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. This 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
When an electrical load is applied to a generator set, block loading occurs. 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 that is already present
If a block load derating is required, refer to ISO 8528 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
Power factor (PF) determines the relationship between true power and apparent power. The true power is also known as the active power. The apparent power is also called kVA. The true power (kW) is the work that is done on the load by the engine. The true power determines the amount of power that is available for the load to do work. The apparent power (kVA) is the total power that is produced by the generator. Power factor can be calculated by using the following formula.
PF = kW / kVA,
kW - kilowatts
kVA - Kilo-Volt-Ampere
KVAR stands for Kilo-Volt-Ampere-Reactive, which is the unit of measurement for reactive power.
Note: The generator does NOT control power factor. Power factor is determined by the load.
In most applications, electric motors, solid-state controls, and transformers determine the power factor of the system. 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. Solid-state controls, variable frequency drivers (VFD), variable speed drivers (VSD), and systems for the UPS can operate at any power factor, leading, or lagging. In this case, the power factor can be between 0.4 and 1.0.
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 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 rated amperage of the generator. A lower power factor increases the possibility of overloading the generator.
Note: Normally, Caterpillar generators are designed for a power factor of 0.8 lagging. Consult your Cat dealer in order to check the generator rating if the operation at less than 0.8 lagging power factor or operation at a leading power factor is desired.
Excitation Systems
Refer to the Operation and Maintenance Manual, "Voltage Regulators" for information on excitation systems.
Low Idle Adjustment
The low idle is typically 1200 rpm. On 60 Hz units, low idle will be approximately 66 percent of the full load speed. On 50 Hz units, low idle will be approximately 80 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 Cat 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 will allow the voltage regulator to resume output.
Standby Generator Sets
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.
Generator Options
Space Heaters
Most of the generators are provided with space heaters. These space heaters are installed for operation in all climates. For more information on space heaters, refer to Maintenance Section, "Space Heater - Check".
Embedded Temperature Detectors
Some 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. RTDtemperature detectors are available. Contact your Cat dealer for more information.
Bearing Temperature Detectors
Bearing temperature detectors are available on large-frame generators. Bearing temperature detectors measure the main bearing temperature. Thus, the temperature of the bearing can be measured or monitored. Bearing temperature measurements may help to prevent premature bearing failure. Bearing temperature detectors are used with customer provided equipment. Contact your Cat dealer for more information.