The D'Este Steam Engineers' Manual; With Electrical Appendix (Paperback)

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1913 edition. Excerpt: ...balanced two-phase circuit one wattmeter might be used and its reading multiplied by two. This condition of balance is impracticable however on commercial twophase circuits. ' WATTMETER Conuscrrons ON Tunes-Prrnsu Cmcurrz The most widely used methods of power and energy measurement on three-phase circuits are: --(a) Two wattmeter method for 3-phase, 3-wire circuits, either delta or star connected. The meter connections for this method are given in Fig. 42. (6) Three wattmeter method for 3-phase, 4-wire circuits. The meter connections for this method are given in Fig. 43. It may be noted that on a perfectly balanced 3-phase circuit a single wattmeter may be used connected as is any one of the three meters shown in Fig. 43, and the reading of the meter multiplied by three to get the total input into the circuit. Such acircuit however could only supply a synchronous machine that was shown by test to provide a perfectly balanced load. The meter connections shown in the preceding pages are all for low-voltage circuits, i. e. in cases where the meters can be connected directly in the circuit to be measured. On high-voltage A.C. circuits it is necessary to employ current and potential transformers for use in connection with meters. Typical connection diagrams are given in Fig. 44 showing such connections. Fig. 42. Two-Wattmeter Method of Energy Measurement on 3-Phase A.C. Circuit NEUTBI Fig. 43. Three-Wattmeter Method of Energy Measurement on 3-Phase A.C. Circuit It may be remarked that current transformers are used under certain conditions on low-voltage A.C. circuits in connection with meters, namely, when the current in the circuit has a high value which must be reduced by a given ratio. T be utmost care murt be exercised in connecting ..