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TTRU1 handheld transformer turns ratiometer

• Ensure batteries are installed. 
• Ensure batteries have sufficient charge. 
  • If using Alkaline batteries, replace batteries. 
  • If using NiMH batteries, charge the TTRU1 using the included USB-C to USB-A or USB-C to USB-C cable. 
    • If charging does not work, replace the NiMH batteries.

• Turn the selection knob to “INFO”. 
  • Run a self-check and follow the direction on screen. 
• Turn the selection knob to “TTR”. 
  • Connect leads H1 to X1, H2 to X2, and run a 1:1 test using the 1ph0 diagram. 
  • Connect to a TRS1 to perform calibration verification. 

• Check that the USB file structure is FAT32 or exFAT. 
• Insert USB drive into the TTRU1, turn the selection knob to “INFO” and select “EXPORT DATA”.

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.

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.

Go/No Go testing provides open circuit, short circuit, and inductance verification of the transformer under test. When an open or short circuit is detected, the TTRU1 will indicate which winding has an issue.  

Short-circuit impedance values should be within 3 % of nameplate values. The TTRU1 allows the operator to input nameplate KVA and Z % and will display the measured percent error on screen.