Back Ground:-
I am working on MS5002C. Control is TMR - Mark 6 Dual fuel (Gas and Liquid) - Non DLN

The unit is in Operation since 3 years.
Unit was online since 2 months.

Operations wanted to Test some faulty alarms created by Gas detectors in Filter house and Turbine compartment. They gave a normal shutdown. As soon as it start coasting down, the unit tripped on "Compressor Bleed Valve Pos Trouble Trip" - L33cb1o
and not l33cb2o

We checked the solenoid, we can hear the click sound as we energize, measured 108 VDC while energize - Ok.

Now, when we start unit, tripped around 1800 rpm
- due to same problem - l33cb1o just shows Close for a second and Opens and Unit Trips.

Tried adjusting L33CB1O - did adjustment

Secondly, started again, monitored l33cb1o / L20CB, the unit tripped again at 3500 rpm on l33cb10 - compressor Bleed Valve Position Trouble Trip. [l33cb1o just closes and Opens back again]
(L20CB was still de-energized - never energized in both cases)

(If solenoid was passing, it should effect both bleed Valves, but here only l33cb1o was doing the trouble.)

So, checked continuity on both limit switches L33cb1o /l33cb2o
a) (Switch to marshaling with knives Open = 9.5 oHMS)

b) (Switch to marshaling with Knives in = 78Kilo Ohms)

c) Each wire w.r.t Panel chassis = 1.8 ohms

L33cb1o was showing mega Ohms for knives open [marshaling to Switch], but later replaced terminals at switch which reads the above for both now.

Q1) Do you think is the problem solved now, Or still have to clear the ground on each wire?

Q2) Is there something else to check apart from the ground?

Q3) Can we start the Unit in this state if urgency by Operations?

Would request your advice on the above.

 

Is the Mark VI annunciating a 125 VDC Battery Ground alarm when 33CB-1 is connected to the panel through the knife switches?

If so, does the ground alarm clear when you open the knife switches and isolate 33CB-1 from the Mark VI? (If not, it could still be the wire(s) is(are) grounded, and there could be more than one ground.)

What kind of limit switch is being used? A mechanical switch, actuated by the position of the valve/actuator, or a proximity (non-contact) switch? Proximity switches have been known to have high leakage currents and cause faulty indications to Speedtronic turbine control systems. If they are mounted inside the turbine compartment, where it gets very hot, this could be the problem. Have you tried replacing the switch?

Also, you haven't said that you used a source of compressed air connected to the supply side of 20CB-1 and actuated the bleed valves to see if they are opening fully (33CB-1 and -2 are supposed to be closed when the bleed valves are fully open). So, it could be the valve is sticking and not fully opening during start-up/shutdown and is "vibrating" when the turbine is spinning causing a faulty indication of not being fully closed during shutdown and acceleration. So, it would be best to check the bleed valve to be sure it's fully open before adjusting or replacing the switch.

I don't believe the compressor bleed valves of a Frame 5 two-shaft unit are supposed to close before 3500 RPM on start-up and acceleration. So, if 33CB-1 is telling you that the #1 compressor bleed valves is closing and the Mark VI isn't trying to close the valve (by energizing 20CB-1), then there's something wrong with either the wiring (loose terminals and/or bad connections--either or both could be between the marshaling cabinet and the switch or between the marshaling cabinet and the Mark VI; etc.), the limit switch (improper adjustment; switch is not firmly mounted with respect to the position indicator; faulty, intermittent switch; bad switch contacts; failing switch leads; etc.), or, and this is NOT very likely (but not impossible) there is something wrong with the Mark VI input 33CB-1 is connected to.

A bad ground, along with high induced AC voltages on contact input wiring, can cause problems like this. (The high induced AC voltages usually come from improper segregation/separation of AC and DC wiring during construction, and is usually difficult to correct.) You can set your voltmeter (a good, true AC RMS voltmeter) to AC and measure each incoming DC supply leg with respect to ground to see if there is any induced AC voltage riding on the DC, or, if the battery charger output filter capacitors aren't working properly.

But, this isn't very likely, unless the turbine has experienced a lot of nuisance Diagnostic Alarms related to contact inputs over the years, or some new wiring/cabling has been recently installed, without proper attention to separation.

It seems more like it's a switch and/or wiring problem.

As for running the unit, that's not a recommendation we can make. You have to use your best judgment and make that determination.

 

Hai,

Limit switch may malfunction though Resistance is ok. Better to replace the switch and start the machine. Before starting, make sure the switch operation by simulation of compressor bleed valve.

Good luck
G.Rajesh

 

1) Tested 20cb with inlet applying pressure 0.7kg/cm2, 0.8 kg/cm2, 4 kg/cm2
No leaks found, no passing.

2) Cleared grounds on wires for limit switch.

3) Operated multiple times the compressor bleed valve Open/close with the above pressures just to check whether it was sticking or no.

Now, Started machine successfully without tripping the Unit.

Thanks CSA & Rajesh for your precious support, tips and guidance to troubleshooting the problem.