Beckwith Electric M‑3311A Transformer Protection Relay

The Beckwith Electric M‑3311A is a solid‑state relay designed for protection of power transformers and associated equipment. It provides overcurrent, over/undervoltage, and thermal protection, with a total of 8 output relays for versatile tripping and alarm functions. The relay operates on a wide AC voltage range of 60–140 VAC, making it suitable for various control power supplies.

This model features adjustable pickup settings, time delays, and multiple curve characteristics, allowing coordination with upstream and downstream protection devices. Its compact enclosure and clear front‑panel indication make it easy to install and monitor.

Key Features

• Protection functions: 50, 51, 27, 59, 49, and 46

• Eight programmable output relays

• AC operating voltage: 60–140 VAC (nominal)

• Adjustable time overcurrent curves (IEC/US)

• Voltage‑restrained overcurrent option

• LED trip indicators and reset button

• Panel or DIN‑rail mounting

Technical Specifications

Input: 60–140 VAC, 50/60 Hz; burden: < 10 VA; CT inputs: 1A or 5A; PT inputs: 120 VAC; pickup accuracy: ±2%; output contacts: 8 x SPDT, 5 A; operating temperature: -20°C to +65°C.

Applications

Commonly used for protection of distribution transformers, generator step‑up transformers, and feeder circuits. The relay is ideal for industrial plants, substations, and renewable energy installations.

Installation and Setting

Mount the relay securely. Connect CT and PT leads, and wire the output relays to breaker trip coils or annunciators. Set the pickup levels, time delays, and curve types using the front‑panel knobs and DIP switches.

Reliability and Maintenance

The solid‑state construction ensures long service life with minimal maintenance. The relay is protected against voltage surges and harmonics. Periodic testing is recommended.

Why Choose the M‑3311A?

This relay offers flexible transformer protection with a generous number of outputs, making it a cost‑effective choice for many applications. Beckwith’s reliability and support add to its value.

In summary, the Beckwith Electric M‑3311A provides dependable transformer protection with versatile output configuration.