ABB SPAJ 140 C Combined Overcurrent and Earth-Fault Relay

Product Overview and Technical Functionality

The ABB SPAJ 140 C is a multi-function secondary relay designed for combined overcurrent and earth-fault protection. This protection unit is utilized in distribution networks, industrial power systems, and marine electrical installations. The device incorporates independent protection stages for selective short-circuit and ground-fault protection of radial feeders, transformers, motors, and generators.

Operating within the ABB SPACOM product family, the SPAJ 140 C features advanced microprocessor technology that continuously monitors phase currents and residual current. The micro-controller processes analog signals through high-precision matching transformers, converting them into digital values for real-time inverse definite minimum time or definite time characteristics analysis.

Protection Stages and Operational Profiles

The relay consists of two main functional blocks: the three-phase overcurrent block and the non-directional earth-fault block. Each block provides low-set and high-set stages to achieve coordinated time-overcurrent grading across complex power distribution topologies.

The low-set overcurrent stage can be configured for definite-time characteristics or standard inverse time curves compliant with IEC 60255 standards. These curves include normal inverse, very inverse, extremely inverse, and long-time inverse profiles. The high-set overcurrent stage operates on a definite-time basis or instantaneous setting, allowing immediate isolation of severe faults to limit thermal and mechanical stress on upstream switchgear.

The earth-fault protection module measures residual current via a core-balance current transformer or a residual connection of phase current transformers. Similar to the phase protection, the earth-fault block offers a low-set stage with flexible time delay characteristics and an independent high-set stage for rapid mitigation of ground insulation failures.

Hardware Architecture and Interface

The mechanical construction of the SPAJ 140 C comprises a robust flush-mounting case fabricated from extruded aluminum profiles, providing superior electromagnetic compatibility shielding. The front panel features an integrated human-machine interface with a digital display and seven-segment light-emitting diodes that indicate specific fault types, tripped phases, and operational statuses.

Programming and parameter configuration are facilitated via the front panel push-buttons or through a serial communication port using the SPA bus protocol. Terminal connections at the rear of the unit utilize heavy-duty screw terminals for current transformer inputs, power supply, and programmable output relays, ensuring stable electrical contact under continuous thermal vibration.

Technical Specifications

The auxiliary power supply module accommodates wide-range input voltages, supporting both alternating and direct current networks. The rated frequency of the measuring circuits is adjustable between fifty and sixty Hertz. The thermal endurance of the current inputs allows continuous loading at twice the rated current, with short-time tolerance up to one hundred times the rated current for one second.

Output contacts are divided into signaling relays and heavy-duty tripping relays. Tripping contacts are designed with high making and breaking capacities, capable of energizing high-voltage circuit breaker trip coils directly without external interposing elements.

Industrial Applications and System Integration

In power distribution networks, the ABB SPAJ 140 C serves as a primary protection asset for incoming and outgoing feeders. In industrial environments, it offers critical thermal and stall protection for large synchronous and asynchronous motors. Furthermore, its compliance with marine class standards renders it appropriate for main switchboards aboard vessels and offshore platforms where electrical stability is paramount.