Fundamentals of automatic transfer switches (ATS)?

Dual power Automatic Transfer Switching Equipment (ATSE) is an electrical device used to automatically switch between two different power supplies

How it works

A dual power automatic transfer switch usually connects two power sources, i. e. a common power source and a standby power source. When the common power supply fails (such as power failure, abnormal voltage, etc.) , the transfer switch will automatically detect the power failure state and switch the load circuit from the common power supply to the standby power supply within the specified time, in order to ensure the continuous power supply of load equipment. When the common power supply return to normal, the transfer switch can automatically or manually switch the load back to the common power supply according to the set conditions.

Structure and composition

Switch Body: is the implementation of power switching components, usually in the form of mechanical switch or electric switch, can be used between different power supply for reliable electrical connection and disconnect operation.
Controller: Used to monitor the status of two power supply, such as voltage, frequency, phase and other parameters, and according to the preset rules and logic to control the action of the switch body. The controller has the functions of signal detection, processing and control, which can quickly and accurately judge the power supply fault and issue switching instructions.
Operating Mechanism: responsible for executing the instructions of the controller, driving the switch body to switch the power supply. The operating mechanism can be electric, pneumatic or electromagnetic to meet different application scenarios and load requirements.

Type

PC class: it belongs to the integral structure, the contact system adopts silver alloy or copper alloy material, has high breaking capacity and reliability, can withstand the impact of short-circuit current, suitable for places with high power supply reliability requirements, hospitals, airports, data centers, etc. .
CB class: Circuit Breaker as the main body, with over-current, short circuit and other protection functions, but its switching time is relatively long, suitable for some places where the power supply continuity is not particularly demanding, but the circuit needs protection, such as industrial plants, commercial buildings, etc. .

Application scenarios

Hospitals: critical departments such as operating rooms and intensive-care unit rooms in hospitals require a continuous power supply. Dual power automatic transfer switches quickly switch to another power supply when one fails, ensure the normal operation of medical equipment to ensure the safety of patients.
Data Center: the Data Center stores a large number of key data, servers and other equipment can not easily power down. Dual power automatic transfer switch can switch to standby power supply in time to prevent data loss and service interruption.
Transportation: airports, railway stations and other transportation hub lighting, signaling systems, security equipment, etc. are dependent on a reliable power supply. Dual power automatic transfer switch to ensure that in the event of power system failure, these important equipment can continue to work to maintain traffic order and safety.
Industrial production: in some industrial production processes that can not be easily stopped, such as chemical, steel and other industries, the dual power automatic transfer switch can switch quickly when the power supply is in trouble, avoiding the shutdown of production equipment, reduce the loss of production.

What are the common faults of dual power automatic transfer switch?
Common faults of dual power automatic transfer switch include abnormal switching, abnormal switching time, contact overheating and burning, controller failure, etc. . The following is the specific analysis:
Unable to switch properly
Power failure detection circuit failure: Detection Circuit components damage, such as voltage transformer, current transformer, resistors, capacitors, etc. failure, will lead to the controller can not accurately detect the state of the power supply, unable to issue a switchover command.
Controller failure: the controller internal microprocessor, memory, logic circuit failure, may make the controller can not work properly, unable to control the switch.
Operating mechanism failure: operating mechanism of the motor, transmission gear, connecting rod and other parts of the failure, such as motor burn, Gear Wear, connecting rod fracture, etc. , will lead to switch can not perform switching action.
Abnormal switchover time
The controller parameters are not set properly: the switching delay time is set too long or too short, which does not meet the practical application requirements. Different application scenarios have different requirements for switching time. If the setting is not reasonable, it may cause the load equipment to be unable to work properly due to the long power off time.
Power supply voltage fluctuation: when the voltage fluctuation of the two power supplies is large, it may affect the judgment of the controller on the state of the power supply, and then lead to the deviation of the switching time.
Overheating and burning of contacts
Poor contact: Contact in long-term use, may appear after oxidation, wear and so on, resulting in increased contact resistance. When there is a current through, will produce a lot of heat, make contact temperature rise.
Load current is too large: if the actual load current exceeds the rated current of the dual power automatic transfer switch, the contact will bear the current is too large, resulting in overheating.
Arc extinguishing system fault: arc extinguishing system problems, such as arc cover damage, lack of arc extinguishing medium, etc. , will make the contact breaking arc can not be extinguished in time, the arc continues to burn will make the contact temperature rises sharply, and the contact burns out.
Controller malfunction
Software failures: errors, Bugs, or version incompatibilities in the controller's program may cause the controller to function abnormally, such as misjudging the power state and failing to control switching properly.
Hardware Failure: the electronic component of the controller, such as chips, capacitors, crystal oscillator, etc. , are damaged due to aging, overheating, overvoltage, etc. , which will make the controller not work properly.
Indicates that the signal is abnormal
Indicator lamp damage: the indicator lamp indicating the status of power supply, switch position and other information can not be displayed normally due to lamp damage, poor line contact and other reasons, which brings difficulties to the operator to judge the status of the equipment.
Signal transmission failure: the signal transmission line between the controller and the indicator lamp is open, short circuit and other faults, which will cause the indicator lamp to be unable to receive the correct signal, thus indicating abnormality.

Advantages and disadvantages of different types of dual power automatic transfer switch

Dual Power Automatic transfer switch is mainly divided into PC level and CB Level 2 types, with different advantages and disadvantages

PC-class dual power automatic transfer switch
Advantages
Simple structure: using integral structure, generally by the conversion contact system, drive mechanism and intelligent controller, no complex release and other protective devices, so the structure is relatively simple, high reliability.
Fast switching speed: able to complete power switching in a short time, usually within 100ms switching time, suitable for high demand for power supply continuity occasions, such as data centers, hospital operating rooms, etc. , can effectively avoid the power switching time is too long to cause equipment downtime or data loss.
High breaking capacity: the contact system uses high-performance materials such as silver alloy or copper alloy, which has high breaking capacity, can withstand large short-circuit current impact, and can reliably break the circuit when the power supply fails, ensure the safety of equipment and personnel.
Non-impact current: in the switching process, through reasonable design and control, can achieve non-impact current switching, less impact on the load equipment, especially suitable for high power quality requirements of precision equipment.
Disadvantages
The protection function is relatively weak: the PC-level dual-power automatic transfer switch itself generally does not have over-current, short-circuit and other protection functions, and needs to be used in conjunction with other protection appliances, which increases the complexity and cost of the system.
High Price: due to its high-performance materials and advanced manufacturing process, as well as the strict requirements for reliability and switching speed, the price of PC-class dual-power automatic transfer switch is relatively high, in some cost-sensitive projects may be limited.
CB class dual power automatic transfer switch
Advantages
With protection functions: Circuit Breaker as the main body, itself has overcurrent, short circuit, overload and other protection functions, can cut off the circuit in time when the circuit fails to protect the load equipment and line safety, the utility model reduces the use of the external protective electric appliances and simplifies the system configuration.
The price is relatively low: compared with the PC-class, the CB-class dual-power automatic transfer switch has a relatively simple structure and manufacturing process, so the price is relatively cheap, and in some occasions where cost control is more strict, such as ordinary industrial plants, commercial buildings and other applications more widely.
Disadvantages
Slow switching speed: due to the relatively complex operation mechanism of the circuit breaker, and the need for certain time to complete the tripping and closing action, the switching time of the CB-class dual-power automatic transfer switch is longer, usually between a few hundred milliseconds and a few seconds, which may not be sufficient for some devices that require very high continuity of power supply.
Limited breaking capacity: although the circuit breaker itself has a certain breaking capacity, the overall breaking capacity of the CB-CLASS dual-power automatic transfer switch is relatively low compared to the PC-class, and when faced with large short-circuit currents, the CB-class dual-power automatic transfer switch has a relatively low breaking capacity, may not be able to reliably break the circuit, there are certain security risks.
Impulse current: in the process of switching, due to the action characteristics of the circuit breaker and the arc at the moment of contact separation, it may produce a certain impulse current, which has a certain impact on the load equipment, especially for some devices that require high power supply stability, additional measures may be required to suppress surge currents.