Issue Caused by Feedback Resistor of Governor in Guide vane Opening

MAINTENANCE LOG SHEET	Date:2079/05/08                                Day: Wednesday
	Time: 12:15PM
Installed Equipment/Part:	Reconnected the 500 Ω current to voltage signal changing resistor at the guide vane feedback circuit of Unit-1.

Reason for Maintenance	In unit-1, the guide vane opening percentage in control room SCADA displays more value than it should have been. While generating 12 MW, guide opening had sometime reached up to 100%.
Primary Suspect	Moisture content in feedback sensor or problem in feedback circuit.

Maintenance Activity	Cleaned the feedback sensor to rule out the possibility of error due to moisture content.Checked the power supply and possible loose connection in sensor connector.Checked the signal converting resistor of the feedback sensor. It was found to be loosely connected to terminal. Then the resistor was firmly soldered and reconnected to the terminal.
Status after maintenance	The output in control room SCADA and unit 1 governor HMI shows the actual guide vane opening percentage. So, this issue is finally solved.
Recommendation	Spare for the 500 Ω resistor is needed in power house and attention in regular monitoring of the intactness of sensor position as well as time to time tracking of actual guide vane opening & output displayed in HMI/SCADA measured by position sensor is recommended.

REFERENCE IMAGES

Image 1: 91.2% Guide Vane Opening Displayed for Active Power of 9.9 MW

Image 2: Loosely Connected Feedback Signal Converting Resistor at Terminal

Image 3: Resistor Reconnected Back to the Terminal

Image 4: 500 Ω Feedback Resistor

Image 5: 79.6% Guide Vane Opening for Active Power of 12 MW after Maintenance.