The low frequency transmission technology has received extensive attention due to its unique advantages in recent years. Through the application of the low frequency transmission system, when the transmission frequency is reduced from 50Hz to 50/3Hz, the cable current carrying capacity can be increased and the reactive power compensation requirement can be reduced, but the space charge accumulation problem inevitably needs to be considered in the power transmission system. In this paper, Space charge behavior characteristics in both DC and low frequency transmission scenarios are investigated. The internal space charge distribution test of the insulating material adopts the Electroacoustic Pulse (PEA) space charge test system based on automatic equalization phase shift (AEPS), realizing space charge test with a high phase resolution of 1.79°. The results show that under the DC electric field, the cathode and anode of the sample accumulate homo-charges; in the case of low frequency, the cathode side mainly distributes hetero-charges under the low field while the anode accumulates homo-charges mainly with few hetero-charges. With the gradual increase of the electric field, homo-charges of the anode appears inside the sample, and the charge accumulation at the electrode-sample interface and the internal area gradually increases. Compared with High Voltage Direct Current (HVDC) transmission, the amount of space charge accumulated inside the cable insulation is less in the case of Low Frequency transmission. Due to the alternation of positive and negative cycles in the low frequency electric field, the charge injection and extraction are faster than under DC, resulting in less internal charge accumulation.

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