Basler CBS 310/320 Current Boosting System

Basler CBS 310/320 Current Boosting System: Full Analysis of Technical Principles and Engineering Applications

System Overview and Model Differentiation

The CBS current boosting system is an external auxiliary excitation module designed for the Basler APR series voltage regulator. Its core function is to extract energy from the generator output current when the generator terminal voltage drops significantly due to faults or heavy loads, providing additional DC current to the excitation winding to ensure that the regulator can still output sufficient strong excitation voltage.

The system consists of two major components:

Current Boost Module: It contains electronic control circuits, rectification and switching components, status indicator lights, and terminal blocks, all enclosed in a fully sealed metal casing.

Current Transformer (CT): Installed on the output lines of phases A and C of the generator, it provides an input current source for the boost module.

The CBS series includes two models:

Model matching regulator output voltage applicable scenarios

CBS 310 APR63-5 90-120 Vdc Low Voltage Excitation System (12.5 Ω– 50 Ω Magnetic Field)

CBS 320 APR125-5 180-240 Vdc High Voltage Excitation System (25 Ω– 100 Ω Magnetic Field)

Engineering Tip: For old units with APR63-5 serial number 2112 and below, CBS 344X should be used as a substitute model. In addition, the CBS 310 has been replaced by the smaller and lower cost CBS 305, and new design or renovation projects should prioritize the CBS 305.

Technical specifications and key parameters

1. Input and output power

CT input capability: 7A continuous/46A (30 second short duration)

Regulator trigger signal: 10 mAdc @ 1.5 Vdc (taken from the CB+/CB - terminals of APR)

Boost output: CBS 310 is 7.2-9.6A @ 90-120Vdc; CBS 320 is 7.2-9.6A @ 180-240Vdc

The power consumption in non boost state is only 24W, and the standby loss is extremely low

2. Suitable range of excitation winding resistance

CBS 310：12.5Ω ≤ R_field ≤ 50Ω

CBS 320：25Ω ≤ R_field ≤ 100Ω

Exceeding this range may result in insufficient boost output or module overload, which needs to be resolved by connecting resistors in series or replacing the appropriate model.

3. Selection of matching CT

The manual provides three CT specifications, which can be selected according to the rated current of the generator:

CT part number adaptation model maximum continuous current secondary turns

BE 21331-001 CBS 310 Special 800 A 209 turns

BE 21433-001 CBS 310/320 Universal 800 A 209 turns

BE 21432-001 CBS 310/320 universal 2400 A adjustable (see selection table)

Working principle and control logic

1. Trigger mechanism

The CBS module itself does not actively regulate the voltage, but passively responds to the strong excitation command of the APR regulator. When APR detects a voltage drop and outputs a strong excitation signal, its CB+and CB - terminals provide a trigger signal of approximately 1.5V/10mA to the CBS module, causing the static switch inside the CBS to conduct and directing the CT induced current into the excitation circuit.

2. Energy source and fault support capability

Three wire/four wire generator: CBS supports continuous excitation supply in case of single-phase and multi-phase line faults.

Four wire generator phase neutral fault: A phase and C phase faults can be fully supported; The B-phase fault is due to the APR input being taken from the other two phases, which still have partial support capability but are not fully loaded.

Tracking the underfrequency curve: The boost level of CBS automatically follows the underfrequency compensation curve of APR, ensuring coordinated recovery of voltage and frequency during a single loading.

3. Response speed

The strong excitation signal from APR to CBS output reaches 90Vdc, with a response time of less than 2 power frequency cycles (i.e.<33ms @ 60Hz), meeting the fast excitation requirements for the initial short circuit.

CT turns ratio selection engineering calculation (core link)

The success or failure of CBS's on-site application depends on the correct selection of CT turns ratio. The manual provides a detailed engineering calculation process, which can be divided into two paths: "standard selection" and "precise selection".

1. Determination of basic parameters

Strong excitation voltage E: CBS 310 takes 90 Vdc, CBS 320 takes 180 Vdc

Short circuit excitation current:

IField=E/RF (RFR F is the excitation winding resistance)

Based on this current value, the corresponding three-phase short-circuit current can be obtained from the short-circuit saturation curve (excitation current → short-circuit current) provided by the generator manufacturer.

2. Result judgment and selection path

The judgment result adopts a path explanation

The short-circuit current is too high (exceeding the acceptable value), and path 3A needs to be connected in series with a current limiting resistor to reduce the excitation current

Acceptable short-circuit current path 3B can be selected directly according to the table

3. Standard Selection Table (excerpt from Table 2-1)

Column 1: Range of three-phase short-circuit current

Column 2: CT maximum continuous current capacity (not less than generator full load current)

Column 3: Turn ratio corresponding to different excitation currents (1.8/3.6/7.2 Adc)

Selection method: Find the row where the short-circuit current is located in column 1 → Find the value closest to the required excitation current in column 3 → The turn ratio corresponding to the intersection point is the result (for example, 4:209 represents 4 turns primary/209 turns secondary).

4. Precise selection method (refinement of Table 2-1)

When the standard selection results in too many primary turns (insufficient window space), precise calculation methods can be used to reduce the number of turns:

Calculate the required CT secondary current: ICT_SEC=IField × 1.25 (redundancy factor)

Calculate primary ampere turns: PAT=209 × ICT_SEC

Calculate the number of primary turns: NPRI=PAT/(1.73 × ILINE_3ph), rounded up to the nearest integer

Verify whether the continuous ampere turns exceed the CT rated capacity

Selection case analysis

Generator: 125kVA/480Vac/150A full load/15 Ω excitation winding

CBS 310 short-circuit excitation current: 90V/15 Ω=6.0A

Check the curve for a short-circuit current of 525A (too high) and determine the target as 450A

Required excitation current 5.14A, series current limiting resistor: RS=90/5.14-15=2.5 Ω

According to the table, the turns ratio is 4:209, with 4 turns x 1 wire x 2 phases=8 conductors passing through the CT window, and the window size meets the requirements

Installation and Wiring Engineering Guide

1. Mechanical installation

The boost module can be installed in any direction and uses 1/4 "fasteners. The appearance is shown in Figure 2-1.

CT requires 5/16 "bolts to be firmly fixed at 6 installation points, and the structure must withstand transportation and operational vibrations.

2. Electrical wiring

The manual provides 5 typical wiring diagrams (Figures 2-5 to 2-9), covering:

Standard wiring for CBS and 208-240Vac generators

CBS and 416-480Vac generator wiring

Wiring scheme with isolation transformer

Wiring in conjunction with MVC manual voltage controller

Dual CT configuration (one CT per phase)

Key wiring principles:

The generator wires must have insulation levels that match the operating voltage, and insulated cables or busbars can be used.

The electric force under short-circuit conditions is extremely high, and the busbar/cable must be reliably fixed to prevent displacement or short circuit.

Connect a DC voltmeter between the P and N terminals of the CBS module (to be used for verifying boost status).

3. Auxiliary terminal description

CB+/CB -: Accept trigger signal from APR regulator (10mA @ 1.5V)

P/N: Boost DC output to excitation winding

CT input: AC current signal from CT (see CT wiring diagram for terminal identification)

Debugging and functional verification

1. Installation verification (no-load+load test)

No load start, measure the P-N terminal voltage, which should be about -1.5 Vdc (negative value indicates standby state).

Apply a load to drop the voltage by ≥ 25%, observe:

BOOST indicator light is on

P-N voltage jumps to ≥ 90Vdc (CBS 310) or ≥ 180Vdc (CBS 320)

Record the voltage recovery time to ensure it is less than 2 cycles.

2. Verification of turns ratio

Measure the generator line current under balanced load

ILI L and CT secondary current ISEC, verify that the actual ratio matches the calculation:

ISEC=1.73×NP×IL/NSEC

If the deviation is greater than 10%, the number of turns needs to be recalculated or the CT wiring needs to be checked.

3. Bench testing (offline verification)

Manual Figure 3-1 provides a simple bench test circuit (including a 120Vac power supply, indicator lights, and switches) for verifying the basic functionality of the CBS module without connecting to a generator

SWI closed → all input lights are on, BOOST light is off (standby)

SWI disconnected → input light turns dark, BOOST light and output light turn on simultaneously (boost simulation)

This test can quickly screen out faulty modules before loading.

Typical troubleshooting guide

Although the CBS system is highly reliable, the following faults occasionally occur and need to be investigated:

Phenomenon 1: BOOST light does not light up when fully loaded/short circuited

Check if the CB+/CB - terminals of the APR regulator output a trigger signal (normally around 1.5V/10mA)

Check if APR has entered the forced excitation mode (if the voltage is below 85% of the set value)

Check if the CT input circuit is open circuit

Phenomenon 2: Insufficient boost output (P-N voltage below rated value)

Check if the CT turns ratio is too small (insufficient primary turns)

Check if the resistance of the excitation winding exceeds the adaptation range (CBS 310 needs to be ≥ 12.5 Ω)

Check if the CT secondary side wiring terminal is correct (confirm the corresponding terminal for 209 turns)

Phenomenon 3: BOOST light mistakenly lights up when unloaded

Check if there is a short circuit or leakage current in the CB+/CB circuit

Check if the APR regulator offset is normal

Phenomenon 4: CT overheating or abnormal noise

Check if it exceeds the maximum continuous current capacity of CT (BE 21331-001 is 800A)

Check if additional eddy currents are generated when the primary conductor passes through the CT window (a single core should be used to avoid multiple turns and forming a closed loop)

Spare parts management and historical model replacement

1. Key spare parts list

Component Part Number Description

Boosting module (CBS 310 matching) 9 1861 00 100 has gradually been replaced by CBS 305

Boosting module (CBS 320 matching) 9 1861 00 101 can still be ordered

CT (800A grade) BE 21331-001 only CBS 310

CT (800A grade, universal) BE 21433-001 CBS 310/320 universal

CT (2400A grade, universal) BE 21432-001 high-capacity unit

2. Precautions for replacing CBS 310 with CBS 305

CBS 305 has a smaller size and lower cost, but its output parameters are consistent with CBS 310 (90-120Vdc/7.2-9.6A).

The definition of terminal blocks may vary slightly, and it is necessary to check the CBS 305 manual before replacing them.

If the matching CT is BE 21331-001, it can continue to be used, but it needs to be confirmed that the secondary turns match (still 209 turns).

3. Maintenance cycle recommendations

Check the CT winding insulation and fastener torque every two years.

Perform bench testing every five years or after fault conditions to verify the boost function.