Table of Contents
Advertisement
2 Mechanical & Electrical Installation
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
• Operating more than one motor from 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.
Operating More than One Motor from One Drive
To disable the overload protection function of the electronic thermal protector of the drive, set L1-01 = 0 [Motor
Overload (oL1) Protection = Disabled].
Note:
If you operate more than one motor from one drive, you cannot use the electronic thermal protection of the drive.
Length of the Motor Cables
If you use long motor cables with a high carrier frequency, the increased leakage current can cause nuisance
tripping of the thermal relay. To prevent this, decrease the carrier frequency or increase the tripping level of the
thermal overload relay.
Nuisance Tripping Because of High Drive Carrier Frequency
High carrier frequency PWM drives make current waveforms that can increase the temperature in overload relays.
It may be necessary to increase the trip level setting when encountering nuisance triggering of the relay.
WARNING
Fire Hazard. Make sure that a secondary problem is not the cause of the overload before you increase the
detection level of the thermal relay. Verify local ordinances for electrical wiring, then adjust electrothermal settings. Incorrect
wiring can cause death or serious injury from fire.
◆
Improve the Power Factor
■
Connect an AC Reactor or a DC Reactor
AC reactors and DC reactors decrease surges in current and improve the power factor on the input side of the
drive.
Connect an AC reactor or a DC reactor to the input side (primary side) in the these conditions:
• To decrease harmonic current or improve the power factor of the power supply
• When there is switching of phase advancing capacitor
• With a large capacity power supply transformer (600 kVA or more).
Note:
• You can use an AC reactor and DC reactor together.
• When you connect a thyristor converter (for example, a DC drive) to the same power supply system, you should use an AC reactor,
regardless of the conditions of the power supply.
• The main circuit terminal block for the drive, and the terminal blocks for the AC and DC reactors come in different shapes. The drive
has a European-style terminal block, and the AC and DC reactors have a circular terminal block. Use caution when you prepare the
ends of the wires.
Connect an AC Reactor
Note:
When you connect an AC reactor to the output side (secondary side) of the driver, set C6-02 = 1 [Carrier Frequency Selection = 2.0
kHz].
108
YASKAWA ELECTRIC SIEP C710617 19A YASKAWA AC Drive CR700 Technical Manual
Advertisement
Table of Contents
