Transformers Ratio Finder TTRF-250

Transformers Ratio Finder TTRF-250

The TTRF-250 is Amperis' fourth generation transformer turns ratio tester. This latest design provides a higher turns-ratio test voltage of 250Vac, provides a wireless Bluetooth PC interface, and features a 44-key "QWERTY"-style membrane keyboard. All these features greatly improve the accuracy of the turns ratio readings, ease of operation, and reliability.

The TTRF-250 determines the turns ratio of the transformer under test using the IEEE C57.12.90 measurement method. The turns-ratio range is from 0.8 to 50,000 to 1. Transformer turns ratio, excitation current, and winding polarity are displayed on the built-in 128 x 64 pixels graphic LCD screen. The TTRF-250 can be used as a standalone unit or can be computer-controlled.

Transformer Test Voltages

To prevent an accidental wrong test-lead hook-up (e.g., when the operator reverses H and X leads), the TTRF-250 outputs a low-level test voltage to verify the hook-up condition before applying the full test voltage to the transformer. Four test voltages (4 Vac, 40 Vac, 100 Vac, 250 Vac) allow the TTRF- 250 to test CT’s and PT’s, as well as power transformers.

Auto-Detect Transformer Configuration

The TTRF-250 can automatically detect 130 specific vector groups for different transformer types defined by ANSI, CEI/IEC, and Australian standards.

Internal Test Record Storage

Up to 112 test records can be stored in the TTRF- 250’s Flash EEPROM memory. Each test record may contain up to 99 turns-ratio, excitation current, phase angle and nameplate voltage readings. Test records can be recalled locally or transferred to a PC via the available interfaces (Bluetooth, USB port, USB Flash drive port).

Bluetooth PC Interface

The TTRF-250 offers an industry-first Bluetooth wireless interface along with an Android App that can be used to remotely control the unit.

Transformer Test Plans

The TTRF-250 can store up to 128 transformer test-plans in its Flash EEPROM. A test-plan is comprised of the transformer nameplate voltages for each tap setting. The calculated turns ratio based on the nameplate voltages is compared with the measured turns-ratio to derive the percentage error and Pass/Fail results. By using a test plan, a transformer can be quickly tested and turns-ratio Pass/Fail reports can be reviewed. Test plans can be created with the PC software and can be transferred to the TTRF-250 via the available interfaces (Bluetooth, USB port, USB Flash drive port).

User Interface

The TTRF-250 features a back-lit LCD screen (128 x 64 pixels) that is viewable in both bright sunlight and low-light levels. The test results screen displays the transformer turns-ratio, excitation current, phase angle, and percentage error. The unit is controlled via a rugged, 44-key, "QWERTY"-style membrane keypad.

Computer Interface

In computer-controlled mode, the unit can be controlled via the Bluetooth or USB interface using the supplied PC software (Transformer Turns-Ratio Analyzer application provided with each unit). This Windows®-based application can be used to run tests and to store test results on a PC. Test results can also be exported to Excel, PDF, and XML formats for further analysis.

Transformer Load Tap Changer Control

Voltage regulator or LTC tap positions can be changed remotely using the unit’s built-in transformer load tap changer. This feature eliminates the need to manually raise or lower tap positions from the transformer control panel.

USB Flash Drive Interface

A built-in USB Flash drive interface provides a convenient method for transferring test plans and test records to or from a USB Flash drive. The user can store up to 999 transformer test plans and test records on a USB Flash drive, and the supplied PC software can be used to view the test records.

USB Flash Drive Interface

The 250V test voltage provided by the TTRF-250 provides more accurate test results when measuring the transformer turns ratios of very large transformers with a built-in LTC. The three figures below show the turns ratio test results and corresponding percentage error of a 600MVA transformer with an LTC in the Lowest position using 40V, 100V, and 250V test voltages. At the 250V test voltage, the percentage error is less than 0.5% as specified in IEC 60076-1 and IEEE C57.12.00-2006-1 standards.

TTRF-250’s Specifications


Portable, lightweight, automatic, 3-phase transformer turns-ratio meter

Physical specifications

18”W x 5”H x 12”D (45.7 cm x 12.7 cm x 30.5 cm ); Weight: 20 lbs (9.1 kg)

Input power

100 - 240 Vac, 50/60 Hz

Measurement method

ANSI/IEEE C57.12.90

Ratio measuring range

0.8 - 50,000 to 1

Turns ratio accuracy

0.8 - 1,999: ±0.1%, 2,000 - 3,999: ±0.25%. 4,000 - 14,999: ±1%, 15,000 - 50,000: ±2% @ 4Vac
0.8 - 1,999: ±0.1%, 2,000 - 3,999: ±0.20%. 4,000 - 14,999: ±1%, 15,000 - 50,000: ±1.5% @ 40Vac
0.8 - 1,999: ±0.1%, 2,000 - 3,999: ±0.20%. 4,000 - 14,999: ±1%, 15,000 - 50,000: ±1.5% @ 100Vac
0.8 - 1,999: ±0.1%, 2,000 - 3,999: ±0.15%. 4,000 - 14,999: ±0.8%, 15,000 - 50,000: ±1.2% @ 250Vac

Test voltages

4 Vac @ 1 Amp, 40 Vac @ 200 mA, 100 Vac @ 100 mA, 250 Vac @ 50 mA

Excitation current reading range

0 - 2 Amperes; Accuracy: ±1mA, ±2% of reading (±1 mA)

Phase angle measure

0 - 360 degrees; Accuracy: ±0.2 degrees ( ±1 digit)


Back-lit LCD screen (128 x 64 pixels) viewable in bright sunlight and low-light levels


Built-in 4.5-inch wide thermal printer

Computer interface

Bluetooth, USB port

External data storage

One USB Flash drive interface port; Up to 999 transformer test records can be stored on a USB Flash drive (not included)

Pc software

Windows®-based Transformer Turns-Ratio Analyzer application is included

Internal test record storage

Can store 112 transformer test records internally. Each record holds the test record header and up to 99 readings.

Internal test plan storage

Can store 128 transformer test plans internally. Test plans can be transferred to the unit from the PC via the Bluetooth/USB port or via the USB Flash drive interface

Load tap changer contact

240 Vac, 2 Amps


Designed to meet UL 61010A-1 and CAN/CSA C22.2 No. 1010.1-92 standards


Operating: -10°C to +50°C (+15°F to +122°F); Storage: -30°C to +70°C (-22°F to +158°F)


90% RH @ 40°C (104°F) non-condensing


2000 m (6,562 ft) to full safety specifications


One 15-foot single-phase set, one 15-foot 3-phase set, one 25-foot extension set, one safety ground, one USB, cable bag

Optional accessories

Transportation case


1 year on parts and labor

NOTE: the above specifications are valid at nominal voltage and ambient temperature of +25°C (+77°F). Specifications are subject to change without notice

Test results using 40V, 100V and 250vTTRF-250’s ConnectionsTTRF-250’s Controls, thermal testTTRF-250’s details

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