AC/DC Current Transformer With Single Winding

Abstract

DC currents in power grids are created by induction from geomagnetic variations and newly also by transformerless power inverters installed in solar power stations. These currents may cause serious errors of current transformers (CTs) measuring the consumed energy, but also cause overload of distribution transformers which may result in blackout. Installing DC current sensors into the grid would be very expensive. We have shown that the existing CTs in the grid can be used in the fluxgate mode to simultaneously measure DC current. Utilizing this mode, the CT AC error is inevitably increased. We analyze the sources of these errors and show techniques to reduce them. The experiments were made on the off-the-shelf 500 A/5A CT. We show that the uncompensated 5A DC current without compensation increases its AC amplitude error from 0.1% to 1%. We also found that the dominant additional error was caused by the increased burden. With the optimized design of the excitation circuit it is possible to sense a DC current component with 10% accuracy and reduce the additional AC error from previously reported 1.5% to 0.1% when the DC current component is compensated. This technique can be widely used to improve the AC accuracy of the existing CTs.

Low Field Optimization of a Non-Contacting High-Sensitivity GMR-Based DC/AC Current Sensor

“…Together, this has greatly improved the operational range of the sensor for low current values. This approach was not seen in other works [ 9 , 17 , 18 , 19 ], or in commercial sensor solution based on AMR [ 8 , 30 , 33 ], Hall [ 31 ], or microfluxgate [ 4 , 6 , 34 ]. The obtained performance makes this setup suitable to be adapted and implemented in various current measurement applications for high precision electronics, smart grid applications and automotive industry.…”

“…In this way, equivalent currents down to 100 μA can be measured. Typical current sensors include the AC/DC current transformers [ 2 , 3 , 4 ], fluxgate magnetometers [ 5 , 6 ], Hall effect sensors [ 3 , 7 ], anisotropic magnetoresistive (AMR) [ 3 , 8 ], giant magnetoresistance (GMR) [ 2 , 3 , 9 , 10 ] and tunnelling magneto-resistance (TMR) sensors [ 2 , 11 ].…”

A Busbar Current Sensor With Frequency Compensation

“…The compensation current flowing through the microfabricated solenoid compensation coil is in the range of 10 mA for the measured current of 1000 A. This high ratio cannot be achieved by a fluxgate-based ac/dc current transformer, due to the high parasitic capacitance of the secondary winding [12].…”

Influence of External Current on Yokeless Electric Current Transducers

“…Hall sensors, which are slim in the measuring direction, fit into the narrow airgap in the yoke and therefore dominate in this application. Other transducers of this type have a small fluxgate sensor in the slot of the yoke, or the whole yoke is ac excited and works as fluxgate sensor [2], [3]. Closed-loop current transducers with yoke easily achieve accuracy below 0.1%.…”