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 with Φ: when there is no "interphase 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 |
In fact, attention should be paid when Φ<80°.
Grounding:
Connect the ground wire before measurement, and disconnect it last after measurement! If there is paint or rust on 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 secondary low-voltage output of the tested phase PT: the small black clip connects to the neutral point (x), and the small red clip connects to the tested phase voltage (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 each of the two small clips, there is a 0.1A fuse to prevent accidental burning of the PT fuse. If the 0.1A fuse is damaged, it should be replaced 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 intensity (bus voltage) by 90°. After integration, it is in phase with the electric field intensity 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. After 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 wave peak value (Ir1p), and the orthogonal component is the capacitive current fundamental wave peak value (Ic1p).
Using B-phase induction signal as reference
Because the electric field influence of the A/C 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 of 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.
