Three-phase unbalance scheme ◆ Accurately adjust the three-phase current of the system to reduce the center line current Bidirectional, continuous, dynamic reactive power compensation, compensation accuracy of 99% ◆ Taking into account the filtering and compensation function to improve the power quality of distribution transformer in the station area ◆Stabilize the system voltage and improve the voltage qualification rate

three-phase unbalance technology ◆ Pure SVG module ◆ Commutation switch of controller ◆ SVG capacitor reactance combination ◆ SVG commutation switch

 

Scheme Introduction

Phase change switch type: switch the single-phase load of heavy-duty phase in the station area to light-load phase, and realize load balance distribution from the load end. The effect of governance is highly uncertain.

Capacitor type: The capacitor type three-phase load automatic adjustment device uses wangs theorem to connect power capacitors between phase lines to realize active power transfer, balance active power between phases, reduce three-phase imbalance and improve power factor. The capacitor type has low cost and can realize level compensation, but the governance effect is poor and there are hidden dangers of harmonics.

Power electronic type: power electronic type three-phase unbalanced automatic adjustment device with IGBT three-phase full bridge power unit as the core, through the current absorption → energy storage → current transfer way, to achieve accurate adjustment of three-phase current. The compensation accuracy of power electronic products is high, but the cost is also high, which does not meet the needs of economic development.

Power electronic phase change switch: "Power electronic phase change switch" combines the advantages of power electronic products and phase change switch, can solve the three-phase imbalance problem from the user side, compared to pure power electronic products significantly lower costs, and can achieve stepless adjustment.

 

Scheme comparison

	commutation switch type	Capacitor type	Power electronic type	power electronic commutation switch
Advantages	Solve the imbalance problem from the load side. Low loss	Low cost, easy installation, low loss	High compensation accuracy, fine reactive power compensation, harmonic control, easy to install	It can not only solve the line imbalance, load side imbalance, but also solve the distribution station area side imbalance, low loss, harmonic and reactive power control.
Disadvantages	Affect the reliability of power supply, heavy installation workload, poor governance effect	Active and reactive power are adjusted proportionally at the same time, there is a level of compensation, compensation accuracy is low, there is a hidden danger of harmonic amplification.	Low loss, can not solve the end imbalance	Large installation workload

At present, the new technology of three-phase imbalance treatment based on "SVG commutation switch" can fundamentally solve the problem of actual load distribution in the station area, and is a better way to solve the three-phase imbalance.

 

"SVG Commutation Switch"

"SVG commutation switch" hybrid compensation device is a set of products for the treatment of three-phase imbalance in low-voltage distribution area. It is suitable for three-phase four-wire 380V/220V low-voltage power distribution system, can quickly and accurately detect the three-phase imbalance problem of low-voltage power distribution system, through the phase change switch real-time power off rough adjustment of single-phase load, SVG fine adjustment mode, so that the three-phase load in the station area is in a relatively balanced state. This product can effectively reduce the loss of transformer and line, inhibit the occurrence of single-phase overcurrent and terminal low voltage, and relieve many hidden dangers caused by three-phase imbalance.

 

Device composition

The "SVG commutation switch" hybrid compensation device consists of an SVG module and multiple commutation switches (proportioning according to the actual situation on site). SVG module is an intelligent control and compensation device integrating sampling, operation, communication, human-computer interaction, intelligent networking and balanced logic algorithm. The commutation switch is an intelligent switching device that integrates sampling, operation, communication and phase sequence switching functions.

Technical principle

The "SVG commutation switch" hybrid compensation device uses wireless communication to communicate, with SVG as the host and the commutation switch as the slave.

An SVG module is installed at the outlet of the distribution transformer to monitor the three-phase imbalance information and issue adjustment commands. Several commutation switches are installed along the user's front end in the branch. The commutation switches can monitor the load information of their own loaded circuit and perform corresponding commutation operations according to the commutation commands issued by the SVG module. If the three-phase imbalance still exists, the three-phase absolute balance can be achieved through the SVG fine-tuning mode.

 

In order to ensure the service life, the commutation switch adopts zero-crossing switching technology to minimize the damage to the action components and electrical equipment. The zero-crossing switching technology is based on the principle of "current zero-crossing removal and voltage zero-crossing input", which can achieve the effect of minimal impact and minimal arc.

Installation Schematic

 

Features

1) Automatic balancing of three-phase load

Real-time monitoring of three-phase imbalance, and automatically adjust the three-phase load according to the imbalance, commutation time ≤ 10ms, does not interrupt the user power supply, will not cause the reset and restart of commonly used electrical appliances, and will not cause damage to electrical appliances.

2) Reduce transformer loss

The transformer is in a relatively balanced operation state, which effectively reduces the iron loss and copper loss of the transformer.

3) Solve low voltage and overvoltage problems

Solve the problem of low voltage and overvoltage caused by three-phase imbalance, and avoid burning out electrical equipment due to overvoltage or affecting the normal operation of electrical equipment due to low voltage.

4) Protect the safe operation of low-voltage distribution network

Avoid heating and old loss caused by long-term excessive neutral current, and eliminate the hidden danger of burning of power distribution equipment such as transformers.

 

Program Features

Maintenance-free, management-free; automatic commutation, without interrupting the user's power supply; reliable interphase protection technology; switching elements do not consume electricity, the device power consumption is small.

 

Product advantages

More reliable-the core devices are well-known brands to ensure the life of the product;

More energy-saving-through the standby threshold and start-stop time period settings can effectively reduce their own operating losses;

More flexible-functional modes can be freely combined, while the field wiring is not limited by the phase sequence, making installation easier;

More intimate-to provide customers with pre-sales and after-sales support, program design and other one-stop services;

More convenient-through mobile phones, mobile terminals and remote background to achieve product status monitoring and debugging;

 

Capacity configuration

Transformer capacity （kVA）	SVG Capacity (kvar)	commutation switch
		Capacity (A)	Quantity
100	30	120	0
200	30	120	3
400	30	120	6

 

Project Application

Case one

A project site: because the electricity load of residential users is single-phase, the distributed power sources such as small wind turbines and photovoltaic panels provided by residents are mostly single-phase power sources, which will cause three-phase imbalance when these power sources are connected to the power grid. The randomness of users' electricity consumption will also cause three-phase imbalance. During the peak period of power consumption, the three-phase imbalance of the power grid will be seriously aggravated as the load increases. If the zero line current is higher than the designed current carrying capacity for a long time, it will cause the zero line overload and burn out, causing a fault. In order to solve the hidden dangers of power quality problems in the power grid, InBev Electric has researched solutions to completely solve the accident impact caused by three-phase imbalance through technical measures.

The solution given by our company is to add a set of three-phase imbalance adjustment device by using the dual governance of line management and distribution station area. The device mainly includes a 35KVAR SVG device installed in the station area and 6 phase change switches installed in the line.

 

Application

 

Power quality diagram of the equipment in the front desk area

 

 

Power quality diagram after SVG exits and commutation switch is put into operation

 

 

Power quality diagram of the system after SVG and commutation switches are all put into operation

 

Change trend curve of three-phase current before treatment

 

Change trend curve of three-phase current after treatment

 

Power supply bureau background data