Voltech logo
    • Login
  • Welcome
  • Applications
  • Products
  • Support
  • Contact Us
Voltech logo
  • Welcome
  • Applications
  • Products
  • Support
  • Contact Us
Contact Voltech
USA 1-239-437-0494
EUR 44 1235 861173
ASIA 44-1235-364-001
or
Email Voltech
Voltech on LinkedIn Voltech on YouTube Voltech on Twitter
    • Login
Technical Document Reader
Document
086-627
Name

The Voltech Handbook of Transformer Testing

Description
This article covers a wide range of transformer theory and Voltech's testing capability.
The Voltech Handbook of Transformer Testing
Back
to Index
Skip Navigation Links.
Expand 1 Transformer Basics1 Transformer Basics
Collapse 2 Available Tests2 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
Expand 3 Examples of Different Transformer Types3 Examples of Different Transformer Types

2.10 TR - Turns Ratio and Phasing


Figure 23

Turns Ratio describes the ratio of the turns between one winding and another. In the above example: -

In the above 'ideal' transformer, applying 10V to the primary would produce 5V on the secondary.

In practice the output voltage of an actual transformer will be slightly less than this due to the parasitic elements described in the equivalent circuit.

Due to those elements the ratio measured is usually the 'voltage ratio, not the actual 'turns ratio'.

Phasing

Applying an AC voltage to the primary of the transformer will produce an AC voltage on the secondary.

This secondary voltage may be in-phase with the primary voltage, or it may be in anti-phase depending on the direction of winding and the termination of the windings.

This phasing is represented by the 'dot' associated with each winding.


a) In Phase--------------------------------------------b) Anti-Phase


a) In Phase--------------------------------------------b) Anti-Phase

For most applications it is important to know that the windings are phased correctly as well as knowing the turns or voltage ratio.

Where Used

The AT offer 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. (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 numbers 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

To measure turns ratio, a test source voltage is applied to one winding, the energised winding, and the voltages across two other windings (one of which may also be the energised winding) are measured using harmonic analysis. The turns ratio is measured by dividing one measured voltage by the other, and making a compensation for the effects of winding resistance.

It is recommended that you choose the winding with the highest number of turns as the one to be energised. A possible exception to this rule is when you wish to measure the ratio between two windings, which should be accurately matched at 1:1. In this case it may be better to energise a third winding with a lower number of turns, to ensure that any measurement errors apply equally to the two windings under test.

You can specify the signal to be applied to the energised winding to have a frequency in the range 20Hz to 3MHz, and an amplitude from 1mV to 5V.

The recommended test conditions depend on the inductance of the energised winding; they are given in the table below assuming that the energised winding is the one with the highest number of turns:

Inductance of the Energised Winding Preferred test signal
Frequency 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 Measurement

Notes: The signal is applied to the primary winding, or the winding, which has the largest number of turns. However, if by doing this, the expected voltage on the winding with the smallest number of turns falls below 1mV, then the test voltage should be increased.

This may also require an increase in the test frequency so that the current taken by the driven winding does not become too large, but in general this frequency increase should be kept as small as possible to avoid problems caused by stray capacitance at high frequencies.

Where Matching in Groups is Important:

In some transformer designs, the turns ratio between a primary winding and a secondary winding is not as important as the ratio between different primaries or different secondaries.

To make the most accurate measurements in such cases apply the test signal to the primary winding and measure the turns-ratio from primary to one of the secondaries.

Then, leaving the primary energised as above, measure the turns ratio between the secondaries.

Next, energise a secondary winding (possibly at a different voltage and / or frequency depending on its inductance) and measure the turns ratio between the various primaries.

In this way windings which should be matched are treated equally during the test.

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.

Prev Next
Email Voltech
USA 1-239-437-0494
EUR 44 1235 861173
ASIA 44-1235-364-001
Site Map
Terms Of Business
Terms Of Use
Privacy
  • Terms Of Use
  • Privacy
  • Terms Of Business
  • Site Map
Contact Voltech
USA 1-239-437-0494
EUR 44 1235 861173
ASIA 44-1235-364-001
or
Email Voltech
 
Submit "Red" = required field
Please, complete all required fields.
Please, select country from the list.
Please, enter a valid Email.
Thank you for your question. We will reply to your request as soon as possible.
An error occurred.
Voltech © 2021
Voltech on LinkedIn Voltech on YouTube Voltech on Twitter
We have placed cookies on your computer to help make this website better.
Please read our Privacy Statement for further information. Otherwise, we'll assume you're OK to continue.
OK, Don't Show This Message Again