Key Factors to Consider When Selecting a Diesel Generator Set
Factors to be considered when selecting a unit include mechanical and electrical performance, the purpose of the unit, load capacity and fluctuation range, automation function, etc.
(1) The purpose of the unit. Because diesel generator sets can be used in three situations: normal use, backup, and emergency. Therefore, different applications have different requirements for diesel generator sets.
(2) Load capacity. The load capacity and load fluctuation range should be selected according to the application, and determine the individual capacity of the diesel generator set and the backup diesel generator capacity. (3
) The environmental conditions for the unit (mainly refers to altitude and weather conditions)
(4) Selection of diesel generator
(5) Selection of generator and excitation method
(6) Selection of diesel generator automation function
Purchasing criteria for diesel generator sets
1. Appearance requirements
(1) The boundary dimensions, installation dimensions and connection dimensions of the diesel generator set shall be in accordance with the manufacturer’s drawings approved in accordance with the prescribed procedure.
(2) The welding of the unit shall be solid, and the welds shall be uniform. There shall be no defects such as welding penetration, undercut, pinch, etc., the welding slag and flux shall be removed, the paint film shall be uniform, without obvious cracks or peeling, and smooth. There shall be no plating spots, rust, etc., and the fasteners of the body shall not be loose.
(3) The electrical equipment of the diesel generator shall be in accordance with the circuit diagram, and the connection points of each wire of the unit shall have obvious signs that are not easy to fall off.
(4) The diesel generator shall have well-grounded terminals.
(5) The sign of the diesel generator shall contain complete contents
2. Insulation resistance and insulation strength
(1) Insulation resistance: The insulation resistance between each independent electric circuit and earth and between circuits must be 2M or more
. (2) Insulation strength: The insulation resistance between each independent electric circuit of the unit and earth and between circuits must be 2M or more. It must be able to withstand AC test voltage for 1 minute without failure or flickering.
3. Phase sequence requirements. The phase sequence of the terminals of the diesel generator set control panel should be arranged from left to right or top to bottom as viewed from the front of the control panel.
4. Requirements for keeping diesel generators in an operational condition: The units must have heating to ensure that oil and cooling medium temperatures are at least 15°C during emergency start-up and rapid load.
5. Reliability check of automatic start-up power supply and automatic shutdown
(1) The diesel generator can be automatically started upon receiving a start command from the automatic control or remote control.
(2) If the unit fails to automatically start for the third time, it must send a start-up failure signal. If a backup unit is provided, the program start-up system must be able to automatically send a start-up command to another backup unit.
(3) The time from issuing the automatic start command to supplying power to the load must not exceed 3 minutes
. (4) After the automatic start of the diesel generator is successful, the initial load capacity must not be lower than 50% of the calibrated load.
(5) For standby units used in conjunction with the main power grid, after receiving a shutdown command from the automatic control or remote control, the diesel generator must be able to automatically shut down when the power grid returns to normal. It can be automatically switched over or automatically shut down, and its shutdown method must comply with the technical conditions of the product.
6. Automatic start success rate. The automatic start success rate is over 99%.
7. No-load voltage setting range requirements. The no-load voltage setting range of the unit must not be less than 95% to 105% of the calibration voltage.
8. Automatic Supply Requirement. The unit must be capable of automatically charging the starting battery.
9. Automatic protection requirements. The unit must be protected against loss of phase, short circuit (below 250KW), overcurrent (below 250KW), overspeed, high and dry temperatures, and low oil pressure.
10. Sine distortion of the line voltage waveform. At the no-load calibration voltage and calibration frequency, the sine distortion of the line voltage waveform shall be <5%.
1 1. Voltage deviation under three-phase asymmetrical load
Under three-phase symmetrical load of 25%, the diesel generator set should be able to operate normally if a resistive load of 25% of the calibrated phase power is added to any phase. The maximum or minimum value of the line voltage is 5% of the average value of the three line voltages.
12. Fuel consumption rate. The calibrated power of the unit is in the range of 120<Ne<600kW, and the fuel consumption rate is ≤260G/Kw.H.
13. Diesel generator consumption rate. The calibrated power of the unit is >40KW, and the consumption rate of the unit is ≤3.0G/Kw.H.
Selection of emergency diesel generators
Emergency diesel generators are mainly used in critical locations, in case of emergency or accidental power outage, the emergency generator set can quickly restore and extend the power supply for a certain period of time. This type of electrical load is called primary load. Equipment, instruments and computer systems with strict requirements for power outage time should be equipped with batteries or UPS in addition to generators.
There are two characteristics of emergency diesel generators.
The first is that they are for emergency use and do not need to be operated continuously for long periods of time, usually only for a few hours (up to 12 hours)
. Emergency generator set as backup Normally, they are in standby mode and only start operating when the main power is completely cut off, and they supply the emergency power load when the main power is restored. When the main power is restored to normal, they immediately switch to shutdown.
(1) Determination of the generator capacity of the emergency diesel generator
The calibration capacity of emergency diesel generator sets is the 12-hour calibration capacity corrected by atmosphere, and the capacity must be verified based on the generator capacity capable of meeting the total emergency calculated load and satisfying the starting requirements. A single maximum capacity motor for the first level load. Emergency generators are typically three-phase AC synchronous generators with a calibrated output voltage of 400V.
(2) Determination of the number of emergency diesel generators
If there are multiple generator sets for backup, usually only one emergency diesel generator set is installed, but two can also be connected in parallel to provide power to ensure reliability. The number of emergency generators should usually not exceed three. When selecting multiple units, each unit should strive to use a complete equipment set with the same model, capacity, similar pressure and speed regulation characteristics, and the characteristics of the fuel used should be consistent to facilitate maintenance and spare parts sharing. If there are two generator sets to serve emergency needs, the self-starting device should enable the two units to act as backups for each other. That is, the self-start command is executed after the main power failure and power outage are confirmed with a delay. If the first unit self-starts three times in a row, if it fails to start, an alarm signal should be sent and the second diesel generator should start automatically.
(3) Selection of emergency diesel generators
Emergency units should choose diesel generator sets with high speed, supercharging, low fuel consumption and the same capacity. High-speed supercharged diesel engines have a larger capacity of a single unit and occupy less space. Diesel engines should be equipped with electronic or hydraulic speed regulating devices with better speed regulation performance. Generators should be equipped with brushless excitation devices. or phase compound excitation devices. Stepping motors are more reliable and have a lower failure rate, and when the capacity of a single air conditioner or the capacity of the motor of the primary load is larger, generator sets with third harmonic excitation are more convenient for maintenance and repair. A unit with a shock absorber should be selected. The common chassis of the exhaust pipe should be equipped with a muffler at the outlet of the exhaust pipe to reduce the noise impact on the surrounding environment.
(4) Control of emergency diesel generators
The control of emergency generator sets requires fast self-starting and automatic input devices. When the main power fails and the power is cut off, the emergency unit must be able to quickly self-start and restore power. The permissible power outage time of the primary load ranges from more than 10 seconds to several tens of seconds. It is determined according to the specific situation. When the main power of an important project is cut off, a determined time of 3 to 5 seconds must first pass to avoid momentary voltage drops, and the time until the city power grid is closed or the backup power is automatically turned on is required. and the emergency generator start-up is commanded. It takes time for the unit to start up and increase to a speed that can withstand the maximum load after issuing the command. In general, large and medium-sized diesel engines also require a pre-lubrication and warm-up process to ensure that the oil pressure, oil temperature and coolant temperature during emergency load meet the specifications of the factory’s technical conditions. The warm-up process can be carried out in advance according to different situations. For example, emergency forces in military communications, important diplomatic activities in large hotels, large-scale mass activities at night in public buildings, important surgeries in hospitals, etc., all require their equipment to be pre-lubricated and in a warmed-up state during normal times, so that they can be started up quickly at any time and minimize the downtime.
To reduce the mechanical and current impacts when the load is suddenly added after the emergency unit is activated, it is best to increase the emergency load stepwise according to the time interval while meeting the power supply requirements. According to national standards and national military standards, the initial allowable load after the successful startup of the automation unit is as follows: When the calibrated power is less than or equal to 250KW, the initial allowable load is not less than 50% of the calibrated load; When the calibrated power is more than 250KW, the initial allowable load is subject to the technical conditions of the factory product; When the requirements for instantaneous voltage drop and transition process are not strict, the sudden addition or removal of load of the general unit should not exceed 70% of the calibrated capacity of the unit.
Selection of commonly used diesel generator sets
Some diesel generator sets need to operate continuously for a certain period of time, or frequently for a long time, to serve as a common power source for electrical loads. This type of generator set is called a common generator set. A common generator set can be used as a common generator set and a backup generator set. In order to provide local residents with the power they need for production and daily life, diesel generators need to be installed in areas such as towns, islands, forest farms, mines, oil fields, etc., far from the large power grid, or in industry and mining. A type of generator needs to operate uninterruptedly during normal times.
Backup diesel generator sets should be installed in important facilities such as national defense projects, communication hubs, radio stations, and microwave relay stations. The power used in such facilities can be supplied from the main power grid. However, after an earthquake, typhoon, war, or other natural disasters or man-made factors damage the municipal power grid and cause a power outage, the installed backup equipment needs to be quickly started and continue to operate uninterrupted for a certain period of time. In order to ensure the power consumption of these important projects for a long time, this kind of standby generator set is also a common type of generator set. Generators commonly used have long operating times and large changes in the load curve, so the capacity, number, type, and control method of the units are different from those for emergency use.
In order to reduce wear and tear and extend the service life of the unit, the commonly used generator units should select medium and low speed units with a calibration speed of 1000r/min or less. Medium or high speed units can be selected as backup units. Units in the same power station should use units of the same model and capacity to use the same spare parts and facilitate maintenance management. For projects with large load fluctuations, units of different capacities in the same series can also be selected. The determination of the generator output calibration voltage is the same as that of the emergency generator set, which is usually 400V, but for projects with large power consumption and long transmission distance, high voltage generator sets can be used.
Diesel Generator Set Ordering Requirements
When ordering a diesel generator set after making the above selection, we usually ask you to specify the following:
(1) Unit model, rated power, rated frequency, rated voltage, rated current, number of phases, power factor, wiring method, etc.
(2) Function and performance requirements of unit automation.
(3) Requirements for the structure, performance and installation dimensions of the diesel engine, generator and control panel.
(4) Requirements for parallel operation of units: If multiple units are purchased at the same time, will they need to be operated in parallel? If parallel operation is required, will measuring instruments and devices required for parallel operation need to be prepared?
(5) Requirements for ancillary equipment of the unit: Many domestic manufacturers count cooling water tanks (radiators), fuel tanks, exhaust mufflers, batteries, etc. as ancillary equipment.
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