Loading of the Generator
When a generator is installed or reconnected, be sure that the total current in one phase does not exceed the nameplate rating. Each phase should carry the same load. Carrying the same load allows the engine to work at the rated capacity. An electrical unbalance can result in an electrical overload and overheating if one phase current exceeds the nameplate amperage.
Allowable combinations of unbalanced loads are shown in Illustration 1. When you operate with significant single-phase loads, the combinations of single-phase load and three-phase load may be used. Such combinations should be located below the line on the graph.
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| Illustration 1 | g00627416 |
Allowable Combinations of Unbalanced Loads | |
Block Loading and Transient Capability
The block loading capability (transient response) of a generator set powered by a gas engine is less than a diesel engine. Most of this difference is directly attributed to the inherently different fuel systems of the two engines. When the governor calls for more power, a diesel engine reacts by adding fuel directly into the cylinder. This method permits the diesel engine to accept 100% block loads with acceptable voltage dips and frequency changes. When the governor on a gas engine calls for more power, the throttle opens. Opening the throttle causes a larger flow of the air/fuel mixture to move through the aftercooler core, the air intake manifold, and into the cylinder. This time delay reduces the gas engine capability for accepting large block loads.
If a block load derating is required, refer to ISO 8268 Standards or SAE J1349 Standards. Also, reference Engine Data Sheet, LEKX4066, "Loading Transient Response" and Engine Data Sheet, LEKX4067, "Block and Transient Response".
Power Factor
The power factor represents the efficiency of the load. The power factor is the ratio of apparent power to total power. This ratio is expressed as a decimal. The power factor represents the portion of the current which is doing useful work. The portion of current which is not doing useful work is absorbed in maintaining the magnetic field in motors. This current is called the reactive load. Engine power is not required to maintain the reactive load.
In most applications, the power factor of the system is determined by these components: electric motors, controls and transformers. Induction motors usually have a power factor that is no larger than 0.8. Incandescent lighting is a resistive load of about 1.0 power factor, or unity. Controls can operate at any power factor. Drivers that have variable frequency or variable speed can operate at any power factor. An uninterruptible power supply can operate at any power factor. In this case, the power factor can be between 0.4 and 1.0.
The power factor of a system may be measured with a power factor meter or determined by calculations. Determine the power requirement in kW by multiplying the power factor by the kVA that is supplied to the system. As the power factor increases, the total current that is supplied to a constant power demand will decrease. With equal loads, a lower power factor will draw more current. A high-power factor will result in full engine load that is less than the generator rated amperage. A lower power factor increases the possibility of overloading the generator.
Note: Normally, Cat generators are designed for a lagging power factor of 0.8. If operation at less than 0.7 lagging power factor is desired, consult your Cat dealer in order to check the rating of the generator.
Excitation Systems
Permanent Magnet Pilot Excited Generators
Permanent Magnet Pilot Excited (PMPE) generators receive power for the voltage regulator from a pilot exciter, rather than the main armature. The pilot exciter consists of a permanent magnet rotor and a stator. The pilot exciter operates independently from the generator output voltage. Constant excitation during a large load application is possible since irregularities in the output voltage are not fed back into the system. Such irregularities can be caused by load conditions. The independent operation also allows the generator to sustain an overload for a short duration.
Low Idle Adjustment
Typically, the low idle on 3500B generator sets is 1200 rpm. There is no low idle stop on generator sets with electronic governors. The low idle is set at the factory on generator sets that have mechanical governors. The low idle is also set at the factory on generator sets that run on natural gas. The low idle should only be adjusted by your Caterpillar dealer if adjustment is required.
Note: Operating the electric set at low idle speed for an extended time will cause some voltage regulators to shut off. The electric set must be completely shut down. Then, the electric set must be restarted. This procedure will allow the voltage regulator to produce an output.
Auto Start/Stop
Most standby units are automatic. Without an operator in attendance, standby units will perform the following functions: start, pick up the load, run and stop.
Standby units will not change the governor speed control or the settings of the voltage level automatically. The governor speed and voltage level must be preset for the proper operation of that unit. Whenever the generator set is operated manually, ensure that the governor speed and the settings of the voltage level are set correctly for automatic operation. Check all switches for the proper setting. The Start Selector Switch should be in the AUTOMATIC position. Emergency Stop Switches should be in RUN position.
Options For the Generator
Space Heaters
Most of the SR4B generators are provided with space heaters. These space heaters are installed for operation in all climates. The space heaters are especially for use in high humidity conditions. For more information on space heaters, refer to Maintenance Section, "Space Heater - Check".
Embedded Temperature Detectors
SR4B generators are available with embedded temperature detectors. The detectors are installed in the slots of the main armature. The main armature is also called a stator. The detectors are used with the equipment that is provided by the customer. Thus, the temperature of the main armature winding can be measured or monitored. Two types of temperature detectors are available: RTD and thermocouple. Consult with your Cat dealer for more information.
Bearing Temperature Detectors
Detectors for the bearing temperature are available on generators with large frames. These detectors measure the temperature of the main bearing. Thus, the temperature of the bearing can be measured or monitored. Bearing temperature measurements may help to prevent premature bearing failure. Two types of temperature detectors are available. These detectors are used with equipment that is provided by the customer. Consult with your Cat dealer for more information.