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I. Inspection of three-phase four-wire active energy meters 1. Current short-circuiting and voltage disconnection method: Short-circuit the incoming and outgoing wires of the currents in phases A, B, and C respectively, or disconnect the voltages of phases A, B, and C. Observe the speed at which the meter’s dial rotates. If the load is stable and balanced, then short-circuiting one phase’s current or disconnecting one phase’s voltage will result in the meter rotating at 2/3 of its normal speed. If there is a significant deviation, it indicates an abnormal measurement. Inspection can also be carried out by applying voltage and current to the same phase simultaneously; in this case, the rotation speed of the wattmeter should be 1/3 of the normal value. 2. Checking the wattmeter’s error: The voltage for calibration is taken from the terminal box of the wattmeter, while the current is measured using a clamp ammeter connected to the secondary side of the current transformer. During calibration, it is important to monitor the relevant parameters displayed on the calibrator’s screen (if the calibrator is equipped with a primary clamp ammeter, it is also possible to easily determine the ratio error of the current transformer), which helps to determine whether the wiring, current, and voltage are normal. If the wattmeter’s error is significant, it needs to be disassembled for further calibration. 3. Check the wiring: Mainly verify whether the polarity of the current transformer matches the current inlet and outlet wires of the electricity meter, whether the voltage phase sequence is correct, whether voltage and current are in phase, and whether the connections are in good contact. II. Inspection during power outage 1. Measuring circuit resistance: With the power off, disconnect one point in the current circuit and use a multimeter to measure the DC resistance of that circuit. Under normal conditions, this resistance is approximately zero; if it is very high, it may indicate incorrect wiring or a short circuit. When measuring the voltage circuit, disconnect at the terminals of the voltage transformer and measure the DC resistance of Uab, Ubc, and Uca respectively. This value should be relatively high; if it is close to zero or extremely high, it could indicate a short circuit or an open circuit, in which case it is necessary to investigate each section separately to narrow down the scope of the inspection. 2. Determining the variation of the current transformer: When measuring the ratio difference of a current transformer on-site, if the transformation ratio of the standard current transformer is f0 and the measured error is δ, the actual variation of the transformer can be determined using the formula f = f0(1+δ). For example, if a 150/5 standard transformer is used and the ratio difference of the transformer is found to be -25%, then f = f0(1+δ) = 150/5(1–0.25) = 200/5; thus, the actual transformation ratio of the current transformer is 200/5. The transformation ratio of voltage transformers can also be determined in the same way. 3. Measuring DC resistance: If it is possible to shut down the power supply at the site, we can also determine this by measuring the DC resistance of the current and voltage coils of the electricity meter. Generally, the DC resistance of the voltage coil in a 220V single-phase electricity meter is around 0.4–1.2 kΩ. For 3×380/220 active electricity meters, the DC resistance of the voltage coil is 0.4–0.8 kΩ, while for 3×100 active electricity meters, it is 70–150 Ω. The DC resistance of their current coils is approximately 0 Ω.