• Megger

Megger® TTR25 Series

Handheld Transformer Turns Ratio Tester
Megger TTR25 Handheld turns ratio tester


  • Single- and three-phase transformer testing
  • Fully automatic, fast and easy-to-use
  • Robust and lightweight
  • Battery-powered
  • Tests turns ratio, excitation current, and polarity
  • Simple, one-button operation
  • Quick-start guide on front panel
  • Operator-selectable languages


The Megger TTR25 is an automatic hand-held battery operated transformer turns ratio test set. It is used to measure the turns ratio, excitation current and polarity of windings in single- and three-phase distribution and power transformers (tested phase by phase), potential & current transformers, and tapped transformers.

The unique design of the TTR25 allows the user to operate the test set while holding it in one hand. It effectively eliminates the user from having to kneel or bend down to operate the instrument and speeds up testing time. Realizing the extreme environments in which the TTR25 must operate, special attention has been paid to making it extra rugged, with a high impact, shock resistant case, yet incredibly lightweight at a mere 870 g (1.9 lbs). Its design makes this instrument well suited for use in a variety of harsh environments. The TTR25 is particularly suited for testing in substations, transformer-manufacturing environments, and meter shops. It features a high-contrast, backlit LCD screen which can be seen in bright or ambient light.

This unit measures a high turns ratio of 20,000:1 accurately with the lowest excitation voltage. The excellent repeatability of the TTR25 helps the users to determine the condition of transformers under test. It is designed for simple, one button operation with the measured results displayed directly on the easy to read LCD or printed to the optional printer. The TTR25 needs no additional software and comes ready to use complete out of the box.

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  • 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 help locate several types of problems within single- and three-phase transformers.
  • It it used to determine the no-load accuracy of CTs and PTs and also determine the need to further test faulty CTs and PTs. The TTR25 applies voltage to the high-voltage winding of a transformer and accurately measures the resulting voltage from the low voltage winding. The ratio of voltages is directly proportional to turns ratio. In addition, the unit measures excitation current and polarity.

Transformer Turns Ration

A Transformer Turns Ratio Test Set such as the TTR25 can directly measure the turns ratio of single-phase transformers as well as three-phase transformers. Deviations in these measurements will quickly indicate problems in transformer windings and in the magnetic core circuits. 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 TTR25 is needed.

Transformer Polarity

Polarity of a distribution transformer becomes of interest in order to determine its proper connection within a power network. The Megger TTR25 will identify normal (in phase) and reverse polarity of the single-phase transformers.


  • Fast, easy hand-held operation. No need to kneel or bend down to operate the instrument.
  • Powered by six standard “AA” alkaline batteries; no charger needed. Provides up to 12 hours of field operation.
  • Measures turns ratio range of 20,000:1, with a high accuracy (±0.1%, 0.8 to 2000) at a low excitation voltage.
  • 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.
  • Perfect for meter shops, the TTR25 can be used for inspection purposes to determine the no-load accuracy of most CTs and PTs. It also can be used to determine the need to test potentially faulty CTs and PTs.
  • Automatic self-calibration for each test.
  • Literature
  • Specifications
Excitation Voltage: 8 V rms for testing distribution or power transformers and PTs; 0.5, 1.5, or 8 V ac rms for testing CTs. The excitation voltage is switched automatically if excitation current exceeds a preset value.
Test Frequency: 55 Hz internally generated providing a universal 50/60 Hz test set
Excitation Current Range: 0 to 100 mA, 4-digit resolution
Turns Ratio Range : 0.8 to 20,000, 5 digit resolution
Transformer Winding Phase Relationship: ANSI C57.12.70-1978CEI/IEC 76-1:1993 and Publication 616:1978 AS-2374, Part 4-1982 (Australian Standard)
Current (rms) accuracy:
(2% of reading + 1 digit)
Turns Ratio Accuracy :

0.1% (0.8 to 2000)

0.15% (2001 to 4000) 0.25% (4001 to 10,000) 0.5% (10,001 to 20,000)
Display full graphics : LCD module, adjustable back-lighting, wide temperature range, 128 x 64 dots (21 characters by 8 lines)