Which tests should be performed on the distribution transformer before installation? What are the two inherent errors in a current transformer?

Before installing a distribution transformer, several critical tests must be performed to ensure its reliability, safety, and efficiency. These tests include:

1. Visual Inspection: Check for any physical damage, proper labeling, and compliance with specifications.
2. Insulation Resistance Test: Measure the insulation resistance between windings and between windings and the ground to ensure adequate insulation.
3. Transformer Turns Ratio (TTR) Test: Verify the turns ratio between primary and secondary windings to ensure correct voltage transformation.
4. Winding Resistance Test: Measure the resistance of the transformer windings to detect any issues with winding continuity or connections.
5. Oil Quality Test (for oil-filled transformers): Assess the quality of the transformer oil by testing its dielectric strength, moisture content, and dissolved gas analysis to ensure it provides proper insulation and cooling.
6. Dielectric Withstand Test (High Voltage Test): Apply high voltage to the transformer to ensure it can withstand operational stresses without insulation failure.
7. Leakage Reactance Test: Measure the leakage reactance to check for any short-circuits between turns.
8. Polarity and Phase Relation Test: Ensure the correct polarity and phase relationship between the transformer windings, which is crucial for proper operation in a multi-phase system.
9. Magnetic Balance Test: Evaluate the magnetic circuit balance of the transformer to detect any core or winding issues.

Inherent Errors in a Current Transformer:

1. Ratio Error (Amplitude Error): This error occurs when the actual transformation ratio deviates from the ideal ratio. It is caused by factors such as core losses (hysteresis and eddy currents) and the magnetizing current. Ratio error affects the accuracy of the current measurement, leading to discrepancies between the primary current and the secondary current.

2. Phase Angle Error: This error occurs when there is a phase shift between the primary current and the secondary current. It is caused by the magnetizing inductance and the burden on the secondary winding. Phase angle error affects the timing relationship between the primary and secondary currents, which can lead to inaccuracies in power and energy measurements.

In summary, comprehensive testing of distribution transformers before installation ensures operational reliability, while inherent errors in current transformers, such as ratio error and phase angle error, can impact measurement accuracy and must be carefully managed.