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About the choice of emergency diesel generator, the user should know some matters

July 04, 2022
According to the classification of use, diesel generator sets can be divided into commonly used diesel generators, standby diesel generators and emergency diesel generators. Emergency diesel generators are mainly used in important places, in an emergency or accidental power outage after an instantaneous power failure, through the emergency generator sets to quickly restore and extend a period of power. This type of electricity load is called primary load. Equipment, instruments and computer systems with strict requirements for power outage time, in addition to generators should also be equipped with battery or UPS power supply.
 
According to the classification of uses, diesel generator sets can be divided into commonly used diesel generators, standby diesel generators and emergency diesel generators. This type of electricity load is called primary load. Equipment, instruments and computer systems with strict requirements for power outage time, in addition to generators should also be equipped with battery or UPS power supply. Emergency diesel generator work has two characteristics.
 
1, for emergency use, the continuous working time is not long, generally only need to run continuously for a few hours (≤ 12H).
 
2, as a backup, emergency generator set is usually in a state of downtime, only when the main power failure, the emergency diesel generator set to start running to supply emergency power load, when the main power supply back to normal, then switch off.
 
(1) Determination of emergency diesel generator set capacity
 
The calibration capacity of the emergency diesel generator set is the 12h calibration capacity after atmospheric correction, and its capacity should meet the total calculated load of emergency electricity and be calibrated according to the requirement that the generator capacity can meet the single largest capacity motor start in the first load. Emergency generators generally use three-phase AC synchronous generators, the calibrated output voltage of 400V.
 
(2) The number of emergency diesel generator sets to determine
 
When there are more than one generator set standby, generally only one emergency diesel generator set is set, and two units can be used in parallel for power supply from reliability consideration. The number of generator sets for emergency supply generally should not exceed 3. When more than one unit is selected, the unit should try to use the same model, capacity, voltage regulation, speed control characteristics of similar sets of equipment, the nature of the fuel used should be the same, in order to carry out maintenance and common spare parts. When there are 2 generator sets for emergency supply, the self-starting device should enable the 2 sets to standby for each other, that is, after a delayed confirmation of the utility power failure, the self-starting command is issued, and if the first unit fails to start for 3 consecutive times, an alarm signal should be issued and the second diesel generator should be started automatically.
 
(3) The choice of emergency diesel generator
 
Emergency units should be selected from high-speed, pressurized, low fuel consumption, the same capacity of diesel generators. High-speed booster diesel engine single capacity, occupying a small space; diesel engine selected with electronic or hydraulic speed control device, speed control performance is better; generator should be selected with brushless excitation or phase reexcitation device synchronous motor, more reliable, low failure rate, maintenance and maintenance is more convenient; when a single air conditioner capacity or motor capacity in the first load, it is appropriate to choose the third harmonic excitation of the generator set; unit installed in a common chassis with The set is installed on a common chassis with shock absorbers; the smoke exhaust pipe outlet should be equipped with a muffler to reduce the impact of noise on the surrounding environment.
 
(4) Emergency diesel generator set control
 
The control of the emergency generator set should have a fast self-starting and automatic input device. When the main power failure, the emergency set should be able to quickly start and restore power supply, the allowable power failure time of the primary load from a dozen seconds to dozens of seconds, should be determined according to the specific circumstances. When the main power supply of the important project is cut off, the first time should be determined by 3-5S, in order to avoid the instantaneous voltage reduction and the time when the city grid is closed or the backup power is automatically put in, and then the instruction to start the emergency generator set should be issued. From the command issued, the unit began to start, speed up to be able to take the full load takes a period of time. General large and medium-sized diesel engines also need pre-lubrication and warm-up process, so that the emergency loading oil oil pressure, oil temperature, cooling water temperature in line with the provisions of the technical conditions of the plant; pre-lubrication and warm-up process can be carried out in advance according to different circumstances. For example, the emergency units of military communication, important foreign affairs activities in large hotels, large mass activities in public buildings at night, important surgical operations in hospitals, etc. should be in pre-lubrication and warming state at ordinary times, so that they can be started quickly at any time to minimize the time of power failure.
 
After the emergency unit is put into operation, in order to reduce the mechanical and current impact when the load is suddenly added, the emergency load should preferably be increased by time intervals in a graded manner under the condition that the power supply requirements are met. According to the national standard and national military standard, the allowable loading of the automation unit since the successful start is as follows.
 
For those whose calibrated power is not greater than 250KW, the allowable loading amount is not less than 50% of the calibrated load.
 
For those whose calibrated power is greater than 250KW, it is stipulated in accordance with the technical conditions of the factory product. If the requirements of instantaneous voltage drop and transition process are not strict, the amount of load suddenly added or unloaded by the unit should not exceed 70% of the unit's calibrated capacity.