Why do we need to use Series Resonant AC Hipot Test System to test power cables?
Publish Time: 2024-09-11 Origin: Site
If the test voltage of the test sample is high and the capacitance is small, the series resonance test method can generally be used.
When W0L=1W0C (C includes CX, C1, C2) in the test circuit, the test circuit produces series resonance, which can generate a high test voltage on the test sample (the test voltage is related to the quality factor of the circuit). If the capacitor C is large, the current in the test circuit is also large, and the current through the resistor is also large. At this time, the test equipment is generally difficult to meet the needs of on-site testing;Usually, this test wiring is only suitable for situations where the capacitance of the test object is small but the test voltage is high, and the test transformer can meet the test capacity requirements but cannot meet the test voltage requirements.
For power cables, the capacitance C of the tested equipment is fixed. To generate resonance in the test circuit, the inductance L or frequency 0 of the test circuit needs to be changed, that is, W0=1, LC or L=1W02C.
The method of changing inductance to meet series resonance requires the use of adjustable reactors, but due to transportation and on-site handling, the volume and weight of the reactors cannot be made very large, so the adjustment range of adjustable reactors is limited.Therefore, the method of adjusting inductance used in on-site testing often cannot meet the testing requirements due to the limited range of the reactor.
Another method is to use frequency modulation, which means that when the reactor and capacitor are fixed, the required voltage can be achieved by changing the frequency of the test power supply to make W0L=1W0C, but a set of frequency modulation power supply device is required at this time.
AC voltage withstand test for power cables
Conduct voltage withstand test on cable lines using AC voltage in the frequency range of 20Hz-300Hz. The test voltage and withstand time shall comply with the requirements in Table 1:
| Rated Voltage U0 /U(kV) | Test Voltage | Time(min) |
| 18/30 and below | 2.5U0(2 or 2U0) | 5( or 60) |
21/35-64/110 | 2U0 | 60 |
127/220 | 1.7U0( or 1.4U0) | 60 |
190/330 | 1.7U0( or 1.3U0) | 60 |
290/550 | 1.7U0( or 1.1U0) | 60 |
Note: Table 1 is excerpted from "Standard for Hand over Test of Electrical Equipment in Electrical Equipment Installation Engineering" GB 50150-2006 P41
In addition to the above national standards, many places or enterprises in China have also issued corresponding local testing standards or enterprise standards. The testing voltage for medium and low voltage cables is 1.6-2.0 times the phase voltage, while the testing voltage for high voltage cables is generally 1.4-1.7 times the phase voltage, with slight differences depending on the local standards. For example, Table 2 shows the enterprise standards of State Grid Corporation of China:
Table 2 Test Voltage and Time of AC Withstand Voltage Test for Cross linked Polyethylene Cable Lines
Rated Voltage U0/U(kV) | Test Voltage | Time(min) | |
| New operational lines or non new operational lines not exceeding 3 years | non new operational lines | ||
18/30 below | 2.5 U0(2U0) | 2U0 | 5(60) |
21/35-64/110 | 2U0 | 1.6U0 | 60 |
127/220 | 1.7U0 | 1.36U0 | |
190/330 | |||
290/550 | |||
Note: Table 2 is excerpted from State Grid Corporation of China's "Test Regulations for Power Cable Lines" Q/GDW 11316-2014 P5
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