Lab 01-Current Transformers.docx.pdf - Power System Protection EL-434 LABORATORY MANUAL Fall 2019 LAB 01 Current Transformers Engr Naveed Iqbal STUDENT

Lab 01-Current Transformers.docx.pdf - Power System...

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Power System Protection ( EL-434 ) LABORATORY MANUAL Fall 2019 LAB 01 Current Transformers Engr. Naveed Iqbal ________________________________________ __________ ___ STUDENT NAME ROLL NO SEC DATE ______________________________________ LAB ENGINEER SIGNATURE & DATE MARKS AWARDED: / 10 ________________________________________________________________ NATIONAL UNIVERSITY OF COMPUTER AND EMERGING SCIENCES (NUCES), ISLAMABAD Prepared by: Engr. Naveed Iqbal Version: 1.00 Last Edited by: Dr. Muhammad Jafar Date: Jan 19, 2019 Verified by: Dr. Muhammad Jafar Date: Jan 20, 2019
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Current Transformers LAB:01 Current Transformers NUCES, ISLAMABAD Page 2 of 8 Learning Objectives: 1) Determining the transformation ratio of a current transformer for various primary currents and investigating the influence of the load on thetransformation ratio. 2) Explain the terms ratio error (current error), accuracy class and rated accuracy limit factor. 3) Testing the performance of the current transformer at over current. 4) Assembling the common current transformer circuit for measurement on three phase network. Introduction In electrical power supply systems, the currents and voltages are constantly measured and monitored to ensure that they remain within certain limits. The measured values are required for three reasons: 1) To provide the maintenance personnel with constant information regarding the state of the system. 2) To be able to determine the amount of power supplied to a customer. 3) To switch off faulty network sections rapidly in case of a fault. Generally the current and voltage values are so high that they cannot be measured directly. For this reason, special transformers are used to reduce these values to a level which can be processed safely and economically: the so-called instrument transformers. The instrument transformers are subject to differing accuracy requirements, depending on whether the values are to be processed for display in the control room, for accounting purposes or for protection. This leads to the grouping of the transformers into so-called accuracy classes. In most cases, these units function according to the transformer principle; they are, however, designed for very low power values (up to approx. 100 VA) on the secondary side. The protection and measuring devices connected to the transformer make up the load. We distinguish between current and voltage transformers, depending on the quantity to be transformed. Current Transformers Current transformers (CT) are constructed as single-phase transformers; the current of the installation flows directly through the primary side. In accordance with the standards, these supply a rated current on the secondary side of 1A, or also 5A at rated operation of the installation. The rated transformation ratio is given in the form of a fraction, e.g. 1000 A/5 A.
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