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 to allow 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 | |
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.
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, 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 (motor starters), variable frequency drivers, variable speed drivers, and UPS systems 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, AVSpare generators are designed for a power factor of 0.8 lagging. Consult your Cat dealer to check the generator rating if operation at less than 0.7 lagging power factor is desired.
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 large load applications is possible because the irregularities that occur in the generator output voltage do not feed into the excitation system. Such irregularities can be caused by load conditions. The independent operation also allows the generator to sustain an overload for a short duration.
The low idle on 3500C HD generator sets is typically 900 revolutions per minute. 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.
There is no low idle stop on generator sets with electronic governors. Low idle is set at the factory for generator sets with mechanical governors. The low idle is set at the factory for generator sets that are powered by natural gas. The low idle should 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 shut down. Then, the electric set must be restarted. Restarting will allow the voltage regulator to resume output.
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 "Start Selector Switch" should be in the AUTOMATIC position. Emergency Stop Switches should be in RUN position.
Most of the SR5 generators are provided with space heaters. These space heaters are installed for operation in all climates. The space heaters are especially useful in climates with high humidity. For more information on space heaters, refer to Maintenance Section, "Space Heater - Check".
Embedded Temperature Detectors
SR5 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. Contact your Cat dealer for more information.
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.
Perform the following checks to ensure proper operation of the power module
- Verify that the generator circuit breaker is in the OPEN position. Opening the breaker is to ensure that the unit is isolated.
- Ensure that the bus system is in working condition. If any bus system components are loose or have shifted, resolve any problem before continuing.
- Install a ground cable from the ground bar inside the load cable connection area. Review the "National Electric Code" (NEC). Refer to sections 250-91(a), 250-92(a), 250-93 and/or 250-94 for further details. Refer to the NEC requirements for sizing the ground wire. When removing electrical cables, the ground wire must be the last cable removed.
- Connect properly sized cables from each phase and the neutral bar to the load.
- Ensure that all fasteners on the bus system are tight and secure. Refer to tables 1, and 2.
- Ensure that cables are connected properly. Do not cross phases or alter phase rotation.
- Ensure that the minimum electrical spacing has not been exceeded. If the spacing has changed, make the necessary adjustments prior to energizing the bus.
| Tightening Torque for Lugs Socket Size Across Torque Flats (Metric) | |||
| Thread Size
mm |
Torque | ||
|---|---|---|---|
| M6 | |
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| M8 | |
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| M10 | |
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| M12 | |
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| M14 | |
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| M16 | |
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| M20 | |
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| M24 | |
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| M30 | |
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| M36 | |
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| Tightening Torque for Lugs Socket Size Across Torque Flats (US) | |
| Thread Size
Inch |
Torque |
| 1/4 | |
| 5/16 | |
| 3/8 | |
| 7/16 | |
| 1/2 | |
| 9/16 | |
| 5/8 | |
| 3/4 | |
| 7/8 | |
| 1 | |
| 1 1/8 | |
| 1 1/4 | |
| 1 3/8 | |
| 1 1/2 | |
Ensure that the mounting bolts are tightened to the proper torque. For standard torques, see Specifications, SENR3130, "Torque Specifications".