How to select a false load for a data center diesel generator set

The selection of a false load for a data center’s diesel generator set is crucial, as it directly affects the reliability of the backup power system. Below, I will provide a comprehensive guide covering core principles, key parameters, load types, selection steps, and best practices.

1. Core Selection Principles

The fundamental purpose of a false load is to simulate the real load for comprehensive testing and validation of the diesel generator set, ensuring it can immediately take on the entire critical load in the event of a mains power failure. Specific goals include:

1. Burning off Carbon Deposits: Running at low load or no load causes a “wet stacking” phenomenon in diesel engines (unburned fuel and carbon accumulate in the exhaust system). A false load can raise the engine temperature and pressure, thoroughly burning off these deposits.
2. Performance Verification: Testing whether the electrical performance of the generator set—such as output voltage, frequency stability, waveform distortion (THD), and voltage regulation—is within allowable limits.
3. Load Capacity Testing: Verifying that the generator set can operate stably at rated power and assessing its ability to handle sudden load application and rejection.
4. System Integration Testing: Conducting joint commissioning with the ATS (Automatic Transfer Switch), paralleling systems, and control systems to ensure the entire system works together cohesively.

2. Key Parameters and Considerations

Before selecting a false load, the following generator set and test requirement parameters must be clarified:

1. Rated Power (kW/kVA): The total power capacity of the false load must be greater than or equal to the total rated power of the generator set. It is usually recommended to select 110%-125% of the set’s rated power to allow for overload capability testing.
2. Voltage and Phase: Must match the generator output voltage (e.g., 400V/230V) and phase (three-phase four-wire).
3. Frequency (Hz): 50Hz or 60Hz.
4. Connection Method: How will it connect to the generator output? Usually downstream of the ATS or via a dedicated test interface cabinet.
5. Cooling Method:
   • Air Cooling: Suitable for low to medium power (typically below 1000kW), lower cost, but noisy, and the hot air must be properly exhausted from the equipment room.
   • Water Cooling: Suitable for medium to high power, quieter, higher cooling efficiency, but requires a supporting cooling water system (cooling tower or dry cooler), resulting in higher initial investment.
6. Control and Automation Level:
   • Basic Control: Manual step loading/unloading.
   • Intelligent Control: Programmable automatic loading curves (ramp loading, step loading), real-time monitoring and recording of parameters like voltage, current, power, frequency, oil pressure, water temperature, and generating test reports. This is crucial for data center compliance and auditing.

3. Main Types of False Loads

1. Resistive Load (Purely Active Load P)

• Principle: Converts electrical energy into heat, dissipated by fans or water cooling.
• Advantages: Simple structure, lower cost, easy control, provides pure active power.
• Disadvantages: Can only test active power (kW), cannot test the generator’s reactive power (kvar) regulation capability.
• Application Scenario: Mainly used for testing the engine part (combustion, temperature, pressure), but the test is incomplete.

2. Reactive Load (Purely Reactive Load Q)

• Principle: Uses inductors to consume reactive power.
• Advantages: Can provide reactive load.
• Disadvantages: Not usually used alone, but rather paired with resistive loads.

3. Combined Resistive/Reactive Load (R+L Load, provides P and Q)

• Principle: Integrates resistor banks and reactor banks, allowing independent or combined control of active and reactive load.
• Advantages: The preferred solution for data centers. Can simulate real mixed loads, comprehensively testing the overall performance of the generator set, including the AVR (Automatic Voltage Regulator) and governor system.
• Disadvantages: Higher cost than pure resistive loads.
• Selection Note: Pay attention to its adjustable Power Factor (PF) range, typically needing to be adjustable from 0.8 lagging (inductive) to 1.0 to simulate different load natures.

4. Electronic Load

• Principle: Uses power electronics technology to consume energy or feed it back to the grid.
• Advantages: High precision, flexible control, potential for energy regeneration (energy saving).
• Disadvantages: Extremely expensive, requires highly skilled maintenance personnel, and its own reliability needs consideration.
• Application Scenario: More suitable for laboratories or manufacturing plants than for on-site maintenance testing in data centers.

Conclusion: For data centers, a «Combined Resistive/Reactive (R+L) False Load» with intelligent automatic control should be selected.

4. Summary of Selection Steps

1. Determine Test Requirements: Is it only for combustion testing, or is a full load performance certification needed? Are automated test reports required?
2. Gather Generator Set Parameters: List the total power, voltage, frequency, and interface location for all generators.
3. Determine False Load Type: Select an R+L, intelligent, water-cooled false load (unless the power is very small and the budget is limited).
4. Calculate Power Capacity: Total False Load Capacity = Largest single unit power × 1.1 (or 1.25). If testing a paralleled system, the capacity must be ≥ total paralleled power.
5. Select Cooling Method:
   • High power (>800kW), limited equipment room space, noise sensitivity: Choose water cooling.
   • Low power, limited budget, sufficient ventilation space: Air cooling can be considered.
6. Evaluate Control System:
   • Must support automatic step loading to simulate real load engagement.
   • Must be able to record and output standard test reports, including curves of all key parameters.
   • Does the interface support integration with Building Management or Data Center Infrastructure Management (DCIM) systems?
7. Consider Mobile vs. Fixed Installation:
   • Fixed Installation: Installed in a dedicated room or container, as part of the infrastructure. Fixed wiring, easy testing, neat appearance. The preferred choice for large data centers.
   • Mobile Trailer-Mounted: Mounted on a trailer, can serve multiple data centers or multiple units. Lower initial cost, but deployment is cumbersome, and storage space and connection operations are required.

5. Best Practices and Recommendations

• Plan for Test Interfaces: Pre-design false load test interface cabinets in the power distribution system to make test connections safe, simple, and standardized.
• Cooling Solution: If water-cooled, ensure the cooling water system is reliable; if air-cooled, must design proper exhaust ducts to prevent hot air from recirculating into the equipment room or affecting the environment.
• Safety First: False loads generate extremely high temperatures. They must be equipped with safety measures like over-temperature protection and emergency stop buttons. Operators require professional training.
• Regular Testing: According to Uptime Institute, Tier standards, or manufacturer recommendations, typically run monthly with no less than 30% rated load, and perform a full load test annually. The false load is a key tool for fulfilling this requirement.

Final Recommendation:
For data centers pursuing high availability, cost should not be saved on the false load. Investing in a fixed, adequately sized, R+L, intelligent, water-cooled false load system is a necessary investment to ensure the reliability of the critical power system. It helps identify problems, prevent failures, and meets operation, maintenance, and audit requirements through comprehensive test reports.