Working principle of transformer clamp ammeter

The transformer type clamp ammeter consists of a meter head with a rectifier. Figure 5-2(a) is the appearance of the clamp ammeter, and Figure 5-2(b) is the clamp ammeter. The current sensor core is in the shape of a clamp mouth. When the handle of the clamp ammeter is squeezed, the core opens, and the current-carrying wire can pass through the gap of the core. When the handle is released, the core closes, and the wire with the measured current becomes the primary coil of the current transformer.

The measured current generates working magnetic flux in the iron core, which generates induced electromotive force in the secondary winding around the iron core, and current flows through the measuring circuit. This current flows into the meter head after rectification according to different shunt ratios. The scale is engraved according to the primary current, so the meter reading is the current in the measured wire. The change of the range is achieved by changing the shunt resistance with the conversion switch.