The PFRS-25 can confirm the mechanical integrity of a transformer by comparing the frequency response of the transformer with the previous known results. Every transformer has a unique frequency response system which changes if the mechanical geometry of the transformer is changed. These changes can occur due to physical movement or transportation. The physical geometry can also change if the transformer experiences high fault current due to internal or external fault. The fingerprint comparison of the frequency response system can be used to detect power transformer problems such as:
- Core movements
- Shorted turns or open windings
- Winding displacements or deformations
- Winding connection problems
- Broken clamping structures
The PFRS-25 injects the voltage of the known value (generator/Reference) at one end of the winding and measures the voltage at the other end of the winding (measure Voltage) over a wide frequency range. The result is plotted at the ration of measure voltage to the reference voltage. The test result plot can be compared with the reference of previous results. When variation is found, it may indicate damage to the transformer. Frequency response analysis can detect many types of faults such as turns to turn short circuit, the condition of transformer oil, and mechanical displacement.
A transformer winding can be represented as an RLC network. Any type of fault that occurs may be a result of a change in this RLC network. Due to these changes, the frequency response may change before shipment, transport, or relocation of the transformer or post fault, etc.
By examining the trace of the transformer with the reference trace following defects of the transformer can be effectively detected with a PFRS-25:
- Shorted turn
- Winding movement/looseness
- Hoop buckling
- Magnetized core
- Core looseness
- Core grounding
- Oil degradation
The included PFRA user-friendly software from PDIC can be used to control the PFRS- 25 and analyze test results. It can compare the test results from a previous test or a reference trace.
The PFRA features a test plan templates library for commonly used transformers. This allows users to quickly create a test plan for a specific transformer for improved productivity. A new test plan can be added very easily by modifying the existing test plan or starting a new test plan from scratch.
The test voltage is settable from 0.2-24 V p-p and allows the user to set the test voltage to the value used for previous tests if it is different than the typical 20 V p-p.
The number of test points between a de- fined frequency band can be customized. The maximum number of test points for a defined trace can be set up to 32,000.
Windows-based sweep frequency response analysis software is included with each PFRS-25. The software can perform tests automatically and can be used to analyze the test data. The test data can be compared with previous data to analyze any changes. The software graphically compares test results as a magnitude vs. frequency plot, phase vs. frequency graph, or display both graphs at the same time. The software provides an analytical tool that can perform correlation coefficients between two traces per the IEEE C57.149-2012 or DL/T 911-2004 standard.
Users can quickly run tests in the field using pre-defined test connections. These include user-defined configurations as well as configurations defined by the IEEE C57.149-2012 standard. Test data can be exported to XML and EXCEL formats. The PFRS-25 software can import SFRA test records allowing the user to compare the PFRS-25 test records against other devices on the market.
The trace can be configured to start from high frequency to low frequency or low frequency to high frequency to match the process followed for the previous trace. This features shows for different methods of acquiring data for the frequency trace.
Any part of the trace can be zoomed in on by just drawing a square using the computer pointing device around the area to be zoomed for easy analysis. When the pointing device is placed on the trace, the software will indicate the frequency (x axis) and dB value (y axis) which helps the user to compare the traces.
The PFRA’s quick test feature can scan the trace in under 6 seconds to confirm that the connections to the instrument are good. Any wrong, loose, or bad ground connections can be detected quickly if the quick test scan does not show the expected trace shape or shows a noisy trace.
The PFRA software can import test results (without any conversion) of all other manufacturers of SFRA instruments. It can also import test results in IEC, CIGRE or CSV format.
The PFRA software does not limit the number of traces that can be displayed. All or in- dividual traces can be shown or hidden and each trace’s color can be configured for easy analysis.
The trace display line thickness can be customized for better visibility and easy analysis.
Comparison of traces with visual indication of Normal, suspect, severe and Obvious condition can be done per IEEE C57.149 and DL/T 911 standard.
PFRS-25 is a lightweight, field portable single box for diagnostic of transformer mechanical integrity. It offers high measurement accuracy of ±0.1 dB for all ratios between +10 dB and -60 dB and ±0.3 dB at ratios above -60 dB. At under 20 seconds (20 Hz- 2MHz), the PFRS-25 has the fastest sweep time of all current FRA instruments, considerably reducing transformer testing time.
Built-in Bluetooth communication enables users to be at a convenient and safe distance from the instrument and the transformer un- der test. This feature is very convenient when the weather is severe. The PFRS-25 instrument can be put on the transformer while a user with a pc can be at a comfortable and safe distance. The unit also provides a visual indication on the front panel and in the software that a connection is active. A standard USB 2.0 interface is also provided.
An optional built-in battery backup can be added for situations where an AC power source is not readily available. The 12 V, 3 AH battery allows a user to test for up to 4 hours without recharging. The instrument can also be used with the AC power while the battery is charging. The software, when connected with the instrument, indicates the charge on the battery.
Simple universal C clamps with BNC connectors are suitable for all different types of bushing connections. They can easily accommodate copper flat and round bushing terminations. Similar ground clamps facilitate fast and easy connections for the ground braid.
A user’s manual is provided with each unit. Also, a quick start guide sticker is provided in the instrument lid. The quick start guide provides the connection information for short circuit as well as open circuit connection and guides the user on how to make proper connections.
- Technical Specifications
|Operating||-26°C to +55°C (-14°F to +131°F)|
|Storage||-26°C to 70°C (-14°F to +158°F)|
|Humidity||< 95% RH, non-condensing|
|AC power supply||90 – 264 V AC, 47 – 63 Hz|
|Internal battery||3.2 Ah, 38 Watts|
|Dimensions||13" x 11" x 6" (34 cm x 29 cm x 15 cm)|
|Weight||10.0 lbs. (4.5 Kg) Includes the field rugged ABS Enclosure|
|Transportation Case||24.5” x 19.37” x 12.22” / 62.33 cm x 49.2 cm x 31.04 cm|
|Frequency Range||0.1 Hz – 25 MHz, user selectable|
|Frequency Resolution||0.01% OR 0.001Hz|
|Frequency Accuracy||0.01% (measurement error)|
|Level Resolution||0.0005 dB|
|Number of Points||Default 1046, Up to 32,000 points (user selectable)|
|Measurement Time||<20 S, fast setting 6 s (20 Hz – 2 MHz)|
|Points Spacing||Log, linear, or both|
|Sweep Settings||20 Hz to 2 MHz|
|Internal Noise Level (average)||>140 dB|
|Dynamic Range||>150 dB|
|Accuracy||±0.1 dB from +10 to -60 dB and ±0.3 dB (min) below -60 dB|
|IF Bandwidth||User selectable; default <10%|
|PC Communication||USB and Bluetooth|
|Standards/Guides||Fulfills requirements in IEC 60076-18, IEEE C57.149-2012, CIGRE Technical Brochure 342, DL/T 911-2004, as well as other international standards and recommendations|
|Compliance Voltage||0.2 – 24 V p-p|
|Measurement voltage at 50 Ω||0.1 – 12 V P-P|
|Channel Protection||Short-circuit and over-voltage protection|
|Sweep Direction||Low to high or high to low|
|Frequency Range||0.1 Hz – 25 MHz, user selectable|
|Frequency Range||0.1 Hz – 25 MHz|
|Input Impedance||50 Ω|
|Sampling Rate||100 MS/s|