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).