The Switching between the Main and Standby Power Supplies of the Dual-Power Supply Control Cabinet
The switching between the main and standby power supplies of the dual-power supply control cabinet is an important link to ensure
the continuous power supply to critical loads. It is commonly found in scenarios with high requirements for power supply reliability,
such as hospitals, data centers, factories, etc. The following are its core principles, composition, and operation key points:
I. Core Objectives of Dual-Power Supply Switching
1. **Seamless Switching**: Automatically or manually switch to the standby power supply when the main power supply fails to avoid
the load from losing power.
2. **Safety Isolation**: Ensure that the two power supplies are **not connected in parallel** to prevent circulating current or short circuits.
3. **Fault Protection**: Cut off the faulty power supply before switching to avoid the spread of the fault.
II. Composition of the Dual-Power Supply Switching System
1. Dual-Power Supply Switching Switch (Core Component)
- **Types**:
- **ATS (Automatic Transfer Switch)**:
- With a mechanical structure and arc extinguishing ability, it can automatically detect the power supply status and switch (such
as Schneider WATSN, ABB TPS).
- **Switching Time**: 50-200ms (suitable for loads that allow a short power outage).
- **STS (Static Transfer Switch)**:
- Based on thyristors, without mechanical actions, the switching time is < 10ms (suitable for precision loads that cannot be powered
off, such as servers).
- **Disadvantage**: High cost, and it needs to be equipped with a heat sink and a bypass switch.
- **Manual Switching Switch**:
- A pure mechanical knife switch (such as the HD13 type), which requires manual operation, and **switching with a load is strictly
prohibited**.
- **Wiring Mode**:
**Key Point**: The input ends of the two power supplies need to be protected by circuit breakers respectively, and the switching switch
is located between the two circuit breakers.
2. Control and Protection Devices
- **Power Supply Monitoring Module**:
Detect the voltage, frequency, and phase of the main/standby power supplies to determine whether they are normal (for example,
triggering a switch when the voltage deviation > ±10%).
- **Circuit Breaker**:
- Each of the main and standby power supply circuits is equipped with one circuit breaker to provide overload/short-circuit protection.
- **Tripping Sequence**: First, open the circuit breaker of the faulty power supply, then switch the switch, and finally close the circuit
breaker of the standby power supply.
- **Auxiliary Components**:
Indicator lights (displaying the status of the main/standby power supplies), alarm devices (acoustic and optical prompts for power supply
failures), and bypass switches (bypassing the switching system during maintenance).
III. Switching Logic and Workflow
1. Automatic Switching (Taking ATS as an Example)
1. **Normal Main Power Supply**: The ATS connects to the main power supply, and the load is powered by the main power supply.
2. **Failure of the Main Power Supply**:
- The monitoring module detects the abnormality of the main power supply (such as power outage, low voltage).
- After a delay of 0.5-3 seconds (to avoid mis-switching due to instantaneous fluctuations), the ATS opens the circuit breaker of the
main power supply.
- The ATS switches to the standby power supply side, closes the circuit breaker of the standby power supply, and the load is switched
to be powered by the standby power supply.
3. **Recovery of the Main Power Supply**:
- It can be set as "give priority to restoring the main power supply" or "continue to use the standby power supply" (manual reset is
required).
2. Manual Switching
- **Scenario**: When maintaining the main power supply or testing the standby power supply.
- **Operation Steps**:
① Open the circuit breaker of the main power supply → ② Operate the switching switch to the standby power supply → ③ Close the
circuit breaker of the standby power supply.
**Note**: It is necessary to cut off the power first and then switch to avoid operating with a load!
IV. Typical Application Scenarios
1. Home Dual-Power Supply System
- **Configuration**:
Mains power supply (main) + Generator (standby) + Manual switching switch + Dual-circuit circuit breaker.
- **Switching Logic**:
When the mains power supply fails, manually start the generator, and switch the switching switch to the generator side.
2. Industrial Precision Loads (Such as Data Centers)
- **Configuration**:
Two mains power supplies (main/standby) + STS static transfer switch + Redundant circuit breaker.
- **Switching Logic**:
When the main power supply has an instantaneous power outage, the STS switches to the standby power supply within 10ms
to ensure that the server does not restart.
V. Selection and Installation Precautions
1. Selection Key Points
- **Rated Current**: ≥ 1.2 times the total load current (for example, if the load is 100A, select a 125A switch).
- **Switching Time**: Select according to the load's tolerance to power outage time (for example, elevators allow 200ms,
and IT equipment requires < 10ms).
- **Protection Level**: Select IP54 for outdoor control cabinets and IP20 for indoor ones.
- **Certification Standards**: It needs to comply with GB 14048.11 in China and IEC 60947-6-1 internationally.
2. Installation Specifications
- **Electrical Isolation**: The incoming lines of the main/standby power supplies need to maintain physical isolation to avoid
short circuits caused by incorrect wiring.
- **Grounding Protection**: The metal shell of the control cabinet needs to be reliably grounded (the grounding resistance
< 4Ω).
- **Clear Marking**: Mark warning words such as "Main Power Supply", "Standby Power Supply", and "No Live Operation
Allowed".
VI. Common Faults and Troubleshooting
| Fault Phenomenon | Possible Cause | Solution |
| The load loses power after switching | The standby power supply is not closed or the circuit breaker trips | Check the voltage of the standby power supply and reset the circuit breaker |
| ATS switches frequently | The power fluctuation threshold is set too low | Adjust the delay time or voltage threshold of the monitoring module |
| Sparking during manual switching | Operating with a load (the isolating switch has no arc extinguishing ability) | Open the load circuit breaker first and then switch the switch |
Conclusion
- **Protection Level**: Select IP54 for outdoor control cabinets and IP20 for indoor ones.
- **Certification Standards**: It needs to comply with GB 14048.11 in China and IEC 60947-6-1 internationally.
2. Installation Specifications
- **Electrical Isolation**: The incoming lines of the main/standby power supplies need to maintain physical isolation to avoid
short circuits caused by incorrect wiring.
- **Grounding Protection**: The metal shell of the control cabinet needs to be reliably grounded (the grounding resistance
< 4Ω).
- **Clear Marking**: Mark warning words such as "Main Power Supply", "Standby Power Supply", and "No Live Operation
Allowed".
VI. Common Faults and Troubleshooting
| Fault Phenomenon | Possible Cause | Solution |
| The load loses power after switching | The standby power supply is not closed or the circuit breaker trips | Check the voltage of the standby power supply and reset the circuit breaker |
| ATS switches frequently | The power fluctuation threshold is set too low | Adjust the delay time or voltage threshold of the monitoring module |
| Sparking during manual switching | Operating with a load (the isolating switch has no arc extinguishing ability) | Open the load circuit breaker first and then switch the switch |
Conclusion
The core of dual-power supply switching is **"safety isolation + rapid response"**. It is necessary to select the switching
method (automatic/manual) and the switch type (ATS/STS) according to the load characteristics, and achieve fault protection
through circuit breakers. In practical applications, it is recommended to have professional electricians design and construct
to ensure compliance with electrical safety specifications.
