Modern Gasworks Practice

ELECTRICAL PLANT IN GASWORKS 40 CO motor is started up for the first time. Ensure that new plant is thoroughly dry before it is put to work. CAUSES OF FAILURE If dif&culty is experienced in getting the plant to operate, the trouble may usually be traced to one of the following causes, which. apply in general to botb dynamos and motors :— (a) Earths.—The generating plant switchboard should be provided with lamps for indicating earths on the system, and when an eartli occurs, it should be located immediately and removed. It can most conveniently be located by means of a “ megger,” an instrument for measuring insulation resistences. If the earth is found to be on the wiring, which is sometimes the case, the cable should be renewed or the defective pieces cut out and. replaced. The usual places where earths occur are at sharp corners or in the junction boxes, or just where the cables enter the motor or switchgear. If the earths appear to be 011 the motor or generator, the brusli gear and all connections should be carefully examined. By lifting the brushes from the commutator the armature can be tested, and, if the earth is on the armature, it is advisable to send the machine to the makers-or some competent repairing works. The causes of earths are frequently moisture, gas fumes, or dirt getting into th.e machmes. Dirt is probably the most common cause of the trouble. (&) Shorts.—Occasionally an armature will become very hot in one place and will spark badly on a definite commutator bar, at the same time smelling very strongly of burniiig varnish. This usually indicates that the coil of the armature is shorted, and it is necessary to take the armature out and have it retumed to the makers. (c) Sparking Commutators.—No machine should ever be allowed to run with. a commutator sparking badly, and if the sparking camiot be cured by moving the brushes or cleaning the commutator, the makers should be requested to examine the machine. The trouble is sometimes caused by the brushes having been movecl from the correct position. Manufacturers usually mark on the machine the correct settings for the brushes, and positions may Le checked from these. When new brushes are fitted they should be carefully bedded so as to conform with. the curvature of the commutator. (d) Fuses Biowing.—The fuse is a protective device, and the faet that it keeps biowing is an indication that something is wrong on the circuit that it is protecting. This may be either a short or an earth, or, of course, there is the possibility that the motor may be overloaded. Careful tests should be made to find out which of these effeets is causing the trouble. (e) Failure to Excite.—Sometimes it will be found difficult to get the generating plant to excite, and no voltage can be obtained. If the plant is being started up for the first time, it is probable that the connections are not correct, and they should be carefully checked with the diagram of connections supplied. If the machine has, however, been run before, and nothing is wrong with. the connections,