- Loss of a single phase on three-phase motors can damage equipment and lead to costly repairs.
- Phase loss can result from a downed power line, a blown fuse or equipment failure in your facility.
- Phase monitors can detect phase loss and disconnect equipment to prevent damage.
Three-phase motors are commonly used in commercial and industrial facilities. Loss of a single phase can damage equipment, resulting in reduced productivity and costly repairs. If three-phase equipment is critical to your operations, phase protection makes good business sense.
What causes phase loss?
The loss of a single phase on a three-phase line may be due to a downed power line or a blown pole-top fuse on the utility system. Phase loss may also result from a single-phase overload condition causing one fuse to blow, or an equipment failure within your facility.
A small phase voltage unbalance will not typically harm a motor. However, greater unbalances often lead to insulation breakdown and shorter equipment life. The complete loss of a phase is essentially an extreme phase unbalance. It is more difficult to detect than simple phase unbalance and it can damage a motor very quickly. If not detected within as little as five seconds, it may lead to costly repair or replacement of the motor.
Phase loss protection
Phase loss protection devices are relatively inexpensive and simple to install. They provide protection by disconnecting equipment from the circuit when phase loss is sensed. The most commonly used phase protection solution is a phase monitor.
In addition to voltage, most phase monitors also measure current or phase angle, which—in addition to small voltage changes—indicates phase loss. Phase monitors detect over-voltage, under-voltage, phase reversal and excessive on/off cycling—all of which can damage motors. They react to total phase loss or phase unbalance. The action taken by the monitor can range from audible or visible alarms to complete shutdown of the motor.
Phase monitors can be installed at each motor, or on the secondary side of the circuit. A shunt trip capacitor should be added when the monitor is placed on the secondary side of the circuit, so it will still operate if there is a loss of power. Choose phase monitors based on the incoming line voltage and the detected frequency.
While phase protection may cost you a small amount of money upfront, it can help save you thousands of dollars in lost production and equipment repair or replacement.