GB625942A - Improvements in and relating to electrical load measuring systems - Google Patents

Abstract

625,942. Current measurements. BRITISH THOMSON-HOUSTON CO., Ltd. Feb. 18, 1947, No. 4702. Convention date, Feb. 18, 1946. [Class 37] A single current-measuring instrument is arranged to obtain a correct measurement of the load on power apparatus when this is operated under two or more different conditions. In the Diesel-electric driving system for a locomotive shown in Fig. 1, a Diesel engine 1 drives a D.C. generator 4 which supplies energy to similar D.C. series driving motors 5, 6, 7, 8. The pair of motors 5, 6 may be connected in series to the generator 4 by closing a switch 9 and opening switches 10, 11 or in parallel to the generator 4 by closing switches 10, 11 and opening switch 9. The motors 7, 8 may be similarly connected by means of switches 12, 13, 14. A shunt 15 has three line terminal connections 16, 17, 18 and instrument connections 20 connected to a millivoltmeter 19. When the motors 5, 6 are in the series or low speed connection, current from this pair of motors flows through the complete length of the shunt 15 between terminals 16, 18, whilst in the parallel or high-speed connection the current of the motor 6 flows through the complete shunt and that from the motor 5 through a selected length between the terminals 16, 17. With the motors in series for low-speed operation, the motors attain their full load before the generator, whilst with the motors in -parallel for high-speed operation the generator attains full load before the motors. The point 17 is so chosen that full load current on the motors during low-speed operation and full load current on the generator during high-speed operation produce the same reading on the instrument 19. For other loads.the instrument 19 correctly indicates motor loading for the low-speed connection and generator loading for the highspeed connection in terms of continuous full load current rating of motors and generator respectively. The instrument 19 may have a scale divided into different coloured portions 21, 22, 23 indicating respectively underload, full load, and overload. The motors may be arranged with another control step in which all four motors are in series, the terminal 17 in this case being midway between the terminals 16, 18. For an alternating current system, a transformer arranged as shown in Fig. 3 may be employed instead of a shunt, the terminals 16<SP>1</SP>, 17<SP>1</SP>, 18<SP>1</SP> being connected in place of the corresponding terminals 16, 17, 18 of the shunt in Fig. 1. The primary winding between the terminals 16<SP>1</SP>, 18<SP>1</SP> has twice as many turns as the primary winding between the terminals 16<SP>1</SP>, 17<SP>1</SP>.