Faulty Speed Turbine sensors

[SA07]

Hi

Every year we get regular breakdown of turbine speed sensors. We replace all 6 sensors per turbine during annual maintenance. However this problem occurs again. We have 2 identical turbo-alternator 45 MW steam 4600 rpm. The turbine is controlled by GE Mark VI. When 2 speed sensors become faulty, the turbine trips.

Speed sensor AI Tek P/N 70084-1713-111 passive , molded high sensitivity, 5/8-18 x 1.125'' -40 C to +150 C

This was highest temperature available from AI TEK in 2008.
When we removed faulty sensors, we noticed the tip of the sensors are worn out a bit. The clearance recommended by the OEM was respected. Sometimes the inner plastic part can move inside the metallic outer casing.
Has someone encountered similar problems? Have you been able to solve it?

 

[itsmoked]

Sounds like you're overheating them. I'd replace one that has failed with a thermocouple and record the temperature for a week and figure it out.

If it is indeed running too hot then you need to mitigate the problem somehow. Use fan cooled sensors, or water-cooled, or pressurized air, or run a cold gun on them. They should last many years UNLESS they're being overheated.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[esperantes]

Did you inform the OEM? If yes, what did they say?
Esperantes.

 

[SA07]

OEM is working on this issue. It seems at other power plant with same OEM they have same problem. We have this issue since 2007. We upgrade to a higher temperature sensor. But still same problem.

 

[waross]

Are you losing your clearance when heat expands the turbine?

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[SA07]

Most of the time, the tip of the faulty sensors are worn out.
We used to 2 methods to install the speed sensors:

Install speed sensor
Move the sensor towards the detecting teeth
1) Measure the voltage on the sensor. When voltage is 9.7 V stop
2) Measure clearance between tip of sensor and detecting teeth Clearance =0.9mm

Plz see attached pics of the speed sensors

 

[waross]

Try 1.4mm or 6.5 V

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[RedSnake]

What do have that reads the sensor signal?

4

BR A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[SA07]

We use a multimeter to read the 9.7 V during installation.
The 6 speed sensors are connected to electronic card in the Mark VI Panel.

 

[RedSnake]

The reason I am asking I am not sure how sensitive the Mark VI Panel is.
If a change of sensor would work.
This one can stand higher temperatures but have to be closer I think.
And the values are a bit different.

Best Regards A


“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein