HDYZ-E zinc oxide arrester charged tester measurement and compensation principle

HDYZ-E zinc oxide arrester charged tester measurement and compensation principle

1 Measurement principle

This instrument uses the projection method shown in Figure 1 to calculate the resistive current of the fundamental wave and each harmonic.

In the picture: U1 fundamental reference voltage

Ix1p fundamental full current peak value

Ir1p fundamental wave resistive current peak figure 1 Projection method

Ic1p fundamental capacitive current peak

Φ The angle by which the fundamental wave full current leads the fundamental wave reference voltage

Calculation formula: Ir1p = Ix1p·CosΦ

Ic1p = Ix1p·SinΦ

The full current of the zinc oxide arrester contains not only the high-order harmonics generated by the nonlinearity of the zinc oxide arrester, but also the high-order harmonics generated by the bus voltage harmonics. Compared with Irp, Ir1p is more stable and true; therefore, it is recommended to use Ir1p as the resistive current indicator. Both Φ and Ir1p can intuitively measure the performance of zinc oxide arresters.

Using a high-performance, low-power ARM processor with a DSP floating-point processing unit, the calculation speed is faster, the calculation accuracy is higher, and the amount of data processed is larger; thus ensuring the accuracy and stability of test data calculations.

2.2 High-precision sampling filter circuit and digital filtering technology can filter out on-site interference signals.

2.3 Use floating-point fast Fourier algorithm to achieve high-precision analysis of fundamental wave, harmonic voltage and current signals.

2.4 It adopts an industrial-grade 5.7-inch 320×240 dot matrix monochrome LCD screen with clear display and friendly human-machine interface; for some important operations and parameter settings, prompt information and help instructions are displayed; the status bar at the top of the screen can display various peripherals Working status and test status information.

2.5 It can measure the electrical parameters of three-phase zinc oxide arresters at the same time, and can automatically compensate for inter-phase interference; it can also measure single-phase, supporting the PT secondary voltage of phase B grounded as the reference voltage; when the measured phase is different from the reference voltage At the same time, the compensation angle can be automatically calculated.

2.6 Provide wired and wireless test methods. The wireless test method is easier and more flexible to operate; it can greatly reduce the work intensity of on-site test personnel.

2.7 The unique induction plate replaces the PT secondary voltage measurement technology, making the measurement safer and faster.

2.8 The voltage collector integrates local display (128×64 dot matrix OLED LCD screen) and phase sequence detection function, which can display three-phase full voltage, voltage fundamental wave, 3rd, 5th, and 7th harmonic effective values, and system frequency value and three-phase voltage phase difference; it is convenient for on-site testers to quickly check the connection between the voltage collector and the PT secondary voltage output terminal and the three-phase voltage parameters.

2.9 The voltage collector adopts double full digital isolation technology, which is safer and more reliable.

2.10 AC and DC dual-use: built-in lithium battery power supply or 220V AC charger power supply adaptive.

2.11 The instrument host and voltage collector have built-in large-capacity rechargeable lithium batteries, which can last for 8 hours on a single charge.

2.12 Intelligent power management: remaining power display, low battery alarm, long-term idle prompt, automatic backlight adjustment.

2.13 Built-in real-time clock, which can display the current time and date in real time; automatically record the test date and time.

2.14 The test data storage methods are divided into local storage and USB storage. The local storage can store 100 test data, and the local storage can be transferred to a USB flash drive. The USB storage can save test data and waveform pictures. The test data is in TXT format. The waveform pictures are in BMP format and can be edited and printed directly on the computer.

2.15 Built-in thermal printer, which can print test data and saved test records; the printing content can be selected, thus saving the use of printing paper

Interphase interference and automatic compensation principle

Figure 2 Interphase interference

When testing zinc oxide arresters arranged in a line in three phases at the same time on site, as shown in Figure 2, due to the existence of stray capacitance, the current phases of A and C phases are shifted to phase B. Generally, the deviation angle is 2°~ About 4°; this will cause the A-phase φ to decrease and the resistive current to increase, and the C-phase φ to increase and the resistive current to decrease or even become negative. This phenomenon is called inter-phase interference.

The way to solve this problem is to use an automatic compensation algorithm, that is, the instrument's built-in "automatic edge compensation" function. Assume that the phase difference between Ia and Ic is 120° when there is no interference, and assume that the interference between B and A and C phases is the same; measure the angle Φca at which Ic leads Ia, and phase A compensation Φ0a=(Φca-120°)/2, phase C Compensation Φ0c= -(Φca -120°)/2. This method actually averages the resistive currents of phases A and C, which is very likely to cover up existing problems. Therefore, it is recommended to evaluate the original data without automatic compensation (that is, the compensation angle is 0°) and evaluate its changing trend.