BRE E09 Labsheet.pdf - Department of Building Services Engineering The Hong Kong Polytechnic University Page E 09-1 B.Eng(Hons Laboratory January 2001

BRE E09 Labsheet.pdf - Department of Building Services...

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Department of Building Services Engineering Page E 09-1 The Hong Kong Polytechnic University E 09 B.Eng (Hons) Laboratory January 2001 Ref. ET 6 /CSL/00 Experiment No. E 09 Polarity Marking and Testing of a Single-phase Transformer Aims To understand the needs and the requirement for the correct marking of the terminals of a single-phase transformer. To determine the core loss of a single-phase transformer using an open-circuit test. To determine the copper loss of a single-phase transformer using a short-circuit test. To derive the simplified equivalent circuit of the single-phase transformer. Introduction A D.C. voltage source has fixed poles, positive and negative at its terminals. We know that we cannot place batteries in a reversed position in the battery compartment of a radio. However, an A.C. voltage source varies the polarity on the terminals repeatedly for a period time. Most electrical appliances can work when the power cord is plugged on the wall outlet in reversed position. (Don't try it without supervision by a qualified person or you may suffer an electric shock). Could we neglect the polarity of terminals for all A.C. apparatus? For a lengthy period, we cannot distinguish the polarity of A.C. voltage source terminals but we can observe the polarity at short instants. If more than one A.C. voltage sources are connected, the polarity of the voltage sources should be clarified. Since polarity changes in A.C. voltage terminals, we don't name the terminals as positive and negative but name them as "head" and "tail". All "head" terminals will have positive or negative polarity at the same instance in a system. Contrarily, all "tail" terminals will have opposite polarity referred to its "head" terminals. Marking is the process of naming the coil (winding) terminals of transformers and motors that operate in an A.C. circuit. We name the head terminal of winding A as A 1 and name the tail terminal as A 2 . In some drawings, the head of winding is marked by a dot. Some transformers mark its tails with "0" and label the voltage values at the head terminals. some examples are given below.

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