ABB SPAJ140C

Description

Product Description
The ABB SPAJ140C is a highly reliable and widely used Combined Overcurrent and Earth-Fault Relay from ABB’s SPAJ series, designed for the protection of feeders, motors, and transformers in medium-voltage and low-voltage electrical power systems. This electromechanical relay is a classic example of robust protection technology, providing essential fault detection and isolation functions. The primary role of the ABB SPAJ140C is to continuously monitor the phase currents and the residual (earth fault) current. When a current exceeds its pre-set pickup value for a pre-set time duration, the relay’s output contacts change state to trip a circuit breaker, thereby isolating the faulty section of the network. For electrical engineers and maintenance technicians in utilities and industrial plants, the SPAJ140C represents a simple, durable, and easily understood layer of protection. Its straightforward design and clear setting scales make it a trusted component for ensuring the selective operation of protection schemes, preventing equipment damage from overloads and short circuits.

Product Parameters

• Device Type: Electromechanical Overcurrent and Earth-Fault Relay.
• Product Family: ABB SPAJ 140 Series.
• Protection Functions:
  • Three-phase overcurrent protection (50/51): With independent time delay settings for low-set and high-set stages.
  • Earth-fault protection (50N/51N): Using the residual current from core-balance current transformers (CTs) or calculated from three phase CTs.
• Current Setting Ranges: Adjustable pickup settings for both overcurrent and earth-fault elements, typically via dials on the front face. Settings are in Amperes, referenced to the CT secondary (e.g., 0.5-5A or 2-20A).
• Time Characteristics: Definite time delay (DT) or Inverse Definite Minimum Time (IDMT) curves (e.g., Normal Inverse, Very Inverse, Extremely Inverse) selectable for the low-set stage.
• Output Contacts: Multiple changeover (Form-C) contacts for tripping, alarming, and signaling.
• Auxiliary Supply: Requires a separate AC or DC auxiliary voltage (e.g., 48-250V AC/DC) to power the relay’s internal circuitry and output contacts.
• Mounting: Panel-mounted device with a standardized footprint.

Advantages and Features

• Simplicity and Reliability: As an electromechanical device with minimal electronics, it offers extremely high reliability, long service life, and inherent immunity to power quality issues and electromagnetic pulses (EMP).
• Ease of Setting and Understanding: Settings are made with intuitive dials and switches on the front. The operating principle is visually clear, making commissioning, testing, and troubleshooting straightforward without specialized software.
• Robust Construction: Built to withstand harsh environmental conditions, including high humidity, temperature variations, and vibration, commonly found in electrical switchrooms and substations.
• Selective Coordination: The availability of multiple IDMT curves allows for easy time-current coordination with upstream and downstream protection devices to ensure selective tripping, minimizing the impact of a fault.
• Proven Track Record: Installed in thousands of facilities worldwide over decades, it is a well-understood and trusted component with a vast base of operational experience.

Application Cases in Application Fields

• Industrial Plant Power Distribution: Protecting an incoming medium-voltage (e.g., 10kV) feeder or a downstream transformer in a factory’s main switchgear.
• Commercial Building Electrical Supply: Serving as the main overcurrent protection for a large office complex or hospital’s medium-voltage supply.
• Water and Wastewater Treatment Plants: Protecting pump motors and feeder circuits in electrical distribution panels.
• Renewable Energy Plants: Providing backup overcurrent protection for circuits in a solar PV or biogas plant’s medium-voltage interconnection.
• Mining: Protecting feeders and motors in electrically noisy and demanding mining environments where reliability is paramount.

Comparisons with Competing Products
The ABB SPAJ140C competes with similar electromechanical relays from other manufacturers, such as the Siemens (now withdrawn) 7SJ series or the Schneider Electric (Square D) IAC/IEL series. Its key competitors in modern installations are numerical (microprocessor-based) relays like the ABB REF6xx series or Siemens SIPROTEC Compact. Compared to numerical relays, the SPAJ140C lacks advanced features like communication, detailed event logging, and customizable logic. However, its advantages are its lower cost, extreme durability, and operational simplicity. It is often chosen for non-critical applications, as a backup to a primary numerical relay, or in environments where simplicity and longevity are valued over advanced functionality.

Selection Suggestions and Precautions

1. CT Coordination is Critical: The relay must be matched to the Current Transformer (CT) ratio. The relay’s current settings (in Amps) refer to the secondary current. Ensure the CT primary rating is suitable for the protected circuit’s full-load and fault current.
2. Auxiliary Supply Match: Verify the relay’s auxiliary voltage rating (AC/DC and voltage range) matches the available control supply in the switchgear panel.
3. Proper Curve and Setting Coordination: Perform a time-current coordination study to select the correct IDMT curve and time multiplier settings. This ensures the SPAJ140C trips after downstream fuses/breakers but before upstream protection, isolating only the faulted section.
4. Testing and Calibration: Electromechanical relays should be periodically tested and calibrated using a primary injection test set to verify the accuracy of pickup currents and trip times.
5. Obsolescence Consideration: The SPAJ series is a mature product line. While highly reliable and supported, for new projects requiring advanced features or integration, a modern numerical relay is typically recommended. The SPAJ140C remains ideal for retrofit, repair, and simple standalone applications.

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