Description
ABB SPAJ115C
Key Technical Specifications
| Parameter | Specification |
|---|---|
| Manufacturer | ABB |
| Model | SPAJ 115 C |
| Product Family | SPACOM |
| Relay Module | SPCJ 2C30 |
| Product Type | Restricted earth-fault and residual earth-fault relay |
| Main Protection | Restricted earth fault, ANSI 87N |
| Backup Protection | Residual/neutral earth fault, ANSI 51N |
| Rated Input Current | 1 A or 5 A |
| Rated Frequency | 50 Hz or 60 Hz |
| Auxiliary Supply | 80–265 V AC/DC or 18–80 V DC |
| Differential Current Input | 1 A / 5 A configuration |
| Residual Current Input | 1 A / 5 A configuration |
| Restricted E/F Pickup | 0.5–5% × In |
| Restricted E/F Operate Time | 35 ms |
| Residual E/F Pickup | 5–40% × In |
| Residual E/F Timing | Definite time or IDMT |
| Residual E/F Time Setting | 0.1–100 s, definite-time mode |
| IDMT Curves | Normal, Very, Extremely, Long-time inverse |
| Communication | Fiber-optic serial bus |
| Data Rate | 300–9600 Bd |
| Service Temperature | -10°C to +55°C |
| Storage/Transport | -40°C to +70°C |
| Enclosure | IP54 |
| Weight | Approx. 3.0 kg |
ABB’s technical manual identifies two separate current circuits: a differential earth-fault current ΔI₀ circuit for restricted earth-fault protection and a residual earth-fault current I₀ circuit for backup protection. The relay module provides a 0.5–5% × In restricted-earth-fault starting range with a specified 35 ms operating time, while the residual-earth-fault stage has a 5–40% × In starting range and supports definite-time or inverse-time characteristics.
The auxiliary supply is configuration-dependent. ABB documents either an SPTU 240S1, 80–265 V AC/DC supply module or an SPTU 48S1, 18–80 V DC module, so the bare SPAJ115C designation should not be treated as sufficient information for a replacement purchase.
SPAJ115C
Product Introduction
The ABB SPAJ115C is a SPACOM-series combined restricted earth-fault and residual earth-fault protection relay designed for generators, motors, and transformers. Its primary protection stage is the restricted earth-fault function, which responds to differential current within the defined protection zone; the residual-current stage provides backup earth-fault protection. ABB identifies the two functions as ANSI 87N and 51N respectively.
The relay is a secondary protection device and depends heavily on the associated current-transformer arrangement. For restricted earth-fault protection, ABB specifies the use of an external stabilizing resistor and places significant requirements on CT ratio, secondary resistance, and knee-point voltage. That means a relay replacement cannot be evaluated independently of the CT circuit and protection-zone design.
Engineering Pain Point
The difficult part of maintaining an SPAJ115C is usually not the relay itself; it is preserving the original restricted-earth-fault protection scheme. CT saturation, unequal CT characteristics, incorrect stabilizing resistance, or excessive secondary-circuit resistance can compromise the stability of the 87N circuit. ABB specifically notes that CT selection and the differential-circuit stabilizing resistor are critical to the sensitivity and reliability of this protection.
Typical Applications
- Generator stator earth-fault protection
- Transformer high-voltage-side earth-fault protection
- Motor earth-fault protection
- Industrial MV/HV switchgear protection systems
- Legacy SPACOM protection panels requiring maintenance replacement
Technical Pitfalls to Avoid
- Do not assume every SPAJ115C has the same power supply. Check the installed front-panel marking and internal supply module. The documented versions are 80–265 V AC/DC and 18–80 V DC.
- Verify whether the CT circuits are 1 A or 5 A. The relay provides separate terminal arrangements for the two ratings. Using the wrong configuration is not a minor wiring discrepancy; it directly affects the protection measurement circuit.
- Check the restricted-earth-fault CT design before commissioning. ABB calls for matched CT characteristics and specifies knee-point and secondary-resistance considerations for stabilized REF protection.
- Do not confuse 87N with ordinary residual-current protection. The ΔI₀ stage protects a defined internal zone, while I₀> provides residual/backup earth-fault protection. Their CT arrangements and protection objectives are different.
- Record the original switch settings. The SPCJ 2C30 module uses front-panel settings and switchgroups to define pickup, timing, latching, blocking, and output-relay routing. A replacement relay should be commissioned against the approved protection settings rather than copied by appearance alone.
- Plan for legacy lifecycle constraints. ABB lists SPAJ115C as inactive since 2009 and provides a SPACOM-to-REX615 retrofit program that explicitly includes . A modern replacement therefore needs an engineering review of wiring, protection functions, settings, and physical installation rather than an assumption of direct interchangeability.
Related Products
- ABB SPAJ 110 C — Dedicated earth-fault relay with low-set and high-set neutral overcurrent stages; it does not provide the same combined restricted-earth-fault architecture as .
- ABB SPAJ 111 C — Sensitive earth-fault protection relay for selective earth-fault applications; functionally different from the dual ΔI₀/I₀ architecture of .
- ABB SPAJ 140 C — Combined overcurrent and earth-fault relay; broader phase overcurrent protection rather than the dedicated restricted-earth-fault function of .
- ABB SPAJ 135 C — Related SPACOM earth-fault protection relay within the same legacy relay family.
- ABB SPAM 150 C — SPACOM motor protection relay intended for motor-specific protection functions rather than the dedicated REF/residual-earth-fault arrangement of .
- ABB SPA-ZC 17 — Fiber-optic bus connection module that can provide the serial-bus interface with external power.
- ABB SPA-ZC 21 — Fiber-optic bus connection module powered from the host relay; available for the documented plastic- or glass-fiber configurations.
- ABB REX615 — Modern protection and control platform included in ABB’s SPACOM retrofit program for and other legacy SPACOM relays. It should be treated as a retrofit project rather than an assumed plug-in replacement.
Procurement note: For an replacement, capture the complete nameplate information, including the RS 421 ordering suffix, rated current (1 A or 5 A), frequency, auxiliary supply, relay module, and bus interface. For a live protection system, also retain the existing CT ratios, stabilizing-resistor value, protection settings, trip logic, and wiring drawings. The ABB manual should be checked against the installed relay before energization.
