High Precision Standard Current Transformers and Voltage Transformers

Instrument transformers are electrical devices that isolate and transform currents or voltages from higher magnitudes to lower magnitudes to provide safety of an end user and to protect a measuring device being used, such as a current or voltage measuring bridge, ammeter, or voltmeter. High voltage or high current is connected to the primary circuit of the instrument transformer and the measuring device is connected to the secondary circuit. High currents are transformed using a current transformer (CT) down to typically 1 or 5 A and high voltages are transformed using a voltage transformer (VT), otherwise known as a potential transformer (PT), down to typically 100 or 110 V. The term Standard CT or Standard VT is used when a highly accurate CT or VT is used for measuring ratio errors in current transformers or voltage transformers during type and routine tests or as a reference standard for the precise measurement of ratio errors during calibration or certification. 

HV TECHNOLOGIES, Inc. is proud to offer the best standard current transformers and standard voltage transformers on the market from EPRO Gallspach GmbH. The instrument transformers manufactured by EPRO are considered the most accurate and reliable on the market and, as they are purely inductive, have the longest service lifetime of 30 plus years without experiencing any changes in accuracy. All CTs and VTs are tailor-made according to the demands of the customer, and based on these, designs can vary from dry insulated, oil insulated, cast resin insulated, single or double pole, and single stage or cascade type, depending on the level of current or voltage that needs to be transformed. Furthermore, size and material of the core, the number and type of primary and secondary taps, and the number of windings is calculated and determined. A calculation and design process is conducted for each individual instrument transformer so that the correct transformer and ratios are used for the specific demand. The below image shows a sample overview of the different CT or VT design types that are available.    

After production is completed, the final accuracy of the CT or VT is tested and fine-tuned in the calibration lab. The ultimate goal is to achieve zero error compared to production’s very own high precision ISO 17025 calibrated reference standard transformer. The accuracy can be guaranteed up to ± 0.005% and ± 0.5 min stemming from the sourcing of the highest quality of core, winding, and insulation materials, as well as the decades of experience of winding, calculation, and tuning of different instrument transformers. 

Main Features of EPRO’s Standard Current and Voltage Transformers:

  • Purely inductive transformers allowing extremely reliable and long service life that are maintenance-free for 30 plus years
  • Accuracy up to ± 0.005% and ± 0.5 min
  • Accuracy is guaranteed over the entire measuring range
  • No measuring drift or loss in accuracy over the lifetime of the CT or VT
  • No effect of environmental factors such as temperature, pressure or humidity on the stability of the transformers 
  • Current measuring range of 1 – 200% for any primary tap with models from 10 A to 20 kA
  • Voltage measuring range of 20 – 120% for any primary tap with models from 500 V to 800 kV (phase-phase or 800/√3 kV)
  • Most often the required measuring range can be covered by a single transformer helping to reduce total investment and make daily work in a testing environment more effective
  • Lower cascade on a cascade design transformer can be operated separately

Toroidal Core Standard Current Transformer Video:


Model NVRD40 Standard Voltage Transformer Video: