**Document**

**Name**

# The Voltech Handbook of Transformer Testing

**Description**

1 Transformer Basics |

2 Available Tests |

2.0 Available Tests On The AT Series |

2.1 CTY - Continuity |

2.2 R - Winding Resistance |

2.3 RLS or RLP - Equivalent Series or Parallel R |

2.4 LS_LP - Primary Inductance |

2.5 LSB_LPB - Inductance With Bias Current |

2.6 QL - Q factor |

2.7 D - Dissipation Factor |

2.8 LL - Leakage Inductance |

2.9 C - Inter-winding Capacitance |

2.10 TR - Turns Ratio and Phasing |

2.11 TRL - Turns Ratio by Inductance |

2.12 Z_ZB - Impedance_Impedance with Bias |

2.13 R2 - DC Resistance Match |

2.14 L2 - Inductance Match |

2.15 C2 - Capacitance Match |

2.16 GBAL - General Longitudinal Balance |

2.17 LBAL - Longitudinal Balance |

2.18 ILOS - Insertion Loss |

2.19 RESP - Frequency Response |

2.20 RLOS - Return Loss |

2.21 ANGL - Impedance Phase Angle |

2.22 PHAS - Inter-winding Phase Test |

2.23 TRIM - Trimming Adjustment |

2.24 OUT - Output To User Port |

2.25 IR - Insulation Resistance |

2.26 HPDC - DC HI-POT |

2.27 HPAC - AC HI-POT |

2.28 SURG - Surge Stress Test |

2.29 STRW - Stress Watts |

2.30 MAGI - Magnetizing Current |

2.31 VOC - Open Circuit Voltage |

2.32 WATX - Wattage (External Source) |

2.33 STRX - Stress Watts (External Source) |

2.34 MAGX - Magnetizing Current (Ext. Source) |

2.35 VOCX - O.C. Voltage (External Source) |

2.36 LVOC - Low Voltage Open Circuit |

2.37 ILK - Leakage Current |

2.38 LSBX - Inductance with External Bias (Series) |

2.39 LPBX - Inductance with External Bias (Parallel) |

2.40 ZBX - Impedance with External Bias |

2.41 ACRT - AC HI-POT Ramp |

2.42 DCAT - DC HI-POT Ramp |

2.43 ACVB - AC Voltage Break Down |

2.44 DCVB - DC Voltage Break Down |

2.45 WATT - Wattage |

3 Examples of Different Transformer Types |

## 2.31 VOC - Open Circuit Voltage.

Open circuit voltage is the voltage appearing across a secondary winding when the primary is energized at a specified voltage and frequency, with the secondary at no-load.

The voltage is dependent not only on the turns ratio of the transformer, but also on the voltage drop in the primary winding due to the magnetizing current.

Example: -

### Where Used

The AT offers two basic alternative ways to confirm that the transformer has been assembled properly, with the appropriate number of primary and secondary turns.

Open circuit voltage measurements are the preferred tests for line frequency transformers, designed to operate over the full extent of the B-H curve, including the non-linear regions. (For other transformers, such as pulse transformers and those used in switched mode power supplies, a measurement of turns ratio is the preferred test.)

Clearly an open circuit voltage test cannot tell you the actual number of turns on a winding, only the ratio between one winding and the next. You should therefore also include a magnetising current test in your program, to give confidence that the absolute number of turns is correct as well as the ratio.

### Measurement Conditions

Open circuit voltage is measured by applying an ac test voltage to a selected winding (usually a primary winding), and measuring the resulting voltage produced on another winding.

If, there are several windings to be tested, the program will execute more quickly if the following points are observed: -

Place all the open circuit voltage (VOC) tests consecutively at the same point in the program.

Use the same energised winding, with the same test voltage and frequency for each test.

If there is a magnetising current (MAGI) test which has the same energised winding and the same test voltage and frequency, place this immediately before the first open circuit voltage test.

### Specifying the Test Limits

The AT offers you three ways to specify the test limits: -

Using a normal AC (rms) measurement.

Using a rectified (mean) measurement.

Using a DC (mean) measurement.

Generally, the AC (rms) value would be used, but you could use the
rectified (mean) or DC (mean) measurements if, for example, you are
testing transformers fitted with a rectifying diode.