Compressors Three Phase Voltage Monitoring Relay RD6-W Digital Setting

Compressors Three Phase Voltage Monitoring Relay RD6-W Digital Setting

Phase and voltage monitoring relay can prevent the badly from unbalance ,so,what's harm when phase unbalance happened

1 .  Increase the power loss of the line. In the three-phase four-wire power supply network, when the current passes through the line conductor, power loss will be generated due to the impedance, and the loss is proportional to the square of the passing current. When the low-voltage power grid is powered by a three-phase four-wire system, the three-phase load imbalance is inevitable because of the presence of a single-phase load. When the three-phase load is unbalanced, there is current through the neutral line. This not only has a loss of phase, but also a loss of the neutral line, which increases the loss of the power line.

2 .  Increase the power loss of distribution transformers. The distribution transformer is the main power supply equipment for the low-voltage power grid. When it is operated under unbalanced three-phase load conditions, the distribution transformer loss will increase. Because the power loss of the distribution varies with the degree of load imbalance.

3 .  Reduction in distribution and output. In distribution transformer design, the winding structure is designed according to load balancing operating conditions. The winding performance is basically the same and the rated capacities of the phases are equal. The maximum allowable output of the transformer is limited by the rated capacity of each phase. If the distribution transformer is operated under a three-phase load unbalanced condition, the light-loaded phase has a surplus capacity, thereby reducing the output of the distribution transformer. The degree of reduction in its output is related to the degree of unbalance of the three-phase load. The greater the unbalanced three-phase load, the more reduction in distribution transformer output. For this reason, the distribution transformer operates when the three-phase load is unbalanced, the output capacity thereof cannot reach the rated value, the standby capacity thereof is correspondingly reduced, and the overload capacity is also reduced. If the distribution transformer is operated under overload conditions, it is easy to cause the distribution to generate heat, and even if it is severe, the distribution transformer may be damaged.

4 . The distribution transformer produces a zero-sequence current. The distribution transformer operates under the three-phase load unbalanced condition and will generate a zero-sequence current, which will change with the degree of unbalance of the three-phase load. The greater the unbalance, the greater the zero-sequence current. If there is a zero-sequence current in the transformer during operation, zero-sequence flux will be generated in the iron core. (There is no zero-sequence current on the high-pressure side.) This forces the zero-sequence flux to only pass through the tank wall and the steel member as a passage. The steel member has a low permeability, and hysteresis and eddy currents are generated when the zero-sequence current passes through the steel member. Loss, so that the temperature distribution of the steel component of the transformer rises or even heat. Transformer winding insulation may also accelerate aging due to overheating, resulting in reduced equipment life. At the same time, the presence of zero-sequence current will increase the loss of distribution transformer.

5 . Affect the safe operation of electrical equipment. The distribution transformer is designed according to

the three-phase load balancing operating conditions. The resistance, leakage reactance and excitation impedance of each phase winding are basically the same. When the distribution transformer operates in three-phase load balancing, the three-phase currents are basically the same, and the voltage drop of each phase in the distribution transformer is also basically the same, then the three-phase voltage of the distribution transformer output is also balanced.
If the distribution transformer operates when the three-phase load is unbalanced, the output current of each phase is not equal, and the internal three-phase voltage drop of the distribution transformer is not equal, which will inevitably lead to unbalanced three-phase distribution output voltage. At the same time, the distribution transformer runs when the three-phase load is unbalanced, the three-phase output current is not the same, and the neutral line will have the current through. As a result, the neutral line produces an impedance drop, which causes a shift in the neutral point, resulting in a change in the phase voltage of each phase. The one-phase voltage with a heavy load decreases, while the one-phase voltage with a light load increases. When the voltage is unbalanced, power is supplied to the user's electrical device that is likely to cause a high-voltage one-phase connection, and the user's electrical device that is connected to a low-voltage one may not be used. Therefore, when the three-phase load is unbalanced, it will seriously jeopardize the safe operation of the electrical equipment.

6 . Motor efficiency is reduced. The distribution transformer operates under unbalanced three-phase load conditions and will cause unbalanced three-phase output voltage. Because the unbalanced voltage has three voltage components of positive sequence, negative sequence, and zero sequence, when the unbalanced voltage is input to the motor, the negative sequence voltage generates a rotating magnetic field and the rotating magnetic field generated by the positive sequence voltage acts as a brake. effect. However, because the positive sequence magnetic field is much stronger than the negative sequence magnetic field, the motor still rotates in the direction of the positive sequence magnetic field. However, due to the braking effect of the negative sequence magnetic field, the output power of the motor must be reduced, resulting in a decrease in motor efficiency. At the same time, the temperature rise and reactive power loss of the motor will also increase with the unbalance of the three-phase voltage. Therefore, the motor operates under three-phase voltage imbalance, which is very uneconomical and unsafe.

♦ Features

--Built-in LCD and keypad afford a precise,digital setting

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

-- Adjustable over- and undervoltage threshold

-- Independent adjustable delay time for phase sequence, phase loss, overvoltage, undervoltage

-- Powered by the measuring circuit

-- 1 C/O & 1NC contacts

-- with Timing, counting and faulure recording

♦ Protective Functions

-- Phase sequence

-- Phase loss

-- Overvoltage

-- Undervoltage

-- Timing

-- Counting
-- Faulure recording
 

♦ Typical Applications

• Pumps • Fans

• Blowers • Motors

• Compressors

♦ Approvals

• CE • CCC

♦ Technical data