Description

Siemens ETU45B Trip Unit

The ETU45B is an electronic trip unit designed specifically for Siemens Sentron 3WL air circuit breakers (ACBs). It provides adjustable, microprocessor-controlled protection functions for low-voltage power distribution networks, monitoring current overloads, short circuits, and ground faults.

Technical Specifications

Commercial and Logistics Status

• Condition: Available as New Original, New Surplus, or Refurbished (fully tested and certified under secondary injection secondary test sets).

• Warranty: 12-month comprehensive warranty from the date of shipment.

• Availability: In stock. Standard dispatch within 1 to 2 business days.

• Lead Time: 3 to 7 business days via international air express (DHL, FedEx, UPS).

• Pricing Note: Price is subject to change based on market availability, current demand, and firmware version. Contact our sales department for a firm quotation.

Core Protection Functions & Settings

The ETU45B utilizes a digital signal processor to analyze true RMS currents, ensuring accurate tripping even in systems with high harmonic distortion.

1. Long-Time Delay / Overload (L-Trip)

• Current Setting ($I_r$): Adjustable step-by-step or via the display screen from $0.4$ to $1.0 \times I_n$ (the rated breaker current determined by the rating plug).

• Delay Time ($t_r$): Adjusts the thermal heating curve replication, typical setting ranges from 2 to 30 seconds at $6 \times I_r$.

2. Short-Time Delay / Short-Circuit (S-Trip)

• Current Setting ($I_{sd}$): Protects against timed short circuits to allow downstream selectivity coordination.

• Delay Time ($t_{sd}$): Configurable fixed delay times (0.1 to 0.4 seconds) or $I^2t$ ramp curves to achieve proper time-grading with downstream molded case circuit breakers (MCCBs).

3. Instantaneous Short-Circuit (I-Trip)

• Current Setting ($I_i$): Immediate, non-delayed opening for high-magnitude short circuits. Can be set to “Deactivated” on specific firmware models when downstream selectivity takes precedence, up to the frame withstand limit.

Modularity and Expansion Capabilities

The ETU45B is highly modular. Base units can be retrofitted or upgraded in the field using plugin internal modules.

                  +----------------------------------+
                  |     ETU45B Base Trip Unit        |
                  +----------------------------------+
                     /             |              \
                    /              |               \
    +-------------------+  +---------------+  +-------------------+
    |  Measurement      |  |  Ground Fault |  |  COM15/COM16      |
    |  Function Plus    |  |  Module (G)   |  |  Communication    |
    |  (Voltage/Power)  |  |               |  |  (Modbus/Profibus)|
    +-------------------+  +---------------+  +-------------------+

• Ground-Fault Protection Module (G): Adds protection against earth faults ($I_g$). It calculates ground currents through vector summation of the phases and neutral or via a direct connection to a external neutral-conductor current transformer.

• Measurement Function Plus: An optional internal card that upgrades the unit from a pure protection device to a power metering module, providing voltage, kW, kVA, power factor, and frequency readings directly on the LCD.

• CubicleBUS Architecture: The ETU45B utilizes an internal communication bus called CubicleBUS. This interface connects the trip unit directly to optional external components, including digital input/output modules and zone selective interlocking (ZSI) controllers.

Engineering and Field Constraints

Rating Plug Prerequisite

The ETU45B cannot operate without a matching Rating Plug inserted into the front faceplate. The rating plug defines the maximum operational current ($I_n$) of the breaker.

Important Deployment Note: Never insert or remove the rating plug while the circuit breaker is closed or carrying current. Doing so risks corrupting the ETU memory or causing an immediate emergency trip of the breaker mechanism.

External Power Requirements

While the protection algorithms function purely on self-power derived from the main circuit breaker current transformers (once current exceeds approximately $0.2 \times I_n$), the LCD display and communication bus require an external 24 V DC power supply to remain active when the breaker is open or lightly loaded. Ensure a stable 24 V DC supply is connected to auxiliary terminals $F1$ and $F2$.

Frequently Asked Questions

Can an ETU45B be used to replace an older ETU25B or ETU27B trip unit?

Yes. The ETU45B can replace the lower-tier ETU25B or ETU27B trip units within the Sentron 3WL family. However, you must transfer the existing rating plug to the new unit and verify that any existing auxiliary CubicleBUS connections or wiring pinouts match. Re-commissioning and secondary injection testing are required post-replacement.

What does a blinking “Query” LED signify on the ETU45B interface?

A flashing “Query” LED indicates that a trip event has occurred or there is a diagnostic warning stored in the internal memory buffer. Press the clear/reset button on the front panel to acknowledge the event and read the fault logs (e.g., overload, short circuit, or internal self-test failure) on the 4-line display screen.

How do I modify parameters on the ETU45B?

Settings can be adjusted manually using the rotary switches located behind the transparent protective cover, or digitally via the front keypad and display. If a COM15/COM16 module is installed, parameterization can also be performed remotely over Modbus or PROFIBUS networks, provided the local/remote hardware write-protection switch is set to the allowed position.