The fault detection and solution of DP Current Transformer (such as open, closed or high precision transformer) needs to be carried out systematic investigation and localization according to the structural characteristics and working principle of transformer. Here's a step-by-step test and tackle strategy:
1, Fault detection methods
1.Appearance and preliminary examination
Check installation status:
Verify that the transformer is fully closed (check that the clasp is locked when opened and closed) to avoid signal loss due to poor contact.
Check that the conductor in the window is neutral. Offset can lead to asymmetry in magnetic circuits, resulting in measurement errors or saturation.
Watch the shell and wiring:
Check for cracks and burn marks on bushing that may cause insulation damage due to overload or short circuit.
Confirm whether the secondary terminal is loose or oxidized, as poor contact introduces additional resistance and affects the accuracy of the signal.
2.Electrical Performance Testing
Secondary lateral circuit detection:
Phenomenon: When a secondary lateral opening is made, the magnetic flux density of the iron core increases dramatically, which can generate high pressure (up to several thousand volts), causing the transformer to heat up, make abnormal noises and even burn out.
Detection method:
Measure the secondary resistance with a multimeter. If it is infinite (open) or well above rated, turn off the power immediately.
Observe if the transformer smells of abnormal heating or burning to help determine the opening position.
Insulation resistance test:
Objective: To verify the insulation performance between the primary winding and the second winding and between the winding and the shell.
Method:
Standard a megohmmeter values are typically ≥ 100M Ω (see Equipment Manual for details).
If the insulation resistance drops significantly, it may leak due to humidity, aging or mechanical damage and may require further drying or replacement.
Ratio and polarity testing:
Variable ratio test:
The output current of the secondary side is measured by caliper and the actual transformation ratio (secondary current/primary current) is calculated by applying a known current (e.g., 5A) to the primary side.
If the actual conversion rate is more than 5% different from the nominal value, it may be due to saturation of iron core, short circuit of winding or circuit air gap of magnetic circuit.
Polarity test:
The phase relationship between the primary and secondary currents is verified by direct current or phase meter to ensure correct polarity (usually depolarization).
Polarity errors may result in a malfunction of the protective device or a reversal of measurement data, requiring rewiring.
3. Operational status monitoring
Load Current Analysis:
The secondary current the waveform of transformer is recorded by the backend system or portable instrument, and the distortion, harmonic or transient overload of transformer is observed.
If the current waveform is seriously distorted, it may be due to the small cross section product of the primary conductor, insufficient transformer capacity or the existence of a strong interference sources nearby.
Temperature monitoring:
The surface temperature of transformer is monitored by infrared thermometer or temperature sensor. During normal operation, the temperature increase should be less than 65 °C (when the ambient temperature is 40 °C).
If the temperature rise is abnormal, it may be due to overload, increased iron core loss or excessive contact resistance, requiring immediate load reduction or maintenance.
2, Common faults and solutions.
1. Second sideways opening;
Reasons: Loose wiring, human error, or internal transformer disconnection.
Solve:
Cut off the power supply immediately and use an insulating tool toshort circuit (short first, then the fault point) to avoid high voltage.
Check that the wiring terminals are loose, tighten again and apply conductive paste; if internal disconnection occurs, a transformer needs to be replaced.
2. Measurement error exceed standards
Reason:
Core saturation (current or frequency deviation above rated value).
Magnetic circuit air gap (open or closed or mounted offset).
The secondary load is too large (long wiring, high load impedance).
Solve:
Adjust the current once to the rated range to avoid long-term overload.
Reinstall the transformer to ensure that the conductor inside the window is centered and the clasp is fastened.
Shorten the length of secondary connection and reduce load impedance (for example, by using a low impedance instruments).
3. Decreased insulation performance
The cause: Insulation layer damage due to humidity, aging or mechanical damage.
Solve:
Slightly humid dry transformers (e.g. hot air circulating ovens, ≤ 80 °C).
If the insulation resistance cannot be restored, the transformer needs to be replaced and the installation environment checked (e.g. to avoid humidity and corrosive gases).
4. Abnormal noise or vibration
Reasons: loose iron core, asymmetric magnetic circuit, or vibration transfer of primary conductor.
Solve:
Tighten the fastening bolts of the iron core to eliminate mechanical looseness.
Reinstall transformer to ensure rigid connection to conductor and reduce vibration transmission.
If the abnormal noise persists, it may be due to a short circuit between the layers of the iron core silicon steel sheet, which needs to be returned to the factory for repair.
3. Preventive maintenance recommendations.
Periodic inspection: Check transformer appearance, wiring, operation and record temperature rise and load current once a quarter.
Cleaning and maintenance: Use a dry soft cloth to remove dust from the shell and avoid using chemical detergents to corrode the insulation.
Load management: Ensure that the secondary load does not exceed the rated capacity (usually 5VA to 30VA) to avoid long-term overload.
Environmental control: installed in a well-ventilated area without strong electromagnetic interference to avoid high temperature, humidity or corrosive environment.