Flexible Coil Current Meter for Large Bus Bar Measurement

Why Flexible Coils Beat Rigid Jaws

Many industrial bus bars exceed 100 mm in width, and substation cables can run in tightly packed bundles where a rigid clamp jaw simply cannot fit. A flexible coil current meter - based on the Rogowski coil principle - uses a thin, flexible loop that bends around any conductor up to several hundred millimeters.

Rogowski Coil Principles

The Rogowski coil is an air-core winding that produces a voltage proportional to the rate of change of current through it. An integrator in the meter converts this to a true RMS reading. Because there is no magnetic core, the device is linear over very wide current ranges and immune to saturation.

Key Specifications

• Coil diameter: 200, 400, 600, 800 mm typical for industrial work.
• Current range: 30 mA to 30 kA - one device covers everything.
• Bandwidth: 10 Hz to 20 kHz - excellent for harmonics analysis.
• Phase shift: less than 1 degree across operating range.

Field Applications

• Generator output bus bars in power plants.
• Switchgear ducts in steel mills, data centers, and chemical plants.
• Tightly packed cable trays where clamp jaws cannot close.
• Harmonic surveys on VFDs and rectifier loads.

Calibration and Care

Calibrate annually with a reference current source. Avoid sharp folds in the coil; the manufacturer specifies a minimum bend radius. Position the coupling joint 90 degrees away from neighboring conductors to minimize interference.

EK Recommendation

The EK flexible coil series offers true RMS measurement up to 10 kA with Bluetooth data logging and PDF reporting for substation field teams.