As a backup power source,
diesel generator sets need to quickly switch power supply when the city power is interrupted. However, if the grid connection operation is improper, it may cause the "reverse power transmission" phenomenon, that is, the current flows back from the generator set to the power grid, which may damage the equipment at the least and endanger personal safety at the worst. This article combines technical specifications and cases to analyze the causes of reverse power transmission and six major preventive measures for you.
1. The "double hazards" of reverse power transmission
Equipment damage
Generator set: Reverse current may cause rotor overheating and winding insulation breakdown.
Grid equipment: Transformers, switch cabinets, etc. may burn due to overvoltage.
Safety hazards
Maintenance personnel may be at risk of electric shock when contacting live lines.
Reverse power transmission causes grid fluctuations and affects the stability of other electrical equipment.
2. The "three major causes" of reverse power transmission
Grid connection operation errors
Starting the generator directly without disconnecting the city power connection leads to parallel connection of dual power supplies.
Protection device failure
Reverse power relay and synchronous device failure, unable to detect current direction
Automation logic defect
ATS (automatic transfer switch) switching logic error, not preferentially disconnecting the mains circuit breaker.
III. "Six core principles" to prevent reverse power transmission
1. Physical isolation: mechanical interlocking device
Install a mechanical interlock between the mains incoming cabinet and the generator outgoing cabinet to ensure that the two cannot be closed at the same time.
Case: A hospital did not install an interlocking device, resulting in reverse power transmission during grid connection, transformer burnout, and maintenance costs exceeding 500,000 yuan.
2. Electrical interlocking: secondary circuit protection
Realize the mandatory sequence of "generator can only start after the mains is disconnected" through relay logic.
Key configuration:
A voltage relay is installed on the mains side to allow the generator to close after detecting no pressure.
A reverse power relay is configured on the generator side to trip immediately when detecting reverse current.
3. Synchronous grid connection: accurate phase matching
Use a synchronous device to ensure that the generator voltage, frequency, and phase are completely consistent with the mains before grid connection.
Technical standards: voltage difference ≤5%, frequency difference ≤0.2Hz, phase difference ≤15°.
4. ATS logic optimization: three-stage switching
Phase 1: The city power is interrupted, and the ATS disconnects the city power circuit breaker.
Phase 2: The generator starts and establishes a stable voltage.
Phase 3: The ATS closes the generator circuit breaker and completes the power supply switch.
5. Labeling and training: personnel behavior control
Post a "grid connection is strictly prohibited" warning label on the control cabinet, and equip it with an electromagnetic lock that requires authorization to operate.
Train operators regularly, and they can only take up their posts after passing the assessment.
6. Emergency plan: rapid response mechanism
Develop an emergency plan for reverse power transmission, and clarify the three-step disposal process of "immediately disconnect all power supplies, check protection devices, and isolate fault points."
Drill requirements: Simulate a reverse power transmission scenario every six months to ensure that the team completes the emergency operation within 3 minutes.
IV. Technology upgrade: intelligent anti-reverse power transmission solution
Intelligent grid-connected controller
Integrated synchronization detection, reverse power protection, and data recording functions, supporting remote monitoring and fault warning.
Energy Management System (EMS)
The Internet of Things monitors the status of the mains and generators in real time, automatically executes the switching logic, and eliminates human errors.
Conclusion
Preventing the reverse power transmission of diesel generator sets requires a three-pronged approach of "hardware protection + software logic + personnel management". Through mechanical interlocking, electrical protection, ATS optimization and other measures, the risk of reverse power transmission can be reduced to less than 0.1%. It is recommended that enterprises entrust professional institutions to test the sensitivity of protection devices every year and update emergency plans to ensure that the emergency power supply is "reliable when used and safe after use".
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