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The original rotating uninterruptable power system (UPS) consisted of old relay logic for the sequencing which often failed when testing, providing an inconsistent and unreliable emergency backup. GCS custom designed a digital Woodward control system to replace the vintage equipment.

  • Fertilizer plant that produces an isolated critical power from a 300hp Motor driving 6 ton flywheel and 150kW alternator.
  • A Detroit Diesel Series 71 V12 engine running at 1800 rpm rated is the backup power source for the rotating UPS
  • Ignition System: Caterpillar EIS 4160 V, 850 kW, 60 Hz@ 1200 rpm
Woodward Atlas-II Digital Control Woodward EG3P Actuation Basler DECS - 100
Controls all sequencing for the start/stop of the rotating UPS, protection monitoring, flywheel energy conservation during transfer to engine power. Advanced fault detection preempting loss of bus and improving the preventative maintenance process. Throttle Bodies with Integrated Electric Actuators
On-Board Drivers
Automatic voltage regulator (AVR) provides better control of bus voltage even during lo ad transients.
Schneider-Electric breakers HMI / SCADA System
Breakers for the alternator and bypass breakers. A special motor breaker to control the motor power. Touch-screen terminal in the engine room for control,monitoring, alarming, trending and event logging.

The normal running of the rotating UPS is to have the electric motor supplying the power to turn a 6 ton flywheel and an a lternator. The critical bus is then supplied by the alternator effectively isolating this bus from the main utility. Should the utility power fail the motor breaker will be opened and the energy in the flywheel will continue to rotate the alternator keepin g the critical bus alive. During this time the diesel engine is started and clutched in to the UPS shaft to take over supplying the rotational power and bring the frequency and voltage back to rated.

A third breaker exists in the system that is used to b ypass the rotating UPS so that maintenance can be carried out if necessary.

The Woodward Atlas - II controls the sequencing of the breakers, start/stop logic for the motor and the engine, and protection relay functionality for the motor and alternator. In a utomatic mode the systems primary goal is to maintain the health of the critical power bus


Prior to installing the new E3 system, the operators had to manually throttle the fuel back with hand valves in the fuel lines and constantly nurse the fuel to the engines until they started. Even then, the process was never consistent from one start to another.


In a generator application, the E3 Control System can be operated in two different closed-loop modes: UEGO Closed Loop or Gas Quality Closed Loop (GQCL).

UEGO Closed Loop utilizes a traditional oxygen sensor in the engine exhaust. The drawback to this mode of operation is the requirement for an oxygen sensor installed in the engine exhaust to be used in the system at all times. Since standard oxygen sensors on the market are designed for automotive-style gasoline engines, not gas engines, both the accuracy and lifetime of traditional sensors in operation on industrial gas engines are typically issues.

Gas Quality Closed Loop (GQCL) is a mode of operation that is built into every Woodward E3 control. This allows the engine to run closed loop not on an oxygen sensor, but on kW load from the generator.

GQCL Block Diagram


Gas Quality Closed Loop mode uses the measured generator power (kWe), manifold pressure (MAP), and manifold temperature (MAT) signals to infer changes in gas quality.
The main advantages of this mode of operation over UEGO closed loop are:

1. The oxygen sensor is not required for normal operation. The oxygen sensor is used only for initial setup and commissioning of the system and is no longer required. This eliminates costly replacement of sensors over the lifetime of the system and the dependence on unreliable devices.

2. The system can compensate for larger changes in gas quality. GQCL mode results in better overall performance due to the engine being able to more accurately control the air-fuel ratio over larger swings in gas quality.

GQCL operation is based on algorithms that are exclusive to Woodward. The only required addition to the system is a kW load feedback signal into the E3 control. In the case of this project, the existing 2301 D contained kW load measuring functionality. An analog output proportional to generator load was programmed and sent to the E3 control to enable the use of GQCL.


The Caterpillar G3500A Series engines were commonly supplied from the factory with Woodward EG3P hydraulic actuators and 2301A speed controls. Although this system was and still is widely used, it does present a few problems. First, the actuator itself is dependent on a clean engine oil supply for its internal pump to function. Second, the original engine design from Caterpillar includes an inconvenient linkage design between the actuator and throttle body that has multiple pivot points and long linkage rods. Each joint introduces another opportunity for shaft play which results in unstable control. In recent years, the Caterpillar factory has changed this throttle actuator design on certain G3500A series engines as a result of these issues. GCS has designed an actuation package that replicates this new factory engine design utilizing the Woodward ProAct ISC actuator.

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