WAGO 750-494 Series Manual

Contents

64 Process Image WAGO-I/O-SYSTEM 750750-494 3-Phase Power Measurement ModuleManualVersion 1.2.0CurrentWhen calculating current-dependent values, the current transformer ratio(CTR) must be taken into account when using a current transformer.Current transformersCurrent transformers are available on the market in different designs. On theprimary side, currents of 20 A, 25 A, 30 A, 35 A, 40 A, 45 A, 50 A, 75 A, 100 A… 5000 A are supported, on the secondary side 1 A or 5 A.For example, transformation ratios of 45:1 A or 200:5 A are possible. Thus, thecorresponding current transformer ratios (CTR) are 1:45 and 1:40.The I/O module allows you to set user scaling using WAGO-I/O-CHECK or viaRegister 32, bits 12, 13 and 14. If the bit is set to 0, user scaling is disabled andthe transformation ratio of the current is 1:1. If a bit is set to 1, user scaling isenabled and the transformation ratio is already taken into account in the I/Omodule.Operating current transformers the user scaling should always be on and theCTR set in the I/O module. Thus a calculation by the higher control system is notnecessary. As the process values are 32 bits long in the PI even big measuredvalues can be processed.Difference to 3-Phase Power Measurement Module 750-493/xxx-xxxWith 750-493/xxx-xxx the process values are only 16 bits long. Thereforecalculations with big CTR values have to be performed by the higher controlsystem.The transformation ratio is set using WAGO-I/O-CHECK or in Registers 39, 40,41. The divisor of the CTR (D-CTR) is set in the registers, i.e. according to theexamples above:• 1A-variants: CTR = 1:45, D-CTR = 45 => Registers39, 40, 41• 5A-variants: CTR = 1:40, D-CTR = 40 => Registers39, 40, 41Therefore, the following setting options and calculations for the measured valuesresult in the process image for the current-dependent variables: