Basler UFOV 250A/260A protection module

Basler UFOV 250A/260A underfrequency overvoltage module: full analysis of technical principles and engineering applications

Product positioning and model differentiation

The UFOV (Underfrequency Overvoltage) module is an independent protection and auxiliary regulation device installed on the input side of generator voltage regulators (such as Basler SR4A, SR4F, SR8A, SR8F, SR32A, etc.), providing two core functions:

Underfrequency voltage suppression: When the generator frequency is 4-7 Hz lower than the rated value, the output voltage reference value of the regulator is automatically reduced to proportionally decrease the generator terminal voltage, avoiding magnetic flux saturation and equipment overheating.

Overvoltage trip protection: When the generator terminal voltage exceeds the preset threshold (usually 125%~150% of the rated value), the circuit breaker connected in series with the regulator power input circuit will trip, completely cutting off the excitation power supply and achieving hardware level protection.

This series includes two models:

Model applicable frequency applicable regulator (partially listed)

UFOV 250A 50 Hz SR4A, SR4F, SR8A, SR8F, SR32A, SR32H, SR63H, SR125H, SR250H

UFOV 260A 60 Hz Same Left (Different Frequency)

Attention: The underfrequency action point of earlier versions (part number 9 0400 00 100/104) was below 10 Hz, while the current A-series version has been optimized to a threshold window of 4-7 Hz. When installing replacement, be sure to check the part number and wiring differences.

Key technical specifications and selection points

1. Input voltage adaptability

The module is equipped with a multi tap transformer that supports single-phase inputs of 120, 208, 240, 416, 480, and 600 Vac, with a factory default of 120 Vac. If the on-site voltage does not match, it can be connected to the corresponding tap through internal wiring. If the generator voltage exceeds 600 Vac, an external voltage transformer (PT) is required for voltage reduction.

2. Underfrequency action characteristics

When the frequency drops below the rated value by 4-7 Hz, the underfrequency circuit inside the module begins to intervene. Its output characteristics are shown in Figure 1-1 (Figure 1-1 in the manual), presenting a voltage frequency curve with a certain dispersion band. For example, when a 60Hz generator drops to 50Hz, the terminal voltage will decrease to 82% to 95% of the rated value (depending on temperature and component tolerances). The voltage drop rate is slightly faster than the frequency drop rate, that is, at 50% frequency, the voltage will be lower than 50%.

3. Overvoltage setting range

The overvoltage trip threshold can be continuously adjusted between 125% and 150% of the rated voltage. The factory preset value is 130%, and users can adjust it appropriately according to the transient characteristics of the system. The matching circuit breaker should be of single pole (part number 05390) or double pole (part number 05391) type, with a rated contact capacity of 50A @ 480Vac.

4. Environmental and mechanical specifications

Working temperature: -55 ° C to+70 ° C, suitable for extremely cold and high temperature environments.

Anti vibration and anti impact: Meet the requirements of 5-500Hz sweep frequency vibration and 15G impact.

The weight is about 4.5kg, and it adopts a "back panel installation" design. The external dimensions are shown in Figure 3-1 of the manual.

Working principle and engineering significance of underfrequency circuit

1. Basic principles

The underfrequency circuit continuously monitors the frequency of the input voltage. When the frequency drops to the action threshold (rated value minus 4-7 Hz), the circuit outputs a DC control signal proportional to the frequency deviation, which is applied to the voltage set point input terminal of the regulator (usually the "A" or "F0" terminal of the SR series), causing the regulator to reduce the excitation output.

2. Collaboration with Field Flashing Relay

During the initial excitation process of the generator, the excitation relay will cover the control function of the underfrequency circuit to ensure that the voltage can be established. Once the excitation is completed and the frequency is normal, the underfrequency circuit enters standby mode. If the subsequent frequency falls into the underfrequency zone, the circuit will immediately take over control. Special attention: If the generator needs to run at low speed for a long time (such as turning or debugging), it is necessary to ensure that the excitation relay is excited, otherwise the underfrequency circuit may not operate correctly.

3. Engineering considerations for curve dispersion

The shaded area in Figure 1-1 represents the inherent dispersion of the voltage frequency relationship, which is due to temperature drift and component tolerance. Engineers should reserve sufficient margin when setting protection coordination to avoid misoperation or insufficient protection caused by dispersion.

Overvoltage protection circuit and circuit breaker selection

1. Protecting Logic

The overvoltage circuit continuously monitors the generator terminal voltage (sharing the same voltage detection input with the underfrequency circuit). When the voltage exceeds the preset threshold and lasts for a certain period of time (actually instantaneous action, but needs to cross the transient peak), the internal thyristor trigger circuit will excite the circuit breaker coil, causing the circuit breaker to trip and cut off the input power supply of the regulator (i.e. PMG or auxiliary winding power supply).

2. Circuit breaker reset and fault analysis

After the circuit breaker trips, it needs to be manually reset before it can be put back into operation. If the circuit breaker repeatedly trips after load shedding, the most likely reason is that the overvoltage setting value is too low, causing the transient overvoltage peak value to touch the trip threshold when the load suddenly changes. At this point, the setting value should be adjusted appropriately to be higher than the normal transient peak, while ensuring that it does not exceed the equipment's tolerance limit.

3. Special applications of bipolar circuit breakers

When the regulator is SR-A series (using "A" terminal) or SR-F/SR-H series (using "F0" terminal), a bipolar circuit breaker (P/N 05391) must be used to simultaneously cut off both power lines and achieve complete isolation. The external dimensions of the bipolar circuit breaker are shown in Figure 3-3 of the manual.

Installation and Wiring Engineering Guide

1. Installation position and direction

The module can be installed in any direction without affecting performance. The installation method of the backboard should refer to Figure 3-1 for drilling and fixing. The circuit breaker is an independent component, installed in the appropriate position on the panel or cabinet according to Figure 3-2/3-3.

2. Change the voltage tap connection

If the input voltage is not 120V, the module needs to be opened and the wire connecting the primary of the transformer needs to be changed from the "120" tap to the corresponding tap (208/240/416/480/600). Be sure to disconnect all power sources when changing connections.

3. Coordination with EMI filters

When the system is equipped with an EMI filtering package (such as EMI 248/208), the N terminal of the UFOV module must be directly connected to the F+terminal of the regulator (or the F+terminal of the filter), and this connection must not be grounded. Please refer to Figures 3-8 and 3-9 for detailed wiring.

4. Key points for wiring verification

The manual provides wiring diagrams for up to 6 different regulator series (Figure 3-4 to Figure 3-9), including SR4A/SR8A, SR32A, SR4F/SR8F, SR32F, etc. When replacing on site, it is necessary to check each line according to the corresponding model's drawing, paying special attention to the differences in terminal definitions between UFOV 250A (new part number 9 1051 00 106) and the old model (9 0400 00 104): the old model uses terminals 3, 4, and 6, while the new model uses P, C, D, and N. Terminal N is newly added and used to connect the common end of the circuit breaker coil (see the terminal comparison table on page 15 of the manual for details).

On site tuning and functional verification

1. Underfrequency action verification

Start the generator to the rated speed, and the regulator works normally.

Slowly reduce the speed of the prime mover and observe that when the frequency drops to the rated value minus 4-7 Hz, the terminal voltage should start to decrease according to the curve in Figure 1-1.

If the voltage does not decrease, check if the wrong model (50/60Hz) is selected or if the input voltage tap is incorrect.

If the voltage drops too early or too late, it is necessary to confirm whether the action threshold is within the 4-7 Hz window (this threshold is fixed and cannot be adjusted, and if there is a deviation, the module needs to be replaced).

2. Overvoltage setting adjustment

The overvoltage potentiometer (located inside the module and usually labeled as "OV ADJ") can be adjusted within the range of 125% to 150%.

Recommended tuning steps: Run the generator without load, gradually increase the excitation to raise the voltage to 135% of the rated value (or target value), slowly adjust the potentiometer until the circuit breaker just trips, and then slightly adjust it back (about 2-3% margin) to avoid normal transients.

During the load rejection test, if the circuit trips, the setting value needs to be increased.

3. Dynamic performance considerations

The manual clearly states that overvoltage circuits are sensitive to voltage change rates - instantaneous spikes during load shedding may be higher than the steady-state set point. Therefore, the setting value should be adjusted based on the transient characteristics of the system, and if necessary, an oscilloscope can be used to observe the load shedding waveform to determine the optimal threshold.

Troubleshooting Logic and Typical Cases

Chapter 4 of the manual provides a troubleshooting table for the system. The following are typical fault scenarios and processing procedures:

Fault phenomenon 1: Underfrequency circuit malfunctions at normal speed

Inspection steps: ① Check if the model matches the system frequency; ② Check if the input voltage is at the correct tap; ③ Replace the module.

Root cause: Mostly due to model mismatch (50Hz module used for 60Hz system, action threshold offset).

Fault phenomenon 2: The frequency has dropped to the operating zone, but the voltage has not decreased

Inspection steps: ① Verify the model and input voltage; ② Confirm that the frequency is indeed below the threshold (4-7 Hz); ③ Check if the wiring is complete (especially if the control terminals P/C/D/N are connected to the corresponding end of the regulator); ④ Replace the module.

Engineering Tip: If the excitation relay continues to engage, it may shield the underfrequency signal. It is necessary to check whether the excitation circuit is released after the frequency is normal.

Fault phenomenon 3: Failure to trip or excessive deviation of trip value during overvoltage

Inspection steps: ① Check whether the wiring of the circuit breaker coil power supply circuit (N and D terminals) is reliable; ② Check if the overvoltage potentiometer is damaged or drifting; ③ Test the resistance of the circuit breaker coil (normally conducting); ④ Replace modules or circuit breakers.

Common root causes: circuit breaker coil burnout or mechanical jamming, or failure of overvoltage triggering circuit inside the module.

Fault phenomenon 4: The circuit breaker repeatedly trips (especially during load shedding)

Analysis and handling: Firstly, eliminate serious faults such as external short circuits, and then adjust the overvoltage setting value appropriately to be higher than the transient peak value of load shedding. If it continues to recur, it may be considered to parallel RC absorption circuits at both ends of the circuit breaker coil (consult the manufacturer) to suppress interference.

Suggestions for spare parts management and replacement upgrade

1. Key spare parts list

Component Basler Part Number Function Description

Circuit board (UFOV 260A) 9 1051 00 100 60Hz module main control board

Circuit board (UFOV 250A) 9 1051 00 101 50Hz module main control board

Choke coil L1 BE 13693-002 input filtering

Choke coil L2 BE 08794-010 output filtering

Transformer T1 BE 14101-002 multi tap input transformer

Single pole circuit breaker 05390 50A @ 480Vac

Bipolar circuit breaker 05391 50A @ 480Vac (for A/F0 terminals)

2. Precautions for replacing old models

The underfrequency action point of the old model UFOV 250/260 (part number 9 0400 00 100/104) is below 10 Hz, and the terminal definitions are different (using 1, 2, 3, 4, 6). If replacing with a new model, it is necessary to rewire according to the terminal comparison table in the manual, especially by splitting the wiring on the original terminal 6 to terminals D and N.

The underfrequency action window of the new module is narrower (4-7 Hz), and in applications with a wider frequency adjustment range, the protection coordination needs to be re evaluated.

3. Lifespan and reliability

The module adopts industrial grade solid-state circuits, with no vulnerable mechanical components (except for circuit breakers), and regular checks on wiring tightness and cleanliness are sufficient. It is recommended to conduct a functional test every two years (including underfrequency and overvoltage action verification) to ensure the integrity of the protection logic.