HCTS – High-voltage test simulator for HVDC cables (IEC 60060-1)

1Test

Test type

Tolerance criterion for the lightning impulse

Shows whether T1, T2 and β′ are within the limits (✓) or outside them (✗). It does not affect the simulation. The criterion for cables over 100 m is a laboratory criterion, not part of the standards cited.

2Breakdown

Simulate a breakdown

3Cable under test

Cable data per unit length, as given in the datasheet.

Length

Capacitance C′

µF/km

Inductance L′ (conductor–screen)

mH/km

Conductor resistance R′c (DC, from datasheet)

Ω/km

Screen resistance R′s (DC)

Ω/km

The impulse current flows in the conductor and returns through the screen: the model uses R′c + R′s, including skin effect at high frequency.

C_tot 0 µFL_tot 0 µHR_tot 0 Ωv 0 m/µsZ₀ 0 Ωε_r,eff 0

4Impulse generator (Marx)

Each stage consists of one or more capacitors, in parallel or in series, charged to the stage voltage. The stages are connected in series, optionally split into p parallel branches.

Impulse polarity

Charging voltage per stage

Number of stages n

Parallel branches p

The n stages can be split into p equal branches connected in parallel, each with n/p stages in series: the generator voltage drops p times and the capacitance rises p times. With p = 1 (the usual configuration) all stages are in series.

Capacitors per stage

Capacitor connection within the stage

Capacitance of each capacitor

µF

Generator internal inductance L_Marx

µH

Total front resistance R_f

Total tail resistance R_t

Charging resistance per stage R_c

Resulting parallel resistance R_p = n_s·R_c/p: 0 kΩ

5HVDC generator

DC voltage source for endurance and superimposed tests.

Polarity

Voltage

Output protection resistor R_DC

MΩ

Series resistor between the HVDC generator and the cable: it limits the current in case of breakdown and decouples the generator from transients. With a resistive divider it forms a voltage divider that slightly lowers the cable voltage.

Impulse/DC coupling

Used only in superimposed tests: it isolates the impulse generator from the DC voltage, which would otherwise charge the Marx capacitors.

Coupling device

Blocking capacitance C_b

6Measuring system

Measuring divider

Enter the rated values of the high-voltage arm, for example 937.5 MΩ and 400 pF for an RC divider.

Rated resistance of the HV arm R_1

MΩ

Rated capacitance of the HV arm C_1

Damping resistance R_d

Stray capacitance to ground C_e

Acquisition

Bandwidth (−3 dB)

MHz

Cut-off frequency of the first-order low-pass filter representing the bandwidth of the measuring chain.

ADC resolution

bit

ADC full scale (0 = automatic)

Automatic: 1.1 times the highest expected voltage, doubled when a breakdown is simulated.

7Circuit stray parameters

Capacitances and inductances of the connections between generator and cable.

Circuit stray capacitance C_ext

HV connection inductance L_ext

µH

8Earthing system

Earth resistance of the laboratory earthing system, measured in DC, and its inductance. In the current model they carry the generator current; the breakdown current, in the cable or at the termination, closes through the cable screen and does not cross them. U_gnd is the resulting potential rise.

Earthing system inductance L_g

µH

Earthing system resistance R_g (measured in DC)

Numerical solution:

Waveform

Peak value U_e

–

Base curve peak U_b

–

Efficiency η

–

Front time T1

–

Time to half-value T2

–

Relative overshoot β′

–

Oscillation frequency f₀

–

Total Marx voltage

–

Energy stored in the Marx

–

Current, breakdown and energy

Peak current

–

Maximum di/dt

–

Ground voltage U_gnd

–

Energy dissipated in the breakdown

–

What HCTS is

HCTS is a free, browser-based simulator of high-voltage laboratory tests on HVDC cables. It models the Marx impulse generator, the cable as a lossy transmission line, the measuring divider and the acquisition chain, and evaluates the recorded waveform according to IEC 60060-1:2025.

Tests: lightning impulse (LI 1.2/50 µs), switching impulse (SI 170/2500 µs) and superimposed HVDC + impulse tests (SLIT and SSIT).
Evaluation: peak value U_e, base curve and U_b, times T1 and T2, overshoot β′ and generator efficiency, with tolerance check.
Breakdown: fault in the cable or at the termination with Toepler arc model, breakdown current, di/dt and ground voltage.
Results: PDF report, CSV data, PNG plots and JSON configurations. Installs as an app and works offline; calculations stay on the device.

Designed for high-voltage laboratory engineers, cable manufacturers and students: it helps to size the test circuit for large capacitive loads such as long cables and to understand how the generator and the measuring system affect the evaluated parameters.

Frequently asked questions

Is HCTS free? Do I need an account?

Yes. HCTS is free and needs no registration or installation: it runs in any modern browser on computers, tablets and smartphones. It can also be installed as an app and used offline.

Which high-voltage tests does it simulate?

Impulse tests on cables: lightning impulse (LI, standard 1.2/50 µs shape) and switching impulse (SI, 170/2500 µs according to IEC 60060-1:2025), with positive or negative polarity, and superimposed tests in which the impulse is added to a DC (HVDC) voltage already applied to the cable: SLIT (superimposed lightning impulse) and SSIT (superimposed switching impulse), as specified for HVDC cable systems (for example CIGRE TB 496 and IEC 62895).

How are T1, T2 and the overshoot β′ evaluated?

According to IEC 60060-1:2025: a double exponential (base curve) is fitted to the record, the residual is filtered with the test voltage function k(f) = 1/(1 + 2.2·f²) and added back to the base curve to obtain the test voltage curve. From it the test voltage U_t, the front time T1 = 1.67·(t90 − t30) and the time to half value T2 from the virtual origin O1 are derived; the overshoot is β′ = (U_e − U_b)/U_e. Every quantity is checked against the tolerances of the standard.

Which circuit is simulated?

An N-stage Marx impulse generator (stage capacitors in series or in parallel, front and tail resistors, internal inductance, optional parallel branches), the inductances and capacitances of the connections, the cable under test as a lossy transmission line (conductor and screen resistance with skin effect), the measuring divider (resistive, capacitive or damped capacitive) and the acquisition chain with low-pass filter and ADC. For superimposed tests the DC source and the blocking element (capacitor or sphere gap) separating the impulse generator from the DC voltage are included.

What is HCTS used for in practice?

To prepare and understand laboratory tests: choose the number of stages, the capacitors and the resistors of the generator to obtain the standard waveform on a large capacitive load such as a long cable, estimate the generator efficiency (impulse peak / Marx voltage) and see how the measuring system affects the evaluated parameters. It is also useful for training. Results are an estimate: they do not replace the test or the review of an expert.

Is my data sent to a server?

No. All calculations run in the browser, on the device; parameters and configurations stay local until you export them. Visit statistics (Google Analytics) are enabled only with explicit consent.

Who develops HCTS?

HCTS was conceived by Marco Moraschi, an electrical engineer, and is developed by backohm (backohm.com). Reports and suggestions are welcome at hello@backohm.com.