Detailed introduction to the purchase points of diesel generators

1. The main factors that should be considered in the selection of diesel generator sets

The factors that should be considered in the selection of the unit mainly include mechanical and electrical performance, the purpose of the unit, the capacity and variation range of the load, and the automation function.
(1) Purpose of the unit. Because diesel generators sets can be used in three situations: common use, standby and emergency. Therefore, the requirements for diesel generator sets are different for different purposes.
(2) Load capacity. The load capacity and load variation range should be selected according to different purposes, and the single unit capacity of the diesel generator set and the capacity of the standby diesel generator set should be determined.
(3) Environmental conditions for the use of the unit (mainly refers to altitude and climate conditions)
(4) Selection of diesel generators
(5) Selection of generators and excitation methods
(6) Selection of automatic functions of diesel generators

2. Standards for purchasing diesel generator sets

3. Appearance requirements

   (1) The limit size, installation size and connection size of the diesel generators sets are in line with the factory product drawings approved by the prescribed procedures
   (2) The welding of the unit should be firm, the welding seam should be uniform, and there should be no welding penetration, undercut, clip Defects such as slag and pores, the welding slag and flux should be removed; the paint film should be uniform, without obvious cracks and peeling; the coating should be smooth, without missing plating spots, rust, etc.;
   (3) The electrical installation of the diesel generator should comply with the circuit diagram, and the connection of each wire of the unit should have obvious signs that are not easy to fall off.
   (4) Diesel generators should have well-grounded terminals.
   (5) The contents of the diesel generator signs are complete

4. Insulation resistance and dielectric strength

   (1) Insulation resistance: the insulation resistance of each independent electrical circuit to the ground and between the circuits should be greater than 2M
   (2) Insulation strength: the independent electrical circuits of the unit should be able to withstand the AC test voltage to the ground and between the circuits 1min, there should be no breakdown or flickering.

5. Phase sequence requirements. The phase sequence of the terminals of the diesel generator set control panel should be sequenced from left to right or from top to bottom when viewed from the front of the control panel.

6. Diesel generators are required to maintain a ready-to-run state. The unit shall have a heating device to ensure that the oil temperature and cooling medium temperature during emergency start and rapid loading are not lower than 15℃

7. Reliability inspection of automatic start power supply and automatic shutdown

   (1) After receiving the start command of automatic control or remote control, the diesel generators sets should be able to start automatically.
   (2) When the unit fails for the third time after the automatic start-up, a start-up failure signal shall be sent; when there is a standby unit, the program start-up system shall be able to automatically transmit the start-up command to another standby unit.
   (3) The time from the issuance of the automatic start command to the supply of power to the load should not exceed 3 minutes
   . (4) After the diesel generator is successfully started automatically, the initial load should not be less than 50% of the rated load.
   (5) After receiving the shutdown command of automatic control or remote control, the unit should be able to stop automatically; for the standby unit used in conjunction with the mains grid, when the grid returns to normal, the diesel generator should be able to automatically switch or stop automatically, and the shutdown method will delay the shutdown. The time should be in accordance with the technical conditions of the product.

8. Automatic startup success rate. The success rate of automatic startup is not less than 99%.

9. No-load voltage setting range requirements. The no-load voltage setting range of the unit is not less than 95%-105% of the rated voltage.

10. Requirements for automatic replenishment function. The unit should be able to automatically charge the starting battery.

11. Requirements for automatic protection function. The unit should have protections for phase loss, short circuit (not more than 250KW), overcurrent (not more than 250KW), overspeed, high water temperature and dry temperature, and low oil pressure.

12. Sine distortion rate of line voltage waveform. Under no-load calibration voltage and calibration frequency, the sinusoidal distortion rate of line voltage waveform is less than 5%.

1 1. Voltage deviation under three-phase asymmetric load The
diesel generator set should be able to work normally under the three-phase symmetrical load of 25%, add a resistive load of 25% of the rated phase power to any phase, and the generator set should be able to work normally, and the maximum line voltage or the minimum value and 5% of the average value of the three-wire voltage.

12. Fuel consumption rate. The rated power of the unit is within the range of 120<Ne<600kW, the fuel consumption rate is less than or equal to 260G/Kw.H
    13 , and the diesel generator consumption rate. The rated power of the unit is >40KW, and the consumption rate of the unit is ≤3.0G/Kw.H
13. Selection of emergency diesel generators

Emergency diesel generators are mainly used in important places. In the event of an instant power outage after an emergency or accidental power outage, the emergency generator set can quickly restore and extend the power supply time for a period of time. Such electrical loads are called primary loads. For equipment, instrumentation and computer systems that have strict requirements on power-off time, in addition to generators, batteries or UPS should be provided for power supply.

The work of emergency diesel generators has two characteristics:
the first characteristic is for emergency use, the continuous working time is not long, generally only need to continue to run for a few hours (≤12H);
the second characteristic is for backup, emergency generator set Usually it is in a shutdown waiting state. Only when the main power supply is all blocked and cut off, the emergency diesel generator set will start to run to supply the emergency power load. When the main power supply returns to normal, it will switch to shutdown immediately.

(1) Determination of generator capacity of emergency diesel generators

The calibrated capacity of the emergency diesel generator set is the 12h calibrated capacity after atmospheric correction, and its capacity should be able to meet the total calculated load of emergency electricity, and it should be verified that the generator capacity can meet the requirements of starting a single motor with the largest capacity in the first-class load. . Emergency generators generally use three-phase AC synchronous generators with a nominal output voltage of 400V

(2) Determination of the number of emergency diesel generators sets

When there are multiple generator sets for backup, generally only one emergency diesel generator set is set up. Considering the reliability, two generator sets can also be selected in parallel for power supply. Generally, the number of generator sets for urgent use should not exceed 3. When selecting multiple units, the units should try to choose complete sets of equipment with the same model and capacity, similar pressure regulation and speed regulation characteristics, and the properties of the fuel used should be the same for maintenance and sharing of spare parts. When there are two generator sets for emergency supply, the self-starting device should enable the two sets to be backup for each other, that is, after the mains power failure is confirmed after a delay, the self-start command will be issued. If the start fails, an alarm signal should be issued and the second diesel generator should be automatically started.

(3) Selection of emergency diesel generators

The emergency unit should choose diesel generators sets with high speed, supercharging, low fuel consumption and the same capacity. The high-speed supercharged diesel engine has a large single-unit capacity and occupies a small space; the diesel engine is equipped with an electronic or hydraulic speed control device, and the speed control performance is better; the generator should choose a synchronous motor equipped with a brushless excitation or a phase compound excitation device, which is more reliable. It is easy to maintain and repair; when the capacity of a single air conditioner or motor in the primary load is large, a generator set with third harmonic excitation should be selected; the generator set is assembled on a common chassis with shock absorbers; smoke exhaust Mufflers should be installed at the pipe outlet to reduce the impact of noise on the surrounding environment.

(4) Control of emergency diesel generator sets

The control of the emergency generator set shall have fast self-starting and automatic input device. When the main power supply fails and is cut off, the emergency unit should be able to quickly self-start and restore power supply. The allowable power-off time of the primary load is from ten to several tens of seconds, which should be determined according to the specific situation. When the main power supply of an important project is cut off, firstly, it should take a certain time of 3-5S to avoid the instantaneous voltage drop and the time when the city grid is closed or the backup power supply is automatically turned on, and then the command to start the emergency generator set is issued. . It will take some time from when the command is issued, the unit starts to start, and the speed rises to full load. Generally, large and medium-sized diesel engines also need pre-lubrication and warm-up process, so that the oil pressure, oil temperature, and cooling water temperature during emergency loading meet the technical requirements of the factory; the pre-lubrication and warm-up process can be carried out in advance according to different situations. For example, emergency units for military communications, important foreign affairs activities in large hotels, large-scale mass activities in public buildings at night, and important surgical operations in hospitals should be in a pre-lubricated and warm-up state at ordinary times, so that they can be started quickly at any time, and the time of power failure can be shortened as much as possible. .

After the emergency unit is put into operation, in order to reduce the mechanical and current impact when the sudden load is applied, the emergency load should preferably be increased according to the time interval when the power supply requirements are met. According to the national standards and national military standards, the first allowable load capacity of the automatic unit after the successful start-up is as follows: for the rated power not greater than 250KW, the first allowable load is not less than 50% of the rated load; for the rated power greater than 250KW, according to the factory product technical conditions. If the instantaneous voltage drop and transition process requirements are not strict, the general unit suddenly added or suddenly unloaded load should not exceed 70% of the unit’s rated capacity.

Fourth, the selection of commonly used diesel generators sets

Some diesel generator sets need to be continuously operated for a certain period of time or often for a long time as a common power supply for electrical loads. Such generator sets are called common generator sets. The common generator set can be used as the common generator set and the standby generator set. Townships, islands, forest farms, mines, oil fields and other areas or industrial and mining enterprises far away from large power grids need to install diesel generators in order to supply local residents with electricity for production and living.
Important facilities such as national defense projects, communication hubs, radio stations, and microwave relay stations should be equipped with backup diesel generator sets. Such facilities can be supplied by the mains power grid. However, due to earthquakes, typhoons, wars and other natural disasters or man-made factors, after the city power grid is damaged and the power is cut off, the standby units that have been set up should start up quickly and continue to operate continuously for a long time to ensure the power consumption of these important projects. The continuous power supply of the load, this standby generator set is also a common type of generator set. Commonly used generator sets continue to work for a long time, and the load curve changes greatly. The selection of unit capacity, number and type and the control method of units are different from those of emergency units.

In order to reduce wear and increase the service life of the unit, the commonly used generator sets should choose medium and low-speed units with a rated speed of not more than 1000r/min, and the standby units can choose medium and high-speed units. Units of the same power station should use units of the same model and capacity so as to use the same spare parts and facilitate maintenance and management. For projects with large load changes, units of the same series with different capacities can also be selected. The determination of generator output calibration voltage is the same as that of emergency generator sets, generally 400V. High-voltage generator sets can be selected for projects with large power consumption and long transmission distance.

(5) Ordering requirements for diesel generator sets

After making the above selections, the ordering of diesel generators sets should generally indicate the following contents:
(1) The model, rated power, rated frequency, rated voltage, rated current, number of phases, power factor and wiring method of the generator set.
(2) Requirements for the automation function and performance of the unit.
(3) Requirements for the structure, performance and installation dimensions of diesel engines, generators and control panels.
(4) Requirements for parallel operation of units: if multiple units are purchased at the same time, whether parallel operation is required, and if parallel operation is required, it is also required to provide the measuring instruments and devices required for parallel operation.
(5) Requirements for auxiliary equipment of the unit: Many domestic manufacturers regard cooling water tank (radiator), fuel tank, exhaust muffler, battery, etc. as auxiliary equipment, and some requirements for installation are allowed when ordering.

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