Electricity meters, with notes on meter testing

RATCLIFF & MOORE : ELECTRICITY METERS [March 23rd,in the stations, at least 5 per cent, may be lost in distribution, due to defective meters.Consequently it pays to test meters properly before fixing, and also at regular intervals afterwards.Most of the well-known makes of meters, if properly adjusted and carefully fixed, may be relied upon for about five years ; but after that time it certainly pays to have them brought in for thorough overhauling and recalibration.Old meters, after careful repairing and recalibrating, are frequently better than when new, and the cost of the work, if carried out in a properly equipped meter department, is comparatively slight.• In the case of large power consumers, where the conditions of supply justify a low rate per unit being charged, an error of 2 or 3 per cent, on the meter reading may make all the difference between a profit and a loss.Extreme accuracy is therefore essential, and it is always advisable in such cases to install duplicate meters, as greater accuracy can then be obtained, and a further advantage is that it is always possible to remove one meter for testing, when necessary, without having to leave the supply unmetered, or having tcf fix a temporary meter. CLASSIFICATION OF METERS.Electricity meters may be grouped into three main classes :-1.Meters suitable for direct current only.2. Meters suitable for alternating current only.3. Meters suitable for direct and alternating current.Each of these groups has its sub-divisions, of which particulars are given later.DIRECT-CURRENT METERS.Direct-current meters may be either of the ampere-hour or the watt-hour type.Most ampere-hour and a few of the watt-hour meters belong to the first class named above.The remaining types of directcurrent watt-hour meters belong to the third class, and may, as a rule, with occasional slight modifications, be used for measuring the energy in alternating-current circuits.Ampere-hoar versus Watt-hour Meters.-Variousclaims are put forward on behalf of both ampere-hour meters and watt-hour meters.A brief comparison of the advantages and disadvantages of these types may therefore not be out of place.The watt-hour type of meter is, if correct, a true energy meter, i.e., it measures correctly the electrical energy in a circuit, independently of variation (within reasonable limits) in any of the three factors (volts, amperes, hours) involved in the quantity measured.The authors are therefore of the opinion that this is the only type of meter which should be legally Tecognised as a measurer of electrical energy, although, at the same time, they quite realise the advantages of ampere-hour meters.