Selecting the appropriate model of primary current generators is a core prerequisite for ensuring the safe conduct of power testing, the accuracy and reliability of data, and the economic efficiency of investment. The selection process should comprehensively consider the testing requirements and equipment characteristics. The following is a detailed parameter interpretation and practical operation steps.
I. Core Selection Parameter Analysis
1. Rated Output Current
The rated output current is the core indicator of a high-current generator and must meet the maximum testing current requirements of the device under test. To avoid the equipment operating at full load for a long time, extend its service life, and reserve safety redundancy, it is recommended to choose a model with a rated output current 20% – 30% higher than the maximum testing demand.
For example, when testing a circuit breaker with a rated current of 630A, its short-time withstand current (thermal stability) may reach 31.5kA/3s. In this case, a device with a rated output current of no less than 35kA or 40kA should be selected to ensure a stable and reliable testing process.
2. Rated Output Capacity / Voltage
The output capacity (unit: kVA) directly determines the equipment’s load-carrying capacity and is closely related to the impedance of the testing circuit. During the selection process, the formula P ≥ I² × Z (where P is the output capacity, I is the testing current, and Z is the total impedance of the testing circuit) must be satisfied. The total impedance of the circuit should include the impedance of the device under test, connection wires, contact resistance at the joints, and all other links.
Since the output capacity and output voltage are related by P = UI, the larger the load impedance, the higher the required output voltage. In scenarios involving long cable connections, multi-turn through-core current transformers, and other inductive loads or high-impedance situations, a model with a higher output voltage (i.e., larger capacity) should be prioritized to ensure the attainment of the preset testing current.
3. Working Power Supply
The input voltage and frequency parameters of the equipment should be determined based on the actual power supply conditions on site. Common input voltage specifications include single-phase 220V and three-phase 380V, with frequencies typically being 50Hz or 60Hz. Generally, high-current generators with a capacity of 100kVA or more should use three-phase 380V power supply to ensure stable operation of the equipment.
4. Accuracy Class
The accuracy class should be flexibly selected based on the testing purpose: for high-precision requirements such as instrument calibration (e.g., current transformer accuracy calibration), high-accuracy models of 0.2 or 0.5 class should be chosen; for routine power-on tests (e.g., equipment on-off detection), an accuracy of 1.0 class is sufficient.
5. Working Mode (Operating System)
The operating system of the high-current generator should match the testing project and is mainly divided into two types:
Short-time operation mode: The most commonly used working mode, usually marked as “rated current × rated time” (e.g., 100kA/1s), suitable for transient testing scenarios such as circuit breaker tripping tests and short-time withstand tests. The equipment can only output the rated current within the specified time and cannot operate continuously for a long time.
Continuous operation mode: Supports stable output of the rated current for a long time, specifically designed for testing projects that require continuous power-on, such as temperature rise tests. When selecting, it is necessary to clearly distinguish between the two to avoid using short-time operation mode equipment for continuous operation tests.
6. Functions and Configurations
(1) Control Method: Manual and Automatic
Manual type: The output current is manually adjusted through a voltage regulator knob, which is simple and intuitive to operate. It is suitable for scenarios with single testing requirements and low operation frequency.
Automatic type: Relying on a PLC or single-chip microcomputer control system, it can preset current change curves, achieving fully automated operations such as automatic current increase, timing, holding, and zeroing. It also has data recording capabilities, offering high testing efficiency and good result repeatability, suitable for batch testing or high-precision testing scenarios.
(2) Portable Design (1) Small current models (output current < 5000A): They are mostly designed as integrated portable units, featuring small size and light weight, which makes them convenient for on-site movement and operation.
Large current models: They are usually of split structure (control console + current boosting transformer), and it is necessary to plan the installation space and transportation route in advance to ensure the convenience of on-site use.
(3) Accessories configuration
It is necessary to confirm whether the accessories are complete based on the on-site test requirements, including whether the length of the test wires meets the connection requirements, whether the wire clamps are compatible with the interfaces of the tested equipment, and whether the standard current transformers (for calibration scenarios) and other accessories are complete, to avoid affecting the test progress due to missing accessories.
II. Standardized selection steps
Clarify the tested object and project: First, determine the type of tested equipment (such as current transformers, circuit breakers, transformers, etc.) and specific test items (such as accuracy calibration, thermal stability test, temperature rise test, etc.).
Extract equipment technical parameters: Refer to the industry standards or technical specification sheets of the tested equipment to clarify the core indicators such as the maximum test current, continuous test time, and accuracy grade requirements.
Estimate the total loop impedance: Comprehensively calculate the total impedance of all links in the test loop, including the tested equipment, connection wires, and contact points, to provide a basis for capacity selection.
Calculate the minimum output capacity: Based on the determined test current and estimated loop impedance, calculate the required minimum output capacity through the formula P ≥ I² × Z, and then derive the required minimum output voltage based on the relationship P = UI.
Comprehensive matching selection: Select the equipment with a suitable model based on the test working mode (short-term / continuous), on-site power supply conditions, budget range, and functional requirements. At the same time, ensure that the rated output current, capacity, and other core parameters have a safety margin of 20% – 30% to ensure test safety and equipment durability.
Post time: Dec-12-2025