**Document**

**Name**

# The Voltech Handbook of Transformer Testing

**Description**

1 Transformer Basics |

2 Available Tests |

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 |

2.0 Available Tests On The AT Series |

3 Examples of Different Transformer Types |

## 2.11 TRL - Turns Ratio by Inductance

### 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.

Turns ratio is the preferred test for signal, pulse and switched mode
power transformers, where the normal operating conditions require only
small excursions of the B-H curve, never extending beyond the linear
regions. Where the magnetic coupling between the primary and secondary is
poor, it is preferable to measure the turns ratio by inductance.

This test measures the inductance of both the primary and secondary and
calculates the turns ratio from these measured values.

(For line frequency transformers, designed to operate over the full extent of the B-H curve, including the non-linear regions, the preferred method is to use an open - circuit voltage test to check for the correct number of turns on each winding.)

Clearly a turns ratio test cannot tell you the actual number of turns on
a winding, only the ratio between one winding and the next.

You should therefore have at least one inductance test in your program to
give confidence that the absolute number of turns is correct as well as
the ratio.

### Measurement Conditions

The inductance of a winding can often depend upon the flux density in the
core/windings.

Since during measurement, the flux density will depend upon the signal
energising the winding, it is important that both windings are energized
at the same level.

This will ensure that both inductances are measured along the same region
of the B/H curve of the core, to give a true ratio.

### Setting the Test Parameters

The simplest method of setting the test parameters is to use the
"Measure" button, to do this you have to program the test from a computer
which is connected to the Auxiliary port of the tester.

There are two other methods of inputting the test parameters, one is to
set the primary voltage and frequency and let the editor set the secondary
voltage, and the second is to set both voltages manually.

### Using the Measure Button to Set Test Parameters

To do this you must be programming the test from a computer that is
connected to the testers auxiliary port.

Select the integration period you require, enter the primary and secondary
terminals, then click on the measure button.

The editor will then enter the test signal and show the measured turns
ratio. Set percentage limits on this ratio and click "OK" (you may select
a polarity test before clicking "OK").

### Using the Auto Button to Set Secondary Voltage

To do this you must know the primary inductance.

Select the test voltage and frequency for the primary from the table below
and enter them in the TRL dialogue box.

Enter the turns ratio, then press the "Auto" button next to the secondary
voltage parameter, the tester will automatically select the appropriate
test voltage for the secondary winding when the program is running.

### Setting the Primary and Secondary Parameters Manually

To do this you will need to know the inductance of the primary and secondary windings.

The optimum test conditions are chosen for an inductance value that is
between the primary and secondary (L_{m}).

Look up the recommended test signal for this inductance.

Enter the recommended frequency for this inductance as the test frequency.

The primary and secondary voltages can be calculated from the following:

Where:

L_{m} = Intermediate inductance

L_{p} = Primary inductance

L_{s} = Secondary inductance

V_{p} = Primary voltage

V_{s} = Secondary voltage

V_{m} = Intermediate voltage

N_{p} = Primary turns

N_{s} = Secondary turns

If you calculate V_{s} or V_{p} to be greater than 5V,
you should set 5V as your test signal. If you calculate V_{s} or V_{p}
to be less than 1mV, you should set 1mV as your test signal.

Intermediate Inductance (L_{m}) |
Preferred test signal | |

Frequency (V_{m}) |
Voltage | |

100nH → 1uH 1uH → 10uH 10uH → 100uH 100uH → 1mH 1mH → 10mH 10mH → 100mH 100mH → 1H 1H → 10H 10H → 100H 100H → 1KH 1KH → 10KH |
300KHz 100KHz 30KHz 10KHz 1KHz 100Hz 100Hz 50Hz 50Hz 50Hz 20Hz |
10mV 30mV 50mV 100mV 100mV 100mV 300mV 1V 5V 5V 5V |

### The Test Conditions for Turns Ratio by Inductance Measurement Specifying the Test Limits

When specifying turns ratio tests, it is preferable to avoid limits which are unnecessarily tight, and which may therefore lead to measurement difficulties.

For example, if two equal secondary windings should have 10 turns each,
the ratio should be 1:1.

One turn in error would produce a ratio error of 10% or - 10% (i.e. 11:10
or 10:11), and therefore limits of +5% and -5% would be suitable to detect
the error.