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Technical Document Reader

**Document**

104-113

**Name**

# Turns Ratio

**Description**

An explanation of Turns Ratio and several methods to obtain best measurements.

1 Introduction to Turns Ratio |

2 Basic Theory |

3 Factors Affecting Turns Ratio Measurements |

4 Types of Turns Ratio Tests |

5 Choosing the Correct Turns Ratio Test |

6 Turns Ratio Conclusion |

## Choosing the Correct Turns Ratio Test

In order to determine which type of turns ratio test is most appropriate for a particular transformer, a number of issues should be considered.

The table below shows each test with a description, the related specifications and a summary of the benefit provided by that test.

## Test. |
## Description / Specification |
## Use or Benefit |

## TR |
Ratio of input to output
volts |
Shows the true
electrical ratio as expected in operation when energizing a primary winding. The ratio measured with this test therefore includes the losses normally found in the transformer, which will result in a ratio greater than that of the physical turns but reflects the real voltage ratio expected by the designer. |

Measurement range: 1:100 000 to
100 000:1 Voltage range: 1mV - 5V Frequency range: 20Hz - 3MHz Accuracy: 0.1% |
||

## TRL |
Ratio of turns calculated
from inductance |
Reduces the effect on
measured turns ratio of transformer losses, giving a closer approximation to the physical turns ratio. This is of particular benefit where actual turns are of interest but the transformer has a large proportion of leakage inductance which may have a significant effect on the voltage ratio. |

Measurement range: 1:30 to 30:1 Voltage range: 1mV - 5V Frequency range: 20Hz - 3MHz Accuracy: 0.1% |
||

## LVOC |
Output volts measured withlow-voltage input |
Similar to TR but
presents the actual output voltage rather than the voltage ratio. This simplifies test limit entry when the transformer specification has been derived from voltmeter measurements. |

Measurement range: 100μV to 650V (100μV to 5V ATi) Voltage range: 1mV - 5V Frequency range: 20Hz - 3MHz Accuracy: 0.1% |
||

## VOC |
Output volts measured withhigh-voltage input |
Similar principal to
LVOC but using a generator with higher voltage and higher power. This is essential if the transformer has a non-linear BH curve and will be operated in the non-linear proportion of this curve, as with iron laminate power transformers. |

Measurement range: 100μV to 500V Voltage range: 1V - 270V Frequency range: 20Hz - 1500Hz Accuracy: 0.1% |
||

## VOCX |
Output volts measured withexternal high-voltage input |
Provides the ability
to test power transformers that are above the capacity of VOC testing. By controlling an external power source with the Voltech AC Interface Fixture, the VOCX test provides fully automatic testing of high-power transformers at their specified working voltage. |

Measurement range: 100μV to 650V Voltage range: 5V - 600V Frequency range: 20Hz - 1MHz Accuracy: 0.1% |