ABB Electrical OS30ACC12 Disconnect Switch

Model Type: POWERLINE Series Electrical OS30ACC12 Disconnect Switch

The current setting value can be set so that it is automatically doubled during start-up. Therefore, the setting value can be set lower than the motor starting current.

Normally it can be set as low as 0.75 times the motor starting current. In addition, an appropriate action time should be set to match.

In this way, when the motor is blocked during operation, the current interruption protection unit can ensure reliable operation.

When the motor is controlled by a contactor, the high value overcurrent protection unit should be blocked and the fuse should be used to protect against short circuits.

The non-directional earth fault unit detects earth faults in the motor and feeder circuits. In the neutral point directly grounded or through the low impedance grounding system, the CT can be connected to a residual ground fault.

The CT can be wired for residual current to obtain the zero sequence current, and the action time of the earth fault protection can usually be set to a smaller value, e.g. 50ms.

In circuits controlled by contactors, the line current can be set to exceed 4 (or 6.8) times the full load current I in the thermal overload unit.

The earth fault unit is blocked so that the contactor will not be damaged by the inability to break the high current and the fault current will be broken by the back-up fuse.

This blocking function is also used to prevent malfunctions caused by false zero sequence currents during start-up due to saturation of the CT on the circuit.

In order to obtain a high sensitivity, the earth fault current action value is generally rounded to 15...40% of the rated motor current. ...40% of the motor's rated current.

In networks where the neutral point is insulated or earthed via a high impedance, it is recommended to use feedthrough zero sequence current transformers.

The ratio of this type of transformer can be flexibly selected according to the size of the earth fault current and the sensitivity of the earth fault protection.

Due to the small input impedance of the relay, it is possible to use current transformers with very small ratios.

For example, the KOLMA zero sequence current transformer with a ratio of 10/1A is small, but it is generally recommended to use a zero sequence current transformer with a ratio of 50/1A or 100/1A or more.