TTRU3 True three-phase transformer turns ratio tester
Performs three-phase step-up ratio tests (patented)
Gives you confidence in your results at any voltage
Performs three-phase tests in less than 10 seconds
Saving you time and money
Smallest and lightest three-phase test set on the market
Built to survive harsh field conditions
Test voltage up to 250 V
Overcome the voltage dependence of large transformers
Automates an OLTC test sequence with one touch
Configure your on-load tap changer (OLTC), press start, and let the TTRU3 take care of the tap changer switching between tests
About the product
Megger’s TTRU3 transformer turns ratio tester is a revolutionary instrument designed to perform three-phase turns ratio measurements using step-up excitation (patented). A single three-phase lead-set connection is all that is required to complete three-phase tests in less than 10 seconds!
The TTRU3 is capable of three-phase excitation and can induce up to 250 V on the primary winding, overcoming the voltage dependence seen on larger transformers. The three-phase source also allows you to test phase shifting and zigzag transformers, and provides you with a guaranteed accuracy of ±0.05 % from -20 °C to +50 °C.
What’s more, the TTRU3 can be connected to a computer, enabling you to download results or control the instrument remotely. There is also an optional 2 inch printer for the instrument, enabling you to have a hard copy of your results if required.
You can also configure test plans and store results directly on the TTRU3 using the built-in 7 inch (18 cm) daylight-viewable touch screen display. To generate reports, results can be downloaded in Excel, and PDF files can be saved to a USB drive.
Last but not least, it’s also the smallest and lightest three-phase test set on the market!
- Single-phase/3-phase capability
- Simultaneous 3-phase
Product documentsAdditional documentation can be found on the support tab
FAQ / Frequently Asked Questions
Yes. Three-phase power transformers are often tested on a per-phase basis with a single-phase source, using relays to switch the power from one phase to another as necessary. Three-phase transformers are produced with a wide range of winding configurations and, in general, are more difficult to test accurately if the low voltage (LV) winding is delta configured. This is because TTR testing assumes that the secondary winding is an open circuit and has no load connected. With a delta-connected LV winding and measurements performed on a per-phase basis, this assumption does not hold, as the winding under test is loaded by its connection with the other two windings in the delta loop. The current circulating in the delta loop leads to internal losses affecting the accuracy of the TTR measurement.
In these cases, it is recommended either to energise the HV winding line-to-line or to use three-phase excitation. Flux distribution will be more uniform, leading to a higher coupling between windings, so the results are less sensitive to excitation voltage. Excitation losses during the test are shared by all three sources, providing higher accuracy results as compared to those obtained with single-phase excitation. Simultaneous three-phase excitation reduces testing time and improves the efficiency of resources.
A transformer turns ratio test checks that a transformer is converting energy in an expected way. The test is also known simply as a turns ratio test. A TTR test is performed by a ratio meter (ratio tester). This test validates the transformer design, the transformer nameplate, and the transformer’s fixed transforming abilities throughout its service life. A TTR test should be performed to confirm that the transformer’s de-energised tap changer is properly positioned and that shorted windings turns do not exist. The ratio meter provides convenient and accurate readings of power transformer ratios and polarities.A transformer turns ratio test works in accordance with the same fundamental electromagnetic phenomena that the transformer operates. The difference is that the TTR test typically uses a low voltage (LV) AC excitation signal (< 250 V AC) on a per-phase base or as a three-phase simultaneous excitation.
During a TTR test, one actually measures the TVR. Afterward, for three-phase transformers, a correction factor that depends on the vector configuration of the windings may need to be applied.It is impossible to measure TTR from accessible points on a transformer. An assumption is made in TTR testing that, because of no-load conditions, the voltage ratio of a transformer (TVR) is equal to the turns ratio (TTR). This, of course, ignores the reality that a true no-load condition cannot be achieved for all winding configurations. Another assumption in TTR testing is that all the flux produced by one winding links with the second winding, ignoring leakage flux. These assumptions, for some transformers, result in ‘false positives’ when looking for problems in a conventional TTR analysis.Finally, TNR is the ratio provided on a transformer’s nameplate, or one that can be calculated from the line-to-line winding voltages provided on the nameplate. In summary, the transformer turns ratio can be expressed as:
Further reading and webinars
TRAX Multifunction transformer and substation test system
MWA300 and MWA330A three-phase ratio and winding resistance analysers
- Check that the power cord is fully inserted into the TTRU3.
- Check that the power source is outputting voltage at acceptable levels and frequency.
- Check that the power cord is fully inserted into the source.
- Check that the power switch is in the correct position ( I ).
- Set the power switch to off ( O ). Wait 30 seconds. Set the power switch to on ( I ).
- Try another power cord.
- Check lead connections.
- Reference the nameplate to ensure leads are connected to the correct bushing.
Check the OLTC wiring diagram and ensure leads are connected to correct terminals.
- Contact your IT department for primary assistance when connecting any device to your PC
- Check the USB cable is fully inserted into the TTRU3
- Check the USB cable is fully inserted into the PC
- Check the TTRU3 is powered on
- Check the TTRU3 software is installed
- Check the TTRU3 software is not running in ‘simulation’ mode
- Check the TTRU3 is running
- Move the USB cable to another USB port on your PC
- Try another USB Cable
- Try another PC
- Check the battery is inserted into the printer
- Charge the printer battery using the supplied charger
- Check the printer paper is inserted properly
- Check the USB cable is plugged into the printer
- Check the USB cable is plugged into the TTRU3 USB port
- Check the printer is turned on by holding down the power button
- Try other USB ports
Interpreting test results
The TTRU3 presents three quantities per measurement: ratio, excitation current, and phase deviation.
The ratio is the measured transformer turns ratio (TTR), calculated using both the voltage applied to one side of the transformer and the induced voltage measured on the other. Calculated TTR is determined from the transformer's nameplate voltages and the k factor, if necessary, as given in the table below. With the measured TTR in hand, a percentage deviation from the calculated TTR can be computed, either manually or automatically by the TTRU3. As per IEEE, the percentage deviation between measured and calculated TTR should be within a ±0.5 % tolerance.
|Transformer configurations / vector groups
|TVR recalculation factor (k), TVR=k*TNR
IEEE documents cases of transformers that have a load tap changer in their low voltage side with an overall low number of turns that will cause some of the tap steps not having the same number of turns as others. Thus, the variation per tap is not uniform and might be outside the 0.5 % tolerance of deviation from nameplate values. In these cases, there are two criteria used to evaluate the results. First, the measured TTR at both extreme ends of the tap changer (highest and lowest) should be within the 0.5 % tolerance from the calculated TTR. Second, for any given tap, all three phases of the transformer should have the same voltage ratios.
The excitation current test is a routine measurement that can be used to detect major problems in the magnetic core structure and winding defects, like shorted turns. An excitation current measurement is often performed as a standalone test using a power factor test set, as it is normally made at rated frequency and voltages up to 10 kV. The results are voltage dependent but, due to the fact that the measurement’s evaluation relies heavily on pattern recognition, the numbers obtained during TTR testing – even when performed at considerably lower voltages – can be used as a good tool to diagnose the issues mentioned above, especially when having previous data from tests performed at the same voltage. A typical “phase pattern” presented by the excitation current test results obtained for all phases at a given tap position of a 3-phase transformer is H-L-H. The excitation current measured for the two outer wound phases should be of similar magnitude while the excitation current of the centre wound phase is the lowest in magnitude.
The phase angle deviation, displayed in either degrees (minutes) or radians, is the phase relationship between the voltage signal applied to the high (or low) winding and the voltage signal measured at the low (or high) voltage winding. The phase deviation together with ratio error can be used as a low cost method of verifying accuracy class of all types of PTs and CTs at ‘zero burden’. The phase deviation between the high and low side of a transformer is generally very small. If there is deterioration or damage in the transformer core, however, the phase deviation can change significantly. Building a transformer core with high permeability, low loss material and with no defects between laminations – in other words, no shorts between adjacent layers in the core – will help minimise the eddy currents and thus reduce the phase deviation. One can therefore state that any significant phase deviation reflects a core which is not efficient. If a transformer exhibits higher losses than expected, the core is the probable cause and phase deviation a visible result.
User guides and documents
Software and firmware updates
To upgrade from 2.2.4 to 3.x.x, the TTRU3 must be returned to a factory or ASC.
TTRU3 3.2.1 Release Notes can be downloaded here
TTRU3 2.2.4 Release Notes can be downloaded here
FAQ / Frequently Asked Questions
The TTRU3 will use ‘step up’ mode, applying voltage to the secondary/tertiary winding and inducing and measuring voltage on the primary winding. In any test mode, the instrument first performs a safety and connection test using a low voltage (less than 1 V). Auto test mode uses the results of this test to verify that testing can progress in step up mode and to determine if a 3-phase test is possible.
Maintenance should be performed only by qualified persons familiar with the hazards involved with high-voltage test equipment. Read and understand Sections 1, 2, 3, 4, and 5 of the User Guide before performing any service.The TTRU3 requires only periodic inspection. Inspect all hardware items to ensure all are in good condition.The TTRU3 may be cleaned periodically. In doing so, do not allow water to penetrate panel holes. An all-purpose, household spray cleaner can be used to clean the panel. Polish with a soft, dry cloth. Clean the cables and mating panel receptacles with isopropyl or denatured alcohol applied with a clean cloth.
You should perform a complete performance and calibration check of your TTRU3 at least once every year. This will ensure that the TTRU3 is functioning correctly over the entire measurement range. Anyone can use the optional Megger TRS1 (Transformer Ratio Standard) to calibrate a TTRU3. This high-accuracy reference ratio standard can provide ratios in both step-down test mode (for traditional ratio test instruments and the TTRU3) and step-up test mode (for the Biddle Hand Crank TTR and the TTRU3). Megger performs a TTRU3 calibration on each new or repaired unit before sending it to a customer.
Any service or repair of this equipment should be performed only by qualified persons who are aware of electrical hazards and the necessary precautions required to prevent injury.Megger offers a complete repair and calibration service and recommends that its customers take advantage of this service for routine maintenance or in the event of any equipment malfunction.In the event a service is required, contact your Megger representative for a product Return Authorisation (RA) number and shipping instructions.Ship the product prepaid and insured and marked for the attention of the Megger Repair Department. Please indicate all pertinent information, including catalogue number, serial number, and problem symptoms.