ABB SPAD346C3 Stabilized Differential Protection Relay

SPAD346C3 is a legacy stabilized differential relay manufactured by ABB, specialized for two-winding transformers, generator-transformer units and partial three-winding transformer protection. It integrates differential protection, three-stage overcurrent and two-stage earth fault protection, equipped with second/fifth harmonic restraint logic to avoid false tripping caused by transformer inrush current and core overexcitation. Digital CT ratio correction ensures high precision matching for high-low voltage side current transformers.

This rack-mounted relay features multi-channel programmable input/output relays, built-in disturbance recorder and RS485 Modbus communication interface. Continuous hardware & software self-monitoring improves system anti-interference performance in power plant and substation harsh electromagnetic environments. ABB stopped mass production in 2012, and it is globally supplied as core overhaul spare parts for legacy power protection systems.

Main Specifications

• Brand: ABB; Model: SPAD346C3; Series: SPAD 346 C Differential Protection Relay
• Core Protection Logic: Stabilized differential, 3-stage overcurrent, dual-stage restricted earth fault protection
• Harmonic Blocking: 2nd harmonic restraint (inrush suppression), 5th harmonic restraint (overexcitation blocking)
• CT Calibration: Wide-range digital CT ratio correction, vector group matching for HV/LV transformer sides
• I/O Configuration: 4 trip output relays, 5 signal alarm relays, 5 programmable external control inputs
• Communication: RS485 Modbus RTU, upload fault records and operation data to upper SCADA
• Power Supply: 100–250 VAC/DC wide universal control power
• Operating Temperature: -25℃ ~ +70℃, high EMC immunity for substation environments
• Built-in Functions: Disturbance recorder, circuit breaker failure protection, real-time current phase display
• Lifecycle Status: Discontinued since 2012, only aftermarket maintenance spare available

Core Functions

• Detect internal transformer faults including winding short-circuit, inter-turn short circuit and earth fault, output trip signal to cut off high-voltage circuit breaker rapidly.
• Harmonic restraint logic eliminates misoperation during transformer energization and overvoltage overexcitation, improving protection selectivity and reliability.
• Three-stage overcurrent and backup earth fault protection provides complete backup protection for transformer external short-circuit and insulation breakdown faults.
• Disturbance recorder stores fault current waveforms and digital event logs, supporting post-fault analysis for accident troubleshooting.
• RS485 bus transmits real-time running status, fault codes and protection setting parameters to ABB PM511 DCS and PP836 HMI operation panel.
• Continuous self-supervision circuit monitors internal CPU, sampling and output loops, triggering alarm output once hardware abnormality occurs.

Application Scenarios

• Spare differential relay replacement for main transformer protection cabinets of thermal power plant and combined cycle power station units.
• Generator-transformer unit protection spare parts for hydropower station synchronous generator high-voltage side switchgear rooms.
• Maintenance backup stock for industrial substation two-winding distribution transformer protection control racks in chemical and metallurgical factories.
• Matching protection device cooperating with ABB Advant OCS DCS system, PM511 CPU and PP836 local operation HMI panel.
• Retrofit overhaul components for petrochemical refinery self-owned power plant transformer and generator safety protection systems.

• Global aftermarket spare inventory for power grid and heavy industry maintenance workshops maintaining legacy ABB power protection hardware.