Relay Tripped at Pasir Gudang Plant

After a series of ACB tripping at Main Switchboard of a chemical plant in SC Plant Pasir Gudang, the client had commissioned PowerQ to investigate the cause. PowerQ had performed the electrical monitoring of the Main Control Central Board and spot measurement of the MSB supplying power to MCC.

The inrush current was recorded at individual motors was performed at using PQ recorder. The data collected has been analyzed and checked against IEEE 519 standards.

Following recommendations implemented to prevent the tripping problem:

• Reset setting of ABB SPAJ relay characteristic to of ACB characteristic. Previously the relay tripping ACB at SSB SAP/CO incomer was set lower than MCC board incomer. Probably this had contributed to the occurrence of nuisance tripping at incomer due to lack of discrimination.
• Resetting and programming the Soft Starter to prevent High Inrush Current. The hooked-up power monitor had captured short-duration inrush as high as 600% (e.g. Main Acid Pump 90kW has approximately full load current of 160A but the start current was 971A. For BL402 the full load current was 317A while start inrush was as high as 974A). If plant is running and a large motor (P408 or BL402) is restart, it is possible tripping might occur.

To avoid this scenario, the soft starter was recommended to be set to limit current to 300% and/or ramp time of the soft starter should be increased. Generally, a ramp time of 8 second should be sufficient to limit inrush below 300%. This was be done in confirmation with process’ requirements. It was recommended that the correct setting of soft starter shall be implemented so as to reduce chances of tripping due to the starting current.