Common electrical measurements on power transformers and CT

Explore essential testing and measurement techniques for power transformers and current transformers (CTs). This course delves into critical procedures for ensuring reliable operation and diagnostics.

Key Applications Covered:

• Initial Energization: Safe and successful startup procedures.
• Reenergization After Repair: Verifying integrity following maintenance.
• Diagnostics After Internal Faults: Identifying and assessing potential issues.
• Scheduled & On-Demand Measurements: Proactive monitoring and troubleshooting.

Core Measurements for Power Transformers:

• Insulation Resistance Measurement (Transformer Insulation Test): Assessing the health of the transformer's insulation.
• Tank Insulation Measurement: Evaluating the insulation of the transformer tank.
• Winding Resistance Measurement: Determining the resistance of the transformer windings.
• Transformation Ratio Measurement: Verifying the transformer's voltage transformation capability.
• Vector Group Determination (Clock Number): Identifying the transformer's phase displacement.

Core Measurements for Current Transformers (CTs):

• Insulation Resistance Measurement: Evaluating the CT's insulation integrity.
• Secondary Winding Resistance Measurement: Assessing the resistance of the CT's secondary winding.
• CT Ratio Measurement: Verifying the CT's current transformation ratio.
• Saturation or Magnetization Measurement: Determining the CT's saturation characteristics.
• Polarity Determination (Direction of Transformation): Identifying the correct CT polarity.

Modern Testing Equipment & Classic Methods:

This course highlights the use of digital test equipment – including digital primary injection systems, digital megohmmeters, and digital microohmmeters – which enhance traditional measurement methods. We'll explore classic techniques that remain relevant, especially when dealing with low resistances.

Understanding Resistance Ranges:

Transformer winding resistances range from microohms to ohms, with high-power transformers often exhibiting lower resistances. Traditional measurement methods, particularly the classic voltmeter method, can be unreliable or impractical for these low resistance values. Careful consideration is required, especially when measuring contact resistances during handling.