woodward mod ii governor digital retrofit

Generation Engineering, P&C Design

Woodward MOD II Governor Digital Retrofit Low cost Option for Woodward MOD II Governors Frequency Response Improvement

Woodward Mod II governor Digital Retrofit: Ravi Mutukutti

Table of Contents Executive Summary ............................................................................ 3 Overview of the Retrofit ..................................................................... 4 Advantages of the Retrofit ................................................................. 4 Details of the Retrofit ......................................................................... 5 1. New Speed sensors inside the SSG ................................. 5 2. Pre-fabricated PLC back plane ........................................ 5 3. Actuator cabinet Control Relays ...................................... 9 4. Actuator Electronics and Devices .................................. 10 5. Example drawing changes ............................................. 11 6. New drawings ................................................................. 12 7. New replacement Panel Layout .................................... 13 8. Appendices...................................................................... 14

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Woodward MOD II Governor Digital Retrofit Low cost option for Woodward MOD II Governors Frequency Response Improvement

Executive Summary Woodward MOD II governors were the last pre-digital era analog electronic governors that were popular around 1980s. The speed sensing technology was a hybrid between digital and analog electronics. BC Hydro has this type of governors installed in PCN, SEV, MCA, REV and few other smaller plants.

Historically this type of governors had a speed jitter issue mainly owing to the flexible coupling between the main shaft and the speed signal generator (SSG). As a corrective measure, BC Hydro had moved to an optical speed sensing system in early1990’s. Later many of the plants including PCN, SEV, MCA and REV have moved away from the optical speed sensing and reverted back to the original SSG design to alleviate various other reasons in favour to the speed jitter. Hence, the original speed jitter issue still prevails.

This governor’s control is based on old analog electronic technology and many electronic cards are not readily available today. These cards are attached to the back plane through edge connectors where susceptible to noise and loose connections with their age. The gain settings of these governors are done through a set of potentiometers (pots) calibrated to a range of values marked around its knob. Over time the repeatability is being lost and they are prone to erroneous gain settings when adjustments are attempted.

Recent governor related issues and forced outages occurred at Mica prompted to explore options to retrofit unit 1-4 governors with digital front end. There is a plan to replace gate limiter motors with the suspicion of an electrical noise from the limiter motor. The field experienced. Although the electronic noise was reduced to somewhat acceptable level, it is not completely eliminated. There are other issues such as speed jitter, noise due to card edge connectors and potentiometers, component obsolesce, calibration errors, etc. still remains and are of concern.

BC Hydro P&C design group has developed a design for low cost retrofit option to address the above inherent Woodward MOD II governor issues by retrofitting the analog electronic front end with a PLC. Total cost of materials, shop assembly, and design is estimated at $25,000 and can be supplied within 6 weeks. The installation time is expected to be 3 weeks.

The new design will eliminate the speed jitter and allow the gate droop if the MW droop hydraulic amplification is detected. It eliminates many obsolete components and new components used will be common to the other BC Hydro digital governors. This makes the governor to be visible on OI/PI system and faster in responding to frequency changes and remote commands from FVO. The new design has provision for precious speed dead band capabilities compared to the limited adjustments in the current analog governor.

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Overview of the Retrofit The analog electronic portion of the governor including speed switches, SSG speed probes, electronic cards, backplane wires, relays and many other electrical components inside the actuator cabinet will be removed. Transducer pilot valve and LVDT connection will be retained. Pre-fabricated back plane with a M580 based PLC, redundant power supply, Releco Relays and wire terminal blocks will be used to replace all the analog electronic based controls. This backplane will be installed inside the same footprint where space cleared by removal of electronic cards, relays and other components. Existing external cabling to the external devices will be retained and re-used. New wiring will be used to connect the new backplane terminals to the actuator terminal strip.

Speed sensors and line driver components will be removed and replaced with two new Zero Velocity Pick-Up (ZVPU) units directly connected to the PLC high speed counter card. New VT transducer will be used to read the generator speed in a 2 out of 3 voting scheme.

Existing speed setter motor (15FM) and power setter motor (65PM) will be removed. The functionality of speed setter and power setter will be performed by the PLC using raise/lower discrete inputs.

The existing MW transducer will be replaced with a new 4-20mA transducer. The LVDT input and Gate Position input also will be wired to the PLC, enabling the unit to be either on MW droop or gate droop.

Existing Mechanical gate limiter, Gate restoring cable, actuator lock mechanism, brake system components, pressure switches etc. will be retained without modification. Mechanical/ Hydraulic components will neither be removed nor replaced.

Advantages of the Retrofit • Eliminates the speed jitter

• Eliminates the potentiometer type adjustment of parameters in favour to the numeric entry

• Eliminates the noise issues due to card edge connectors and analog electronics

• Eliminate obsolete components

• Adds the Gate Droop capability

• HMI Visibility and control

• OI/PI Visibility

• Common components compatible and in par with other digital governors

• Precious dead band adjustments

• Feed Forward Gain functionality will be introduced

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• PID Gains can be parameterize numerically

Details of the Retrofit

1. New Speed sensors inside the SSG Speed sensors and line driver components will be removed and replaced with two new Zero Velocity Pick-Up (ZVPU) units directly connected to the PLC high speed counter card. New VT transducer will be used to read the generator speed in a 3 out of 2 voting scheme. 12VDC power will not be required and can be removed from the SSG. New ZVPUs are the same type used in BC Hydro Digital governors and SSAs.

An example installation of ZVPU speed sensors at Speed Signal Generator (SSG)

2. Pre-fabricated PLC back plane New M580 Schneider PLC will be the heart of the governor. The pre-fabricated backplane will contain redundant DC-DC converters, PLC rack with required IO cards, RELECO Relays, and set of terminal strips. It will use the same footprint freed by removal of analog electronic cards and other electrical components. The PLC reads the speed via ZVPU probes and VT signal when it is available. It keeps track of speed setpoint and control the starting and stopping of the turbine when it is offline. It also keeps track of power setpoint to regulate power when the unit is online. Bump less transfer between different modes will be achieved using setpoint follow-up. An HMI will be installed on the cabinet door and at the UCB for remote control and monitoring capability. PLC will be connected to the Plant LAN for Governor OI/PI visibility.

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The white existing backplane where various components mounted on both sides, will be removed and replaced with a new pre-fabricated back plane; which contains a PLC, power supplies, relays and other components. The new backplane will fit into the same mounting screws.

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Below picture shows the back side of the existing backplane with multiple speed switch and other relays. These relays will be replaced with the new relays mounted on the new backplane.

Discrete input card will read the following relay contact inputs:

1. Start/Stop from 65SDX

2. Online/ offline from 65DCO

3. Actuator Lock from 65AL solenoid input

4. Spare Input (Future)

5. Manual / Test/ Gov from 43GT

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6. Synchronous Condense Close Bias from 65SCB

7. Gate Position Below Gate Limit from 33LF

8. Power / Gate setpoint Lower from US2(65PL relay coil input)

9. Power / Gate setpoint Raise from US3 (65PR relay coil input)

10. Speed setpoint Lower from 15FL

11. Speed setpoint Raise from 15FR

12. Creep Detect Enable from 20BTX

13. Low Gate Limit input from 65LGL

14. Pilot Valve Open Bias status from 65PV

15. Power supply Monitoring

16. Parameter Write Enable Switch discrete Input

Discrete Output Card will give the following outputs which are wired to individual RELECO relays:

1. Governor Healthy 65SF replacing old 65SF and 65EPF (for Actuator Lock)

2. Governor Alarm 74GOV

3. Creep Output 39C

4. Speed Switch 14-15








12. Spare discrete Outputs (5)

High speed counter card will read speed from:

1. Speed proximity probe (ZVPU) #1

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2. Speed proximity probe (ZVPU) #1

3. Generator VT interface

4. Bus VT interface (future)

Analog Input Card will read from:

1. Watt Transducer (Unit Active Power 4-20mA)

2. Gate MLDT position (Future 4-20mA)

3. Aux. Servo LVDT position (+/-10VDC)

4. Gate Limiter Position (0-10V)

Analog Output card will control the Governor Transducer Valve and signal the RPM meter as follows

1. Control output to Power Amplifier (+/-10VDC)

2. RPM meter (0-1VDC)

3. Actuator cabinet Control Relays Following existing relays inside the actuator cabinet will be replaced with RELECO Relays:

1. 3AL: Energized to enable Governor action/ De-energized to Lock

2. 65PV: Pilot Valve switch over to BIAS control

3. 71QPHT: Oil Pump Control Timer Relay

4. 65DCO: Damping Changeover (Online) Relay

5. 39C: Creep Detection

6. 65SF: Speed Signal Fail used to drop 3AL

7. 33TGLX: Gate Lock Indication and enable 65SD

8. 14-1: Under Speed Switch 15%





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14. 12-105: Over Speed Switch 105%



Following existing relays inside the actuator cabinet will be removed without replacement:

17. 65EPF: E pulse Fail : not needed since 65SF can be used for the same Alarm point

18. 65MI: Modules in the Rack Interlock

19. 65PLX: Power Setter Lower: not needed since 65PM will be removed

20. 65PRX: Power Setter Raise : not needed since 65PM will be removed

21. 65PM/LL: Power setter Motor Lower limit: not needed since 65PM will be removed

22. 65PM/RL: Power setter Motor Raise limit: not needed since 65PM will be removed

23. 65SCR: Fast Return from Sync Condense : not needed since PLC can internally do the same function

24. 43GTX / 43GTY: Governor MODE GOV or TEST

25. 65LGL: Low Gate Limit Enable : not needed

26. 65DCOX: not needed

27. 65GLX: not needed

28. 52X: Breaker status for self-seal 65SCR : not needed since 65SCR will be removed

4. Actuator Electronics and Devices Following devices inside the actuator cabinet will be removed without replacement:

1. 15FM motor and associate resisters, Limit Switches, Potentiometers

2. 65PM motor and associate resisters, Limit Switches, Potentiometers

3. Electronic Cards with the Woodward card cage /rack

4. Generation Ramper Card

5. MW Filter

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5. Example drawing changes MCA Unit #3 drawings are presented here with the proposed changes as an example case.

212-H04-WD8204: The Relays 3AL, 65PV, 65SCB, 33TGLX which are inside the actuator cabinet will be removed and rewired into new RELECO relays on the new PLC back plane. New wires will be wired into the lower half termination area. 65SCR will be removed since fast return from Sync Condense will be implemented within the PLC.

212-H04-WD8205: The Relay 65DCO, which is inside the actuator cabinet will be removed and rewired into new RELECO relay on the new PLC back plane. New wires will be terminated into the lower half termination area. The pilot valve control coming from the old governor electronic rack will be removed and will be connected to the PLC Analog Out card through the ATE-36 power amplifier module mounted on the new back plane. This ATE-36 will convert the 4-20mA PLC output into +/-15VDC required by the pilot valve.

212-H04-WD8206: The Relay 65LGL, which is inside the actuator cabinet will be removed. The speed setter motor (15FM) and all the wiring associated with it will be removed including limit switches, motor speed control resistors and potentiometers. The 15FL and 15FR contacts will be wired to the new PLC backplane as speeder R/L discrete inputs. Gate Limit Motor (65GLM) and associated control will be retained. The spare potentiometers for gate limit and gate position will be wired to the PLC analog input card.

212-H04-WD8207: The Relays 52X and 65TSX inside the actuator cabinet will be removed. The power supply wires that feed 12VDC to SSA line driver and +-15VDC feeding speed switches will be removed. Primary and Standby 125VDC feeding the new PLC back plane will be taken from the same 125VDC power supply inputs (Primary from BB-47, 48 and Standby from BB-44, 45). This drawing will be replaced with a new drawing having the same drawing number in the next revision.

212-H04-WD8208: The relay 65EPF and 65MI will no longer be required and will be removed. 39C, 65SF, 14-1, 14-15, 14-25, 14-25, 14-85, 14-95, 12-105, 12-140, 12-150 which are inside the actuator cabinet will be removed and rewired into new RELECO relays on the new PLC back plane. New wires will be wired into the lower half termination area. This drawing will be replaced with a new drawing having the same drawing number as the next revision.

212-H04-WD8209: The Relays 65PL, 65PR, 65PM/LL and 65PM/RL which are inside the actuator cabinet will be removed. The power setter motor, 65PMand all the wiring associated with it will be removed including limit switches, motor speed control resistors and potentiometers. The connections of 65PL and 65PR will be routed to the PLC discrete input card for power setpoint raise lower inputs. This drawing will be replaced with a new drawing having the same drawing number in the next revision.

212-H04-WD8211: The line driver electronics and the speed sensor which are on the SSG will be removed. The cabling from SSG to actuator cabinet will be retained and re-used. New Zero Velocity Pick Ups (ZVPU) will be installed and will be wired into the

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High Speed Counter Card of the new PLC. All the analog electronic cards (Rotation telemetry, creep detection, Line receiver, speed switches, 65SS, 65AP, 65AI, and Power Amp) will be removed. PLC analog output will drive the new ATE-36 power amplifier to control the Pilot Valve. The LVDT position and Gate position will be wired into the PLC analog input card. PLC discrete output card will drive speed switches (14-xx, 12-xx), creep detection (39C) and speed fail (65SF). PLC discrete input card will read various relay commands needed for governor functions. This drawing will be replaced with a new drawing having the same drawing number as the next revision.

212-H04-WD8212: The Watt transducer inside the UCB will be replaced with a new one with 4-20mA output device and will be wired into the Analog input card of the PLC. Existing cabling between UCB and Actuator cabinet will be retained and re-used. New VT interface will be installed to read VT frequency and wired into the High Speed Card of the new PLC. Watt transducer Amplifire card, filter, Generation Ramper (65GR), Power setter motor (65PM) and associated resisters will be removed.

212-H04-D436: The 15F limit switch contacts used in Runback circuit of 15FL and 15FR will be removed since run back is implemented inside the PLC with 65DCO and 52X.

The 65PM limit switch contacts used in Runback circuit of 65PL and 65PR will be removed since run back is implemented inside the PLC. 65PL and 65PR relays will be removed as well. The connections where 65PL and 65PR relays were connected will be routed to PLC discrete input card as power setter raise/lower inputs.

6. New drawings Below new drawings show the PLC equipment.

212-H04-WD4200: Digital Governor Block Diagram

212-H04-WD8203: Governor Control Cabinet Backplane Layout

212-H04-WD8207 R4: Governor Control Cabinet 24VDC power supply (new) and Actuator Cabinet Lights existing

212-H04-WD8208 R5: Governor Control Cabinet PLC Discrete Outputs replacing old analog speed switches

212-H04-WD8209 R3: Governor Control Cabinet PLC Discrete Inputs replacing old governor set point Raise/ Lower and other inputs

212-H04-WD8210: New drawing showing Governor Control Cabinet PLC Analog Inputs and Outputs

212-H04-WD8211 R6: Governor Control Cabinet PLC High Speed Counter Inputs from VT and ZVPU sensors

212-H04-WD8220 R4: New drawing showing Governor Control Cabinet backplane Wiring Diagram (upper half) replacing old Woodward analog electronic cage

212-H04-WD8221 R7: New drawing showing Governor Control Cabinet backplane Wiring Diagram (lower half) replacing old Woodward analog electronic cage

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7. New replacement Panel Layout

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8. Appendices

• Simplified Block Diagram

• New Drawings

• Revised drawings

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Revision History R0 MCA report was formulated from REV report 2017-03-03

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woodward mod ii governor digital retrofit

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