltage winding to that in
the low voltage
winding.
A Transformer Turns Ratio
Test Set such as the TTR100 can directly measure the ratio of single
phase, as well as three phase transformers. Transformer ratio can
change due to several factors, including physical damage from
faults, deteriorated insulation, contamination and shipping damage.
If a transformer ratio deviates more than 0.5 percent from the rated
voltage ratio, it may not operate reliably. To measure small ratio
changes such as this, the accuracy of a Megger TTR100 is needed.
Excitation
Current
The TTR100 is capable of measuring
exciting current by applying voltage to one of the transformers
windings. An accurate measurement of exciting current can provide
information about the condition of a transformer’s core. Unwanted
circulating currents or unintentional grounds can affect the
exciting current and indicate a problem.
Phase Angle
Deviation
The phase angle deviation is the relationship between the voltage
signal applied to the high voltage winding and the voltage signal
extracted from the low voltage winding. The phase deviation between
the high and low side of a transformer is generally very small.
However, the phase deviation can change significantly if there is
deterioration or damage in the transformer core. The TTR100 can
measure this phase relationship with the resolution necessary to
detect a problem.
Additional information
about a transformer’s electrical properties can be found in the IEEE
Standard Test Code for Transformers, C57.12.90, or by contacting
Megger’s technical support group.
Winding
Resistance
Measuring the DC resistance of transformer windings will aid in
identifying problems such as shorted or open windings, as well as
loose connections. The Megger TTR100 can measure the DC resistance
of both single phase and three phase transformer windings.
Transformer
Polarity
Polarity of a distribution transformer becomes of interest in order
to determine its proper connection within a power network. The
Megger TTR100 will identify subtractive and additive polarity of the
single-phase distribution transformers.
Features and Benefits
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Faster, easier handheld
operation. User no longer has to kneel or bend down to operate the
instrument. Powered by rechargeable battery, provides up to
fifteen hours of field operation.
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Report header information
such as company name, substation name, transformer manufacturer,
transformer
ratio, operator, temperature and %RH can be entered and saved via
the alphanumeric keypad.
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Measures the widest turns
ratio range in the industry (20,000:1) with the highest accuracy
(±0.1%, 0.8 to 2000) at a low excitation voltage.
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Enables the operator to
enter the ratio of the transformer and all of its taps. This
allows the operator to know immediately when a tap is outside the
acceptable limits so that problem taps can be easily identified.
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Records ratio errors for
bushing CTs to an accuracy of ±0.1% nameplate. This reduces the
need for additional test equipment and improves set-up time.
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Measures the phase
deviation (in minutes, degrees or centiradians) of the transformer
primary versus secondary. This quickly indicates problems in the
transformer such as partial shorted turns and core faults. This
measurement is also useful in verifying phase errors in all types
of PTs and CTs.
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Perfect for meter shops,
the TTR100 can be used for inspection purposes by using it to
determine the no-load accuracy of most CTs and PTs. It also can be
used to determine the need to further test potentially faulty CTs
and PTs.
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The TTR100 is ideal for
use by transformer manufacturers. Its unique testing procedures
and storage capability allows an operator to set up and test
single and three-phase transformers (with multiple tap changers
and bushing CTs) in minimal time.
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A “Quick Test” mode
provides a fast determination of the turns ratio, excitation
current, phase angle deviation, and winding resistance in single-
and three-phase transformers and CTs. In addition, polarity is
provided for CTs and single-phase transformers.
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Displays all measured and
calculated values for each test including ratio, excitation
current, ratio error, phase angle deviation, transformer vector
group, winding resistance and polarity thus providing
comprehensive and conclusive data.
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Automatic
self-calibration for each test.
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Rugged, lightweight
design ideally suited for a harsh field and substation
environment.
- Three user selectable standards: ANSI,
IEC, and Australian. Also meets IEC1010 as well as CE.
- Six user selectable languages: English,
French, German, Italian, Portuguese and Spanish.
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