The difference between thermal relay and motor protector - Solutions - Huaqiang electronic network
The difference between a bimetallic thermal relay and a motor protector is significant, especially when it comes to reliability and performance. According to statistics, out of 100 motor burnout incidents, 30 are caused by the failure of thermal relays to function properly. This is largely due to inherent design limitations that make them prone to issues like thermal fatigue. After repeated overheating, the bimetallic element may not return to its original state, leading to false trips or complete failure. As a result, many engineers avoid using thermal relays in critical motor protection applications from the start.
Motor protectors have been used in China for over 30 years, yet motor burnouts still occur frequently. The reasons behind this are mainly threefold: first, there is often confusion during the design phase about which functions are essential versus which are just added features—more isn't always better. Second, current sensors used in these devices are not always ideal, making it difficult for motor protectors to meet key requirements such as preventing false trips, ensuring compatibility with traditional thermal relays, and operating reliably in harsh environments. Third, users haven’t seen immediate benefits from using motor protectors, which has limited their adoption.
Over 97% of low-voltage motor failures are caused by overcurrent conditions. These can stem from overload (stall), long starting times, phase loss, overvoltage, undervoltage, or poor contact in the three-phase lines. Overcurrent due to overload or voltage fluctuations typically causes a balanced increase in all three phases, while issues like phase loss or imbalanced voltage lead to an uneven rise in one or two phases. Therefore, high-precision sinusoidal current sampling is crucial for effective motor protection.
Damaging a motor isn't just costly—it also leads to downtime, which can significantly impact production schedules. Removing a damaged motor from a machine can be time-consuming and labor-intensive. In critical industrial settings, even a short delay can result in substantial financial losses. Additionally, the repaired motor often doesn't perform as well as the original, accelerating the depreciation of the entire system. With copper prices at historic highs, protecting motors from damage has become more important than ever.
A small motor costing tens of thousands of yuan is not worth protecting with an unreliable thermal relay. Even small motors consume very little energy—20A is roughly equivalent to 60W, 60A to 80W, and 150A to around 100W—but they still require proper protection. In the past, energy was abundant, and conservation wasn't a priority. Today, with growing environmental concerns and rising energy costs, it's clear that a reliable motor protector is no longer optional—it's a necessity. The development of an ideal motor protector is not just a technical advancement; it's a societal imperative.
Longhua Manxueling Trading Company , https://www.mxlvape.com