In the process of using a circuit breaker, adjusting its opening and closing speed is essential to ensure safe and reliable operation. Conducting an accurate speed test is the most direct way to identify the cause of any unqualified speed performance. Understanding the correct testing methods and the reasons behind speed reduction plays a critical role in properly assessing the circuit breaker's functionality.
First, let’s explore the common causes of reduced speed in a circuit breaker:
1. **Power Supply Issues**
The power supply serves as the energy source for the circuit breaker to open and close. If the voltage is too low, it can affect the speed. In electromagnetic mechanisms, a weak voltage may cause the closing core to move slowly, reducing the closing speed. In hydraulic systems, if the first-stage ball valve opens too little during the opening process, high-pressure oil cannot be released quickly, which slows down the opening speed. Similarly, if the ball valve doesn’t open enough, the pressure in the closing oil line builds up too slowly, ultimately affecting the closing speed.
2. **Insufficient Energy Storage or Pressure**
In spring-operated mechanisms, if the energy storage spring isn't fully charged, or in hydraulic systems if the pressure is too low, the opening and closing speeds will decrease. In pneumatic mechanisms, a faulty closing spring can also lead to slower closing speeds.
3. **Improper Adjustment of the Operating Mechanism**
In electromagnetic mechanisms, issues such as premature switching of the auxiliary switch, incorrect polarity of the closing coils, or a short closing ram can all reduce the closing speed. For spring mechanisms, insufficient spring force or jamming in the transmission system can lower the opening speed. In hydraulic systems, small openings in the secondary valves or throttle pads can slow down either the opening or closing speed, depending on where the restriction occurs. Blockages in the pipeline, inflexible pistons, or improper installation can also contribute to speed reduction.
4. **Poor Adjustment of the Circuit Breaker Body**
Excessive over-travel, excessive contact pressure, or stiff contact fingers can reduce the opening speed. Additionally, poor buffer performance or mechanical jams in the transmission system can negatively impact both opening and closing speeds.
Second, it’s important to note that some field technicians mistakenly believe that if the intrinsic time, closing time, or other timing parameters are within acceptable limits, the speed must also be okay. However, this is not always true. According to real-world data, many circuit breakers have qualified breaking and closing times but still fail in speed tests. If the speed is too low or too fast, it can increase arc duration, leading to higher temperatures and potential damage to the arc-quenching medium. This can result in welded contacts or burning, especially in single-phase breakers. For three-phase breakers with linkage mechanisms, speed variations can significantly affect synchronization.
Finally, accurate speed measurement is crucial. In practice, there is often inconsistency in how the just-opened and just-closed points are determined—some rely on over-travel, while others use electrical disconnection points. These differences in definitions and measurement methods can lead to conflicting results, causing incorrect assessments. Therefore, it is vital to follow standardized procedures, ensure uniformity in determining the just-opened and just-closed points, and maintain consistent testing practices for reliable speed measurements.
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