Typical power diagrams for emergency and production generator sets-converted

1. Typical power for emergency and production generator sets Typical power diagrams for emergency and production generator sets Turbines and diesel engines Typical power for emergency and production generator sets main types of main engines used in engine driven generator sets for industrial sites and commercial buildings are: Diesel engines, gas turbines and steam turbines. Turbines are mainly used for production assemblies, while diesel engines can be used for both production and standby assemblies. Typical power diagrams for emergency and production generator sets The topics covered in this article do not depend on the type of motor being used, and therefore the general term Generator set will be used. The choice of the main engine is determined by considerations such as availability and type of fuel and is not covered in this technical article. Since diesel engines are used very often, specific information about diesel generator sets is provided. 1. Emergency generators The typical supply of essential loads for commercial buildings, small industrial sites or for back-up power to unit substations in a larger site, is shown in Figure 1. Under normal operating conditions, the essential load is supplied by the mains. In the event of loss of this supply, the Q3 bus link circuit breaker tripped, the generator set is started, and then the load is supplied by the emergency generator set by closing the generator circuit breaker Q2. Critical loads which cannot accept any power failure are supplied by the inverter. The inverter is equipped with a static switch which will immediately bypass the rectifier / inverter module in the event of an internal fault and thus ensure a continuous power supply. Typical generator set sizes for this diagram are: 250 kVA to 800 kVA. The advantage of this scheme is its simplicity and clarity. All essential loads are connected to the same busbar as the generator set. No load shedding is therefore necessary. UPS backup time

2. can normally be limited to 10 minutes since the UPS will be powered by emergency power. Typical power diagrams for emergency and production generator sets The UPS normal and emergency power supplies must be taken from the essential busbar. For large industrial sites, a centralized backup power system as shown in Figure 2 is often used. The main emergency distribution board is normally supplied by the utility, although at some sites one of the generator sets may be running continuously. The emergency switchboard is designed to allow the generating sets to operate in parallel and to be connected to the distribution network. Automatic transfer of utility to emergency power is performed in each substation. As the emergency distribution panel is normally supplied, rapid transfers without loss of load in the installation can be used. Using a centralized emergency power supply has the following advantages: 1. fewer generators for the site (normally a maximum of 2), 2. permanently supplied emergency power supply allowing the use of rapid transfer systems,

3. 3. no loss of emergency power due to the maintenance of a generator set. The generator sets for such systems are normally in the range of 1 to 4 MW. Load test of a 500 kVA generator 2. Production generators For remote sites that do not have public service, several generators are used. A typical distribution system is shown in Figure 3. The number of sets N will depend on the power required, but as the generators require periodic maintenance, the power of the plant must be able to be supplied by N – 1 sets without load shedding. The size of the generator set should be such that they are charged at least 50%. A low load factor can be detrimental to assemblies. For example, Diesel engines loaded less than 30% will not achieve proper operating temperature resulting in poor combustion and degradation of the lubricating oil. Plant operation at N – 2 sets must also be taken into account, this case occurring when one set is maintained and one additional set is lost. The highest initial load factor F that can be used with N generators installed, so that load shedding is not required for N – 2 operation can be determined from: For example, the highest load factor for N = 6 will be 80%. Bus tie breakers are often used for maintenance purposes. During normal operation of the installation, the circuit breakers are normally closed. Short-circuit calculations must always take into account operation with N generators, because it is normal to connect groups on standby before deactivating them for maintenance reasons. A power supply using local generation is generally much weaker than a utility. It is therefore likely that load shedding will be necessary to maintain the stability of the system in the event of a failure. Determining the load to lose requires dynamic grid simulation for different fault conditions, such as generator loss or short circuit. Before the study, it is necessary to determine which operating configurations should be considered. Operating Conditions with Coupling Circuit The circuit breaker in both open and closed position will greatly increase the complexity of the load shedding system as each busbar can be operated independently and will require specific load shedding criteria. For most plants, it is recommended to only use the standard operating configuration for dynamic simulations and definition of the load shedding strategy. Figure 3 shows each generator having its own transformer. The use of generator transformers has several advantages: 1. Offers flexibility in the choice of generator voltage, 2. Reduces peak short circuit current on the main board 3. Allows the use of high impedance generator ground (reduces the risk of generator damage).

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