High voltage

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Where does electricity comes from? We want electricity to be always available and we simply don’t think about it when we turn on the light, computer, or television. The operation of household as well as industrial devices is just normal and ordinary in our daily lives. On contrary, we quickly realize how dependent we are on electricity when a power outage appears. That could happen even due to a small failure (interrupt) in the measuring system on the electrical network that could cause a total collapse of the system. The electrical network (grid) is extensive and complex electromechanical system which always operate synchronous. It consists of both larger and smaller units (e.g., generators, turbines, high/medium/low voltage transformers, power lines and measuring systems that observe performance parameters). Moreover, a major development in the field of electrification of transport (higher power, high currents) and more complex consumer needs due to using a variety of electronics have both brought additional distortions and instabilities into the system.

To minimize system failure and to avoid dissatisfaction as well as economic and material damage, system disruptions must be detected first, and then appropriate action must be taken as soon as possible. Several types of different instruments for measuring high voltages and other electricity parameters were developed. One of them are transformer oil testers which measure dielectric strength of oil in transformers, there are various IR/AC/DC HIPOT testers and multifunctional instruments that measure several characteristic parameters (e.g., insulation resistance at different measurement voltages, short circuit currents, open circuit voltages, they generate AC or DC voltages that are used for testing of insulated parts of the network). Most voltmeters/multimeters cannot measure higher voltages directly, therefore high voltage probes, high voltage differential probes and high voltage dividers are used for conversion to lower levels that are acceptable and safer for measuring with ordinary multimeters/voltmeters. Instead of conventional voltmeters, oscilloscopes can also be used to observe time variation of high voltage signals using probe or divider.

SIQ is also specialized in calibration of high voltage equipment. Calibrations are usually performed in laboratory. However, the calibrations could be performed on the field if needed and requested by the customer (e.g., high voltage measurement up to 40 kV DC and 20 kV AC).  In addition to the specified equipment (transformer oil meters, high voltage probes, high voltage differential probes, high voltage dividers), high voltage generators or meters, electrostatic voltmeter, insulation parameter testers and other instruments related to high voltage could be calibrated.

Calibration of test equipment at SIQ

Transformer oil testers

Transformer oil testers are calibrated up to 85 kV AC in a frequency range 45–65 Hz. Additionally, voltage of each electrode can be checked separately.

High voltage probes, high voltage differential probes

The standard calibration parameters are:

  • high voltage (AC/DC)
  • input resistance
  • rise time
  • frequency response (e.g., bandwidth).

Frequency response and rise time are measured with oscilloscope. We recommend using customer’s oscilloscope since the probes are typically used in that way. However, the bandwidth of the oscilloscope should exceed the bandwidth of the probe otherwise the performance of oscilloscope limits the performance of the probe.

High voltage generators and high voltage meters

The standard calibration parameters are DC voltage up to 120 kV and AC voltage up to 85 kV.


The main calibration parameters are:

  • AC or DC voltage
  • insulation resistance
  • insulating voltage (IR)
  • measuring current
  • resistance up to 100 GΩ at different measurement voltages

Other parameters are:

  • short-circuit current
  • open-circuit voltage
  • different measuring currents

Calibration could be performed at 50 Hz and/or 60 Hz.

High voltage dividers

Calibration is carried out by generating high voltage (AC/DC), and by considering divider ratio. The calibration could be performed also by using customers oscilloscope or other measuring equipment.

High voltage meter for calibration of ESD generators

The meter has a very high input resistance (i.e., 10 GΩ) and thus allows the measurement of peak voltage of very fast and short pulses in the nanosecond range. The meter is typically used for calibration of open-circuit voltages of ESD generators, according to requirements of IEC 61000-4-2 and ISO 10605 standards. The standards require calibration of open-circuit voltage up to 30 kV. SIQ can provide accredited calibrations up to the maximum measuring range of the instrument (i.e., 30 kV) or up to 120 kV.

Electrostatic voltmeter

The electrostatic voltmeter allows contactless measurement of high voltages (potentials) of metal plates. The standard calibration parameter is DC voltage accuracy up to 10 kV. SIQ performs unaccredited calibration for both polarities with a resolution of 10 V.

Multifunctional instruments, electrical safety testers

Typical calibration parameters are:

  • insulation resistance
  • ground resistance
  • voltage
  • current
  • short-circuit current
  • open-circuit voltage
  • voltage at different frequencies
  • measuring time

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  • SIQ Ljubljana