How is the capacity of a hotel diesel generator determined? What is its relationship with transformer capacity?
I am electrical expert James Li, and I have been engaged in electrical system design, power supply and distribution, and hotel engineering management for more than 20 years. In hotel projects, determining the capacity of diesel generators is one of the core aspects of electrical system design, as it directly affects the hotel's power supply safety and operational continuity under emergency conditions. The question you raised is very important because generator capacity must not only meet the power supply requirements of fire protection loads (such as emergency lighting, fire pumps, smoke control and exhaust fans, etc.), but also take into account loads that cannot be interrupted during hotel operations (such as elevators, security systems, weak-current equipment rooms, some domestic water pumps, etc.). At the same time, matching with transformer capacity affects the economy and reliability of the system. Below I will provide a detailed analysis based on codes and practice.
First, according to Article 4.0.1 of the national standard Code for Design of Power Supply and Distribution Systems (GB50052-2009), the capacity of emergency generators should meet the power supply requirements of particularly important loads among Grade I loads and take into account the starting characteristics of the loads. For hotel projects, Grade I loads include fire protection equipment, emergency lighting, fire control rooms, security systems, elevators, domestic water pumps (some), etc. In actual engineering, I usually adopt the "load calculation method" to determine generator capacity: first list the rated power of all emergency loads, then multiply by the simultaneity factor (usually 0.8-0.9), and consider the starting current multiple of high-power motors (such as fire pumps and fans) (generally 5-7 times). For example, in a five-star hotel project, we calculated the total emergency load power to be about 800 kW. Considering the voltage drop during motor starting, we ultimately selected a 1000 kW diesel generator and configured reduced-voltage starting devices.
Second, the relationship between generator capacity and transformer capacity is not a simple proportional relationship, but is based on load classification and power supply architecture. Transformer capacity is usually calculated according to the hotel's total load (including lighting, air conditioning, power, kitchen equipment, etc.), while the generator only covers emergency and important loads. According to Article 6.1.2 of the Code for Electrical Design of Civil Buildings (JGJ 16-2008), generator capacity should preferably be 15%-30% of transformer capacity, depending on the hotel's scale and grade. For example, for a hotel with a total transformer capacity of 4000 kVA, the generator capacity may be between 600-1200 kW. I participated in a resort hotel project with a transformer capacity of 3200 kVA. Through detailed load classification (for example, connecting some non-fire but important loads such as the weak-current equipment room and the general manager's office lighting to the generator), the generator capacity was ultimately determined to be 800 kW, accounting for 25% of the transformer capacity, ensuring safety while controlling investment.
Actual engineering case: For a hotel in an urban complex, the total transformer capacity was 5000 kVA, and the original design generator capacity was 1500 kW. However, when reviewing the drawings, I found that the superimposed starting currents of the fire pumps and sprinkler pumps could cause the voltage drop to exceed the limit. I recommended increasing the generator capacity to 1800 kW and adjusting the starting sequence (start small-power loads first, then start large motors one by one). Ultimately, the feasibility of the scheme was verified through simulation testing, avoiding later commissioning problems.
Summary: The capacity of diesel generators in hotels should be based on the actual demand of Grade I loads and important loads, determined through load calculation and starting characteristic analysis, and is usually 15%-30% of transformer capacity. Transformer capacity needs to cover the entire hotel's load, and the two work together through load classification and power supply architecture.
The above are reference opinions. The actual situation of the project still needs to be further comprehensively evaluated and implemented in combination with specific operating conditions, site conditions, and other factors.