CN1003626B - Equalized power-adjusting method for operating-frequency induction furnace - Google Patents

Abstract

The present invention relates to an electric supply balancing and power adjusting method for power frequency induction electric furnaces, which is suitable for different technical power requirements of thermal insulation, furnace drying, forced smelting, etc. for power frequency induction electric furnaces. Because a balancer adopts a star-shaped connection method, so that the higher flexibility of the power adjustment of the electric furnaces can be displayed, the accident excess current to a system, which is brought by the short circuit and the COS4 control loss of the electric furnace, is limited, the requirements for an electrical system are reduced, the reliability of a smelting device and the accident resisting capacity are enhanced, the starting impact is small, and the automatic adjustment is easy to realize.

Description

Line frequency furnace balance power regulation circuit

The present invention is a kind of circuit without voltage adjusting device adjusting line frequency furnace operate power, is particularly suitable for regulating under deposite metal and other running statuses usefulness of power.

The three-phase balancer of existing line frequency furnace is triangle and connects (referring to accompanying drawing 1).The major defect that this connection exists is: the main contactor life-span is short; It is difficult to close a floodgate; Because changing, powerfactorcos causes system's overcurrent easily; Need add voltage adjusting device and regulate power.

The power adjustments of existing line frequency furnace is to select for use general electrician's voltage adjusting device to solve.The shortcoming of induction voltage regulator is to have rotation partly, makes difficulty, the cost height; The shortcoming of tapped transformer is to consume more switchgear, needs to safeguard the range limited system of voltage-regulation; The shortcoming of autotransformer is that adjustable range is little, and contact partly often needs to safeguard.The method of these several adjusting power all makes the electric induction furnace manufacturing cost higher.

In view of the problem that prior art exists, the objective of the invention is to seek a kind of need not be special voltage adjusting device but utilize the three-phase equilibrium device of electric induction furnace own to realize the regulating circuit of furnace power balance.The technical characterictic that claim 1 provides has reached above-mentioned purpose.The present invention is a kind of power supply balance adjustment circuit that is used for line frequency furnace, it is characterized in that interphase reactor, balanced capacitor and electric furnace three connect (referring to accompanying drawing 2) with star connection, its mid point is earth-free, control the voltage that is added on the body of heater by control capacittance, remain X in the adjustment process _C=X _L

Line frequency furnace all needs to carry out temperature-power control in fusing, insulation, baker, blowing out various running statuses such as bank up a fire.Power adjustments principle of the present invention is referring to accompanying drawing 3.Electric furnace moves (voltage, current phasor figure are referring to accompanying drawing 4,5) under rated load power.X is arranged this moment _L=Xc= $\mathrm{R/}\sqrt{3}$ Quantitative relation.Electric furnace moves under non-rated power, is by changing the parameter X of operating interphase reactor to the power adjustments in the load _LAnd the parameter X c of balanced capacitor, and keep both to equate (vector correlation is seen accompanying drawing 6,7) realized.As can be seen from Figure: the star connection mid point N ' that the floats variation of position generation in the drawings is a voltage Variation.Voltage , can 8 calculate acquisition with reference to the accompanying drawings.Among the figure:

Z _L=jX _L

Z _C=-jX _C

Try to achieve:

With following formula as can be seen, With Same-phase,

Following formula shows that the voltage that is added on the body of heater controls by regulating Xc.During three-phase equilibrium, the voltage that is added in stove end inductor is supply voltage $\sqrt{3}$ Doubly.In adjustment process, three-phase current is in non-equilibrium state, and unsymmetrical current △ I can 9 calculate with reference to the accompanying drawings:

△I＝I _A-I _C

The maximum of asking △ I at first is the parametric equation of finding the solution about angle α

1/2-sinα+cosαsin（150-α）＝0

Try to achieve: α=65 ° 37 '

By the uneven degree that α obtains, △ I can reach 28% of electric furnace rated value when maximum, usually in allowed band.

The influence that furnace power factor angle φ changes system can 10 be calculated as follows with reference to the accompanying drawings:

Wherein: Z=R(cos ²φ+jcos φ sin φ)

φ＝arctgR/X

The advantage that compared with the prior art the present invention has is that the furnace power adjustable range is wide, is not subjected to power limitations, is suitable for being incubated, the requirement of explained hereafter aspect such as baker, Qiang Lian, has shown greater flexibility; Because X _L, X _CExistence, limited electric furnace short circuit and the cos φ accident overcurrent of bringing to system out of control, reduced requirement to electrical system, improved the reliability and the accident defensive ability/resistance ability of smelting equipment; It is little to start impact, can directly start; Circuit has carried out suitable simplification, is easy to realize automatic adjusting.

In view of this balance power regulation circuit has above-mentioned all advantages, believe that the present invention will have good practical prospect in the field of adopting line frequency furnace.

Accompanying drawing thes contents are as follows:

Fig. 1 is the three-phase balancer schematic diagram of delta connection.

Fig. 2 is the three-phase balancer schematic diagram of star connection.

Fig. 3 is the power adjustments electrical schematic diagram.

Fig. 4 is the polar plot of each phase voltage under poised state.

Fig. 5 is the polar plot of each phase current under poised state.

Fig. 6 is electric furnace each phase voltage vector when moving under non-rated power state.

Fig. 7 is electric furnace each phase current polar plot when moving under non-rated power state.

Fig. 8 is an offset voltage

Calculating chart.

Fig. 9 is the unsymmetrical current calculating chart.

Figure 10 changes systematic influence degree calculating chart for powerfactorcos.

The embodiment of the invention is as follows:

Certain line frequency furnace important technological parameters is:

Rated capacity 3T

Inductor rated power 750KW

Inductor rated voltage 500V

Transformer capacity 1250KVA

Transformer secondary voltage 320V

Compensation condenser capacity 4520KVAr

Reactor 320V 1500A

Balanced capacitor YY0.4～10,750KVAr

The main contactor vacuum contactor

Balance pressure regulation contactor CJO40.22 level

Compensation condenser is regulated 9 groups of 2360KVAr

Electric furnace uses an automatic regulator, regulates electric furnace and power factor.Adjuster is made up of panel (comprising indicating device, mains switch, manual selection switch, button, power knob etc.) and terminal block.Terminal block will Insert, as the test side.Adjuster has two groups of control lines, controls the automatic adjusting of the power adjustments and the power factor of electric furnace respectively.Totally 8 groups of furnace power factor compensation condensers, the adjusting of capacity below 384KVAr are partly by the geometric progression grouping.Furnace power is regulated totally 22 grades, regulates 2 capacitors for every grade, has 2 capacitors to be in and waits to drop into, and the capacitor that withdraws from enters when waiting to drop into state, formerly waits to drop into capacitor and is attempted by reactor one side immediately.So just to balanced capacitor Xc, interphase reactor X _LRegulate simultaneously, also promptly regulated furnace power.

Claims (1)

1, a kind of power supply balance power regulation circuit that is used for line frequency furnace, it is characterized in that interphase reactor, balanced capacitor and electric furnace three connect with star connection, its mid point is earth-free, controls the voltage that is added on the body of heater by control capacittance, remains X in the adjustment process _C=X _L

Images