Tjeerd de Jong
In high-voltage networks, it is important that the high-quality components in the substation and other parts of the electricity grid are protected against overcurrent and short-circuit currents. In addition, it must be possible to settle the energy consumed (kWh) with the various customers with a high degree of accuracy. Both cases require measuring transformers. Measuring transformers convert the current and voltage in high voltage systems to values that can be measured by measuring instruments and protective equipment.
Measuring transformers is a collective name for current and voltage transformers while combinations of both types are also possible, the so-called combined measuring transformers. A current transformer transforms a large primary current into a galvanically isolated secondary, lower value and consists of one or more cores and corresponding secondary windings (active part). Different versions are available, depending on the application, but basically there are two versions, namely metering core and protection core. When protection cores are used, this is usually secondary with a 1A current because this results in lower losses in a cable than with a 5A core. The corresponding power and accuracy class is selected to suit the system. For instance, 5P20, which means that the current transformer has a maximum error of 5% at 20 times the rated current.
Tjeerd de Jong
A voltage transformer is used to measure voltage and transforms a high primary voltage to a lower value of usually 100V. They are also used for measurement and protection and have various options in terms of accuracy class and power. However, when transforming the voltage from primary to secondary, a voltage error can occur due to the iron and copper losses of the voltage transformer and the power consumed by the measuring instrument. It is also important that the phase angle between the current and voltage of the primary grid is transferred to the measuring circuit without any displacement. Losses in the transformer will also result in the phase angle error. The voltage transformer is therefore defined by these factors. For example, a metering core with an accuracy of 0.2 implies a voltage error of 0.2% and an angular error of 10 minutes and 0.30 centigrade.
Batenburg Energietechniek represents Arteche for measuring transformers for voltages up to 800kV. Arteche has various models of current transformers in its range, with paper-oil, gas and cast resin (dry) as an insulation medium. Ideal for use at metering points in the network due to their very high accuracy. Excellent frequency response and ideal for measuring power quality and harmonics. The most common applications are the protection of high-voltage lines, capacitor banks and power transformers.
Arteche can supply inductive and capacitive versions of the voltage transformers. Inductive transformers are suitable for the discharge of high-voltage lines and capacitor banks and equipped with oil or gas insulation. A combined measuring transformer is a current transformer and an oil insulated inductive voltage transformer built into a housing. The capacitive voltage transformer allows for the transport of high frequency signals over the high-voltage lines. The latter is only available in the paper-oil version. Batenburg Energietechniek supplies measuring transformers to all energy grid companies and/or installing supply companies such as Alliander, Enexis, Spie, Joulz and many others.