Electrical Testing Calculators & Tools

Eight free, browser-based calculators for the tests that fill a substation commissioning programme: relay protection, transformer windings, turns ratio and VLF insulation testing. No account, no download, and no test data leaves the page — every result is computed in the browser.

1. Relay protection testing calculators

2. Transformer testing calculators

3. VLF insulation testing calculators

4. Which instrument fits the job?

The calculator tells you what the test requires; the instrument has to deliver it. These are the direct matches. Where a job spans several instruments — for example a full transformer commissioning programme — the product family page is the better starting point.

Test job	Calculator	Recommended instrument	Why this match
Overcurrent / IDMT timing	IDMT curve calculator	VAE-430 / VAE-660	Three-phase 0–40 A per channel; the six-phase VAE-660 adds channels for differential schemes.
High-burden relay + long leads	Lead voltage drop calculator	VAE-430 / VAE-660	Per-phase power is 420 VA (VAE-430) or 300 VA (VAE-660); the calculator shows when burden plus lead drop exceeds it.
Distance protection zones	Distance impedance calculator	VAE-430 / VAE-660	The voltage and current channels reproduce the R–X test point; the calculator checks it against Mho or quadrilateral zones.
Fault level for relay settings	Short circuit calculator	VAE-430 / VAE-660	Calculates 3LG, LL, 1LG and 2LG currents from transformer kVA, uk% and zero-sequence impedance.
Winding resistance and unbalance	Temperature correction calculator	TWO-1100S	The ohmmeter measures the resistance; the calculator puts every reading on the same temperature basis.
Turns ratio and tap verification	Turns ratio calculator	TTR-400	The meter measures the ratio; the calculator supplies the expected value and the acceptance band.
VLF withstand voltage	VLF voltage calculator	VLF-30-90	30–90 kV output range with 0.1–0.01 Hz operation for cable and equipment classes.
VLF set selection by load	VLF selection tool	VLF-30-90 series	Matches the cable capacitance to the frequency the set can hold at test voltage.

5. How to use the results

Enter the actual test conditions, not round numbers. Winding temperature, tap position, CT ratio and lead length all change the answer. A calculator fed with nominal values produces a nominal result that will not match the site record.

Treat a pass as a screening result. Every page states the standard behind the formula and the usual acceptance limit, but the specification, the manufacturer’s instruction book or the utility’s test sheet is what governs. Where the two disagree, the document wins.

Keep the instrument reading and the calculated value separate. The calculator is for comparison and test-point preparation. The commissioning record should contain the measured value, the instrument used and the conditions — not only the calculator output.

6. Frequently asked questions

Are these calculators free?

Yes. There is no account, no email gate and no download. Each page runs a small script in your browser; the values you enter are not sent to the server or stored.

Do they work on a phone or tablet on site?

Yes. The pages use a single-column layout on narrow screens and standard number inputs, so they work in a mobile browser without an app. For long test sessions a tablet or laptop is more comfortable.

Which standards do the calculators follow?

IDMT timing uses IEC 60255-151 and IEEE C37.112. Winding resistance correction uses IEC 60076-1 and IEEE C57.152; turns ratio uses IEC 60076-1; short-circuit currents use symmetrical components and the IEC 60909 peak factor; VLF test voltage uses IEEE 400.2-2024. Each page repeats the exact formula and constants it applies.

Can I use the output directly in a commissioning report?

Use it to prepare test points and to compare readings, but record the measured value and the instrument that produced it. The calculator output is a derived value, not a measurement, and it does not replace the acceptance criteria in the governing specification.

Which test set should I use for a 40 A relay test?

The VAE-430 provides three current channels at 0–40 A with 420 VA per phase at 40 A. If the scheme needs six simultaneous currents, or a high-burden relay needs more single-phase power, the VAE-660 provides six channels at 0–30 A and a 1×1000 VA / 180 A parallel output. Run the lead voltage drop calculator before assuming the set can drive the burden.

Do the calculators cover DGA or oil testing?

No. Dissolved gas analysis belongs to our sister brand PAS DGA at pasdga.com. This site covers electrical test instruments: relay, transformer, CT/PT and VLF.

7. Related reading

The calculators sit inside a larger test sequence. These articles explain the procedure behind each number:

• Overcurrent relay testing procedure — pickup, timing and the IDMT test points this calculator prepares.
• Secondary injection testing guide — how the injected current reaches the relay, and what the test proves.
• How to choose a relay test set — channels, per-phase power and portability.
• Transformer winding resistance testing — measurement method and what a changed reading means.
• Transformer turns ratio testing — tap-by-tap verification and tolerance interpretation.
• Transformer commissioning test sequence — where resistance, ratio and insulation tests fit.
• IEEE 400.2-2024 VLF test requirements — the voltage and duration rules behind the VLF calculators.