WAGO 750-494 Series Manual

Contents

WAGO-I/O-SYSTEM 750 Connect Devices 73750-494 3-Phase Power Measurement ModuleManualVersion 1.2.07.3.2 Current TransformersFor measuring currents greater than 1 A resp. 5 A you have to use external currenttransformers.Normally, the selection of the current transformers is not a critical factor. Theinternal resistance in the current path of the 3-phase power measurement moduleis so low that it can be neglected when considering the overall resistance of thecurrent loop.The transformers must provide a rated secondary current of 1 A resp. 5 A. Therated primary current Ipn shall be equal or higher than the currents to be measured.The normal, permissible overload level of 1.2 x Ipn presents no problem for the3-phase power measurement module, but can, however, lead to minormeasurement inaccuracies.Do not operate with open load!Please note that current transformers from some manufacturers shall not beoperated with an open output circuit! Connect the I/O modules to the currenttransformers’ secondary windings before commissioning the current transformers!7.3.2.1 AccuracyPlease note that the overall accuracy of the measuring setup consisting of the3-phase power measurement module and the current transformers essentiallydepends on the transformers’ accuracy category.Do not use transformers of class 0.5 for accounting purposes!A measuring system with a class 0.5 current transformer cannot be approved orcertified for accounting purposes as the 3-phase power measurement module isnot an approved utility billing meter as defined in the standard for electricitymeters (DIN 43 586).7.3.2.2 Types of CurrentThe 3-phase power measurement module can measure any types of current up to afrequency of 3.3 kHz. As currents are frequently generated by power inverters andcan contain frequencies lower than 50 Hz or even a DC portion, an electronictransformer should be used for these applications.7.3.2.3 Overcurrent Limiting Factor FSThe overcurrent limiting factor (FS) for current transformers indicates at whichmultiple of its rated primary current saturation occurs which protects the