Power meter reversal causes and treatment methods - Database & Sql Blog Articles

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The torque generated by an electric power meter depends on the relative direction between the voltage and current in the meter. If the current direction in one of the coils is reversed, the torque will also reverse. This can cause the pointer to swing or even hit the stop. To avoid this issue, markings such as “*”, “+”, or “-” are placed near the terminals. When connecting the power meter, the “*” terminals of both the current and voltage coils should be connected to the same polarity to ensure consistent current flow from “+” to “-”. This is known as the “generator end code” for proper wiring.

Even when the power meter is properly wired, there may still be cases where the pointer reverses. This can happen in two situations: first, if the load side actually has a power source, causing the load to generate power instead of consuming it; second, in three-phase power measurements, especially when the power factor (cosφ) is less than 0.5. In such cases, the power meter may show a negative reading. To get an accurate measurement, you need to reverse the polarity of either the voltage or current coil. By switching the polarity, the reading can be adjusted by adding a negative sign in front of the value.

Therefore, when measuring single-phase power and the meter is reversed, simply reversing one coil will allow you to take the reading with a negative sign. For three-phase power measurements, if one of the meters shows a negative reading, the total power should be calculated as the difference between the two readings. This requires careful attention to ensure accuracy and avoid errors in the final result.