Beckwith M‑3311A 4‑Coil Transformer Protection Relay

The Beckwith M‑3311A is an advanced solid‑state relay specifically configured for protecting 4‑coil (multi‑winding) power transformers. This model provides differential protection across all four windings, along with backup overcurrent and thermal protection. It is essential for safeguarding complex transformer arrangements found in industrial plants, substations, and renewable energy collector systems.

The relay utilizes a percentage restraint differential principle to ensure stability during external faults and inrush conditions. It features independent slope and pickup settings for each winding, allowing precise coordination with transformer characteristics.

Key Features

• 4‑coil differential protection with adjustable slopes

• Independent pickup settings per winding

• Backup overcurrent protection (phase and ground)

• Second‑harmonic restraint for inrush blocking

• Fifth‑harmonic restraint for over‑excitation

• Target indicators for faulted winding identification

• Compact panel‑mount case

Technical Specifications

CT inputs: 1A or 5A (4 sets); frequency: 50/60 Hz; pickup range: 10–50% of CT; restraint slope: 20–80% adjustable; operating time: < 30 ms at 2x pickup; output: 3 x SPDT; power supply: 125/250 VDC or 120/240 VAC.

Applications

Ideal for three‑winding transformers with a tertiary winding, autotransformers, and phase‑shifting transformers. Also suitable for large industrial transformers with multiple secondary windings.

Installation and Configuration

Mount the relay in a standard panel. Connect all four sets of CTs. Configure pickup, slope, and restraint settings via front‑panel controls. Test points are provided for calibration.

Reliability and Maintenance

Solid‑state construction ensures high reliability. Conformal coating protects against harsh environments. Periodic testing is recommended.

Why Choose the M‑3311A?

This relay offers specialised protection for complex transformers with multiple windings, ensuring selective and rapid fault clearing. Beckwith Electric’s engineering ensures dependable performance.

In summary, the Beckwith M‑3311A 4‑coil relay provides comprehensive protection for multi‑winding transformers, minimising outage risks and equipment damage.