**Document**

**Name**

# Turns Ratio

**Description**

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 |

## Basic Theory

The turns ratio of a transformer is defined as the number of turns on its secondary divided by the number of turns on its primary.

The voltage ratio of an ideal transformer is directly related to the
turns ratio:

The current ratio of an ideal transformer is inversely related to the
turns ratio:

Where Vs = secondary voltage, Is = secondary current, Vp = primary voltage, Ip = primary current, Ns = number of turns in the secondary winding and Np = number of turns in the primary winding.

The turns ratio of a transformer therefore defines the transformer as step up or step-down.

A step-up transformer is one whose secondary voltage is greater than its primary voltage and a transformer that steps up voltage will step-down current.

A step-down transformer is one whose secondary voltage is lower than its primary voltage and a transformer that steps down voltage will step-up current.