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. If one phase current exceeds the nameplate amperage, an electrical unbalance can result in an electrical overload and overheating.
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.
| |
| Illustration 1 | g00627416 |
|
Allowable Combinations of Unbalanced Loads | |
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 (power factor for the load)
- The percentage of load before the application of the block load
If derating for the block load is required, refer to ISO 3046 Standards 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 represents the efficiency of the load. 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.
In most applications, electric motors and transformers determine the power factor of the system. Induction motors usually have a 0.8 or smaller power factor. 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 increases, the total current that is supplied to a constant power demand will decrease. For example, a 100 kW load at a 0.8 power factor will draw more current than a 100 kW load at 0.9 power factor. High power factor will result in full engine load at less than the rated amperage of the generator. A lower power factor increases the possibility of overloading the generator.
Note: If no other power factor is specified, Caterpillar generators are designed for a 0.8 lagging power factor.
Permanent Magnet Pilot Excited Generators
Note: The standard generator is designed with internal excitation. The PMPE generator is standard.
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 permanent magnet stator. The pilot exciter operates independently from the generator output voltage. Constant excitation during a large load application is possible because the irregularities that occur in generator output voltage are not fed back into the exciter. Such irregularities can be caused by load conditions. The independent operation also allows the generator to better sustain an overload for a short duration. The pilot exciter also ensures that the generator will start properly even if the rotating field becomes completely demagnetized.
Generator sets normally have a higher low idle setting than industrial engines. Low idle will be approximately 66% of the full load speed of 60 Hz units. Low idle will be approximately 80% of the full load speed of 50 Hz units.
There is no low idle stop on generator sets with electronic governors. On generator sets with mechanical governors and natural gas generator sets, the low idle is set at the factory. The low idle should only be adjusted by your Caterpillar dealer if adjustment is required.
Most standby units are installed with controls that will start the unit automatically. Standby units perform the following tasks without an operator in attendance: start, pick up the load, run and stop.
Standby units cannot change the governor control automatically. Standby units cannot change the voltage settings automatically. The governor speed and voltage level must be preset for the proper operation of the standby unit. Whenever the set is operated manually, be sure that the governor speed and voltage levels are correct for automatic operation. Check all switches for the proper setting. The start select switch should be in the AUTOMATIC position. Emergency Stop Switches should be in RESET position.
A generator space heater is installed as standard. These space heaters are installed for operation in high humidity conditions.
Perform the following checks to ensure proper operation of the power module
- Verify that the generator circuit breaker is OPEN. 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 electrode for the site to the ground stud or studs. Ground studs are located beside the bus bars on the side of the power module. 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 table 1.
- 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 | |||
| socket size | N·m | lb in | lb ft |
| 1/8 | 5.1 | 45 | 4 |
| 5/32 | 11.3 | 100 | 8 |
| 3/16 | 13.5 | 120 | 10 |
| 7/32 | 16.9 | 150 | 12 |
| 1/4 | 22.6 | 200 | 17 |
| 5/16 | 31.1 | 275 | 23 |
| 3/8 | 42.4 | 375 | 31 |
| 9/16 | 67.8 | 600 | 50 |
The load pan door provides user access to both generator load connections and to terminals and connectors for customer interconnect wiring. There are two safety features regarding this access door that enhance personnel safety.
Auto-lock feature - an electrically controlled dead-bolt type lock is provided to lock the door automatically, to prevent access to the load connection bus bars while energized. The onboard EMCP genset controller senses the bus voltage and energizes the locking mechanism.
Breaker trip feature - a switch is used to detect the load pan door is closed. This is used to prevent the on-board generator breaker from closing if the load pan door is open. The feature prevents the breaker from closing by issuing a trip signal directly to the breaker.