POWER GRID CORPORATION OF INDIA LIMITED Presentation on ‘FREE GOVERNOR OPERATION” By D.K.Guru & S.P.Barnwal

FREE GOVERNOR OPERATION WHY FREQ COMPARISION MAY-02 & MAY-03 GOVERNOR BEFORE GOVERNOR GOVERNOR RESPONSE IN NER DEAD BAND GOVERNOR TIME LAG BLOCKED GOVERNOR ROLE DROOP FREQUENCY DECAY RATE BACKLASH TYPES OF CONTROLS DROOP RESPONSE IN SR ABT & GOVERNOR ADVANTAGES GOVERNOR TYPES TIME DELAY CHARACTERISTICS PROBLEMSA FINAL WORD

ROLE OF SYSTEM OPERATOR LOAD GENERATION BALANCE 50

WHY DOES FREQUENCY DROP ? Sudden addition of load causes a drop in frequency. An increased load is supplied through an increase in the load angle by which the rotor lags the stator field. It means a loss of Kinetic Energy of the rotating M/c and a slower speed of rotation i.e. a lower frequency. f = (P/2) X (N/60) Where f = frequency of the system P = no of poles of the M/c. N = rpm of the M/c.

Load Frequency control Free Governor Opertaion Under Frequency Operation PRIMARY CONTROLS

ABT AND GOVERNOR POST ABTFREQUENCY WITHIN 49 TO 50.5HZ ACHIEVED BY STAGGERING OF LOADS FLUCTUATION IN FREQUENCY INCREASED

HUMAN GOVERNOR OPERATION SYSTEM ~ TG X GOVERNOR

GOVERNOR SPEED GOVERNOR IS THE CONTROLLING MECHANISM WHICH CONTROLS THE INPUT TO THE PRIME MOVER AUTOMATICALLY WHEN THERE IS A CHANGE IN SYSTEM SPEED (FREQUENCY) WHEN THERE IS A CHANGE IN SYSTEM FREQUENCY GOVERNOR RESPOND BY CAUSING VALVES/GATES TO OPEN/CLOSE TO INCREASE/DECREASE THE INPUT TO THE PRIME MOVER

MISCONCEPTION Governors attempt to restore frequency to normal. In reality, Governors attempt to restore load generation balance, using frequency change as a signal.

CHARACTERISTICS 1.Respond promptly to a small change in speed. 2.Adjust the throttle valve with a minimum of overshoot. 3.Have sufficient power to overcome friction losses and unbalance forces in the throttle valve. 4.Permit very little speed fluctuation under constant load and steam conditions.

► There are several basic types of governors utilizing the above principles: ► 1.Mechanical shaft - The familiar fly weight type. A hand adjustment permits speed regulation at the machine. ► 2.Direct acting orifice - This consists of a shaft driven positive displacement type oil pump which delivers pressure to a spring diaphragm connected to the governor valve stem. Since the delivered oil pressure is directly proportional to shaft speed, control is accomplished. Hand or automatic speed regulation is possible. ► 3.Oil relay - Built to utilize lube oil pressure or a separate governor oil pressure, a double acting oil relay piston permits more precise control of the governor valve. It is integral to the turbine and usually designed by the turbine manufacturer. ► 4.Precision oil relay - A separate shaft-driven oil relay offers more precise control. Utilizing its own oil system, this type governor is not made by the turbine manufacturer. If more governor valve operating force is needed, a second double acting servo-motor may be utilized. ► 5.The electronic governor usually provides more precise and reliable speed control. The speed measurement signal can be generated in two ways. One method is by utilizing a magnetic pickup in proximity to a toothed wheel/gear mounted on the turbine shaft. Another method is to utilize a shaft-mounted permanent magnet generator where the poles rotate and produce an electronic pulse measured by a microprocessor. In the first case, only two pairs of wires connect to the unit. One supplies 48 VDC that is the required operating voltage; the other connects to a magnetic pickup on the turbine shaft. In the second case, no external power is required, as the unit is powered from the turbine shaft rotation. In the first case, output air (normally 3-15 lbs.) goes to the diaphragm of a standard control valve in the inlet steam line to the turbine. In the second case, hydraulic pressure drives a pre-piloted servo-motor that operates the governor valve.

DEAD BAND DEAD BAND OF THE SPEED GOVERNORING SYSTEM IS THE TOTAL AMOUNT OF CHANGE IN STEADY STATE SPEED WITHIN WHICH THERE IS NO ACTION BY GOVERNOR. Turbine rated output MW Dead band percent of rated speed IN 50HZ BASE < 5MW HZ 5 to 30mw HZ > 30mw HZ IEC - 45

DROOP CHARACTERISTICS THE AMOUNT OF SPEED (OR FREQUENCY) CHANGE THAT IS NECESSARY TO CAUSE THE MAIN PRIME MOVER CONTROL MECHANISM TO MOVE FROM FULLY CLOSED TO FULLY OPEN. NORMAL RANGE -3 TO 5% THE MINIMUM RATE OF CHANGE OF SPEED SHOULD NOT BE LESS THAN 0.4 TIMES OF ITS DROOP. THE MAXIMUM RATE OF CHANGE OF SPEED SHOULD NOT BE MORE THAN 3 TIMES OF ITS DROOP.

GOVERNOR TIME LAG TIME TAKEN BY GOVERNOR TO JUST BEGIN CHANGING POWER OUTPUT TO STABILISE FREQUENCY. OR TIME BETWEEN A CHANGE IN GENERATOR SPEED & CHANGE IN TURBINE POWER.

Dead band 0.25 sec Valve opening 0.5 sec Steam flow 4 seconds During transient state Governor is of little help. Effect is felt during steady state TIME DELAY IN GOVERNOR OPERATION

BLOCKED GOVERNOR BYPASSING THE GOVERNING FEEDBACK MECHANISM TO MAINTAIN FIXED GENERATOR OUTPUT. DISADVANTAGES:- SYSTEM INSTABILITY RESTORATION OF SYSTEM FREQUENCY TO NORMAL TAKES MORE TIME AFTER A DISTURBANCE.

FREQUENCY DECAY RATE Approximate Freq 5 X Lost Generation Decay Rate= In Hz / sec Remaining Generation Example:- 2200MW 200MW Generation Lost Freq decay rate = (5 X 200) / 2000 = 0.5 Hz /second

POINT A POINT B POINT C POINT D POINT A - GENERATION LOSS POINT B – GOVERNOR ACTION STARTED POINT C - FREQUENCY AFTER GOVERNER ACTION POINT D – FREQUENCY AFTER OPERATOR ACTION

The distance through which one part of connected machinery, as a wheel, piston, or screw, can be moved without moving the connected parts. BACKLASH

BOILER CONTROLS BOILER FOLLOWING SYSTEM TURBINE FOLLOWING SYSTEM INTEGRATED CONTROL SYSTEM

ADVANTAGES 1.Reduce the random change of frequency 2.Mitigate effect of load generation mismatch 3.Prevents wastage of fuel during low load condition 4.Faster restoration from grid disturbance

PROBLEMS 1. Steam deposits on the valve stem (or stems). 2. Lubrication deposits (i.e., soaps, dirt, detergents, etc.) in the top works of the valve exposed to the elements. 3. Mechanical failures of the valve resulting from bent stems, either in the valve proper or the upper works, damaged split couplings, etc., all within about a 6" area near the center of the valve mechanism. 4. Galling of the piston in the hydraulic latch cylinder. 5. Jamming of the screw spindle in the larger cylinder-type valve design due to forcing by operations personnel

FREE GOVERNOR OPERATION Mother of all Controls Self healing mechanism Collectively Control Most equitable Reduces risk of collapse Makes restoration easy World wide mandatory practice