Principles and troubleshooting of phase sequence protection and phase loss protection in cold storage | Electrical protection for three-phase compressor burning machine
Three phase 380V semi enclosed screw compressor, phase sequence protection and phase loss protection are the first line of electrical defense to prevent motor reverse and phase loss operation from burning out the winding.
Phase sequence protection: detects the three-phase phase, and if the phase sequence is reversed and locked directly, it cannot be started; Phase loss protection: If one phase is missing in three phases, the current will sharply increase and trip within a few seconds.
The controller of the Xiteluo three-phase unit integrates phase sequence and phase loss protection, and some independent phase sequence relays can adjust the delay separately to avoid false alarms caused by instantaneous voltage fluctuations.
Characteristics of phase loss operation: compressor buzzing, unbalanced current, three-phase current difference exceeding 15%, continuous operation for several minutes, winding overheating and burnout.
Many construction sites randomly switch phase lines, reverse the phase sequence, reverse the oil pump, and fail to establish oil pressure. When starting up, there is a direct oil pressure difference alarm, which makes it easy for beginners to misjudge oil circuit faults.
Loose cable crimping, oxidation of air switch contacts, and erosion of contactor contacts are the most common causes of phase loss on site, not the power supply itself.
Foreign trade overseas construction sites with unstable voltage, excessive three-phase voltage imbalance, frequent triggering of phase sequence protection false alarms, require the installation of three-phase voltage stabilization devices.
After the protection alarm, do not directly short-circuit the phase sequence relay to forcibly start, as the motor will reverse and the oil pump will fail, causing the cylinder to quickly lock up.
Maintenance points: Measure three-phase voltage and three-phase operating current every quarter, record and compare; Replace the contactor contacts promptly if they turn black or burn out.
Parallel multi head unit, each compressor is independently equipped with phase sequence protection, and cannot share a common main phase sequence protection. Single channel faults cannot be isolated.
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FAQ
What are the direct consequences of reversing the phase sequence? The oil pump is reversing and unable to establish oil pressure.
2. Typical risks of phase loss operation? Current imbalance, short-term burning of motor windings.
How to configure phase sequence protection for parallel units? Each machine head is independently protected.
Can phase sequence protection be short circuited to force startup? Strictly prohibited, it is highly likely to damage the compressor.
5. How much should we be cautious about the imbalance of three-phase current? The difference exceeds 15%.
6. Common reasons for missing phases? Contact points of the contactor are corroded, wiring is loose, and oxidized.
How to deal with overseas voltage imbalance? Install a three-phase voltage regulator.
