1. Design ideas for diesel generators
1.1 Collection of conditions required for design
a. Meteorological conditions: The rated capacity of the diesel generator is tested at 40 °C. As long as the external environment does not exceed 40 °C for a long time, the diesel generator can be designed according to the rated value.
b. Altitude conditions: The increase in altitude will cause the diesel generator set to degrade. If diesel generators are selected in the plateau, it is not recommended to consider the possibility of load operation.
c. Water quality conditions: If the water quality is too hard, it will cause the circulating water of the water cooling system to precipitate scale, reduce the heat conduction effect of the conduction outer wall, and reduce the cooling water circulation efficiency, resulting in the unit temperature rise too fast and an accident, so the diesel generator set needs to be set in the hard water area. Consider circulating water to soften in advance.
d, load capacity, etc.: The statistics of equipment capacity need to meet the requirements of the current regulations, such as the particularly important load in the primary load, and then meet the individual requirements of the construction party for the functional characteristics of the project, respectively, statistics, designing the fire load and important The larger the usual load, as the rated capacity of the diesel generator set.
1.2 Determine the type of diesel generator use
a. A commonly used power station is a diesel generator set used during normal work.
b. Standby power station, used in the event of a power outage.
c. Emergency power station, use of important loads, such as fire fighting equipment, etc., usually not used.
1.3 Preliminary design
Complete the estimation of the capacity of the diesel generator. According to the author's engineering practice summary, the preliminary design stage can be estimated from 10% to 15% of the total capacity of the transformer. For example, the total capacity of the 4 000 kVA transformer can be selected as a 500 kW diesel generator set; or It can also be estimated by building area: for buildings above 10 000 m2, it can be estimated by 10 ~ 15 W / m2, and buildings below 10 000 m2 can be estimated by 15 ~ 20 W / m2, such as 40 000 m2 For buildings, a 630 kW diesel generator set can be selected.
Complete the schematic diagram of the main line of the diesel generator set system: 1 Determine whether the diesel generator is operated in stand-alone mode or in parallel. 2 Then determine whether the important load and the fire load are separately set to the bus section. When it is necessary to supply power at different times, it is required to cut off the important non-fire load in the fire state. For such design requirements, the diesel generator outlet cabinet should be separately set. 3 The emergency generator power supply switch and the system power supply switch are mechanically locked.
Carry out equipment layout and complete the preliminary layout of the equipment room. Refer to JGJ 16-2008 “Electrical Design Code for Civil Buildings†6.1.3 for the specific layout requirements of the unit.
2, construction drawing design
The steps are similar to the preliminary design, except that the calculation of the design is more complete and detailed, the calculation method is slightly different, and the degree of completion is higher. The model, specifications, parameters, etc. of the busbar, motor, switch, and equipment should be indicated in the figure. Complete the flat and sectional view of the diesel generator room, and draw the plane layout and installation dimensions of the diesel generator, the inlet and outlet cabinet switch cabinet, the busbar, the trench, the trunking, and the grounding device. The vertical distribution system diagram includes the number of diesel generators, the capacity, the number of terminal distribution boxes in each terminal, and the number of the circuit from the power point.
2.1 Selection of diesel generator load capacity during construction drawing stage
If the class and the second type of load are simply added to select the diesel generator capacity, the selected capacity is too large, because in the fire state, only the operation of the fire fighting equipment is required, the secondary load is not used, and the non-fire state is in the non-fire state. When the power grid is out of power, the fire-fighting equipment is not used. Therefore, it is recommended to calculate the fire-fighting load and the important non-fire-fighting load separately. The larger value is used as the basis for determining the capacity of the generating unit. This kind of practice needs to meet the relevant requirements of the fire department and the construction party. Claim. Another method is to select the generator according to the fire load and the important non-fire load total capacity during design, which can meet the important load power demand during non-fire protection, and can ensure the fire load work needs during fire protection. The capacity is also larger and the cost is also high, which is generally not recommended.
2.2 Loads on diesel generators
Generally, it is the following part. The specific setting needs to be increased or decreased according to the requirements of the project design task book in the case of the project itself:
1 passenger ladder, fire pump, fire alarm system, weak motor room, cold storage freezer, sewage pump, fire elevator drainage pump, water treatment, living water pump, fire fan, security power, fire broadcast, parking system power supply.
2 lighting needs diesel generators to provide places: control room, switch room, weak motor room, transformer and power distribution room, service center, generator room, fire pump room, fire fan room, elevator machine room, stairwell, elevator front room, evacuation instructions And other public areas for emergency lighting.
2.3 Calculation of capacity of diesel generator
According to the requirements of J.G. 16 -2008 "Electrical Design Code for Civil Buildings", the requirements of 6.1.2 are taken as the basis for selecting the capacity of diesel generators.
Precautions for diesel generator load capacity: After selecting the diesel generator according to the large calculation value, you should still pay attention to the following items:
1 good economic power is 0.75 times of rated power. It is the output power of diesel generator set that can be operated for a long time without time limit. When running at this power, the fuel economy is low and the failure rate is low, so P good = 3 / 4 × P rated, that is, the calculated power is 0.77 times the rated power is more suitable.
2 The building type of the office building is similar to the UPS selection specification. When the electronic computer occupies the main power supply load, the rated output power should be greater than 1.5 times the sum of the rated power of all computer equipment. For a large calculation load of 1.3 times.
3 It is recommended in the design to indicate that the diesel generator set is not allowed to run for a long time at less than 50% of the rated power, because the diesel generator oil consumption is easy to increase and the diesel combustion is caused when operating at less than 50% of the rated power. Insufficient to produce carbon scale, which increases the failure rate of diesel generators and shortens the service life of the unit.
4 It should be noted that the nominal working power of the nameplate is the large working power within 12 h, while the long-term operating power is 90% of the nominal working power, which is the power at 25 ° C at an atmospheric pressure (100 kPa) humidity of 30 %. When designing a diesel generator, both powers can be expressed.
2.4 System design of diesel generator set
The diesel generator room is often located in the basement level, and one or more diesel generator sets are installed. The unit is operated by single machine or multiple units (the type of the vehicle: from the same period, the coarse synchronous period, the quasi-synchronous period), and the diesel generator is In the fire state, the equipment in the accident state is supplied with power, and it is determined according to the usage requirements of Party A. If separate power supply is required, it is necessary to consider separately setting the outlet cabinet.
In the power distribution system, the power supply of the first and second stage loads is simultaneously supplied by the two-way mains. When the mains power is lost, the other mains can be powered by the low-voltage bus-end terminal or by hand-powered. When the kV independent high-voltage power supply loses power, after the ATS switch is switched, the diesel generator is started, the start signal is sent to the diesel generator room, the signal delay is automatically started from 0 to 10 s, and the diesel generator set reaches the rated speed within 15 s. After the voltage and frequency, put it into the rated load operation. The unit should be in the state of standing start, with automatic starting device to ensure that the building is always in two power supply states. When the mains is restored for 30 to 60 s, the mains supply will be automatically restored. After the cooling delay of the diesel generator set, it will automatically Shutdown, emergency conversion of diesel generators when two mains electricity loses power at the same time.
In the low-voltage power distribution system, the emergency bus section needs to be set up, and the emergency busbar compartment is separately set to ensure the reliability of the power supply. The emergency busbar is powered by the diesel generator set to ensure the normal operation of the important load. The phase sequence of the diesel generator must be The phase sequence of the original power supply system is the same.
2.5 Applicable environment for diesel generators
The diesel generator set can meet the mains failure, the diesel generator starts within 15 ~ 30 s, the unit ground control, and the quick self-starting device is installed for 3 consecutive times, the total time is no more than 30 s, and the generator can allow 25% of the short-time load, but for the most important load in the primary load, the power supply that interrupts the power supply time is less than 15 s. Since the start-up time of the diesel generator cannot meet the requirements, an online uninterruptible power supply unit can be installed at the end, such as To achieve millisecond power supply, it is necessary to first set up a battery static uninterruptible power supply (UPS), and then set up a diesel generator set.
2.6 Fuel tank setting for diesel generators
In the engine room or in the oil storage room, there should be a daily fuel tank for 3 ~ 8 h continuous operation. However, when the oil volume exceeds 1 000 L, it is better to install an oil storage tank outside, and the daily fuel tank volume is not allowed to exceed 1 m3. When it is outdated, it is necessary to set up another oil storage tank outside. If the condition is unknown, the 15 m3 buried oil storage tank can be set outdoors. The size is 3000 × 6 000 × 3 200 mm. The total oil storage capacity can generally guarantee the full capacity of the unit. For more than 24 hours, such as two 1 200 kW diesel generators, a 15 m3 buried oil tank can be set to meet the needs of 24 h fuel.
The oil tank inlet and outlet pipe of the diesel generator room is a household fuel tank, and a spare pipe is set up. As shown in Fig. 6, two daily fuel tanks are provided with two inlet pipes and two spares. Reserve 4 × Φ80 mm inlet and outlet pipes to the outdoor storage tank. The buried depth of the outdoor storage tank can be - 1. 0 ~ - 1. 3 m.
Estimation of the fuel consumption of the diesel generator: 1 When the load rate is 50%, the fuel consumption is 0.115 l / h · kW. 2 l / h · kW When the load rate is 75%, the fuel consumption is 0. 2 l / h · kW. 3 When the load rate is 100%, the fuel consumption is 0.3 l / h · kW.
Example of tank tank estimation: Tank volume estimation can be calculated as: V = P × GT / A. Where: V - the volume of the daily fuel tank, m3; P - unit power, kW; G - fuel consumption per kW per hour, l; T - supply time, h; A - full factor.
Example: Two 600 kW diesel generators P = 1 200 kW, with a load factor of 75%, the fuel consumption is G = 0. 2 l / h · kW, T = 3 h, A = 0. 8, then V = 1 200 × 0. 2 × 3 / 0. 8 = 900 l, ie 0. 9 m3, the 1 m3 daily fuel tank can be used to meet the oil demand of 3 h.
The tank volume estimation can also be carried out by the above method: the difference is T = 24 h or higher, and the rest of the selection is unchanged, then V = 1 200 × 0. 2 × 24 / 0. 8 = 7 200 l, is 7. 5m3, choose 10 m3 buried storage tank, if you want to meet 36 h or two 1 200 kW generator sets, you can choose 15 m3 tank.
2.7 Equipment control requirements for diesel generator systems
1 The control panel of the generator needs to be equipped with short circuit, overload, ground fault and over and under voltage protection devices. The switch is usually manual operation.
2 Monitor or control various operating parameters to ensure the normal operation of the unit, and at the same time, it can issue pre-alarm and fault alarm signals.
3 It can have the control device of the expandable fieldbus (RS485 or LonWorks, etc.) interface complying with the open standard, and has universal gateway support, which can be connected to the building BA system.
4 It is necessary to separately set the battery pack (voltage 24 V) as the control power supply. The capacity should ensure that the diesel generator is continuously started no less than 6 times, and the rectification charging device is set. The output voltage should be higher than the battery voltage by 50%, and the output current Not less than the discharge rate current of the battery 10h.
5 The unit can be fully loaded and the voltage regulation rate is ± 0.5%.
6 When all mains interruption power supply is detected, the start signal is taken from the auxiliary contact of the voltage transformer before the low voltage main switch of each group of transformers in the substation. After the signal is calculated by logic, the signal is sent to the diesel generator control cabinet. The unit starts up automatically and supplies power to the load within 15 s. When the mains returns to normal, the power supply automatically switches, and the unit automatically stops at a time, and the mains supplies power to the load. Diesel generator sets cannot be operated in parallel with the mains.
7 Emergency generator power supply switch and system power switch are equipped with mechanical lock.
8 Static characteristic refers to the change of the speed of the diesel engine load when it is gradually loaded with no load. It is usually controlled below 5% of the rated speed n. The dynamic characteristic refers to the change characteristic of the sudden change of the speed of the load at no load and full load. The settling time is suddenly changed from no load to full load. From the start of the transition to the time when the unit is re-stabilized, the settling time is no more than 7 s, generally 5-7 s, and the other voltage change is from cold state to hot state at full load. The output voltage of the state changes, generally not more than 2% of the rated voltage.
2.8 Grounding of diesel generator sets
Diesel generator rooms should generally have three types of grounding:
1 Working grounding: According to the requirements of the “People's Regulationsâ€, when a generator set is used, the neutral point should be directly grounded. When the two units are combined, the neutral point can be grounded or used in the absence of circulation. Install a current limiting reactor to ground. For example, if a diesel generator set is used in a project, when only one unit is operated alone, the corresponding knife switch and contactor are closed, and the neutral point of the single unit operation is directly grounded. At this time, the contactor of the other unit is broken. When two units are running side by side, the neutral point of the unit is grounded via the knife switch. Due to the contactor interlocking, only one of the two contactors is allowed to be connected, and the contactor of the other unit must be Disconnect, this can avoid the neutral conductor to generate circulation, which can be similar to the selection of transformer neutral grounding wire, refer to the parameters of the atlas (03D201 - 4 "10 / 0. 4 kV transformer room layout and equipment for transformer and power distribution In the component installation: “Selection of transformer low-voltage side outletâ€), if the project is 1 200 kW diesel generator, YJV - 1 × 185 mm2 grounding cable can be selected, and the rated current of the corresponding knife switch and contactor is 400 A, as shown in the figure. 7 is shown.
2 Protective earthing: The normal uncharged metal casing of the diesel generator set must be grounded.
3 Anti-static grounding: The equipment and piping of the fuel system need to be grounded.
4 The above groundings share the grounding device with other grounding of the building, that is, the joint grounding method is adopted.
2.9 Other considerations for diesel generator set design
The short-circuit current of a diesel generator can generally be considered at 10 times the rated current. The capacity of a single motor is recommended to be no more than 25% of the generator capacity.
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