A thermal relay is a protector that uses the thermal effect of current to cut off the circuit. When the thermal overload relay is used for overload protection in the motor, it often work with ac contactor to form an electromagnetic starter, and then to be used in the control and protection circuit of the three-phase asynchronous motor. If the motor is overloaded for a long period of time, under-voltage or phase-failed during operation, the current of the motor will exceed the rated value. At this time, the thermal overload relay will cut off the control circuit of the motor, thus to effectively protecting the motor.
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The role of thermal relay and overload relay's installation wiring
1. The role of thermal relay
and overload relay’s
installation wiring
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2. what is a thermal
overload relay ?
What is the role of
the thermal relay?
Thermal relay
installation and
wiring
CONTENTS
01 02
03
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3. St
what is a thermal
overload relay ?
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4. A thermal relay is a protector that uses the
thermal effect of current to cut off the circuit.
When the thermal relay is used for overload
protection in the motor, it often work with ac
contactor to form an electromagnetic starter,
and then to be used in the control and
protection circuit of the three-phase
asynchronous motor. If the motor is overloaded
for a long period of time, under-voltage or
phase-failed during operation, the current of
the motor will exceed the rated value. At this
time, the thermal overload relay will cut off the
control circuit of the motor, thus to effectively
protecting the motor.
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5. The working principle of the thermal relay is
that the current flowing into the heating
element generates heat to make the bimetal of
different expansion coefficients to deform.
When the deformation reaches a certain
degree, the link is pushed to break the control
circuit, thereby making the contactor lose
power. And the main circuit is disconnected to
achieve the overload protection of the motor.
As an overload protection component of the
motor, the thermal relay has been widely used
in production due to its small size, simple
structure and low cost.
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6. St
What is the role
of the thermal
relay?
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7. It is mainly used for overload protection of asynchronous
motor. His working principle is that after the overload
current passes through the heat element, the bimetal is
heated and bent to push the action mechanism to drive
the contact action, thereby disconnecting the motor
control circuit to realize the motor power off for overload
protection. In view of the fact that the transfer of heat
takes a long time during the bending of the bimetal, the
thermal relay cannot be used as a short circuit protection,
but can only be used as an overload protection. The
symbol is FR.
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8. When the current through the thermal relay to the motor
exceeds the set value for a certain period of time (the internal
thermal differential element, the larger the excess value, the
shorter the operating time), the auxiliary contact actions to
disconnect the contactor coil which controls the motor for the
overload protection.
The thermal relay is mainly used for protecting the overload
of the motor in the electric drive system and controlling the
heating state of other electrical equipment. The purpose is to
prevent the equipment such as the motor from being
seriously overloaded for a long time which will accelerate the
aging of insulation elements,shortening service life and even
burning of the motor.
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9.
10. When the motor is overloaded for a period of time
(there is an adjustable value on the thermal relay
to set the current value), a certain amount of heat
is accumulated inside the thermal relay to cause
the relay to operate. After confirming the cause of
the overload, press a button on the relay to
resume.
The overload protection is not over-current
protection, and fuses are generally used for over-
current.
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13. Try to use copper wire as much as possible. If the aluminum
wire to be connected to the copper terminal of the thermal
relay, the contact resistance is large, the connection is likely to
be heated and the thermal relay may move in advance or
malfunction.
The thermal element
of the relay shall be
connected in the main
circuit, and its
breaking control
contact shall be
connected in series in
the auxiliary circuit.
The wires which to be
connected to the
output and input
terminals of the thermal
relay should be
correctly selected
according to the rated
current of the motor.
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14. The cross-sectional area of the copper
wire has a great influence on the
accuracy of the operation of the thermal
relay. If the selected wire is too thin,the
axial heat conduction is poor and may
make the thermal relay action in
advance; if the selected wire is too thick,
the axial heat conduction is fast and the
thermal relay may lag in operation.
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15. 04
03
02
01
05
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