RUDOLF offer a comprehensive range of Current Transformers for measuring and protective applications. Four types are available: the Tape Wound Ring type. Encapsulated type. Resin-Case type and Split Core type.Transformers’ functions are:✓ Isolation and separation of circuits and equipment for measuring, protection etc. from high voltage power lines.✓ To avoid disturbances due to carrying high currents✓ Reduction of short-circuit currents up to admissible values for sensitive protection and measuring equipment✓ To obtain currents and voltage values proportional to those wanted to be measured or monitored in order to be sent to appropriate measuring instrumentsIt is important to note that a bad selection or installation of measuring/protective transformers can provoke either malfunctioning events in the installation as well as the impossibility of guaranteeing a proper operation of protection systems at critical moments.1) ChoiceFor a proper selection of a measuring transformer (measuring or protective) we must know:✓ The ending application (measuring or protection)✓ Main characteristics of the working environment or use conditions (indoor or outdoor, maximum working temperature, etc.)✓ Mam characteristics of the power line the transformer will be connected to:• Dimensions of the cable or bus-bar• Measuring range of the current to be measured (maximum, minimum current to be measured)• Overload (level and duration)• Mains nominal voltage (low. medium or high voltage)• Short-circuit current• Mains nominal frequency✓ Main characteristics of the instrument or relay associated to the transformer (accuracy, rated current, rated output, etc.)✓ Distance between transformer and the associated instrument, as well as the cross section of the cable used for the link between both elements2) InstallationThe transformer is formed by one or more primary windings (marked as P1. P2). one or more secondary windings (marked as S1. S2) and a core of ferro-magnetic material (Fe-Si. Fe-Ni. etc.)The primary is the own bus-bar of the installation in case of a passing bar transformers. For wound primary transformers, the primary is already wound inside the own transformer, thus these transformers are equipped with suitable holding pieces for their final assembly to the installation.At any power system a consumption direction is stated (from power utility incoming mams to loads) as well as a generation direction is (from generators to power utility incoming mams). According to this basis, the P1 side of the transformer will correspond to the power utility incoming mains side and the P2 side of the transformer will correspond to the load size. For the secondary output terminals, a correspondence between S1 and S2 indications in the transformer and the associated instrument must be followed.In case that the polarity of the transformer is inverted, the phase angle of the current is inverted by 180 . therefore, measuring instruments or network analyzers whose current signal is supplied by this transformer will give incorrect readouts for such magnitudes whose calculation process depends on the phase angle (power, energy, power factor), but voltage and current readouts will be correct.3) Relevant StandardsTransformers are designed, made and tested according to following harmonized standards:✓ IEC 44-1 (replaces IEC 185)✓ UNE 21088✓ BS 7626
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