Governor Services 

  Mechanical Cabinet Conversions
Digital Conversion – Mechanical Cabinet Governor

Our scope of supply typically includes equipment, engineering and site supervision. Each system is engineered to the specific requirements of the plant.

Control hardware includes a PLC-based digital control cabinet with touchscreen local operator interface, pilot valve electro-hydraulic interface manifold(s), and electronic speed and servomotor position sensors. The existing low pressure oil system is usually retained.

Installation can be done by your crew, or we can provide complete turn-key services. During the outage, an experienced Field Service Engineer will be on hand to assist with installation and provide final commissioning and testing services. Click any component below for more details.

PLC Governor System
The heart of each new governor system will be an Allen-Bradley™ Programmable Logic Controller (PLC).

The PLC will be mounted in a NEMA 12 cabinet that includes:

Local Control Switches and Meters
The following devices can be mounted on the door of each cabinet to provide a backup Local Operator Interface. This list can be customized to suit your preferences.

Local Operator Interface: Color Touchscreen
A 6” color touchscreen is proposed to serve as the Local Operator Interface. The touchscreen will be mounted on the control cabinet door and will communicate with the PLC governor system. An Emergency Stop push button will also be provided.

The touchscreen computer operates independently and automatically establishes communication with the PLC upon boot-up; no operator intervention is required. System screens are stored in non-volatile memory.
The basic screens described below will be provided by AGC. Touchscreen software can be provided to allow site staff to modify or add new screens.

The system will have the following capabilities:

Primary Speed Sensing – PT Interface
Primary speed sensing will be done via an American Governor Speed Signal Module connected to a generator Potential Transformer (PT). Our high-resolution Speed Signal Module provides one 0-200% analog output for metering and one high-resolution analog output for synchronizing and on-line droop control.

The module is compliant with IEEE 125 “IEEE Recommended Practice for Preparation of Equipment Specifications for Speed-Governing of Hydraulic Turbines Intended to Drive Electric Generators.”

Back-up Speed Sensing
Redundant speed sensing offers enhanced reliability by backing up the primary PT speed signal with an independent speed signal from a new Zero Velocity Pick-Up (ZVPU) mounted on the generator. This high-resolution pick-up detects the rotation speed of a toothed wheel (provided by others) that is mounted on the generator shaft.

The ZVPU can reliably detect rotational speed down to 0.0 rpm and is thus ideally suited for brake actuation and creep detection, if required. The governor can use either signal under normal operation, and software will be provided in the Governor PLC to detect failure of either the Primary or Back-up speed signal, which will generate an alarm.

Loss of both signals will result in Emergency Shutdown of the unit.

Cabinet Power Supply
A 125VDC/24VDC cabinet power supply will be provided to power the proportional valve, accessory equipment and field devices.

Electro-Hydraulic Interface (EHI) Assembly
The EHI assembly is the basic connection between the PLC Governor and the existing distributing valve. The EHI controls the flow of oil to the distributing valve, which regulates the flow of oil to the servomotor to open or close the wicket gates.

The assembly includes the following devices:

Proportional Control Valve
Enables servomotor control via PLC during normal operation. This high-response valve provides closed-loop control of distributing valve spool position.

Solenoid Shutdown Valve
Enables emergency shutdown independent of the PLC. When de-energized, the solenoid valve causes the distributing valve spool to move fully in the close direction, causing the servomotor to close at the fastest rate allowed by the stop nuts.

Hydraulic Manifold
A custom manifold for the mounting of valves. Includes shutdown shuttle assembly for independent shutdown via solenoid valve (blocks control flow from proportional valve).
Redundant EHI assemblies are available for customers seeking enhanced reliability. This arrangement enables the plant to keep running in the event of a failure in the proportional valve. Algorithms in the PLC system detect this failure and automatically switch to the other valve. Fully redundant configurations are also available that are controlled by separate PLC systems.

Filter Assembly
A single or dual filter assembly will be provided and is required to meet the recommended oil cleanliness specifications for the new EHI control valves. The assembly will have a 10-micron filter element and will include a high differential pressure (DP) indicator. The dual filter assembly features a manual changeover valve to permit filter replacement during operation.

Distributing Valve Position Feedback (LVDT)
The EHI requires an accurate and stable distributing valve position signal in order to function closed-loop. A Linear Variable Differential Transformer (LVDT) will be provided for relay valve feedback. Mounting hardware, signal conditioner and connector will be included and redundant configurations are available.

Software within the PLC selects the most appropriate signal to use, and generates an alarm upon failure of either signal.

Servomotor Position Feedback (MLDT)
The Magnetostrictive Linear Displacement Transducer (MLDT) is a superior non-contacting device that is mounted directly on the servomotor to provide electronic feedback of servomotor position. Mounting hardware and connector will be included and redundant configurations are available.

Software within the PLC selects the most appropriate signal to use, and generates an alarm upon failure of either signal.

Assemble, Wire & Test
American Governor will wire the complete PLC Governor system in Ivyland, PA or Amherst, WI. Your system will be connected to our Turbine Simulator, which will be programmed to mimic site conditions. All hardware and software will be tested completely before leaving our factory.

PLC Control Software
American Governor will provide custom governor control software adapted from proven software algorithms. Control functionality can include some or all of the following: