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
| Type | RD6-W |
| Measuring circuit | L1,L2,L3 |
| Rated voltage | 380VAC ,50/60Hz |
| Monitoring functions | phase sequence, phase loss, overvolatege, undervoltage, timing,
counting |
| Overvoltage setting range | 380-600V adjustable |
| Undervoltage setting range | 100-380V adjustable |
| Hysteresis | 1-20V adjustable |
| Delay time for overvoltage and undervoltage | 1-20s adjustable |
| Delay time for phase loss | 1-20s adjustable |
| Delay time for phase sequence | 1-20s adjustable |
| Indicators | LCD indicating voltage,current,operation status |
| Output contacts | 1 C/O,1NC |
| Contact capacity | 6A ,250VAC |
| Dimensions (H x W x D) | 80×40×54mm |
| Mounting | DIN rail |
