Outage

A day just before unit outage, operation section usually coordination with maintanace section about schedule of outage work. After final coordination, Permit to work officers ( part of operation section) have instruction lists to operators for do isolation systems after save condition.

The work permit which can be released for maintenance section on a day before unit outage only install the scaffold on each area where no access, and for operation departement are trying to do soot-blower for de-slagging and preparation for lowering coal silo.

Picture below is unit shutdown chart for right on 00:00 the Generator will be de-synchronized, preparation for reducing load from maximum load should be started on 21:30. On that time all coal silo level should be less that 50% level.

In the unit load below 50%, operators can do Gas Air Heater Emergency Drive test. The Gas Air Heater syetem explanation can be read on http://idpowerstation.blogspot.com/2010/12/air-heater.html. Generally explanation, Gas Air Heater has two drive, electric motor (normal operation) and air drive (emergency operation). This air drive should be in function if electric drive get problem.

After Generator de-sychronize, Turbine over-speed test could be carry out. The mechanism of Turbine trip is very complicated and will be detail explanation on http://idpowerstation.blogspot.com/2012/09/overspeed-trip-device.html. Turbine main stop valves should be close / shut if the turbine speed reach 10% higher than normal speed. Turbine trip caused by over-speed could be an automatic or by handle mechanism operated.

After Turbine over-speed trip test done, the operation section will do Boiler and Turbine cooling down. Boiler cooling down needs around 1 day and Turbine cooling down needs around 1 week.

Boiler cooling down use drought system. After Riser tube metal temperature reach 35 degree celcius, drought system can be stop and isolated. Permit For Work Officers will be issue document for install scaffold and gondola inside furnace.

Turbine turning gear can be stopped if turbine metal temperature reach 150 degree celcius or lower. After that Generator hydrogen de-gassing can be started, Seal oil system and stator cooling can be stopped.

The consumption of cooling water reduce due to many equipmnets stopped, so that cooling water system can be stopped and emptying electric power can be started. That time electrical work for example de-energize Generator Transformer for inspection and cleaning 500kv isolator can be started.

One or two days before firing, all the work must be finish, and start up procedure could be carry out http://idpowerstation.blogspot.com/2008/12/economizer-protection-of-economizer.html