ABB SPAD346C｜Differential Relay｜

SPAD346C

SPAD346C

The SPAD 346 C is an integrated multi-function numerical differential protection relay manufactured by ABB (part of their SPACOM protection relay family).

It is primarily used in power generation, transmission, and heavy industrial electrical distributions to protect two-winding transformers, generator-transformer units, and large generators from short circuits and internal faults.

Core Hardware Architecture

The SPAD 346 C chassis integrates three distinct functional relay sub-modules:

SPCD 3D53: Three-phase stabilized differential protection module.

SPCD 2D55: Earth-fault relay module.

SPCJ 4D28: Combined overcurrent and earth-fault protection module.

(Note: Variant models like the SPAD 346 C3 streamline the package by containing only the SPCD 3D53 differential module for applications where external backup protection is already present).

Key Technical Specifications & Functions
Feature Description
Primary Protection Three-phase biased differential protection for winding short-circuits and turn-to-turn faults.
Backup Protection Three-stage non-directional/directional overcurrent and multi-stage earth-fault protection.
Harmonic Restraint

• 2nd Harmonic: Blocks tripping during transformer magnetizing inrush.

• 5th Harmonic: Prevents false trips under non-harmful transformer over-excitation (with automatic release under severe overvoltage).

Vector Group & CT Matching Software/digital vector group matching (e.g., Y/Δ) and digital CT ratio correction ($0.40 \text{ to } 1.50$), eliminating the need for interposing CTs.
Rated Currents ($I_n$) Configurable for $1\text{ A}$ or $5\text{ A}$ inputs on either HV or LV side.
I/O & Contact Outputs

• 4 Trip Relays & 4 Signal Relays.

• 5 Configurable Opto-isolated Control Inputs (e.g., Buchholz relay, oil temp alarms).

Disturbance Recorder Integrated digital fault recorder logging up to 6 analog channels and 11 binary signals for post-fault analysis.
Communication Protocol Uses ABB’s SPA-bus protocol via rear optical fiber/RS-485 interfaces for DCS or SCADA integration.
Typical Applications

Two-winding Power Transformers: Short-circuit and ground-fault protection without external phase-matching hardware.

Generator-Transformer Units: Full protection against internal inter-turn and phase-to-phase faults.

Three-winding Transformers: Applicable if at least 75% of the short-circuit power originates from a single direction.