Application Case of Commutating Switch Type Three-Phase Imbalance Rectification Device (Chongkou Brothers Street Substation)

The ETCR5500 Commutating Switch Type Three-Phase Imbalance Rectification Device is an independently developed, real-time, intelligent automatic load control system by our company. It orderly controls the phase switching of single-phase loads to effectively rectify the issue of three-phase imbalance in substations. This device has been successfully operating for several years in substations installed by the State Grid and Southern Grid, with notable rectification results. The following introduces the application case of this device in the Chongkou Brothers Street Substation of the Liwan District.

In the Chongkou Brothers Street Substation of the Liwan District, equipped with a 500kVA box-type transformer, there are three low-voltage output branches. The substation faces a consistently high load throughout the year, with significant fluctuations in power usage. The current imbalance across phases is severe, with the currents of different phases alternating in magnitude throughout the day. In June 2018, the neutral line current exceeded 450A, with the highest current in the heavily loaded phase exceeding 900A, and about 400A in the lightly loaded phase. The transformer's average load rate is around 73%, with a maximum load rate of 94%. The average imbalance degree of three-phase current in the substation is 44%, with a maximum imbalance of 82.444%. This substation represents a typical case of severe three-phase imbalance, where manual phase adjustment has repeatedly failed to resolve issues of single-phase overload and low voltage for users, often leading to complaints due to single-phase overload tripping and low voltage.

Figure 1 - Statistics on Customer Complaints

Initially, a survey of the substation load was conducted using the ETCR1220 Substation Identifier, ETCR6420 Clamp Meter, and ETCR9000 High Voltage Clamp Meter for topological testing and load current measurement of the substation. Following this, an installation plan was developed: employing 13 phase-switching units, an installation location map was drawn.

Figure 2 - Installation Location Map for Phase-Switching Switches

The construction team installed the main controller and phase switcher according to the location map.

    

Figure 3 - Installation of Phase-Switching Switches

The device was put into operation on June 27, 2018. The effect of the rectification was immediate and significant, with the average imbalance degree dropping from 44% to 8.433%. There were no outages caused by low-voltage branch switch overload burning, nor were there any complaints about low voltage. After the device was commissioned, the neutral line current was reduced to below 50A, demonstrating a very significant energy-saving and loss-reduction effect.

Figure 4 - Three-Phase Imbalance Data Before Device Commissioning

Figure 5 - Three-Phase Imbalance Data After Device Commissioning

Figure 6 - Load Curve Before Rectification (June 17, 2018)

Figure 7 - Load Curve After Rectification (June 28, 2018)