Hitachi Machine Tripping on TCP AC Supply Failure


Thread Starter


Dear Friends,

We have a Hitachi H-25 (25 MW) gas turbine. recently due to tripping of one of our auxiliary transformers, our supply to Gas turbine auxiliary MCC had tripped. GT MCC has all gas turbine drives including MOP and MHOP (hyd. pump). we have no shaft attached auxiliary drives.

Normally whenever Mains supply fails in GT MCC, Emergency power comes up within 2 seconds and machine does not trip due to accumulator present in hydraulic line (which does not allow Hyd oil pressure to go low below tripping point). But this time when our GT MCC AC supply failed, local HMI UPS did not give back up. thus local HMI PC failed. also another phenomena happened was that during this whole process control shifted from remote HMI to local HMI, which now was in OFF condition, and all drives came in manual mode.

I am assuming that as all my drives were in manual none of them started again when power was restored and machine tripped on low Hyd pressure.

Unfortunately due to loss of local HMI supply all trends vanished after AC supply failure of GT MCC so i am having trouble for exact diagnosis.

Can anyone help me know is there any reason that my control shifted from Remote HMI to local? and why did all drives come in manual mode?
does AC supply failure to TCP have any effect on it?


We don't know what kind of control system is used on the H-25 GT at your site. Many H-25 GTs use GE Mark* turbine control systems, and for the most part Hitachi seems to adhere to many of the proven GE control system practices and philosophies--but not always.

Generally, HMIs (for GE-design turbine control systems) do NO control or protection. All the control and protection is accomplished is done by the turbine control panel, and the HMI is just a means for monitoring unit operation, sending commands to the turbine control panel, configuring the turbine control panel, and managing alarms from the turbine control panel. But, in GE systems which follow the GE control system practices and philosophy the HMI doesn't do any control. (As with all things designed by GE in Salem, VA, there are exceptions to every rule--but in this case they were few and far between.)

This means that the turbine, if running, can continue to run without the HMI. Difficult for the operators, but, that's the intent of the philosophy--for the turbine and driven device to continue to run until such time as the HMI can be returned to service. This presumes there is AC power available for the various pumps and fans and devices. But, presuming only the HMI(s) were lost, the turbine control panel--would, under normal circumstances--continue to keep the unit running. Loss of the HMI(s) would not--under normal circumstances--cause the Mark* to shut the unit down.

Now, if AC power was lost to all auxiliaries ("drives") then that's another story. Of course, without Hydraulic Oil and Trip Oil pressure then the unit can't continue to run, so it would most likely trip.

In general, the Mark* turbine control panels are powered by 125 VDC, sometimes 24 VDC, and sometimes 120/220 VAC. Sometimes, there are multiple power sources (125 VDC, primary, and 120/220 VAC back-up, for example), and usually only Mark* steam turbine control panels use only AC, but usually have a back-up AC source. You haven't told us how the turbine control panel is powered, but if it has a 125 VDC source and a 120/220 VAC back-up then unless the DC was also lost at the same time as the AC then the turbine control panel should have continued be energized.

If the turbine control panel was a Mark* and it was energized, then usually there is something called a Trip History Log which is captured by memory in the turbine control panel (in addition to the Trip History Logs stored on the HMI(s)--which would not have been available if AC was lost). So, before the unit was re-started it was likely possible to upload the Trip History from the Mark* memory to the HMI once power to the HMI was restored.

Now, all of the above refers only to GE-design Mark* (Speedtronic) turbine control systems. You haven't told us, and we don't know, what kind of turbine control system is in use at your site. So, the above may or may not be applicable.

As for the motor starter ("drives") switching control from AUTO to MANual, that--presuming Hitachi followed standard GE control philosophy and practice--would also have been done only in the turbine control panel, not the HMI. And, I can imagine a scenario where, if the turbine control panel was de-energized (which you didn't say, but it would be helpful to know if it remained energized during the event, or if the panel lost all power during the event and was de-energized) then it's likely the logic resets all the "drives" to MANual control when it is re-energized as a default (right or wrong). Most GE "drives" (motor starters) have maintained H-O-A switches (HAND-OFF-AUTO) which, if in AUTO, would remain in AUTO if AC was lost to either the MCC line-up or the turbine control panel. But, again, that's typical GE control philosophy and practice, and I, personally, don't have much experience with Hitachi turbines and their control practices and philosophy.

That's all I can add, based on the information provided. I believe, that many turbine control system packagers/providers also follow similar control philosophies and practices--letting the turbine control system do all the control and protection, and only using the HMI for operator interface and configuration. At least that's the way I think it should be done, because that provides the most reliability for unit operation.

Hope this helps! When you write, since this site doesn't use avatars or signatures, it would be helpful if you could tell us something about the control system, the fuel(s) burned, and other relevant things about the unit and its auxiliaries at your site. Contrary to popular belief, all H-25 machines are NOT alike, and all GE frame heavy duty gas turbines are NOT all alike. There can be very subtle differences which can mean very different operation and control, and there can be large differences which don't really affect operation and control. But, there are differences in most machines from any manufacturer, even if they have the same model number. Technologies have changed dramatically over the years, for both machines and auxiliaries, as well as control systems.
Thanks CSA!!!

we checked the TCP HIACS log by again simulating GT MCC input changeover. DC backup had failed. battery bank did not provide support so DC voltage had dropped to 50V from 110V, leading to TCP shutdown for a small time, which caused all drives to come in Manual mode.

Manoj Agrawal