By sion932 
In the power system, high-voltage cables are like the “energy arteries” of the city. Once insulation failure occurs, it can cause power outages for maintenance or even lead to fires and explosions. The root cause of the 2022 subway shutdown accident in a certain city was actually the failure to detect cable insulation aging in a timely manner – and series resonance technology is the core means of preventing such accidents. Today we will unveil the veil of this critical testing technology.
1、 What is series resonance?
Imagine a doctor using ultrasound to perform non-invasive examinations on the human body, and the series resonant device is the “B-ultrasound machine” of high-voltage cables. It forms a resonant circuit through reactors, frequency modulation power supplies, and test cables, generating tens of thousands of volts of high voltage at specific frequencies to accurately detect insulation defects in cables.
Core advantages compared to traditional power frequency withstand voltage:
Energy consumption reduced by 60%: only system loss power needs to be provided
50% reduction in equipment volume: no need for bulky transformers
Security Enhancement: Automatic Voltage Reduction Protection Equipment upon Breakdown
2、 Four key factors that affect testing effectiveness
Frequency matching accuracy: The resonant frequency needs to be accurate to ± 0.1Hz, otherwise it will cause voltage instability
Reactor configuration scheme: Select the series/parallel mode of the reactor according to the cable length (e.g. multiple reactors need to be connected in parallel for distances over 10km)
Environmental interference control: On site electromagnetic interference must be below 50dB, otherwise it will affect partial discharge detection
Equipment synergy: It is necessary to cooperate with the DC high-voltage generator for pre-processing to eliminate residual charges in the cable
3、 Collaborative Operations of Related Technologies
1. * * Golden combination with DC testing * *:
**DC high voltage generator * * first undergoes polarity testing → series resonance for AC withstand voltage → * * partial discharge tester * * locates defects
2. * * Intelligent Diagnostic System * *:
Inputting test data into an AI analysis platform can predict the remaining lifespan of cables (with an error rate of less than 5%)
3. * * Preventive maintenance closed-loop * *:
Test data directly connected to * * relay protection tester * *, dynamically adjust protection threshold
4、 Three advanced techniques for conducting effective testing
1. * * Intelligent tracking of resonance point**
When using the frequency conversion resonance test device of HVHIPOT , the automatic frequency scanning function (30-300Hz) is enabled, which increases the efficiency by three times compared to manual adjustment.
2. * * Partial discharge interference shielding technique**
During on-site testing at the substation:
-Using double shielded cable connection
-Install RFCT anti-interference sensor
-Choose homework during low load hours at midnight
3. * * Deep Data Mining**
Comparing the * * dielectric loss * * values (tan δ) tested over the years, if the annual growth rate is greater than 0.2%, a warning of insulation degradation trend will be issued.
frequently asked questions
**Q1: What is the required test voltage for a 35kV cable? **
A: According to DL/T standards, 2U0 (i.e. 70kV) needs to be applied for 60 minutes, and the * * variable frequency series resonant device * * can accurately control voltage fluctuations of ≤ 1%.
**Q2: How to determine if resonance has been established? **
A: Key indicators: The current suddenly rises to its maximum value, the voltage waveform shows a perfect sine, and the power factor is ≥ 0.95.
**Q3: What should I do if there is a sudden drop in pressure during testing? **
A: Stop the experiment immediately! It may be due to cable breakdown or equipment failure, and a DC high-voltage generator is needed to conduct leakage current testing to locate the problem point.
**Q4: Can testing be conducted in humid weather? **
A: When the air humidity is above 80%, it should be paused, as moisture can cause flashover on the surface of the casing. Suggest cooperating with SF6 micro water tester to monitor environmental parameters.