**Take a look at what’s wrong with this control chart, for the control of dual-speed fans
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**Take a look at what’s wrong with this control chart; it is used for controlling a two-speed fan. Fans for Class A warehouses
Since the internal structure of the motor is unknown, one can only rely on the control schematic diagram. A fan is used in this system; under normal conditions, when powered by 1KM, the fan operates at low speed to exhaust air. When a gas alarm is triggered, KT is automatically disconnected, causing 1KM to lose power. After a delay, 2KM is activated, and the fan operates at high speed to quickly exhaust air and reduce the concentration of hazardous gases. Once the gas alarm signal disappears, KT and 1KA lose power, allowing the fan to be switched to low-speed operation.
As I understand it, when looking at the main circuit diagram, it seems similar to the star-delta reduced-voltage starting diagram, but what is shown in the diagram is quite different. First, press the start button SB1; 1KM is powered, but is it only three-phase power? Can the motor rotate? When the combustible gas probe triggers an alarm, ZK is activated and a voltage of 2KM to 3KM is applied; the motor is connected in star configuration. However, the issue is that the thermal relay is connected to the short-circuit wire – will it be able to provide protection?
Here is the description from the design institute: 1. Warehouses 1, 2, 3, and 4 are equipped with regular exhaust ventilation as well as emergency exhaust ventilation; they are divided into four ventilation systems based on the building’s fire compartmentation. The fan uses an explosion-proof, low-noise cabinet-type centrifugal fan unit (with two speed settings); it operates at low speed for normal exhaust and at high speed in emergency exhaust situations. The fan is installed on the roof, with a backup fan provided. 2. Explosion-proof fans should be equipped with manual switches in outdoor locations that are easy to access, and they should start in conjunction with devices for detecting and alerting to flammable or harmful gases. The power supply load level for all fans shall not be lower than that of the process power supply.
I was wrong; the fan can indeed rotate. What I meant was that the diagram and the instructions are opposite to each other – during an accident, the motor operates at low speed
1. To find out how a two-speed motor achieves this functionality, it is necessary to consult the manufacturer’s documentation to determine whether coil taps or pole reduction is used for that purpose; based on this information, it is then possible to assess whether the control circuit diagram is correct. 2. Regarding the issue with the thermal relay, it’s best to ask the design team whether it only provides protection at low speeds, and does not offer protection in emergency situations at high speeds If that is not the case, both the thermal relay and its contact position need to be adjusted. 3. Regarding whether it should be the opposite of the diagram, it is better to make a decision after understanding the internal structure of the motor. Not very professional; for reference only.
I’m sorry, I misunderstood. I just understood that the motor speed is changed by altering the number of pole pairs. Haha, the diagram itself is fine; at most, the location of the thermal relay at high speeds isn’t optimal