Five technical measures to prevent electric shock and arc flash injuries when using motors

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Five technical measures to prevent electric shock and arc flash injuries when using motors [Copy link]

Factory workers often work on motors and pumps, which puts them at risk of electric shock and arc flash injuries. A friend from abroad introduced five technical measures to prevent motor damage to the human body. Here I share them with you. 1. Upgrade to smart motor relays In the past, only expensive large motors used full-featured relay protection, while smaller motors only had basic overload relay protection. As the cost of microcontroller chips decreases, it is feasible to install smart relays on small motors without adding much cost. Currently, relays use two methods to protect: first, they cut off power when dangerous conditions occur. Second, they monitor and report conditions so that workers can take timely measures to prevent small problems from developing into major hidden dangers. There are many reasons for motor failure, such as overload, blocked loads, phase imbalance of motor power, and ground faults. If the motor is damaged, it will cost a lot to repair or replace the motor. The current new generation of relays can detect and respond to these problems. More advanced motor relays can detect all of the above problems, as well as ground leakage current, ground faults, undercurrent, motor overheating (via a dynamic thermal model of the motor), overvoltage, undervoltage, reverse sequence, phase loss, and voltage imbalance. Some can even detect changes in power factor, allowing them to detect flow loss caused by blocked inlets or dry wells. Typically, such relays transmit the problems they detect (and the current state of the motor) to the control system via a standard plant network. These smart motor relays can also increase worker protection by tripping at their instantaneous settings when a hazard occurs while a person is operating on the operator panel.

Current-limiting fuses disconnect quickly during high-value faults

2. Use motor protection relays with Bluetooth capabilities When a motor fails, maintenance usually requires workers to open the motor's chassis, read the fault code from the electrical control panel and read the motor protection relay. Opening the motor chassis increases the risk of workers facing arc flash. Some motor protection relays can communicate with a technician's smartphone via Bluetooth. Workers can read fault codes on their smartphones, and the distance between the phone and the relay will be far, which can effectively protect workers' safety and protect them from electrical hazards because there is no need to open the motor's chassis door. At the same time, using smartphones at work to receive motor detection and share real-time data through the phone's Bluetooth can make it easier and more efficient to monitor motor operation. 3. Use new fuses Certain new fuses, called current-limiting fuses, can open quickly enough to achieve the purpose of rapid current limiting. This can prevent or reduce damage to the motor and prevent more serious problems such as fires and explosions. Because of the fuses used in traditional equipment, maintenance personnel tend to replace fuses with the same type as before without considering the benefits of upgrading to a new fuse type. Therefore, maintenance personnel are better off using more advanced fuses. 4. Install arc flash detectors Arc flash is caused by a short circuit, where a high-energy conductor is connected to the ground or another conductor, which produces a burning burst of visible and invisible light and a strong explosion. In fact, arc flash is the second-most dangerous hazard faced by electrical maintenance personnel in power plants. Arc flash is very different from electric shock. When a person is electrocuted, the current passes through sensitive tissues (mainly nerves) in the human body, causing the impact. Arc flash usually occurs when the air is conductive, and its main cause is the current drawn out when two contacting conductors separate again. When an arc occurs, the gap formed is filled with ions, and its number rises rapidly, especially in high-voltage/low-resistance power supply situations, such as power transmission lines. This situation is more obvious. Any circuit greater than 50V has the potential to produce an arc flash. Arc flash detectors are typically used in panels with voltages greater than 300 V. When an arc is detected, the arc flash detector sends a trip signal to the circuit breaker in less than 1 millisecond. The circuit breaker will open in 30 to 50 milliseconds, which is enough to prevent arc flash hazards. At present, some manufacturers directly produce arc flash relays. 5. Add an industrial ground fault circuit interrupter (GFCI) Industrial ground fault circuit interrupter (GFCI) is the name in the United States, and it is called leakage protection in China. Water and process fluids are conductive. When motors are used in many humid places, such as submersible pumps, mixers and similar process equipment, people are at increased risk of electric shock. This is why bathrooms and kitchens need to use ground fault circuit interrupter (GFCI) sockets. Leakage protection quickly disconnects the circuit when a ground fault is detected to avoid electric shock. In the wiring system in the home, on a power socket, the current of the live wire (Hot) and the neutral wire (Neutral) should be equal under normal circumstances. GFCI monitors the current difference. Once the difference is greater than 6 milliamps (Milli Amps) (according to UL943 standard, the disconnection time is 25 milliseconds when the leakage current is 6mA), it can cut off the power supply in an instant after 0.025 seconds (according to UL943 standard, the disconnection time when the leakage current is 4-6mA under 500 ohm impedance), thereby ensuring personal safety. The GFCI interrupts electricity faster than the blink of an eye to prevent deadly electrical shock.

How Industrial Ground Fault Circuit Interrupter (GFCI) Works