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Three-phase unbalanced load
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Three-phase unbalanced load

 

 Accurately adjust the three-phase current and reduce the central line current

 Bidirectional, continuous and dynamic reactive compensation, with compensation accuracy of 99%

 Considering the filter compensation function to improve the power quality of the distribution network

 Stabilize system voltage and increase voltage pass rate

 

Three-phase unbalance technology

 

 Pure SVG module

 Controller+ phase-change switch

 SVG+ combination of capacitor and reactor

 SVG+ phase-change switch

 

Introduction of the solutions

 

Phase-change switch type: switch the single-phase load of the heavy-load phase in the distribution network to the light-load phase, and realize load balance distribution from the load end. The control effect has great uncertainty

 

 

Capacitor type: The capacitor type three-phase load automatic regulating device uses wangs theorem to connect power capacitors across phase lines to realize the transfer of active power, balance the active power of phase to phase, reduce the unbalanced degree of three-phase and improve the power factor. Capacitor type has low cost and can realize the step compensation, but the control effect is poor with harmonic hazard.

 

 

Power electronic type: Power electronic type three-phase unbalance automatic regulating device takes the three-phase full-bridge power unit composed of IGBT as the core and realizes the accurate adjustment of three-phase current by means of current absorption, energy storage and current transfer. As an active product, it can also linearly compensate reactive current and harmonic current. The power electronic products have high compensation accuracy, but the cost is also high, which does not meet the economic development needs.

 

 

Power electronic type+ phase-change switch: Combined with the advantages of power electronic products and phase change switches, the "power electronic type + phase-change switch" can solve the three-phase imbalance from the user side. Compared with pure power electronic products, the cost is significantly reduced, and step-less adjustment can be realized.

 

At present, the new three-phase unbalance control technology based on "SVG+ phase-change switch" can fundamentally solve the problem of actual load distribution in the distribution network, which is a good way to solve the three-phase imbalance.

 

“SVG+ phase-change switch”

 

The “SVG+ phase-change switch” hybrid compensation device is a set of products used to control three-phase unbalance in the low-voltage distribution network. It is suitable for 380V/220V low-voltage distribution system of three-phase four-wire system, which can quickly and accurately detect the three-phase unbalance of low-voltage distribution system. It can adjust the single-phase load roughly without power failure in real time through phase-change switch, and SVG fine adjustment mode can make three-phase load in the distribution network in a relatively balanced state. This product can effectively reduce transformer and line loss, suppress single-phase over-current and end low-voltage, etc., perfectly removing many hidden dangers caused by three-phase unbalance.

 

 

1. Device composition

 

The “SVG+ phase-change switch” hybrid compensation device consists of one SVG module and multiple phase-change switches (which are matched according to the actual situation in the field).SVG module is an intelligent control and compensation device integrating sampling, computation, communication, human-computer interaction (HCI), intelligent networking and balance logic algorithm. The phase-change switch is an intelligent switching device integrating sampling, computation, communication and phase-sequence switching.

 

2. Technical principle

 

 

The “SVG+ phase-change switch” hybrid compensation device adopts wireless communication, with SVG as the master and phase-change switch as the slave.

Install an SVG module at the exit of the distribution transformer to monitor the three-phase unbalance and issue an adjustment command. Install several phase-change switches along the front end of the user side for the branch circuit to monitor the load of the self-loading circuit and change phase according to the phase-change command issued by the SVG module. If the three-phase imbalance still exists, the three-phase absolute balance can be realized by fine adjustment mode through SVG.

In order to ensure the service life, the phase-change switch adopts the zero-crossing switching technology, so as to minimize the damage caused by the switching on the action elements and the electrical equipment. Based on the principle of "current zero-crossing for switching-off, voltage zero-crossing for switching-on", zero-crossing switching technology can achieve the effect of minimum impact and electric arc.

 

 

 

 

3. Functional features

 

1) Automatically balance the three-phase load

Real-time monitoring of the three-phase unbalance, and automatic adjustment of the three-phase load based on the unbalance, with the phase-change time ≤10ms, no interruption of the power supply for users, no reset and restart of common electrical appliances and no damage to electrical appliances.

2) Reduce transformer losses

The transformer can be in a relatively balanced operation state, effectively reducing the iron loss and copper loss of the transformer.

3) Solve the problem of low voltage and over-voltage

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

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

Avoid the heating and ageing caused by the excessive current of neutral line for a long time to eliminate the hidden danger of burning down power distribution equipment such as transformer.

 

Features

Maintenance-free and management-free;

Automatic phase change without interrupting the power supply for the user.

Reliable inter-phase protection technology:

Switching elements do not consume electricity, with little power consumption for the device

 

 

4. Product advantages

 

More reliable - adopt well-known brands for all the core devices to ensure the service life of the products;

More energy-saving — set the standby threshold and start-stop time to effectively reduce its own running loss;

More flexible — the functional modes can be freely combined, and the on-site wiring is not limited by phase sequence, so the installation is easier;

More intimate — provide the one-stop services such as pre-sales & after-sales supports and solution design for customers;

More convenient — monitor and debug the product status through the mobile phone, mobile terminal and remote background;

 

 

3.5 Capacity configuration

 

 

Transformer capacity

(kVA)

SVG capacity

(kvar)

Phase-change switch

Capacity (A)

Quantity

100

30

120

0

200

30

120

3

400

30

120

6

 

 

4 Project application

 

4.1 Case A

 

 A project site: Because the power load of residents is single-phase, and the distributed power sources such as small wind turbines and PV panels prepared by residents are mostly single-phase, the three-phase imbalance will be caused when these power sources are connected to the power grid. The randomness of the user's electricity consumption also causes three-phase imbalance; With the increase of load during the peak period of power consumption, the three-phase unbalance of the power grid is seriously intensified. If the zero line current is higher than the designed current capacity for a long time, it will cause the zero line overload to burn and cause failure. In order to solve the hidden dangers of power quality in the power grid, IN-Power Electric has studied the solutions to thoroughly solve the accident effects caused by the three-phase imbalance through technical measures.

The solution provided by our Company: Add a set of three-phase unbalance regulating device by dual control of line and distribution network, which mainly includes a 35KVAR SVG device installed in the distribution network and 6 phase-change switches installed in the line.

 

Application situation

 

 

 

Power quality diagram of distribution network before the switch-on of the device

 

 

Power quality diagram after SVG exits and phase-change switch is switched on

 

 

Power quality diagram of the system after both SVG and phase-change switch are switched on

 

 

The change trend curve of three-phase current before control

 

 

The change trend curve of three-phase current after control

 

Background data of power supply bureau

 

Before compensation

After switching-on of the phase-change switch

After switching-on of SVG+ phase-change switch

Phase A voltage

238

238

235

Phase B voltage

230

236

237

Phase C voltage

245

233

235

Phase A current

267

219

273

Phase B current

332

220

269

Phase C current

195

240

268

N-wire current

103

74

34

Harmonic voltage distortion rate:

6%

7.5%

3.3%