It is not necessary to install a motor thermal overload relay when operating a single motor
from a single AC drive. The AC
drive has UL recognized electronic motor overload protection
built into the drive software.
Note: Disable the motor protection function (L1-0 1 = “0”) when using an external motor thermal overload relay.
The relay should shut off main power on the input side of the main circuit when triggered.
n
General Precautions when Using Thermal Overload Relays
The following application precautions should be considered when using motor thermal
overload relays on the output of AC drives in order to prevent nuisance trips or overheat of
the motor at low speeds:
• Low speed motor operation
• Use of multiple motors on a single AC drive
• Motor cable length
• Nuisance tripping resulting from high AC drive carrier frequency
Low Speed Operation and Motor Thermal oL Relays
Generally, thermal relays are applied on general-purpose motors. When general-purpose
motors are driven by AC drives, the motor current is approximately 5 ~ 10% greater than if
driven by the commercial power supply. In addition, the cooling capacity of a motor with a
shaft-driven fan decreases when operating at low speeds. Even if the load current is within
the motor rated value, motor overheating may occur. A thermal relay cannot effectively protect
the motor due to the reduction of cooling at low speeds. For this reason, apply the UL
recognized electronic thermal overload protection function built into the drive whenever
possible.
UL recognized electronic thermal overload function of the drive: Speed-dependent heat
characteristics are simulated using data from standard motors and force-ventilated motors.
The motor is protected from overload using this function.
Using One Drive with Multiple Motors
Turn off the electronic thermal overload function. Please refer to the appropriate product
instruction manual to determine which parameter disables this function.
The UL recognized electronic thermal overload function of the drive cannot be applied when
using multiple motors on one drive.
Long Motor Cables
When long motor cables and high carrier frequency are used, nuisance tripping of the thermal
relay may occur due to increased leakage current. Therefore, reduce the carrier frequency or
increase the tripping level of the thermal overload relay.
Nuisance Tripping Resulting from High AC Drive Carrier Frequency
Current waveforms generated by high carrier frequency PWM drives tend to create additional
temperature rise in overload relays. Therefore, it may be necessary to increase the trip level
setting when encountering nuisance triggering of the relay.
7.4 Installing Peripheral Devices
YASKAWA ELECTRIC TOEP C710606 25B YASKAWA AC Drive J1000 Installation & Start-Up Manual
179
7
Peripheral Devices &
Options
2/6/2008-14:44
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