Toshiba W7 manual ASD Characteristics, Motor Braking, Over-current Protection, ASD Capacity

resistor. The braking resistor must be suitably matched to the load. Dynamic braking is also effective in reducing the DC bus voltage during a momentary over-voltage condition.

CAUTION

If under extreme conditions the dynamic braking system or a component of this system were to fail, the dynamic braking resistor may experience an extended over-current condition. The DBR circuit was designed to dissipate excessive amounts of heat and if the extended over-current condition were allowed to exceed the circuit parameters, this condition could result in a fire hazard.

To combat this condition, the 3-phase input may be connected using contactors that are configured to open in the event of an extended DBR over-current condition or an internal circuit failure. Using a thermal sensor and/or overload protection as the 3-phase input contactor drive signal, the contactors will open and remove the 3-phase input power in the event of an extended DBR over-current or system over- voltage condition.

Motor Braking

The motor may continue to rotate and coast to a stop after being shut off due to the inertia of the load. If an immediate stop is required, a braking system should be used. The two most common types of motor braking systems used with the W7 ASD are DC Injection Braking and Dynamic Braking.

For further information on braking systems, see DC Injection Braking Current on pg. 65 and

Dynamic Braking Enable on pg. 68.

ASD Characteristics

Over-current Protection

Each W7 ASD model was designed for a specified operating power range. The ASD will incur a trip if the design specifications are exceeded.

However, the ASD may be operated at 100% of the specified output-current range continuously or at 120% for a limited time as indicated in the section titled Current/Voltage Specifications on pg. 155. Also, the Overcurrent Stall Level setting may be adjusted to help with nuisance over-current trips.

When using the ASD for an application that controls a motor which is rated significantly less than the maximum current rating of the ASD, the over-current limit (Thermal Overload Protection) setting will have to be changed to match the application. For further information on this parameter, see Electronic

Thermal Protection #1 on pg. 70.

ASD Capacity

The W7 ASD must not be used with a motor that has a significantly larger capacity, even if the motor is operated under a small load. An ASD being used in this way will be susceptible to a high-output peak current which may result in nuisance tripping.

Do not apply a level of input voltage to an ASD that is beyond that which the ASD is rated. The input voltage may be stepped down if required with the use of a step-down transformer or some other type of voltage-reduction system.

12 W7 ASD Installation and Operation Manual