Selection of Emergency Diesel Generator

The emergency diesel generator is mainly used in important places. In case of an emergency or emergency power failure, the power will be cut off immediately, and the emergency generator set will quickly restore and extend the power supply for a period of time. This type of electrical load is called a primary load. Equipment, instruments, and computer systems with strict requirements for power outage time should be equipped with batteries or UPS power supply in addition to generators.

The work of emergency diesel generator has two characteristics:

The first characteristic is to respond to urgent needs, and the continuous working time is not long, usually only requiring a few hours of continuous operation (≤ 12H);

The second feature is standby. The emergency generator set is usually in a state of shutdown and waiting. Only when all the main power supply drums are cut off, the emergency diesel generator set can start to operate to supply 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 generator

The calibrated capacity of emergency diesel generator set is the calibrated capacity of 12h after atmospheric correction. Its capacity shall meet the total calculated load of emergency power, and shall be calibrated according to the requirement that the generator capacity can meet the starting requirements of single capacity motor in the first level load. Emergency generators generally use three-phase AC synchronous generators, with a rated output voltage of 400V.

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

When there are several generator sets for standby, generally only one emergency diesel generator set is set. Considering the reliability, two generator sets can also be used for power supply in parallel. The number of urgently needed power generation units should generally not exceed 3. When selecting multiple units, the unit should try to choose a complete set of equipment with the same model and capacity, similar voltage and speed regulation characteristics, and the properties of the fuel used should be consistent for maintenance and shared spare parts. When there are two generator sets in urgent need, the self starting device shall enable the two units to be standby for each other, that is, after the delay confirmation of mains power failure, the self starting command will be issued. If the first unit fails to self start for three consecutive times, the alarm signal will be issued and the second diesel generator will be started automatically.

(3) Selection of emergency diesel generator

High speed, supercharged, low fuel consumption diesel generator set with the same capacity should be selected as the emergency unit. The high-speed turbocharged diesel engine has a large single unit capacity and occupies little space; The diesel engine is equipped with electronic or hydraulic speed regulation devices, which have good speed regulation performance; Generators should choose synchronous motors equipped with brushless excitation or phase compound excitation devices, which are more reliable, have a low failure rate, and are more convenient for maintenance and repair; When the capacity of a single air conditioner or motor is large in the first level load, it is advisable to choose a generator set with third harmonic excitation; The machine is assembled on a shared chassis with shock absorbers; A muffler should be installed at the outlet of the smoke exhaust pipe to reduce the impact of noise on the surrounding environment.

(4) Control of emergency diesel generator set

The control of emergency generator sets should have fast self starting and automatic input devices. When the main power supply fails and loses power, the emergency unit should be able to quickly start and restore power. The allowable power outage time for the first level load ranges from tens of seconds to tens of seconds, which should be determined according to the specific situation. When the main power supply of an important project is cut off, the first step is to determine the time after 3-5 seconds to avoid instantaneous voltage drop and the time when the municipal power grid is closed or the backup power generator is automatically put into operation, and then issue the command to start the emergency generator set. It takes some time from the command to be issued, the unit to start, and the speed to be able to carry full load. Generally, large and medium-sized diesel engines also require pre lubrication and warm-up processes to ensure that the oil pressure, oil temperature, and cooling water temperature during emergency loading meet the specifications of the factory's product specifications; The pre lubrication and warm-up process can be carried out in advance according to different situations. For example, emergency units for military communication, important foreign affairs activities in large hotels, large-scale mass activities in public buildings at night, and important surgical operations in hospitals should always be in a pre lubricated and warm up state, in order to quickly start at any time and minimize power outage time.

After the emergency generator is put into operation, in order to reduce the mechanical and current impact during sudden load application, the emergency load is increased in a graded manner according to time intervals while meeting the power supply requirements. According to national standards and national military standards, the first allowable loading capacity of automation generator after successful self starting is as follows: for those with a rated power not exceeding 250KW, the first allowable loading capacity shall not be less than 50% of the rated load; For those with a rated power greater than 250KW, it shall be in accordance with the technical specifications of the factory. If the requirements for instantaneous voltage drop and transition process are not strict, the load suddenly added or unloaded by the generator set should not exceed 70% of its rated capacity.