Primary Current Injection System

Dual Canopy Mechanic Electrical Engineering Co., Ltd. is one of the leading manufacturers and suppliers of Primary Current Injection System in China. Please feel free to wholesale discount products for sale here and get quotation from our factory. Customized orders are welcome.

The Primary Current Injection System is a specialized high-current, low-voltage test set designed to inject a controlled AC current directly into the primary side of electrical apparatus. Unlike secondary injection test sets that simulate signals to relays, the primary injection system tests the entire current path, including current transformers (CTs), wiring, connections, and the primary conductors of circuit breakers or busbars.

This system is essential for verifying the actual operating conditions of protection schemes. It confirms that CTs are correctly wired, have the correct ratio and polarity, and that the entire protection chain-from the primary conductor to the relay-functions as intended under realistic load or fault currents.

Our systems range from portable units (500A-1000A) for site maintenance to high-capacity station-class units (2000A-50000A) for substation commissioning and factory testing. They are indispensable tools for transformer commissioning, switchgear testing, and protective relay verification.

1. Power Supply: AC: 220V ± 10% · 25A, 50Hz/60Hz
2. Current Output: AC: 1000A · 5V or 500A · 10V, Capacity: 5KVA
3. Current Output Waveform Distortion: ≤ 5%
4. Display: Primary Current, Secondary Current and Turns Ratio,
Accuracy: ±0.5%,
Primary Current Range: 0 - 1100A, Resolution: 0.1A;
Measurement Current Range: 0 - 6A, Resolution: 0.001A;
Current Duration:
1000A Range: 1000A 2 - 3 minutes,
500A Range: 3 - 6 minutes;
500A Range: 2 - 3 minutes;
5. Dual Protection (Overload Electronic Protection and Software Protection);
6. Operating Environment: Temperature -10 - 40℃, Relative Humidity ≤ 80%;
7. Size: 430mm × 260mm × 260mm;
8. Weight: 29Kg;

1. Current Transformer (CT) Testing
Ratio Test: Inject the rated primary current (e.g., 1000A) into the CT primary side and measure the secondary current to verify the accuracy of the transformation ratio.
Polarity Test: Use DC or AC methods to determine whether the polarity of the CT primary and secondary sides is correct (subtractive/additive polarity), thereby preventing false tripping of differential protection systems.
Volt-Ampere Characteristic Test (Excitation Characteristics): In conjunction with a voltage regulation device, measure the CT's excitation curve to assess the degree of core saturation and determine if the CT is suitable for differential protection applications.
Secondary Burden Test: Measure the actual load impedance on the CT secondary side to ensure it falls within the rated specifications.
2. Circuit Breaker and Switchgear Testing
Primary Injection Trip Test: Inject a high current (simulating a short-circuit current) into the circuit breaker's primary side to verify its opening time and operational reliability.
Main Circuit Contact Resistance Measurement: Employ a high-current method (e.g., injecting over 100A) to calculate the main circuit resistance by measuring the voltage drop across the contacts; this method provides a more accurate reflection of the actual contact condition under high-current loads than a standard micro-ohmmeter.
Busbar and Switchgear Temperature Rise Test: Inject the rated current for an extended period while monitoring the temperature rise of the busbars and contacts to verify their thermal stability.
3. Comprehensive Verification of Protection Wiring
Differential Protection Commissioning: Prior to commissioning transformer or busbar differential protection systems, perform a primary current injection test to verify the CT polarity, transformation ratio, and secondary circuit wiring, ensuring that the differential protection system does not suffer from false tripping.
Overcurrent Protection Setting Verification: Inject the specified setpoint current value to verify the pickup current and operating time of the protective relay device.
4. Pre-Commissioning Testing for Power Transformers
Before a power transformer is officially put into service, utilize a primary current injection system to perform CT verification and differential protection wiring checks; this constitutes a critical step in preventing false tripping of the transformer's differential protection system.

What kind of services can we provide?

 

1. Capacity Calculation Support: Based on the customer's test object parameters (e.g., CT rated current, transformation ratio, secondary burden; or busbar cross-sectional area), we calculate the required test current magnitude and equipment power, recommending the most suitable model.
2. Customized Solutions: We provide customized designs to address special requirements (such as ultra-high currents exceeding 50kA, specific waveforms, or automated control).
3. Technical Consultation: We provide solutions to technical challenges related to CT testing, verification of differential protection wiring, and other complex issues.
4. Standards Compliance Guidance: We assist customers in interpreting the requirements of CT testing standards, such as IEC 60044 and GB 1208.

 

Q1: What is the difference between primary current injection testing and secondary injection testing? Why is primary injection necessary?
A: Secondary injection involves injecting small current or voltage signals directly into a protective relay device; it can only verify the logic and settings of the protection device itself, but cannot verify the Current Transformers (CTs) or the primary wiring.
Primary injection involves injecting a high current into the primary side of the equipment, thereby verifying the entire protection chain: Primary Conductor -> CT -> Secondary Wiring -> Relay.
Necessity: Primary injection can detect potential hazards that secondary injection cannot identify-such as reversed CT polarity, incorrect transformation ratios, open circuits in the secondary loop, or poor contact on the primary side. For critical differential protection schemes, primary current injection is a mandatory procedure prior to commissioning.

Q2: Why is the primary current injection method recommended when performing CT polarity testing?
A: The primary current injection method (whether AC or DC) is the most intuitive and reliable method for determining polarity. By injecting current into the primary side and observing the deflection direction of the ammeter on the secondary side, the polarity can be determined directly. Compared to secondary-side simulation methods, this approach eliminates potential wiring errors within the CT itself and more accurately simulates actual operating conditions.

Q3: Can a primary current injection system be used to measure busbar contact resistance?
A: Yes, and it yields superior results. Traditional loop resistance testers typically output currents ranging from 100A to 200A. For busbars with large cross-sections, measurements taken with such low currents may not accurately reflect the actual contact status (for instance, a surface oxide film might be broken down under high-current conditions). By utilizing a primary current injection system-injecting currents of 1000A or higher to measure voltage drop and calculate resistance-one can obtain a much more accurate reflection of the busbar's contact resistance and temperature rise characteristics under rated current conditions.

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