29 May 2024

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Protection relays then and now

In the past, manufacturers assembled generator protection systems from electro-mechanical and later electronic relays. Each relay contained only one or some dedicated protective functions.

In the 90s manufacturers offer digital (numerical) relays with multiple functions in one relay on increasing scale, that are accepted by the conservative world of power systems. Now the modern relays have been developed so far that they contain fully integrated generator protection systems with a much greater functionality.


This generator protection system was assembles from elektronic GEC Midos relays.

A number of  protection relay brands and types are given below.

Schneider Electric Sepam type G87 is Schneider’s most suitable multifunctional protecion relay for middle large and large generators to my opinion. Other multifunctional protection relays for generators from the Sepam 80 series are G82 and G88, but they are not provided with differential protection. Furthermore the G40, G60 and G62 from respectively the Sepam 40 and 60 series are available.

GE Multilin type G30, G60 and 489 are multifunctional protection relays. The UR family relays G30 and G60 are meant for respectively small/middle large generators. The 489 belongs to the SR family and is a more cost-effective option to protect small and middle large generators.

Alstom of Schneider Electric MiCOM type P34X is a serie multifunctional protection relays for generators that have been designed on the St. Leonards Avenue in Stafford (England). This factory has worldwide still an extended installed base of electronic relays of the GEC Midos range. Alstom has some Midos relays still in production. The fabriek has been owned by Siemens, English Electric, General Electric Company (GEC) and GEC Alsthom. In 2004 Alstom T&D was sold to Areva and in 2010 Areva Ltd. split up and bought by Alstom and Schneider Electric. 

Beckwith Electric type M-3410A and M-3425A multifunctional protection relays for respectively small and large generators. The M-3425A is almost similar to the precursor M-3425, but some functionality was added. Funny detail is that the AEG type PG851 and the Reyrolle type Gamma 4 are provided with a different cover, but  the do have a lot of similarities with the M-3425!

ICE Group type NPG800, NPG800R and GMS7001 are digital multifunctional protection relays for generators with limited functionality. Especially the differential protection is missing in these relays, however this protection function is required for middle large and large generators. In a number of European countries this company still uses the former name CEE. CEE has worldwide still an extended installed base of electronic relays.

Schweitzer Engineering Laboratories SEL type 700G and 300G are the multifunctional protection relays for generators. If you want to protect middle large or large generators with this relay, do not forget to order the optional differential protection functionality!

Siemens Siprotec type 7UM61 and 7UM62 are multifunctional  protection relays for respectively small/middle large and middle large/large generators.

ABB type REG650 and REG 670 are multifunctional  protection relays for respectively small/middle large and middle large/large generators. On the ABB website the older, modular built REG 216 protection system for generators is still mentioned. The REG 316, the smaller brother of the REG 216, is not mentioned on the website anymore. Before the REG216/316, ABB provided electronic relays of the SPACOM series.

Also manufacturers like Woodward (SEG), Microelettrica and Basler Electric provide generator protection relays.


See also