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Home / Technical Articles / 5 Steps To Safely Shutdown a Large Generator

Removing generator from service

Normally, units are removed from service through operator initiation of distributed control system (DCS) commands or turbine trip buttons that shutdown the prime mover.

5 Steps To Safely Shutdown a Large Generator
5 Steps To Safely Shutdown a Large Generator (photo credit: SIEMENS)

Closure of steam or fuel valves will then initiate anti-motoring or reverse power control circuits that isolate the unit electrically by opening the generator circuit breakers, field breakers, and depending on the design, unit auxiliary transformer (UAT) low side breakers.

If limit switch circuitry or anti-motoring / reverse power relays fail to operate properly, the unit may stay electrically connected to the system in a motoring condition. If excitation is maintained, this condition is not harmful to the generator.

However, the turbine blades may overheat from windage. On steam generator units, the low pressure turbine blades are impacted the most, with typical withstands of 10 minutes before damage.

Generator circuit breaker (photo credit: Alstom)
Generator circuit breaker (photo credit: Alstom)

Operating steps

The generator unit can be safely shutdown (removed from service) with the following operating steps:

1 // Verify that there is no steam flow or fuel flow in the case of combustion turbine units to ensure that the unit will not overspeed when the generator circuit breaker(s) are opened.

2 // Transfer the unit auxiliary power to the alternate source if opening the unit breakers will de-energize the unit auxiliary transformer (UAT).

3 // Reduce or adjust the generator’s output voltage (voltage regulator) until the field current is at the no load value, and transfer from automatic voltage regulator mode to the manual mode of operation.

4 // Open the generator circuit breaker(s).

5 // Open the generator field breaker.

750kVA (kW) generator start, run and shutdown (VIDEO)

Reference // Electrical Calculations and Guidelines for Generating Stations and Industrial Plants – Thomas E. Baker (Purchase from Amazon)

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Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.


  1. Kevin Ronald
    Oct 27, 2015

    Thanks a lot Edvard Csanyi for sharing this amazing blog about shutting down the large generator. I am using Siemens breakers for my home, Can anyone please let me know How can I safely shut down a large Siemens generator? Am I needing to use the same process or it’ll be different.

    Many thanks in advance!!

  2. Nguyễn văn Đức
    Sep 19, 2015

    Dear sir!
    You can expland to me more detail for those steps.
    The popose of that

  3. Yossef Taborda
    Sep 16, 2015

    Dear Sir

    All generators operating in standy-by mode, shall be tested regularly. With temperature control, fuel, coolant, batteries, oil level. Regular testing can detect potential problems and avoid unpleasant surprises when you need to use.

  4. Nikolay
    Sep 11, 2015

    I heard that for large units once the generator is shut down, its shaft needs to be rotated slowly so that it doesn’t cool sagged

  5. Emmanuel Britto F.
    Sep 11, 2015

    The main steps depend on the type of shut down is required.
    There are two types of shut down: regular and emergency.
    The most severe conditions normally apply to emergency shut down for in this case the faster the possible lead the generating unit to standstill is required.
    The requirements are many and it would be tedious to describe all the operations but some significant measures must be taken such as reduce the power flow between the system and the generator and open the main circuit breaker as soon as the flow is very low are important.

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