Selection and Debugging of Basler CBS 212A Current Boosting System

Application and Selection Guide of Basler CBS 212A Current Boosting System in Generator Excitation Support

In industrial diesel generator sets, marine generators, and emergency power systems, starting large capacity motors or short circuit faults in the near area often cause a sudden drop in generator terminal voltage, resulting in insufficient excitation current, and in severe cases, even causing the unit to lose step or trip protection. To solve this problem, the Basler CBS 212A Current Boost System utilizes the power current transformer (CT) in the generator output circuit to directly extract energy, providing instantaneous and high-intensity magnetic field current support for the excitation system, ensuring smooth motor start-up and reliable fault clearance. This article is based on the official technical specifications of CBS 212A, systematically explaining its working principle, selection and matching, parameter tuning, and key points of on-site application, to help electrical engineers correctly configure the device in new or renovated projects and improve the dynamic stability of the power generation system.

Product positioning and core values of CBS 212A

CBS 212A is a passive excitation boosting device designed specifically for brushless generators (50/60Hz). When the voltage of the generator drops to the threshold where it cannot maintain the rated excitation current due to load impact, the device responds instantly and extracts energy from the high current CT at the output of the generator to provide the excitation system with a maximum forced excitation current of 20Adc for 10 seconds. This feature makes it particularly critical in the following scenarios:

Directly starting a large motor (such as a compressor, water pump, or crusher) with a starting current of 6-8 times the rated current results in a voltage drop of over 20%.

The short circuit fault in the vicinity of the generator outlet needs to be quickly cleared and the system stability maintained.

Replace expensive permanent magnet generators (PMGs) or auxiliary winding solutions to reduce equipment costs and installation complexity.

Compared with traditional PMG, CBS 212A does not require additional permanent magnet machines and rectifier bridges, but utilizes existing CT energy, with a more compact structure and higher reliability, especially suitable for renovation projects.

Working principle and connection method

As shown in Figure 1 (typical application wiring diagram), the input side of CBS 212A is connected to two power CTs (selected according to the current range) at the generator output terminal, and the output side is connected to the stator winding of the exciter or the auxiliary input terminal of the AVR. Its internal circuit includes:

CT input rectification and filtering: convert CT secondary current into DC voltage.

Voltage detection and comparator: Real time monitoring of generator terminal voltage (sampled through voltage transformer PT), triggering output when the voltage is lower than the preset "action point".

Controllable silicon/transistor switch: During operation, it guides CT energy to the excitation circuit while limiting the output voltage to the set value (60/120/220Vdc optional).

Exit logic: When the generator voltage returns to a certain hysteresis (5V or 10V) above the operating point, the boost will be automatically cut off to avoid overexcitation.

The device is fully self powered and does not require an external control power supply. Its response is instantaneous (in milliseconds), ensuring support in the early stages of voltage drops.

In depth interpretation of key electrical specifications

3.1 Output power and voltage selection

Output DC voltage: 60V, 120V, or 220Vdc can be selected through internal jumpers to adapt to the rated voltage of different excitation systems.

Output current capability: 20Adc (lasting for 10 seconds), sufficient to meet the strong excitation requirements of most small and medium-sized brushless generators (<1000kVA).

Output limiting: Based on the selected voltage level, it can also be fine tuned within the range of 50% to 100% through a potentiometer to match the optimal operating point of the exciter.

Selection tip: If the rated voltage of the generator excitation machine is 90V, the 120V gear should be selected and the amplitude limit should be adjusted to around 75% to avoid overexcitation.

3.2 Voltage detection and action threshold

Rated detection voltage: 120V or 240Vac (jumper selection, corresponding to PT secondary side).

Adjustment range of action points:

120V gear: 70-131Vac

240V gear: 140~262Vac

This range is far below the rated value, ensuring that it is only started when the voltage drops severely to avoid normal load fluctuations and misoperation.

Return coefficient (Dropout):

120V gear: action point+5Vac

240V gear: action point+10Vac

For example, if the operating point is set to 100Vac (120V system), the voltage needs to rise above 105Vac before exiting the boost, providing a certain hysteresis to prevent oscillation.

3.3 Selection Table for Matching Current Transformers (CT)

CBS 212A must be equipped with two dedicated power CTs, as shown in the table below (partially truncated):

CT model variable ratio applicable to generator 3-phase short-circuit current (300% rated) system voltage level

BE25925001 1:8 125～250A ≤600V

BE25926001 1:17 250～500A ≤600V

BE25927001 1:34 500～1000A ≤600V

... (up to 8000A)

BE34704001~BE34709001 Same Left Same Left ≤ 15kV (medium voltage)

Important note:

Two CTs are necessary, installed on the two phases (or two phases of the three phases) of the generator output to synthesize the required energy.

The CT marked with "†" has a pre wound primary winding (without a conductor through window), and when in use, the generator lead wire needs to be directly connected to the primary terminal of the CT, rather than through the core.

The "3-phase short-circuit current" in the table refers to the line current flowing through the generator during a three-phase short circuit at the end (usually around 300% of the rated current), not the long-term operating current. When selecting, it is necessary to estimate based on the rated current and short-circuit factor of the generator.

Calculation example: If the rated current of the generator is 400A and the short-circuit current is calculated as 1200A at three times, then BE25928001 (with a transformation ratio of 1:69, covering 1000-2000A) should be selected.

3.4 Environmental and Mechanical Specifications

Working temperature: -40 ° C to+60 ° C (suitable for outdoor cabinets)

Shock/Vibration: 15G shock resistant, suitable for marine and vehicular environments

Weight and size: 15 pounds (6.8kg), with a size of 343 × 230 × 121mm, using a sturdy metal shell, can be wall mounted or installed inside a cabinet.

Key points for on-site installation and wiring

4.1 CT installation and polarity

Two CTs should be installed on the output side of the generator (near the generator end) to ensure that the true short-circuit current is measured.

The polarity (P1/P2) of CT must be consistent, otherwise the phase difference of the secondary output will affect the boosting effect and even cause device failure. When connecting to the CT secondary terminal of CBS 212A, it should be strictly connected according to the instructions marked (usually K1, K2).

Open circuit is strictly prohibited on the secondary side of CT, and short circuit protection is required before connecting to CBS.

4.2 Voltage detection wiring

The voltage detection terminal is connected to the secondary side (120V or 240V) of the generator terminal PT, and it should be noted that the phase should be in phase with the CT to ensure that the voltage and current phases are consistent (used for internal power direction discrimination? The actual CBS is amplitude detection, only voltage amplitude is required, but for safety reasons, it is recommended to be in phase).

The detection voltage should be within the rated range. If it exceeds 240V, an external step-down PT is required.

4.3 Output Connection

The output DC terminal (+/-) is connected to the stator winding of the exciter (usually in parallel or series with the excitation output of the AVR, depending on the system design). The common connection method is parallel connection: CBS output and AVR output are isolated by diodes and jointly supplied to the excitation machine. When CBS operates, its voltage is higher than AVR output, and it naturally undertakes the excitation task; AVR is cut off due to reverse bias.

If using a series connection method (cutting off AVR when CBS intervenes), it is necessary to add switching contactors, which is more complex, and parallel connection is generally recommended.

4.4 Grounding and Shielding

The device casing must be grounded, and the CT signal line uses shielded twisted pair cables. The shielding layer is grounded at one end to prevent interference and false triggering.

Parameter tuning and debugging steps

5.1 Setting output voltage

Open the front panel of the device, find the output jumper (J1), and select the 60, 120, or 220V range according to the rated voltage of the exciter.

Turn the "Output Limit" potentiometer clockwise to the maximum (100%) and wait for further adjustments.

5.2 Setting the operating point voltage

Measure the PT secondary voltage (such as 120V) at the rated no-load voltage of the generator.

Adjust the "Operation Point" potentiometer to achieve an action value of approximately 70% to 80% of the rated voltage. For example, for a 120V system, set the operating point to 85V (corresponding to the expected drop below 85V when starting the large motor before starting).

An adjustable ratio autotransformer can be used to simulate voltage drop, observe the action indicator light (if any) or measure whether the output voltage is established.

5.3 Verification of Boosting Effect

Actually start a large motor and use a waveform recorder to record the generator voltage, excitation current, and CBS output current.

Check if the CBS output quickly rises to the set limit when the voltage drops below the operating point.

After the motor is successfully started, the voltage is restored, and it is confirmed that CBS exits when the hysteresis value (about 5V) is above.

5.4 Fine tuning output limit

If the excitation current is too large or too small during the start-up process, the "Output Limit" can be adjusted to reduce or increase the output DC voltage, so that the generator terminal voltage during start-up is not lower than the allowable minimum value (such as 85% rated).

Common troubleshooting and countermeasures

Possible causes and solutions for the phenomenon

When the large motor starts, the voltage still drops severely, and CBS has no response. ① The action point is set too high (the drop voltage has not reached the action point); ② CT selection is too small, resulting in insufficient output power; ③ CT polarity is reversed and adjusted to a low operating point (such as from 85V to 75V); Verify whether the CT ratio meets the short-circuit current requirements; Check the CT secondary current waveform with an oscilloscope

CBS frequently malfunctions (starting with normal load fluctuations), the action point is set too low, and the action point should be appropriately raised near the operating voltage (such as from 75V to 85V), and the amplitude of load fluctuations should be checked

CBS does not exit for a long time after startup, resulting in the failure of over excitation return hysteresis setting or slow voltage recovery. Check whether the actual value of PT secondary voltage has truly recovered to above hysteresis; If the return difference is insufficient, you can consult the manufacturer to see if it is adjustable (this model is fixed)

The output DC voltage cannot reach the set value, and the CT capacity is insufficient or the output limiting potentiometer is not adjusted to the maximum. Verify the CT ratio to ensure that the short-circuit current is within the CT rated range; Rotate the 'Output Limit' clockwise needle to the end

If the device heats up severely and works continuously for too long (more than 10 seconds) or has poor heat dissipation, check whether it is caused by the motor starting time being too long, and consider adding starting current limiting measures; Ensure ventilation in the installation space

Comparison with PMG scheme and suggestions for replacement and upgrade

The traditional PMG scheme requires the addition of permanent magnet generators, PMG voltage regulators, and rectifier bridges on the generator shaft, which not only increases costs but also requires installation space and mechanical reliability. CBS 212A:

No mechanical modifications required, only through electrical connections, suitable for retrofitting old units.

Dynamic response is faster, as CT directly extracts energy without the inertia delay of PMG.

Lower cost, especially suitable for multiple units to share spare parts.

However, it should be noted that the boost energy of CBS 212A is limited by the magnitude of the short-circuit current. If the short-circuit ratio of the generator is low (such as<3 times), it may not be able to provide sufficient excitation current. At this time, a higher transformation ratio CT or an active magnetic assistance scheme should be considered. For systems with high short-circuit currents (such as near substations with large short-circuit capacity), it is necessary to limit the output amplitude of CBS to prevent excessive excitation.

When replacing similar devices that have been discontinued (such as early models of the Basler CBS 200 series), the wiring and installation dimensions of CBS 212A are basically compatible, and only the CT ratio and voltage gear need to be checked.

Regular maintenance and lifespan management

Periodic functional testing: Once a year, simulate voltage drop and check whether the action value and output current are normal.

CT circuit inspection: Regularly tighten the CT wiring terminals to prevent increased contact resistance from affecting energy harvesting efficiency.

Heat dissipation inspection: Clean the heat sink to ensure that the ambient temperature does not exceed 60 ° C.

Electrolytic capacitor lifespan: The internal filtering capacitor has a lifespan of about 10 years. If there is an increase in output ripple, you can contact the manufacturer to replace the capacitor component.

Selection Decision Process

Confirm the rated current and short-circuit factor of the generator (usually provided by the manufacturer).

Calculate 300% short-circuit current (600A if rated at 200A).

Select the corresponding CT model based on the system voltage (≤ 600V or ≤ 15kV) and short-circuit current range by referring to the table.

Select the rated voltage of the exciter and determine the output gear (60/120/220V).

Determine the operating point voltage (usually 70%~85% of the rated PT voltage).

Purchase one CBS 212A and two matching CTs.