Editing Motor–generator (section)

==Modern use of motor–generators==
Motor–generator sets have been replaced by [[semiconductor devices]] for some purposes. In the past, a popular use for MG sets was in [[elevator]]s. Since accurate speed control of the hoisting machine was required, the impracticality of varying the frequency to a high power AC motor meant that the use of an MG set with a DC hoist motor was a near industry-standard solution. Modern AC [[variable-frequency drive]] electronics with compatible motors have increasingly supplanted traditional MG-driven elevator installations, since electronic AC drives are typically more efficient by 50% or more than MG DC-powered machinery.<ref>{{cite web | url=https://www.machinedesign.com/motors-drives/article/21829047/inefficiency-of-saving-motorgenerator-sets | title=StackPath | date=October 2000 }}</ref>

Another use for MG sets was in the southern region of [[British Rail]]. They were used to convert the 600 V DC – 850 V DC line supply voltage from the [[third rail]] into 70 V DC to power the controls of the [[Electric multiple unit|EMU]] stock in use. These have since been replaced with solid state converters on new rolling stock.<ref>{{cite web| url=https://aboutgenerators.com/ |title=Generators Guide }} Thursday, 11 March 2021</ref> MG locomotives have also commonly been used for long distance rail Diesel locomotive transmission throughout the world, due to reliability and wear issues with mechanical and fluid transmissions, but this is generally being replaced with smaller engines with conventional or MG transmission on each carriage. Long distance electric locomotives with high voltage overhead power supply used MG transmission, but this is generally being replaced with distributed motor drive on each carriage with electronic power control and conversion.<ref>{{Cite web |date=17 February 2015 |title=Network Rail Guide to Overhead Electrification 132787-ALB-GUN-EOH-000001 February 2015 Rev 10 |url=https://www.bathnes.gov.uk/sites/default/files/sitedocuments/Planning-and-Building-Control/Planning/nr_a_guide_to_overhead_electrification.pdf |publisher=Alan Baxter }}</ref>

Similarly, MG sets were used in the [[PCC streetcar]] to produce a 36VDC output from the 600VDC traction supply. The low voltage output charges the streetcar's batteries and supplies current for control and auxiliary equipment (including headlights, gong ringers, door motors and electromagnetic track brakes).

Motor–generator sets were often used to provide the high-current D.C. power for carbon [[arc lamp]]s in large [[movie projectors]] in the 1950-60's era, before the carbon electrode arc light was replaced with modern [[xenon arc lamp]] projection systems (starting in 1963 in the U.S.).

In industrial settings where harmonic cancellation, frequency conversion, or line isolation is needed, MG sets remain a popular solution.{{citation needed|date=December 2015}} A useful feature of motor–generators is that they can handle large short-term overloads better than semiconductor devices of the same average load rating. Consider that the thermally current-limited components of a large semiconductor inverter are solid-state switches massing a few grams with a thermal time constant to their heat sinks of likely more than 100 ms, whereas the thermally current limited components of an MG are copper windings massing sometimes hundreds of kilograms which are intrinsically attached to their own large thermal mass. They also have inherently excellent resistance to [[electrostatic discharge]] (ESD).