Dynamic Braking Option, Motor Protection; Install An Electromagnetic Contactor (Mc) At The Input Side Of The Drive; Installing A Thermal Overload Relay On The Drive Output - YASKAWA GA700 Series Technical Manual

3.11

Dynamic Braking Option, Motor Protection

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Install an Electromagnetic Contactor (MC) at the Input Side of the Drive

You can use an MC as an alternative to a molded case circuit breaker (MCCB) when:
• The protective functions of the drive have been triggered
• An emergency stop occurred, and the sequence de-energizes the drive.
If an MC on the input side of the drive (primary side) stops the drive, regenerative braking will not operate, and
the drive will coast to stop.
NOTICE: When you connect electromagnetic switches or magnetic contactors to the output motor circuits, make sure that you
sequence them correctly. If the output motor circuit sequence is incorrect, it can cause damage to the drive.
NOTICE: Damage to Equipment. Do not energize and de-energize the drive more frequently than one time each 30 minutes. If
you frequently energize and de-energize the drive, it can cause drive failure.
Note:
• When machinery must not restart after recovery from a momentary power loss that occurred during run, install an MC at the input side
of the drive and set a sequence that does not automatically set the Run command to ON after recovery of power.
• When it is necessary to stop momentary power loss, for example to maintain a circuit that has momentary power loss, use a delayed-
release MC.
• Use an MC (magnetic contactor) to make sure that you can fully remove power to the drive when necessary. Wire the MC to open
when a fault output terminal is triggered.
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Protect the Braking Resistor/Braking Resistor Unit
Use an MC on the input side (primary side) to prevent damage to the braking resistor/braking resistor unit.
WARNING! Fire Hazard. When you use a braking unit, use a thermal relay on the braking resistors and set a fault contact
output for the braking resistor unit to disconnect drive main power through an input contactor. Incorrect braking circuit protection
can cause the resistors to become too hot and cause serious injury or death.
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Installing a Thermal Overload Relay on the Drive Output

A thermal overload relay disconnects the power line to the motor during a motor overload condition to prevent
damage to the motor.
Install a thermal overload relay between the drive and motor in these conditions:
• When you operate more than one motor with one drive
• When you operate the motor directly from the power line with a power line bypass
When you operate one motor with one drive, it is not necessary to install a thermal overload relay. The drive has
electronic motor overload protection in the drive software.
Note:
• When you install a thermal overload relay, set parameter L1-01 = 0 [Motor Overload (oL1) Protection = Disabled].
• Set up a sequence that will trip an external fault (coast to stop) for the contacts of the thermal overload relay.
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General Precautions When Using Thermal Overload Relays
When you use a motor thermal overload relay on the drive output to prevent nuisance trips and overheating of the
motor at low speeds, be sure to think about these application precautions:
• Operation of a low speed motor
• When you operate more than one motor with one drive
• Length of the motor cables
• Nuisance tripping because of high drive carrier frequency
Operation of a Low Speed Motor
Usually, you use thermal overload relays on general-purpose motors (standard motors). When a drive drives a
general-purpose motor, the motor current is approximately 5% to 10% more than with a commercial power
supply. When a motor with a shaft-driven fan operates at low speeds, the cooling capacity decreases. This can
cause the motor to overheat when the load current is in the motor rated value. Enable the electronic thermal
protection in the drive when possible to prevent this problem.
The electronic thermal overload function uses the relation between the speed and heat characteristics in the
variable speed control range to simulate the cooling ability of general-purpose motors and forced-vented motors to
prevent damage to the motor.
YASKAWA SIEPC71061705H GA700 Series Technical Manual

3.11 Dynamic Braking Option, Motor Protection

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