The instrument inputs the PT secondary voltage as the reference signal, and simultaneously inputs the MOA current signal. Through Fourier transform, the voltage fundamental wave U1, the current fundamental wave peak value Ix1p, and the current-voltage angle Φ can be obtained. Therefore, the component in phase with the voltage is the resistive current fundamental peak value (Ir1p), and the orthogonal component is the capacitive current fundamental peak value (Ic1p):
Ir1p=Ix1pCOSΦ Ic1p=Ix1pSINΦ
Considering that δ=90°—Φ is equivalent to the dielectric loss angle, it is also very simple to evaluate MOA directly using Φ: when there is no "inter-phase interference", Φ is mostly between 81° and 86°. According to the requirement that "the resistive current should not exceed 25% of the total current", Φ should not be less than 75.5°. The following table can be used for segmented evaluation of MOA performance:
| Performance | <75° | 75°~77° | 78°~80° | 81°~83° | 84°~89° | >89° |
| Φ | Poor | Bad | Fair | Good | Excellent | Interference |
Actually, attention should be paid when Φ<80°.
Grounding:
Connect the ground wire before measurement, and disconnect the ground wire last after measurement! If there is paint or rust at the grounding point, it must be cleaned thoroughly.
Reference Voltage
Insert one end of the reference voltage signal line into the reference voltage socket, and connect the other end to the PT secondary low-voltage output of the phase under test: the small black clip connects to the neutral point (x), and the small red clip connects to the phase voltage under test (a/b/c). When using the external application method, connect to the measuring winding of the step-up transformer. If the PT is far away, an extension line can be used. Near the two small clips, there is a 0.1A fuse each to prevent accidental burning of the PT fuse. If the 0.1A fuse is damaged, replace it with a fuse of the same specification.
2. Induction Mode:
An electric field induction sensor is set on the MOA base. Its induced current leads the electric field strength (bus voltage) by 90°. After integration, it is in phase with the electric field strength or bus voltage, so the signal from the electric field induction sensor can be used as a measurement reference. The instrument inputs the electric field induction sensor signal and simultaneously inputs the MOA current signal. Through Fourier transform, the electric field fundamental wave E1, the current fundamental wave peak value Ix1p, and the current-electric field angle Φ can be obtained. The component in phase with the electric field is the resistive current fundamental peak value (Ir1p), and the orthogonal component is the capacitive current fundamental peak value (Ic1p).
Using the B-phase induction signal as reference
Because the electric field influence of the A/C two side phases on the B-phase base cancels out, the induction plate should be placed on the B-phase MOA base at a position symmetrical to the A/C phases to obtain correct phase information for the B phase. The electric field on the A/C phase MOA bases is affected by the B phase, so do not place the induction plate on the A/C phase MOA bases.
3. Wireless Mode:
Use a wireless transmission terminal to transmit the PT secondary voltage signal to the voltage acquisition part of the instrument, thereby replacing the long wire connecting the PT.
Wireless Transmission Terminal
Current Signal
First insert the leakage current signal line plug into the instrument, then clip the other end (or attach it via an insulating rod) to the upper end of the MOA discharge counter of the phase under test. In the laboratory, the MOA without a discharge counter can be placed on an insulating board, and the current signal can be taken from the lower end of the MOA.
4. Three-Phase Simultaneous Measurement:
Current Signal
First insert the leakage current signal line plug into the instrument, then clip the four clips at the other end (or attach them via insulating rods) to the upper ends and ground ends of the A, B, C phase MOA discharge counters. Near the clips, there is a 0.1A fuse to prevent incorrect connection to the PT. If the fuse is damaged, replace it with a fuse of the same specification. The current signal cannot use extension lines.
