2301A SPEED CONTROL Caterpillar


Installation And Operation

Usage:

Chapter 3. Operation and Adjustment

Initial Pre-Start Settings

------ WARNING! ------

WARNING-OVERSPEED

Overspeed with resultant equipment damage, personal injury, or death is possible when setting up a control system. Read this entire procedure before starting the prime mover for the first time.

--------WARNING!------

------ WARNING! ------

CAUTION-DO NOT TURN POTS BEYOND THEIR STOPS

The Rated Speed Potentiometer is the only multi-turn pot in this control. All other pots are single-turn. Take care not to turn these pots beyond their stops.

--------WARNING!------
1. RATED SPEED
a. Set the RATED SPEED potentiometer to minimum (fully counterclockwise in ten-turn potentiometer).
b. Set the external SPEED TRIM, if used, to mid-position.
2. RESET- Set at mid-position. (One-turn potentiometer).
3. GAIN- Set at mid-position. (One-turn potentiometer).
4. RAMP TIME- Set at minimum (fully ccw, one-turn potentiometer- be careful not to overtorque the pot ).
5. LOW IDLE SPEED- Set at minimum (fully ccw, one-turn potentiometer- be careful not to overtorque the pot ).
6. DROOP- Set optional external droop (if used) at minimum (fully counterclockwise, one-turn potentiometer- be careful not to overtorque the pot ).
7. ACTUATOR COMPENSATION (One-turn potentiometer)
a. DIESEL, GAS TURBINE, FUEL-INJECTED GASOLINE PRIME MOVERS: Set the ACTUATOR COMPENSATION potentiometer at 2 on the 0 to 10 scale.
b. CARBURETED GAS OR GASOLINE or STEAM TURBINE PRIME MOVERS: Set the ACTUATOR COMPENSATION potentiometer at 6 on the 0 to 10 scale.
8. START FUEL LIMIT- Set at maximum (fully cw one-turn potentiometer- be careful not to overtorque the pot ).
9. Be sure the actuator is connected to terminals 9 (+) and 10 (-).

Start-up Adjustments

1. Complete the installation checkout procedure in Chapter 2, and the initial prestart settings above.
2. Close the Close for Rated contact. If the external droop feature is being used it should already be set at isochronous, fully ccw be careful not to overtorque the pot).

NOTE: This is for initial prime mover start-up only. For normal start-up, the Close for Rated contact should be open if the prime mover is to start at idle.

3. Apply input power to the control.
4. Preset rated speed.

If a signal generator is not used, set the RATED SPEED potentiometer at minimum (fully counterclockwise).

If a signal is not used set the signal for the frequency of the speed sensor at rated speed, and connect it to terminals 7 and 8. (The rated speed frequency in Hz equals the rated engine speed in RPM times the number of teeth on the speed sensing gear, times the ratio of engine speed to speed-sensing-gear speed, divided by 60.) Put the Close For Rated contact in rated (closed) position set the speed trim potentiometer (if used) to mid position. Connect a dc analog voltmeter to terminals 9 (+) and 10 (-) to read actuator voltage.

If the actuator voltage is at minimum (about 0 volts) slowly turn the RATED SPEED potentiometer clockwise (counterclockwise for reverse acting controls) until the voltage just begins to move toward maximum.

If the actuator voltage is at maximum, slowly turn the RATED SPEED potentiometer counterclockwise (clockwise for reverse acting controls) until the voltage just begins to move toward minimum.

Continue to very slowly adjust the RATED SPEED potentiometer in the appropriate direction, trying to stop the actuator voltage between the minimum and maximum voltages. Because it is not possible to stop the motion, cease adjusting when the voltage changes very slowly. The RATED SPEED potentiometer is now set very close to the desired speed. A slight adjustment when the engine is running will achieve the exact speed.

5. Check the speed sensor.

Minimum voltage required from the speed sensor to operate the electronic controls is 1.0 Vrms, measures at cranking speed or at the lowest controlling speed. For this test, measure the voltage while cranking, with the speed sensor connected to the control. Before cranking, be sure to prevent the prime mover from starting. At 5% of the lower value of the control's speed range, the failed speed sensing circuit is cleared. For example 100 Hz is required on the 2000 to 6000 Hz speed range (2000 Hz x .05 = 100 Hz).

------ WARNING! ------

WARNING-START-UP

Be prepared to make an emergency shutdown when starting the engine, turbine, or other type of prime mover, to protect against runaway or overspeed with possible personal injury, loss of life, or property damage.

--------WARNING!------

Adjust for Stable Operation

If prime-mover operation is stable, go to the "Speed Setting Adjustment" procedure.

If the prime-mover is hunting at a rapid rate, slowly decrease the gain (turn the potentiometer counterclockwise) until performance is stable. Adjusting the gain may cause a momentary speed change which can be minimized by turning the gain potentiometer slowly.

If the prime-mover is hunting at a slow rate, slowly increase the RESET setting (turn the potentiometer clockwise) until the prime-mover stabilizes. If increasing the RESET potentiometer setting does not stabilize the prime mover, it also may be necessary to either:

* Slowly decrease the Gain (turn the potentiometer counterclockwise) or
* Slowly decrease the Gain and increase the ACTUATOR COMPENSATION.

Speed Setting Adjustment

With the prime mover operating stably, and the external speed trim potentiometer (if used) set at mid-position, adjust the RATED SPEED potentiometer to bring the prime mover to the desired operating speed.

Dynamic Adjustment

The object of the GAIN AND RESET potentiometer adjustments is to obtain the optimum, or desired, stable, prime-mover-speed response.

NOTE: Adjusting the GAIN may cause momentary changes in speed which can be minimized by turning the GAIN potentiometer slowly.

Increasing the setting of the GAIN potentiometer provides faster transient response (decreases the magnitude of the speed change from a sudden change in load). To achieve optimum response, slowly increase the GAIN (turn the potentiometer clockwise) until the actuator becomes slightly unstable, then slowly turn the Gain back counterclockwise as necessary stabilize the actuator. Step load the generator, or bump the actuator terminal shaft, to make sure that the prime mover returns to the proper speed with little overshoot or undershoot of the speed setting. To reduce overshoot, increase the RESET setting (turn the potentiometer clockwise).

When the RESET potentiometer is in the lower part of its adjustment (0 to 3 on the scale), increasing the RESET clockwise may require decreasing the GAIN (turn the GAIN potentiometer counterclockwise) to maintain stable operation.

If the prime mover is slow in returning the proper speed, decrease the RESET by turning the potentiometer counterclockwise.

Figure 3-1 illustrates prime mover starts with the RAMP TIME potentiometer fully counterclockwise (no ramp- be careful not to overtorque the pot), step loadings at four different RESET potentiometer settings, and stable, steady-state running conditions. These are typical performance curves on a naturally aspirated (non-turbocharged) diesel engine.

NOTE: Optimum performance is not necessarily obtained with the GAIN potentiometer at the maximum stable clockwise position. In some cases, the gain must be reduced slightly to ensure stability under widely varying conditions.

Actuator Compensation Adjustment

If the ACTUATOR COMPENSATION is set as described under INITIAL PRESTART SETTINGS, no further adjustment is normally required. If a slow periodic instability remains, slightly increase the ACTUATOR COMPENSATION (turn the potentiometer clockwise), and repeat the GAIN and RESET adjustments. Continue to increase the ACTUATOR COMPENSATION and readjust the GAIN and RESET until stability is achieved.

If a fast instability or extremely active actuator is evident, slightly decrease the ACTUATOR COMPENSATION (turn the potentiometer counterclockwise). If necessary the ACTUATOR COMPENSATION may be set fully counterclockwise ( be careful not to overtorque the pot). This may be required when engine torsionals cause excessive fuel-linkage movement.

Low Idle Speed Adjustment

1. The prime mover should be at a rated speed with the LOW IDLE SPEED potentiometer set at maximum (fully clockwise ( be careful not to overtorque the pot). Open the external CLOSE FOR RATED contact.
2. Decrease the LOW IDLE SPEED (turn the potentiometer counterclockwise) until the recommended idle speed is reached.

If the RATED SPEED setting is changed, LOW IDLE SPEED will also be changed and may require readjustment. Changing the LOW IDLE SPEED does not change the RATED SPEED setting.

NOTE: Make certain that the prime-mover speed is controlled by the LOW IDLE SPEED potentiometer in a range above the minimum-fuel position (mechanical stop) of the actuator or prime-mover fuel rack.

Ramp Time Adjustment

Adjust the RAMP TIME potentiometer to achieve satisfactory prime mover acceleration to rated speed with minimum overshoot. First start at the fully clockwise (maximum ramp time- be careful not to overtorque the pot position and work back in the counterclockwise direction until the unit ramps as rapidly as desired. Ramp time will be adjustable from 1 to 22 seconds from idle to rated.


Figure 3-1. Diesel Engine Performance Curve

Start Fuel Limit Adjustment

NOTE: Start-fuel limit is not recommended for use with reverse-acting controls. With loss of speed signal, the reverse acting control will position the actuator at the start-fuel level if the failed-speed-signal override is activated. Reverse-acting systems normally require the control to demand full fuel on loss of speed signal to allow the mechanical backup governor to control the system. The Start Fuel Limit can be deactivated by turning the potentiometer fully clockwise ( be careful not to overtorque the pot).

With the prime mover operating at rated speed and no load, record the voltage across the actuator terminals 9 (+) and 10 (-). Shut down the prime mover and activate the Failed Speed Signal Override by closing the override contact. The voltage to the actuator should now be adjustable by the START FUEL LIMIT potentiometer. Set the actuator voltage about 30% higher than the voltage obtained at rated speed for forward-acting controls and 30% lower than rated speed voltage for reverse-acting controls. Remove the Failed Speed Signal Override contact if not required to start the prime mover.

Start the prime mover and observe the start time, overshoot of speed setting, and exhaust smoke obtained. If the prime mover does not start, turn the START FUEL LIMIT potentiometer slightly clockwise until the prime mover starts. The START FUEL LIMIT may be adjusted as required to optimize the prime-mover starting characteristics. The fuel-limiting function us turned off automatically when the speed control takes over.

NOTE: For prime movers not requiring start-fuel limiting, the START FUEL LIMIT function can be deactivated by turning the potentiometer fully clockwise ( be careful not to overtorque the pot).

Speed Sensor Check

If the sensor is a magnetic pickup, measure the voltage across terminals 7 and 8 to be sure there is a minimum of 1.0 volts at cranking speed, and a maximum of 30Vrms at rated speed. If the voltage exceeds 30 volts, increase the gap of the speed sensor, and be sure that there is still a minimum of 1.0 volts at cranking speed.

Droop Adjustment

The amount of droop is not critical in many installations. If the engine needs to run in droop but the amount is not critical set the droop potentiometer in mid-position, then adjust load with the speed-setting potentiometer.

When paralleled with an infinite bus, the generator frequency cannot change, and unless a load-sensing module is being used, the control must be in droop to maintain stable operation. With the droop potentiometer at mid-position, parallel the generator, then increase the Rated Speed potentiometer until the desired amount of load on the engine achieve.

Too much droop will cause the engine to overspeed should the load be suddenly lost. Excessive droop will also cause the engine to be sluggish in response to load changes.

Too little droop will cause instability, similar to that experienced with improperly adjusted GAIN and RESET.

Units running against an isolated bus often need droop set to a particular level, to prevent excessive off speed when load changes. Droop is usually expressed as a percentage and calculated by the following formula:

To set a specified amount of droop using an isolated bus for the load:

1. Set the droop potentiometer to mid-position. (Use a 2K potentiometer, connected to terminal 14 (cw), 13 (wiper), and 15 (ccw).
2.

NOTE: Start the prime mover and adjust the RATED SPEED potentiometer for rated speed with no load.

3. Apply full load.*
4. Adjust the droop potentiometers to give desired speed.


Figure 3-2. Droop Adjustment

5. Remove the load and repeat steps 2 through 4 until engine speed returns to 60Hz when the load is removed.

Example: Operating at 60Hz, 57 Hz at full load indicates 5% droop.

*-If only 50% loading is possible, 58.5 Hz would indicate 5% droop. See Figure 3-3.

To set a specified amount of droop on an infinite bus load:

1. With the generator not paralleled, adjust the RATED SPEED (or speed trim) potentiometer to give a speed above 60 Hz by the percentage of droop required.

Example: Droop of 5% would require raising the speed to 62 Hz.

2. Mark the potentiometer position and re-adjust the RATED SPEED (or speed trim) potentiometer for 60 Hz.
3. Turn the external droop potentiometer full cw for maximum droop.
4. Synchronize the generator with the bus and close the tie-breaker.


Figure 3-3. Droop Base Load with 5% Droop

5. Return the RATED SPEED potentiometer to the mark made in step 2.
6. Load the generator by turning the droop potentiometer counterclockwise until full load is achieved.
7. Unload the generator by turning the RATED SPEED (or Speed Trim) potentiometer ccw until no load is achieved.
8. Open the tie-breaker and repeat steps 1 through 6 until no further adjustment of the external droop is required in step 6.

NOTE:

* Droop is 10% per volt.
* Auxiliary is 3% per volt.
* Synchronizer Input is 0.667 of 1% per volt.
* Speed Trim is 10% per volt.

Chapter 4. Description of Operation

Introduction

The 2301A Speed Control monitors prime-mover speed and maintains it at the correct operating level. With the addition of a load sensor the system will share the load with other generators when two or more systems are running in parallel.

Speed Control

The system, as shown in Figure 4-1, consists of:

* A magnetic pickup (MPU), to sense the speed of prime mover.
* A frequency to voltage converter, to convert MPU frequency to a voltage for use in the 2301A internal circuits.
* A speed reference to which the prime mover speed is compared. (Idle and Rated speed references are provided by the 2301A Speed Control. The speed reference being used is selected by the operator with an external switch.)
* A speed summer/amplifier with an output proportional to the amount of fuel or steam required to maintain the reference speed at any given load
* An actuator to position the fuel or steam mechanism (injector rack or steam valve) of the prime mover.


Figure 4-1. Speed Control System

The MPU generates an ac signal with a frequency proportional to prime-mover speed.

The frequency-to-voltage converter receives the MPU frequency signal and changes it to proportional dc voltage.

The speed-reference circuit generates a dc reference voltage to which the speed signal voltage is compared.

The speed-signal voltage is compared to the reference voltage at the summing point. If the speed-signal voltage is lower or higher than the reference voltage, a signal is sent by the control amplifier calling for an increase or decrease in speed. The actuator is controlled by this signal, repositioning the fuel valve or rack until the speed-signal voltage and the reference voltage are equal.

Auxiliary Inputs

Terminals 11 through 17 are used for auxiliary inputs which change the reference voltage and thus the output of the speed control. These inputs include speed trim, droop, SPM synchronizer, and the auxiliary input, (usually from a load sensor and parallel lines).

Failed Speed Signal Circuit

A failed-speed-signal circuit monitors the speed-signal input. When no signal is detected, it calls for minimum fuel. The minimum-fuel signal is sufficient to cause the actuator to go to the minimum position. Incorrect linkage adjustments or other restrictions in the external system may prevent prime-mover shutdown.

For controls with actuator current of 20 to 160 mA, minimum fuel is defined as:
* Actuator current of less than 10 mA for forward-acting controls.
* Actuator current greater than 180 mA for reverse-acting controls.
For controls with actuator current of 40 to 320 mA, minimum fuel is defined as:
* Actuator current of less than 20 mA for forward-acting controls.
* Actuator current greater than 360 mA for reverse-acting controls.

A contact to override the failed-speed-signal circuit can be connected in series with terminal 4 and low voltage dc power. ( This power is available on terminal 2 for units supplied with 10 to 40 Vdc power and from terminal 6 on those units supplied with about 120 Vac or dc power. Temporarily closing the contact overrides the failed-speed-signal circuit as required for start-up.

The control must be to each system for optimum performance. The potentiometers for setting and adjusting these circuits are located in the upper right corner of the control as shown in Figure 4-2. They include:


Figure 4-2. Speed Control Adjustments

* The RATED SPEED potentiometer, adjusted so the converter-speed voltage and the reference-speed voltage are equal at the desired operating speed.
* The LOW IDLE potentiometer, adjusted so the converter-speed voltage is correct for the desired idle speed.
* The START FUEL LIMIT potentiometer to provide a means of limiting the full-rack position when starting diesel engines. Adjustment of the potentiometer sets the maximum actuator position from no speed until the speed control calls for a fuel setting lower than the of the start-fuel limit. The limit is automatically placed in the circuit whenever the speed monitor input declines below the Failed Speed Signal level. Setting the Start Fuel Limit potentiometer full cw will raise the limit above the maximum fuel position, making the limit non-effective.
* RESET, GAIN and ACTUATOR COMPENSATION potentiometers adjust the control amplifier to accommodate various types of prime-movers. Reset adjustment affects reaction time when recovering after a sudden load change. The magnitude of the speed change resulting from a sudden change in load is controlled by adjusting the Gain potentiometer. Actuator Compensation compensates for the time the actuator and the prime-mover system take to react to signals from the control.
* The RAMP TIME potentiometer sets the time required for the prime-mover to accelerate from ideal to rated speed.

NOTE: Droop and Speed Trim settings change at 10% of the existing reference per volt. The Auxiliary input causes a 3% speed change per volt. The Synchronizer input causes a 0.666% change of reference speed per volt.

Actuator Circuit Protection

The speed control is protected from shorts or overloads in the actuator circuit at terminals 9 and 10 by an automatic circuit breaker. The circuit breaker will reset automatically after the short or overload is corrected and the control has a few minutes to cool down.

Reverse Acting Controls

The reverse-acting 2301A Speed Control and its actuator are designed so that zero voltage to the actuator correspond to maximum fuel to the prime mover. The actuator usually used with a reverse-acting control has a mechanical governing mechanism included (see Figure 4-3). The speed setting of this mechanical governor is slightly higher than the speed setting of the 2301A. Should the electronics fail, the actuator will try to go to a maximum fuel but will be stopped when it gets to the speed setting of the mechanical governor, providing continued operation of the prime mover, although at a speed which is slightly higher than the electronic control speed reference.


Figure 4-3. Reversing Acting System

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