Transformer & Test Conditions
Acceptance Criteria
Test Readings by Transformer
Rule note
Winding resistance in Ω as measured at the winding temperature above. Insulation resistance in MΩ at 1 minute. HV: Pass means no breakdown or flashover. A blank reading shows the unit as incomplete. P = primary, S = secondary, E = earth.
| Serial | Primary R (Ω) | Secondary R (Ω) | IR P–E (MΩ) | IR S–E (MΩ) | IR P–S (MΩ) | HV withstand | Ratio | Polarity |
|---|
Record details
Test Details
Unit Results
| Serial | Primary R at 20 °C (Ω) | Dev. (%) | Secondary R at 20 °C (Ω) | Dev. (%) | IR P–E at 20 °C | IR S–E at 20 °C | IR P–S at 20 °C | HV | Ratio | Polarity | Result |
|---|
PASS* means every limit is met but there is a note to review, such as a winding resistance far from the batch median.
Build-up
How each unit is checked
Every step is shown so a reading can be checked by hand.
1. Winding resistance
Copper winding resistance rises with temperature, so each reading is brought back to 20 °C and compared with the reference. Without a reference, it is compared with the batch median.
A high reading suggests a poor joint or lead termination, and a low one suggests shorted turns or the wrong rating. Against a given reference a deviation beyond the tolerance fails the unit. Against the batch median it only raises a note, because a median cannot show that the whole batch is wrong.
2. Insulation resistance
Three pairs are read: primary to earth, secondary to earth and primary to secondary. Each is checked against the minimum, and each is corrected to 20 °C for comparison, using the rule of thumb that insulation resistance halves for every 10 °C rise.
3. HV withstand
The result is Pass or Fail. If the applied voltage or duration is below what you set as required, a Pass is not accepted, because the unit has not been tested to the level required.
4. Ratio and polarity
When switched on, the measured ratio is compared with the nominal ratio of the type, and polarity must be recorded as Pass.
Worked example, unit T1
| Item | Value |
|---|---|
| Winding temperature 30 °C | factor 1.0393 |
| Primary R measured 0.0624 Ω | 0.0600 Ω at 20 °C |
| Reference 0.060 Ω, deviation | +0.07 % |
| Secondary R 0.0581 Ω | 0.0559 Ω at 20 °C |
| Reference 0.056 Ω, deviation | −0.17 % |
| IR P–E 2,000 MΩ at 30 °C | 4,000 MΩ at 20 °C |
| HV 10 kV for 60 s, no breakdown | Pass |
| Result against ±10 % and 100 MΩ | PASS |
Unit and record result
A unit fails if any check fails. It is incomplete if a required reading is missing or invalid, and passes with notes if only a review note is raised. The record fails if any unit fails, is incomplete if any unit is, and otherwise passes.
What this tool does not do
It holds no standard's limits: the reference resistance, minimum IR, HV level and tolerances are yours to set from the specification or the manufacturer. It assumes copper windings and a rule-of-thumb insulation correction. It does not cover no-load or load losses, temperature rise, or the secondary open-circuit behaviour; use the isolating transformer calculators for those.
AGL Transformer Test Analyzer: Frequently Asked Questions
Quick answers on how isolating transformer test readings are corrected, checked and recorded.
What does the AGL Transformer Test Analyzer do?
It checks test readings for each isolating transformer: winding resistance, insulation resistance, HV withstand and, where applicable, ratio and polarity. It corrects readings to 20 °C, compares winding resistance with a reference or with the rest of the batch, checks every reading against your limits, and issues a pass or fail record that you can sign.
How is winding resistance corrected and checked?
Each reading is brought back to 20 °C with R20 = RT ÷ [1 + 0.00393 × (T − 20)] and the deviation is (R20 − Rref) ÷ Rref × 100. A high reading suggests a poor joint or lead termination, and a low one suggests shorted turns or the wrong rating. Against a given reference, a deviation beyond the tolerance fails the unit. Against the batch median (3 or more units) it only raises a note, because a median cannot show that the whole batch is wrong.
How is insulation resistance corrected and checked?
Three pairs are read: primary to earth, secondary to earth and primary to secondary. Each is checked against the minimum you set, and each is corrected to 20 °C using the rule of thumb that insulation resistance halves for every 10 °C rise, IR20 = IRT × 2^((T − 20) ÷ 10). Correcting a warm reading to 20 °C raises it, so applying the minimum to the reading as measured is the stricter choice above 20 °C.
How is the HV withstand result treated?
The result is Pass or Fail, where Pass means no breakdown or flashover. If the applied voltage or duration is below what you set as required, a Pass is not accepted, because the unit has not been tested to the required level. Use the same basis (AC rms or DC) for the applied and required values. HV testing is hazardous and must follow your site safety procedure.
How are ratio and polarity checked?
When switched on, the measured ratio is compared with the nominal ratio of the type, with deviation = (ratio − nominal) ÷ nominal × 100, and polarity must be recorded as Pass. The ratio is primary current ÷ secondary current, so 6.6/6.6 A is 1.000 and 20/6.6 A is 3.030.
What do PASS, PASS*, FAIL and incomplete mean?
A unit fails if any check fails. It is incomplete if a required reading is missing or invalid, and it passes with notes (shown as PASS*) if every limit is met but a review note is raised, such as a winding resistance far from the batch median. The record fails if any unit fails, is incomplete if any unit is, and otherwise passes.
Does the tool contain standard acceptance limits?
No. It holds no standard's limits. The reference resistance, minimum insulation resistance, HV level, duration and tolerances are yours to set from the specification or the manufacturer. In the worked example the limits are ±10 % and 100 MΩ. It assumes copper windings and a rule-of-thumb insulation correction.
Is the result an approved test certificate, and what does it not cover?
No. It is a working test record, not an approved test certificate, and the acceptance limits are project criteria. It does not cover no-load or load losses, temperature rise, or the secondary open-circuit behaviour, so use the isolating transformer calculators for those. Confirm limits, test voltages and the test method against the specification and the manufacturer before accepting a transformer.