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With the rapid development of electrified railway, its influence on power supply and consumption system side is increasingly prominent. Because the railway is a 27.5kV single-phase load, if the balance compensation is not carried out, the voltage of the public access point will be seriously unbalanced, which will have a serious impact on other loads of the network point.

In recent years, affected by the surrounding electrified railway, the 110kV power supply voltage of Alashankou crude oil station is unbalanced, resulting in 6kV motor load current imbalance protection action and frequent tripping, which seriously affects the stability of energy transmission.

The field main wiring is shown in the figure below.

A double power supply and double circuit substation is set in Alashankou crude oil station to supply power for production facilities in the station. The two power sources are respectively from Shankou substation and Sanbei substation. The operation mode is two main transformers, one main transformer and one standby transformer, which are supplied by dual power supply of A pump line and SAN pump line. The line where the electric pump is located is the outgoing branch of the busbar at the low voltage side of the main transformer, which supplies power to the pump through the soft start cabinet.

After the power supply of the incoming line is switched to A pump line, the pump often stops from time to time. The reason for the trip is due to the protection action of the pump current imbalance. It is found that there is a serious imbalance phenomenon in the field after 6kV power grid voltage test. The source of the imbalance voltage comes from the 110kV A pump line power supply system, because its 110kV power supply supplies power to the surrounding railway system.

The field 6kV voltage unbalance test data is shown in the figure below:

According to the analysis of test data, the highest value of grid voltage unbalance is 3.5%, and the maximum value of 95% probability is 0.96%. According to the national standard GBT 15543-2008 power quality three phase voltage unbalance, the negative sequence voltage unbalance is generally not more than 1.3%, and the short-term voltage unbalance is not more than 2.6%.

The existence of negative sequence voltage will lead to a large negative sequence component in pump current, and the existence of negative sequence current will lead to unbalanced protection action.

In order to solve the problem of pump shutdown problem on site, Liaoning RongxinXingye Power Technology Co., Ltd. arranged a set of 6kV, 3.6Mvar RSVG system on site to control the voltage imbalance of 6kV system side grid. The equipment adopts delta-connection topology structure and air-cooled indoor cabinet installation mode. RSVG adds negative sequence voltage suppression function on the basis of original reactive power compensation.

The voltage unbalance data after SVG is put into operation is shown in the figure.

According to the analysis of test data, the maximum value of voltage unbalance is 1.54%, and the maximum value of 95% probability is 0.21%. The voltage unbalance has been significantly improved. It meets the requirements of GBT 15543-2008 power quality three phase voltage unbalance. After RSVG was put into operation, the sudden shutdown of pump does not happen again.