Patent GB-190402707-A (GB)
Title: Improvements in connection with Electrostatic Wattmeters.
Inventor: WILSON ERNEST
Filed: 1904-02-03
Granted: 1904-12-22
Abstract: 2707. Wilson, E. Feb. 3. Electrometers.-In the use of an electrometer for measuring power in a single alternating-current circuit, the needle is connected to one main w, and the pairs of quadrants are charged from an air transformer d, e, the primary winding d of which is in the second main v ; a well insulated condenser is also connected to the quadrants a, b, and is of capacity great enough to render negligible the variations in the capacity of the electrometer. In the arrangement shown in Fig. 1, two adjustable condensers o, p are used in series, the connection between them being connected to the casing f of the electrometer, to the middle of the secondary winding e of the transformer, and to the main v. Inductive resistances i, k are placed in the connec- tions to the ends of the secondary winding e, and these connections are adjustable by contacts and switches r, s. The potential differences between the quadrants and the case f are thus caused to be in phase with the main current, and equal to one another. When only one condenser is used, one pair of quadrants is connected directly to the casing of the electrometer, one end of the con- denser, one end of the secondary winding, and the main v, the other pair of quadrants being con- nected as shown at i, r, s ; this arrangement is applicable only when the power factor of the circuit is high, and in a further modification, applicable generally, the condenser contains a third set of plates connected to the second main o and to the casing of the electrometer. In another arrange- ment of connections, with one condenser, the two pairs of quadrants are connected adjustably to the ends of an inductive resistance, one pair being also connected adjustably to one end of the secondary winding, while the other pair is con- nected to the casing of the electrometer, one end of the condenser, and the second main : the remaining ends of the secondary winding and con- denser are connected together. In either arrange- ment, the primary and secondary windings of the transformer should be wound together, and the primary winding should be formed of strip, or hollow, or of insulated strands, to avoid " skin " effect." The electrometer, connected as de- scribed, may be used as the watt measuring part of a Frager watt-hour meter. In either arrange- ment, a volt-meter may be connected to the ends of the condenser, to measure the main current. The arrangements are applicable to polyphase systems. The above described methods are appli cable with ordinary quadrant electrometers, but a form of electrometer suitable for high electric pressures is shown in Fig. 6. Brass quadrants 4 are carried by insulated pillars 3, and carry insu- lated bridges 7 and circular guard-plates 14. Two aluminium needles 8 are carried by a stem 9, which is supported by two thin steel wires, between the bridges 7, the upper of which is connected by a coiled wire to an insulated terminal 17. The stem 9 also carries a mirror 10, or a pointer, and an aluminium brake disc 12, which is acted on by permanent magnets 13.