We know that when the circuit frequency f=1/2π√LC, the circuit resonates, and at this time the voltage on the test object is Q times the output voltage of the high-voltage end of the excitation transformer. Q is the system quality factor, i.e., the voltage resonance multiple, generally ranging from tens to over a hundred. First, adjust the output frequency of the variable frequency power supply to make the circuit resonate in series, then under the condition of circuit resonance, adjust the output voltage of the variable frequency power supply to make the test object voltage reach the test value. Due to the resonance of the circuit, a relatively small output voltage of the variable frequency power supply can generate a high test voltage on the test object CX.

Quick selection of series resonance "system capacity/voltage level"



1. Formula for series resonance system capacity



Where:



U - test voltage (note)



f - resonance frequency (i.e., the actual working frequency of the system)



C - capacitance



2. Test voltage corresponding to conventional cables. U (see figure on the right)



3. Resonance frequency for cable testing. Generally take f=35Hz



4. Capacitance. C



5. Calculation method for series resonance system capacity W



3. Demonstration of GDTF-108kVA/108kV series resonance conventional test objects



(1) Cables:



10kV/35kV voltage levels



(2) Main transformers:



10kV/2.5MVA 35kV/3.5MVA 110kV/20MVA (neutral point test)



10kV/4MVA 35kV/10MVA 110kV/50MVA (neutral point test, test voltage ≤80kV)



10kV/10MVA 110kV/180MVA (neutral point test)



(3) Others



AC withstand voltage test for 10kV switches, PT, CT



AC withstand voltage test for disconnectors and circuit breakers at 35kV and below voltage levels



AC withstand voltage test for 35kV switchgear



GDTF-270kVA/270kV series resonance conventional test objects



(1) Cables:



10kV/35kV/110kV voltage levels



(2) Main transformers:



10kV/3.5MVA 35kV/54MVA 66kV/100MVA 110kV/50MVA 220kV/31.5MVA



10kV/25MVA 35kV/31.5MVA 110kV/110MVA



35kV/50MVA 110kV/50MVA



35kV/20MVA 110kV/60MVA



35kV/31.5MVA 110kV/315MVA



35kV/31.5MkVA



(3) Others



AC withstand voltage test for 10kV switches.



AC withstand voltage test for substation equipment such as 35kV switches, GIS, transformers, insulators, etc.



AC withstand voltage test for CT, PT, switches, circuit breakers, insulators, and busbars at 66kV and below voltage levels



AC withstand voltage test for GIS, CT, PT, switches, circuit breakers, insulators, arresters, and busbars at 110kV and below voltage levels