Basic Requirements for Standby Diesel Generator Sets
The requirements for power supply units can be categorized into two main groups:
- General Requirements: These apply to all power units and power plants equipped with internal combustion engines, regardless of their application (Prime, Standby, or Emergency power). These standards are defined by existing regulatory documents, codes, and industry guidelines, specifying the essential characteristics of standby power units. Key parameters include:
- Functional Parameters: Rated power, voltage, frequency, and power factor.
- Operational Conditions: Ambient temperature, humidity, dust levels, and altitude above sea level.
- Environmental Durability: Transportability via road, rail, and other logistical means.
- Design Features: Primary engine cooling methods and protection against atmospheric/environmental impact.
- Power Quality and Storage Conditions.
- Operational Requirements:
- Start-up Time: The time required for a diesel engine to reach its rated speed and accept a permissible load must not exceed 10 seconds (for units up to 100 kW) and 20 seconds (for units up to 500 kW).
- Hot Standby Maintenance: To meet these start-up times, the engine must be maintained in a "hot standby" state, preventing critical fluctuations in lubricant and coolant temperatures. This is achieved through: Specialized jacket water heaters installed directly on or external to the diesel generator; Space heating or the use of "Thermostart" systems (flame start systems), which pre-heat the intake air to ensure automatic starting even at ambient temperatures around 20°C.
- Immediate Load Acceptance: The unit must be capable of accepting maximum permissible load immediately after reaching rated speed. This optimizes engine utility from the first second of operation and allows for a reduction in installed capacity.
- Response Time: Minimizing the interval between the start command and full load acceptance reduces the duration of battery-powered support, thereby lowering the required battery capacity and overall system cost.
- Minimum Load Reliability: The unit must ensure reliable continuous operation at a minimum rated load of 25-40%. At lower loads, operation should be limited to 1-2 hours, potentially followed by a "burn-off" (load banking) session.
The Risks of Low-Load Operation (Wet Stacking)
Operating a diesel engine at low loads results in low exhaust temperatures. Consequently, lubricating oil in the combustion chamber does not burn completely. Instead, it deposits and cokes on turbocharger components, piston heads, exhaust valves, and manifold walls.
- Consequences: Prolonged operation in this mode without periodic burn-off leads to a reduction in the turbocharger nozzle area, obstructing normal engine function.
- Explosion Hazard: Furthermore, during subsequent starts, any fuel entering the exhaust system can trigger an explosion, often resulting in catastrophic damage to the diesel generator.
Starting Reliability and Systems
The probability of start failure must not exceed 0.001–0.002 per attempt.
- Electric Starters: Reliability is ensured through three start attempts of 8 seconds each, with 10-second intervals.
- Pneumatic (Compressed Air) Starts: A single attempt should not exceed 8 seconds. Increasing the number of pneumatic attempts is counterproductive, as the expanding air cools the cylinders and hinders ignition.
- System Choice: Most standby units utilize electronic/electric starting. Pneumatic systems are typically reserved for high-power units where an electric starter cannot provide the necessary breakaway torque.
Conclusion: When selecting a standby unit, meeting these specific technical requirements is critical depending on the user's equipment characteristics, while other factors may be adjusted or simplified based on the application.