3 Phase 3 wire Three Phase Voltage Monitoring Relay under-voltage protective device

In daily life, the loads we touch, such as electric lamps, televisions, refrigerators, fans and other household appliances and single-phase motors, are operated with two wires in the circuit, which are all single-phase loads. In the three-phase four-wire system, multiple single-phase loads should be connected as far as possible to the three-phase circuits, rather than being concentrated in one of the three circuits. If the impedance and the nature of the load connected to each of the three-phase circuits are the same, the loads in the three circuits are symmetric. Under load symmetry, because the phases of the phase currents differ from each other by 120°, the sum of the currents flowing through the neutral line at each moment is zero, and the neutral line is removed, and it is possible to supply power using a three-phase three-wire system.

However, in reality, the three-phase load formed by a plurality of single-phase loads connected to the three-phase circuit may not be completely symmetrical. The midline is particularly important in this case, not dispensable. The voltage across the load of each phase of the neutral line is always equal to the phase voltage of the power supply and will not change due to the asymmetry of the load and the change of the load, just as each phase of the power supply separately supplies the load of each phase separately. Can work properly. If there is no neutral line under the condition of asymmetric load, three-phase three-wire power supply with asymmetrical load is formed. Due to the asymmetry of the load impedance, the phase current is also asymmetric and the load phase voltage is naturally not symmetrical. Some phase voltages may exceed the rated voltage of the load, the load may be damaged (bulb burned), some phase voltages may be low, and the load may not work properly (bulbs dimmed). As in the figure, the load impedance of each phase changes due to lighting, turning off the lamp, and other factors. Both the phase current and the phase voltage change, the light turns on and off, and other electrical appliances cannot work properly or even become damaged.
Bad. It can be seen that in the three-phase four-wire power supply line, the neutral line plays a role in ensuring that the load phase voltage is symmetrical and unchanged. For an asymmetrical three-phase load, the neutral line cannot be removed, fuses or switches cannot be installed on the midline, and it is necessary to use The steel wire with better mechanical strength serves as the center line.

♦ Features

-- Compact modular size

-- Three-phase monitoring of phase sequence, phase loss, over- and undervoltage and phase unbalance

-- Powered by the measuring circuit

-- 2 C/O contacts

-- 5 LEDs for status indication

♦ Protective Functions

-- Phase sequence

-- Phase loss

-- Overvoltage

-- Undervoltage

-- Phase unbalance

♦ Typical Applications

• Pumps • Fans

• Blowers • Motors

• Compressors

♦ Approvals

• CE • CCC

♦ Technical data