The Diseases Of Electrical Machinery
Forfatter: Ernst Schulz
År: 1904
Forlag: E. & F. N. SPON, Ltd.
Sted: London
Sider: 84
UDK: 621.311
Edited with a preface, by Silvanus P. Thompson
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82
THE DIS EAS ES OF
measures the amperes in the armature circuit. It is
advisable to run the machine at least two hours befbre
taking the final amperemeter reading ; because as the
machine warms up a little, the copper resistances are
increased, while the bearing friction diminishes slightly.
The armature current, multiplied by the voltage, gives
the value of the magnet and friction losses very accu-
rately.
Example i.
Continuous-current shunt dynamo, 40 kilowatts,
600 revolutions per minute, 110 volts. Armature
resistance (measured) = 0'0055 ohms. With full load
(364 amperes) at 110 volts, and 60 revolutions per
minute, the machine had a shunt current of 6 am-
peres.
The machine was connected as a motor, and an
accurate amperemeter was connected in the armature
circuit; the reading on this, after running several hours,
was 15 amperes.
Loss in the armaturej & 6 X 0’0055= 725 watts,
winding . j o o ‘t uj / j
Loss in the magnet) 6 =66owatts.
winding . .)
No-load loss . . =15x110 =1650 watts.
Total losses 3035 watts.
Efficiency of the machine :
40.000 40,000 ~ 0/
----------——— = —------------------= o 93, i.e. 93 /o-
40,000 + 725 + 660 + 1650 43,035