Mark VI Supply Getting Off Frequently

H

Thread Starter

himanshu khoriwal

hello this is Himanshu Khoriwal from India.

I am working as power plant operation engineer in Indian Oil CO. Ltd. Here we are having Co generation plant containing three no. of gas turbines along with respective HRSGs. Each GT is rated for 30 MW of power generation at standard conditions.

Now let me come to the problem.
Mark 6 125V DC supply getting of by itself frequently in one of the three GTs while in standby condition, followed by automatic operation of auxiliary drives. But while on UPS supply 110V AC, it is not showing such behavior.

Kindly suggest and share your experiences.
 
Himanshu Khoriwal,

Is the Mark VI a Mark VI or a Mark VIe?

What Process Alarms <b>AND</b> Diagnostic Alarms which are being annunciated while the unit is on standby?

When you say the 125 VDC supply is "getting off by itself ... while in standby in condition, ..." specifically, where is the 125 VDC supply getting interrupted? A circuit breaker?

Is it the main circuit breaker supplying 125 VDC (presumed to be from a battery) to the Mark VI turbine control panel tripping? If so, what is the ampere rating of the circuit breaker?

Is there a "125 VDC BATTERY GROUND" Process Alarm annunciated on the Mark VI HMI before the breaker trips?

What have you done to try to troubleshoot the problem--and what were the results of your troubleshooting?

When the Mark VI loses 125 VDC power, do all the LEDs in the Mark VI turbine control panel go out?

Does the Mark VI get a secondary source of 125 VDC via a <DACA> module (which converts AC applied to the turbine control panel to DC)?

If so, what does "...But while on UPS supply 110 VAC, it is not showing such behavior." mean? Why isn't the UPS power not continuously supplied to the Mark VI?

Here's why I'm not clear about your post. Most Mark VI turbine control panels are supplied by a 125 VDC breaker in a breaker panel which is supplied by a 125 VDC battery. There is rarely an intermediate breaker between the Mark VI and the 125 VDC breaker panel--sometimes there is, but not usually. AND, on packages supplied by GE the same 125 VDC breaker usually feeds the Generator Protection/Control Panel--most often, but not always.

Further, those Mark VI panels which have a secondary 125 VDC source, that usually is provided via a GE <DACA> module, which produces the 125 VDC from an AC source (could be 110 VAC or 220 VAC) which is connected to the <PD> (Power Distribution) module in the Mark VI panel. Some Mark VI panels actually get 125 VDC from another external source (sometimes another 125 VDC battery) which is connected to the <PD> module. There is circuitry on the Mark VI <PD> module which chooses the higher of the two DC voltage sources and uses that to provide the power to the Mark VI turbine control panel.

A Mark VIe heavy duty gas turbine control panel has a different power scheme. It is usually powered by a 125 VDC battery, and more often by an AC source through a <DACA> module. And, there are usually several circuit breakers in the Mark VIe turbine control panel that can be used to isolate the various sources. There is a similar 125 VDC high source selection scheme in the Mark VIe.

So, to understand your problem it is necessary to understand what kind of turbine control panel the units are using, and to understand how the 125 VDC is being "offed". If it's a circuit breaker, then it's entirely possible there's a problem with the circuit breaker. The typical 125 VDC current drawn by a Mark VI is approximately 10A when the unit is running, and approximately 5A when the unit is not running (on standby). And, the typical breaker which supplies 125 VDC from the battery is usually 50A (on a GE package), but it's also supplying the Generator Protection/Control Panel. So, it would have to be a large current draw--or a pretty serious short--to trip such a circuit breaker.

Or, there could be a 125 VDC battery ground which gets VERY bad (a short circuit, essentially) and causes the 125 VDC breaker to trip.

But, without clarification (answers to all the questions above) it's really impossible to say anything more.
 
K
> Is the Mark VI a Mark VI or a Mark VIe?
Ans. Mark VI

>When you say the 125 VDC supply is "getting off by itself
>... while in standby in condition, ..." specifically, where
>is the 125 VDC supply getting interrupted? A circuit
>breaker?
Ans- Mark is supplied through 125v DC distribution board having no circuit breaker ,only switch fuse units. This DCDB is supplied through 125v battery charger and this battery charger is supplied 415v AC through air circuit breaker.

>Is there a "125 VDC BATTERY GROUND" Process Alarm
>annunciated on the Mark VI HMI before the breaker trips?
No. such alarm appeared.

>What have you done to try to troubleshoot the problem--and
>what were the results of your troubleshooting?

ans. two things might have been faulty...first is 125 battery charger voltage profile might have a voltage dip ..second some card problem in mark 6 panel. to check first one voltage profile was checked of battery charger and was found normal.

to check second one mark supply changed over to 110V AC panel and kept under observation whether mark display gets off or not.But it showed normal behavior on 110V AC supply. Thus both the things are not becoming culprit as per these observations.

>Does the Mark VI get a secondary source of 125 VDC via a
><DACA> module (which converts AC applied to the turbine
>control panel to DC)?
yes ,it gets through UPS 110V AC.

>If so, what does "...But while on UPS supply 110 VAC, it is
>not showing such behavior." mean? Why isn't the UPS power
>not continuously supplied to the Mark VI?

it is used as back up.
when 125 v DC fails, it should automatically changeover to UPS supply but it has also not happened during these problems.
 
Himanshu Khoriwal,

Does the fused switch have some sort of automatic operating/opening means that is opening the switch, or are the fuses opening?

Let's try this another way. When the 125 VDC is offed, how do you restore the 125 VDC to the Mark VI?

Are you confusing the Mark VI with the HMIs? You mention a Mark VI display, are you referring to the LEDs on the Mark VI card edges (the UCVx cards and the VME cards in the Mark VI processor racks), or the HMIs? The HMIs are not part of the control and protection of the turbine and auxiliaries; they are only a means for sending commands to the Mark VI, monitoring operation and managing alarms (Process Alarms and Diagnostic Alarms). The Mark VI can operate and do basic protection functions without any HMIs, but it wouldn't be possible to monitor the operation or send commands or manage alarms.

Do the other Mark VI panels automatically switch from 125 VDC to 110 VAC on loss of DC?

If only one of three Mark VI turbine control panels is experiencing this problem, then it should be possible to determine what is different on the panel that is experiencing the problem and correct the problem.
 
K
>Does the fused switch have some sort of automatic
>operating/opening means that is opening the switch, or are
>the fuses opening?
no it does not have. It is only protected through fuses which are found normal after mark control system getting off.

>Let's try this another way. When the 125 VDC is offed, how
>do you restore the 125 VDC to the Mark VI?
it restores by it self. it becomes off for 40-50 sec and then restores.

>Are you confusing the Mark VI with the HMIs?
sorry to create confusion. Here i am discussing about complete mark control system of gas turbine.

>Do the other Mark VI panels automatically switch from 125
>VDC to 110 VAC on loss of DC?
yes..they do

>If only one of three Mark VI turbine control panels is
>experiencing this problem, then it should be possible to
>determine what is different on the panel that is
>experiencing the problem and correct the problem.
Ans..this is not getting identified.
 
Himanshu Khoriwal,

I believe the 125 VDC is not being interrupted at all--but that the over-/undervoltage protection in the Mark VI power supplies mounted on the right sides of the processor racks are operating in response to a dip or spike in the voltage from the 125 VDC system. The power supplies have internal crowbar circuits that operate when the voltage dips below approximately 90 VDC or goes above approximately 140 VDC. It's likely there is either a problem with the battery charger voltage regulator, or the charger's output capacitor, or there is some other device powered by the battery that is causing a dip or spike when it is energized or de-energized.

This could be made worse if the battery charger voltage setpoint is not properly adjusted, and/or the equalizing function is turned on when the Mark VI is energized. (The Mark VI should be de-energized any time the battery charger equalizing function is used.)

There are also zener diodes on the <CPF> (Conditioning Power Filter) which have been known to fail, and usually after being stressed.

This would also explain why the automatic switchover to AC isn't happening--because the DC isn't really being lost. It's just dipping or spiking momentarily causing the rack-mounted power supply crowbar circuits to operate, but not the automatic switchover.

Please write back to let us know what you find! This is a serious problem which is likely shortening the lives of the Mark VI power supplies.
 
Himanshu Khoriwal,

You say this occurs when the unit is on Cooldown. Can you relate some DC event that occurs during Cooldown with the power supply issue?

Also, I think I'm beginning to understand the power distribution description you have been trying to provide. Most Mark VIs I have seen had a <PD> core, which was a silver module with a door, and a TCPD (Turbine Control-Power Distribution) card mounted in the back. The TCPD had switches and fuses and LEDs and plugs. The 125 VDC comes into the <PD> at the small terminal board below the door, and Terminals 1 and -3. BUT, that 125 VDC usually comes from the <CPF> (Conditioning Power Filter), which is fed from another DC breaker somewhere, usually outside the Mark VI panel. It's usually in a DC distribution panel with other breakers that supply the emergency DC lighting in the compartments, and the fire detection system, and sometimes MV or HV switchgear (Medium- or High Voltage). If there's a breaker that supplies a load that is being energized or de-energized during cooldown at about the same time this incident is occurring, that would be something to look into.

Also, the 125 VDC battery supplies the Emer. L.O. Pump, and for some machines that burn liquid fuel, it also supplies the D.C Fuel Forwarding Pump. I know of many sites that perform periodic tests of the D.C pumps when the unit is on Cooldown. Does this happen at your site?

That's about all I can think of. Again, please write back to let us know what you find as you progress to the resolution of this issue!
 
B
Himangsu,

Plz confirm me one thing. When the problematic gt is in s/b.
Arrange to provide its supply from a separate dc source....say from another GTs battery charger.

After that watch and see....and reply please.
 
Your 125VDC power system will consist of a battery charger and a 125VDC battery bank. With a good battery bank how can there be any voltage variation or noise on the 125VDC supply?
 
K
thanks a lot sir for your really helpful response.
respect for you.

sir can you please explain about equalizing function?
 
Forgot to add the equalize function/mode is usually selected by a switch on the battery charger.

Again, it should only be enabled/used when the Mark VI is NOT energized.

What is the 125 VDC at the Mark VI <PD> input terminals (without the AC being applied)?

What is the nominal battery voltage of the battery system?

How many cells in the battery?

What is nominal voltage of each cell?

What is the normal battery charger voltage? What is the voltage setpoint for the equalizer function/mode?
 
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