Standard Voltage Transformers

EPRO Gallspach GmbH’s Standard voltage transformers are used in the industry since decades. They are internationally well known for maximum reliability and accuracy. 
As the devices are purely inductive, properly handled, the lifetime is up to 30 years and more without any accuracy drift or any changes.


What is a standard voltage transformer?

A standard voltage transformer is a test device and is used for measurements on high voltage. The devices are used as measurement standards for measuring and/or for calibration of instrument transformers. The high accuracy of the standard VT plays a major role here.
All devices offer a very wide range of 40-120%. This means in this percentage of rated voltage EPRO can guarantee the maximum accuracy of the devices.
The standard voltage transformers are designed in such a way that they are passive, i.e. they do not require an external supply.


Where standard voltage transformers are used?

International calibration and metrological institutes as PTB Germany, INMETRO Brazil, VMI Vietnam among many others are using these devices as national standard for accuracy measurement. In the private sector, these devices are used in the labs of various manufacturers of instrument transformers and transformers and others for accuracy and power measurement.


In which execution are standard voltage transformers available?

The Standard voltage transformers are available as single pole and double pole execution from 1kV up to 800/√3kV in various models. The smallest models up to 6kV are dry insulated, starting from 15kV the models are oil insulated and the larger models are designed in a cascade execution.


Which standard transformer is the most accurate?

The model NVRD 40 is a special execution, some people call it the most accurate standard VT in the world for 40 kV, so it is not by chance that this device is used at a lot of private and governmental calibration units.


Are standard voltage transformers also available in mobile execution?

A big variety of the standard voltage transformers are also available in mobile execution for testing on site and transport in a truck. This mobile (outdoor) execution can be distinguished from the other devices by the light grey silicone rips on the outside. 


How does an accuracy measurement work?

For the accuracy measurement on a test object (current as well as voltage), a control transformer, a test transformer, a standard current or voltage transformer and a measuring bridge are required.
By adjusting the control transformer upwards, the test transformer (current or voltage) generates a high voltage or a high current.
This current/voltage is measured by the standard voltage or current transformer and the test object and will be transmitted to the secondary side, i.e. converted to low voltage or low current.
The measuring bridge compares the ratio of the standard voltage or current transformer and the test object, in detail the values of errors in amplitude (%) and phase (minutes per angle).
The more accurate the standard voltage or current transformer is, the more accurate is the result of the measurement.
Please find at the bottom of this page the high accuracy of our devices for each type of standard transformer.


Where do i find more informations about standard voltage transformers?

Please see an overview of the available models here at the product data sheets. Please always consider that the mentioned datasheets are examples. Any customers request considering tappings on the primary side, different voltages on the secondary, operation frequencies of 50 and 60 Hz and other wishes can be fulfilled.