Megger Coil Configuration

A Megger is a portable instrument used for measuring the insulation resistance of electrical conductors or equipment. It applies a high DC voltage across the insulation and measures the small current that flows through it to determine the resistance value. The operation of the Megger relies on the interaction of magnetic fields produced by internal coils.

The primary components responsible for the measurement indication in a Megger are its coils. These coils create magnetic fields proportional to the electrical quantities they are measuring.

A typical Megger instrument contains two main types of coils:

• Pressure coil(s)
• Current coil(s)

The pressure coil(s) are connected across the source voltage, essentially measuring the voltage applied to the circuit under test. The current coil(s) are connected in series with the insulation resistance being measured, sensing the leakage current that flows.

The specific configuration of these coils in a standard Megger design involves a particular count for each type to ensure accurate measurement of high insulation resistances.

Based on the common construction of a Megger instrument for insulation resistance testing, it is equipped with:

• Two pressure coils
• One current coil

The two pressure coils are often arranged in a way that helps compensate for voltage fluctuations, providing a reference force. The single current coil provides a force that opposes the pressure coils' force, and the balance between these forces determines the pointer's position on the resistance scale, indicating the insulation resistance value.

Therefore, a Megger typically utilizes two pressure coils and one current coil for its operation.