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, thus allowing 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 |
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Allowable Combinations of Unbalanced Loads | |
The block loading is the instantaneous application of an electrical load to a generator set. This load may be anywhere from a moderate percentage of the rated load up to the rated load.
The block loading capability of a generator set depends on the following factors.
- Engine transient response
- Voltage regulator response
- Type of the voltage regulator
- Altitude of operation of the generator set
- Type of load
- The amount of load
If derating is required in order to block load, refer to ISO 3046 or SAE J1349 Standards. Also, reference Engine Data Sheet, LEKX4066, "Loading Transient Response" and Engine Data Sheet, LEKX4067, "Block and Transient Response".
Note: ISO stands for International Standards Organization.
The power factor is the ratio of apparent power to total power. The power factor is expressed as a decimal. The power factor represents that 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 or other devices. This current is called the reactive load. This current does not require engine power to be maintained.
In most applications, electric motors and transformers determine the power factor of the system. Induction motors usually have a power factor of 0.8 lagging. Incandescent lighting is a resistive load of about 1.0 power factor, or unity.
The power factor of a system may be determined by a power factor meter or 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 goes up, the total current that is supplied to a constant power demand will go down. A 100 kW load that is at 0.8 power factor will draw more current than a 100 kW load that is at 0.9 power factor. A high-power factor will result in a full engine load at less than the generator rated amperage. A lower power factor increases the possibility of overloading the generator.
Note: The Caterpillar generators are rated at a power factor of 0.8 lagging unless the generator is specified otherwise.
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 voltage level settings automatically. The governor speed and voltage level must be preset for the proper operation of that unit. Whenever the set is operated manually, ensure that the governor speed and the voltage level settings are set correctly for automatic operation. Check all switches for the proper setting. The Engine Control Switch should be in the AUTOMATIC position. Emergency Stop Switches should be in RUN position.
Refer to this Operation and Maintenance Manual, "Voltage Regulators" for information on excitation systems.
The low idle is typically 900 rpm. On 60 Hz units, low idle will be approximately 83 percent of the full load speed. On 50 Hz units, low idle will be approximately 70 percent of full load speed.
The low idle is set at the factory on generator sets with mechanical governors. 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 allowing the voltage regulator to resume output.
The generator can be equipped with space heaters. The space heater is installed for operation in high humidity conditions. 120 V space heaters are available.