Beckwith M-3311 Transformer Protection Relay Setting and Engineering Application

M-3911 Target Module: Provides 24 target LEDs and 8 output LEDs to visually display protection actions and output status.

Redundant power supply: Optional dual power modules improve power supply reliability.

Programmable Logic (BECO Logic)

M-3311 has built-in BECO Logic function, which can generate new output control signals by Boolean logic combination (OR, AND, NOR, NAND) of input status, output status, and protection element action flags through IPScom software. For example, the temperature controller alarm contacts can be combined with overcurrent signals to achieve air cooling interlocking or lockout pressure regulation. This feature greatly enhances the flexibility of the device and adapts to various special secondary circuit requirements.

Key points of tuning and configuration

1. Setpoint Groups

The relay supports 4 independent constant values, which can be switched through HMI, communication, or external input to adapt to different operating modes (such as parallel/split, summer/winter load levels). The switching process does not affect the normal operation of the protection.

2. CT and VT wiring

CT input: There are a total of 11 current inputs, covering three-phase winding current and neutral/ground current. Rated 5A or 1A optional, continuously withstand 3 times the rated value, and withstand 100 times the rated value in 1 second.

VT input: single voltage, rated at 60-140Vac, can be connected to phase voltage (L-G or L-L) or open delta. The wiring method needs to be configured with VT Config (VA, VB, VC, VAB, VBC, VCA, VG) in the Nominal Settings.

Phase rotation: ABC or ACB can be selected to ensure correct differential phase correction.

3. Differential protection CT tap compensation

The CT tap value (CT Tap) of each winding needs to be calculated and set based on the actual CT transformation ratio and transformer voltage ratio to ensure minimal differential current during external faults. Tap range 1.00~10.00 (5A rated) or 0.20~2.00 (1A rated).

4. Precautions for grounding differential

The time delay of 87GD should not be less than 2 cycles to avoid transient unbalanced misoperation. When the zero sequence current is extremely small, the directional component automatically exits and becomes non directional, requiring coordination with the system grounding method.

5. Temperature controller monitoring

BECO Logic can be connected to the alarm contacts of the transformer temperature controller (such as oil temperature, winding temperature) to start the fan, issue an alarm or lock the on load voltage regulation according to the temperature level. Figure 1 (original manual Figure 1) is a typical application example.

Example of Engineering Application Wiring

The manual provides various typical wiring diagrams (Figure 3-Figure 8):

Typical single line diagram of dual winding/triple winding transformer (Figure 3): Clearly display the signal flow of CT layout, differential, overcurrent, grounding, and voltage input.

Dual power plant unit protection (Figure 4): Integrating the generator and transformer into the same differential zone to expand the protection range.

Integrated unit protection for power plants (Figure 5): applicable to generator transformer units.

Three winding transformer with parallel reactor and ground fault protection (Figure 6): shows the coordination of ground differential and zero sequence overcurrent.

Main backup bus coupled radiation substation (Figure 7): Combined with bus protection logic.

Figure 8 is a typical three wire connection diagram, with detailed labeling of the external terminal arrangement (Figure 2). Attention should be paid to the high-speed characteristics of output contacts 1-4, torque requirements for wiring terminals (12 in lbs for terminals 1-34, 8-9 in lbs for terminals 35-63), and only dry contacts are allowed for input terminals (internal wet connections, external pressure may damage the device).

Testing standards and reliability

M-3311 complies with multiple international and industry standards:

Insulation withstand voltage: IEC 60255-5, 3500Vdc (1 minute) for each independent circuit to ground and between circuits, 1500Vdc for IRIG-B and RS-485 circuits.

Impulse voltage: 5000V peak to peak value, 1.2/50 μ s waveform, 500 Ω impedance.

Electromagnetic compatibility: electrostatic discharge IEC 61000-4-2 Class 4 (8kV contact); Fast transient IEC 61000-4-4 Class 4 (± 4kV, 2.5kHz); Radiation immunity IEEE C37.90.2 (25~1000MHz, 35V/m).

Output contact: IEEE C37.90 (30A closed for 0.2 seconds at 250Vdc); UL 508 (8A current carrying, 6A disconnection at 120Vac).

Environment: Working temperature -20 ℃~+70 ℃, humidity 93% (40 ℃), vibration response 0.5g, vibration resistance 1.0g.

Certification: cULus Listed (NRGU/E128716), compliant with CAN/CSA C22.2 No.14.

Physical parameters and storage requirements

Size: 19 "wide x 5.21" high x 10.20 "deep (3U), weight approximately 20.4 pounds (excluding options), shipping weight 28 pounds.

Power supply: Wide range AC/DC universal (85~265Vac or 80~288Vdc), or low-voltage DC (18~56Vdc), with a power consumption of 20VA. Optional redundant power supply.

Storage: It is recommended to maintain a temperature of 5-40 ℃, humidity of ≤ 80% (below 31 ℃), and avoid dust, corrosive gases, rainwater, and sunlight.