Description

The EGB-P is an electrically controlled, proportional output actuator with an integral backup mechanical (centrifugal) governor. It is normally used with a Woodward integrating electric control unit to form a complete governing system.

When operating on the electrical side, the actuator terminal (output) shaft assumes a position in direct proportion to the magnitude of the electrical output signal from the electric control unit. The magnitude of the input signal to the actuator is determined by the position required of the fuel or steam control to maintain the desired prime mover speed under varying conditions of load.

Applications

EGB proportional actuators are normally used on units which must continue to operate, even if the electrical governor fails. The combination of an electrically powered actuator and a mechanical ballhead governor in the same unit provides an extra aspect of reliability for control systems which must provide emergency service.

Proportional actuators are also particularly suited for use with prime movers operating in tandem to drive a common mechanical load. In these applications, a single electric control can be used for two or more proportional actuators connected in series with the output of the electrical control unit. With each actuator receiving the same current signal, the output shafts will take the same angular position and direct the same amount of fuel or steam to each prime mover. Because the EGB has droop built into the mechanical governor section it can operate these tandem units should the electrical control signal fail for any reason.

Two Controls

The EGB-P governor/actuator (Figure 1-1) is, in effect, two controls in one; an electric actuator and a mechanical governor, each independently capable of positioning the output or terminal shaft.

During normal operation, the electric section controls fuel or steam to the prime mover. The mechanical governor controls the prime mover during starting and also functions as a backup governor to prevent runaway should the electric control system fail in such a manner to call for maximum fuel. The speed of the mechanical governor is set slightly higher than the electrical governor and should the speed of the controlled unit reach this level the mechanical governor will assume and maintain control of the prime mover.

An EGB-P unit operating with droop will have the mechanical side set about five percent higher than the electrical side. If the unit is not using droop, the mechanical side may be set only one or two percent higher than the electrical side.

With standard confirmation (direct acting), the EGB-P output servo will go to minimum position should the electric control signal fail to zero volts. The EGB-P may be installed with a “reverse acting” control which will call for maximum fuel should the electric signal fail to zero volts causing the continued operation of the controlled unit by the mechanical governor side starting when the engine speed increases to the speed setting of the mechanical control.

The operating element of the electric section of the actuator is an electro hydraulic transducer. The transducer consists of a solenoid attached to the pilot valve plunger controlling oil flow to and from the power piston (see Figure 4-1).

The solenoid responds to the output of an electric control unit and moves the pilot valve plunger up or down. Through connecting linkage the servo piston moves the terminal (output) shaft of the actuator. The engine or turbine fuel linkage attaches to the actuator shaft.

Specifications

All EGB proportional actuators and governors described in this manual operate in identical fashion.

EGB-10, 13, 35, and 50 models provide operating power through a terminal shaft located in the aluminum column. The work capacities are related to the amount of hydraulic pressure available to the power cylinder.

The EGB-29 and 58 models operate with a power cylinder which has its own terminal shaft as part of the power cylinder. The EGB-29 and 58 are identical except for the difference in internal hydraulic pressures.

EGB-10P 11 J / 8 ft-lb

EGB-13P 14.2 J / 10.5 ft-lb

EGB-35P 38 J / 28 ft-lb

EGB-50P 54 J / 40 ft-lb

EGB-29P 39 J / 29 ft-lb

EGB-58P 71 J / 52 ft-lb

Speed Setting Motor

The speed setting motor permits changes in the speed setting of the mechanical governor section to be made from a remote location. The motor is mounted externally on top of the actuator (see Figure 1-2) with its output shaft connected to the manual speed adjusting screw through a friction clutch. The clutch allows speed setting changes to be made either remotely, via the speed setting motor, or at the actuator, via the manual speed setting control knob. Two limit switches can be provided when the speed setting motor is used. The switches are actuated by the dial stops on the manual speed adjusting mechanism and may be connected to limit the speed setting motor travel at the desired minimum or maximum speeds or to provide a remote visual indication when the minimum or maximum speed setting has been attained. The motor is of the split field, series wound, reversible type and is available for use with all standard voltages. Refer to Woodward manual 03505, Speed Adjusting Synchronizing Motor, for maintenance and parts information.

Shutdown Solenoid

The shutdown solenoid can be used for normal shutdown and/or as a backup to the safety shutdown system. The engine, turbine, or other type of prime mover should be equipped with safety systems entirely separate from the governor. However, the safety system may be interfaced with the shutdown solenoid to cause the governor or actuator to go to minimum during safety systems shutdown. As with all safety shutdowns, proper operation should be confirmed periodically. See the prime mover manufacturer’s instructions.

The solenoid is mounted internally within the actuator column (see Figure 1-3). It is connected, via tubing and internal passageways, to the upper side of the dashpot land on the relay valve plunger in the hydraulic amplifier section of the actuator. When the solenoid is energized, oil pressure on the upper side of the dashpot land is dumped. This allows the oil pressure acting on the under side of the dashpot land to raise the relay valve plunger which, in turn, dumps the trapped oil under the power piston. The oil pressure acting on top of the power piston then forces the piston to move to the minimum fuel position. (Reference Figure 4-2 Schematic View of Relay Valve Plunger and Shutdown Solenoid.)

Pneumatic Starting Device

The pneumatic starting device is used in applications where the electric control unit is unable to provide a signal to the actuator for starting the prime mover. This would be the case in installations where the electric control unit is dependent upon a frequency signal or upon the generator being driven for its power and thus would not emit a signal until the generator was excited. The starting device is a simple air operated plunger with spring return which is used to push the electric actuator pilot valve downward. The oil pressure generated at cranking speed will then cause the actuator output shaft to move in the increase direction so the prime mover can be started. The device is mounted on the actuator cover directly over the electric actuator pilot valve (see Figure 1-4) and is designed for use with air pressures in a range of 690 kPa to 1.7 MPa (100 to 240 psi). A starting device is not needed on reverse acting units.

Manual Starting Device

Installations which lack an electric or air pressure signal when the prime mover, which is controlled by the governor is not running, can be fitted with a simple Manual Starting Device. The starting device is a plunger with a spring return mounted in the governor/actuator cover directly over the actuator pilot valve plunger. When the starting plunger is pushed down on the actuator pilot valve plunger the oil pressure generated at cranking speed will cause the terminal shaft to move in the increase direction so the prime mover can be started under control of the mechanical governor side of the EGB-P. A starting device is not needed on reverse acting units.

Installation

Locating Actuator

Refer to Figure 2-2, 2-3, or 2-5 for complete physical dimensions of the actuator. Adequate clearance must be provided for installation and removal and for access to the drain cock and oil filler cup.

Take particular care to mount the actuator squarely in respect to the prime mover accessory drive pad and to the interconnecting linkage from the fuel or steam control. A gasket should be used between the actuator base and drive pad.

If the governor/actuator has a splined drive shaft, make certain the actuator shaft slips into the prime mover accessory drive coupling freely enough to drop into place of its own weight.

If a keyed type actuator drive shaft is used, the gear placed on the shaft must be checked for proper backlash with its mating drive gear. There should be neither excessive backlash nor binding. Vibration or other irregularities, caused by uneven gear teeth, shaft run-out, etc., when transmitted to the actuator will adversely affect actuator operation and result in erratic governing.

EGB-10, 13, 35, and 50

The linkage between the actuator output shaft and fuel or steam control should be adjusted to use a minimum of 30 degrees (2/3 of the 45 degrees of travel available) of the actuator output shaft travel from the rated speed, no-load position, to the rated speed, full-load, position. Adjustment of the fuel linkage must provide for the control of fuel from “OFF” to “FULL FUEL” within the limits of the actuator output travel.

Recommendations for linkage from the prime mover manufacturer should be used when available.

EGB-29 and 58

The linkage between the actuator output shaft and fuel or steam control should be adjusted to use a minimum of 20 degrees (2/3 of the 30 degrees of travel available) of the actuator output shaft travel from the rated speed, no-load position, to the rated speed, full-load, position. Adjustment of the fuel linkage must provide for the control of fuel from “OFF” to “FULL FUEL” within the limits of the actuator output travel.

Recommendations for linkage from the prime mover manufacturer should be used when available.