Numeric LT Motor Protection Relay UBZ-304
Novatek Electro India UBZ-304 is a high-end numerical motor protection relay designed for Low Tension (LT) asynchronous motors. While conventional relays often focus purely on current, the UBZ-304 acts as a comprehensive “black box” that monitors electrical, thermal, and mechanical parameters simultaneously.
How the UBZ-304 Works
The UBZ-304 operates as a microcontroller-based digital device. It sits between the power supply and the motor, receiving inputs from external Current Transformers (CTs) and direct voltage connections.
- Continuous Sensing: It samples RMS values of phase/line currents and mains voltage in real-time.
- Logic Processing: The internal processor compares these values against more than 90 programmable parameters. It doesn’t just look for “high current”; it uses mathematical models to calculate Thermal Heat Balance, identifying if the motor is overheating even if the current hasn’t hit a hard trip limit yet.
- Insulation Monitoring: A unique feature is its ability to perform a pre-start check of the insulation resistance. If the resistance between the stator and the housing is too low, it will prevent the motor from starting to avoid a catastrophic winding failure.
- Control Logic: It controls the motor via a magnetic starter (contactor). It can also manage complex starting sequences like Star-Delta or cascade starting using its secondary programmable relay.
Key Differences from Conventional LT Relays
Most standard LT relays (like thermal overload relays or basic electronic relays) offer limited protection. Here is how the UBZ-304 stands out:
| Feature | Conventional Thermal/Electronic Relays | Novatek UBZ-304 |
| Parameter Range | Usually Current-only (Overload/Phase Loss). | Multi-functional: Voltage, Current, Frequency, and Power. |
| Insulation Check | None. | Pre-start insulation resistance test to prevent burnouts. |
| Pump Protection | Requires separate dry-run sensors. | Built-in Dry-run protection (based on minimum current/torque). |
| Communication | None (Standalone). | Modbus RS-485 & RS-232 for SCADA/DCS integration. |
| Diagnostics | Simple Trip Indicator. | Fault Logbook (stores last 50 faults) and LCD display of real-time RMS values. |
| Customization | Fixed curves or simple dials. | Over 90 programmable settings via front panel or PC software. |
Unique Protection Layers
- Voltage Quality: It protects against “dirty” power—including frequency deviations, phase sequence reversal (preventing the motor from running backward), and voltage unbalance.
- Mechanical Protection: It detects Rotor Blocking (stalled motor) and Torque Loss (broken belt or dry pump) far faster than a thermal strip would.
- Advanced Ground Fault: Uses zero-sequence current detection to spot insulation leaks before they become full-blown short circuits.
When should you use it?
The UBZ-304 is best suited for critical industrial applications (2.5kW to 315kW) where downtime is expensive—such as submersible pumps, large compressors, or conveyor systems—where you need to know why a motor tripped, not just that it did.
