CN101794979A - Star connection three-phase electric heating circuit open-phase protection device - Google Patents

Abstract

The invention relates to a star connection three-phase electric heating circuit open-phase protection device, which consists of QF: a circuit breaker, KM: a contactor, KA: a relay, SB: a button, HL: an indicating lamp and HA: a buzzer. An electric heater 1, an electric heater 2 and an electric heater 3 of terminals of three windings of a three phase power supply are connected together to become a common point O, three end lines are led out of beginning ends U, V and W, and the connection is named as star connection or Y-connection.

Description

Star connection three-phase electric heating circuit open-phase protection device

Technical field the invention belongs to circuit open phase protection field, is a kind of three-phase electric heating circuit open-phase protection device in the industrial equipment that relates to concretely.

In the technical background three-phase circuit, owing to disconnect a phase, cause the motor single-phase operation, this is the main cause that three phase electric machine burns out.After the phase failure, if applied load is constant, because the motor useful torque reduces, then the electric current in the winding will increase, and will make burn-down of electric motor.Take off device and existing circuit breaker (comprising residual current circuit breaker) all has the long delay thermal overload release and move electromagnetism wink, circuit overload is played practical protective effect.Therefore, in the control circuit of motor, adopt circuit breaker widely.But in use,, cause the phase failure unavoidable because of the reasons such as blown fuse of the power transformer phase failure or front.At present, three phase mains phase failure protector product is more, but the general circuit complex structure, the production cost height.

Summary of the invention the present invention is directed to the shortcoming of above-mentioned main equipment operation, has developed a kind of simple in structure, easy to maintenance, three-phase electric heating circuit open-phase protection device that cost is low.

The present invention is realized by following concrete technical scheme:

The resistive electric heating equipment of technical pure adopts the three-phase star connection more.Be about to every phase load end and be linked to be 1 N (neutral point N), head end U, V, W receive on the power line respectively.Line voltage between two end line U and the V should be the poor of two corresponding phase voltages, promptly

$\left\{\begin{array}{c}{\stackrel{\·}{U}}_{\mathrm{UV}}={\stackrel{\·}{U}}_U-{\stackrel{\·}{U}}_V\\ {\stackrel{\·}{U}}_{\mathrm{VW}}={\stackrel{\·}{U}}_V-{\stackrel{\·}{U}}_W\\ {\stackrel{\·}{U}}_{\mathrm{WU}}={\stackrel{\·}{U}}_W-{\stackrel{\·}{U}}_U\end{array}\right.$

The line voltage swing utilize geometrical relationship can try to achieve into:

$U_{\mathrm{VW}}=\sqrt{3}{U}_V$ $U_{\mathrm{WU}}=\sqrt{3}{U}_W$

The line voltage of star connection is phase voltage

Times, and line current equals phase current.Under the condition of load symmetry, because the position between each phase current differs 120 ° mutually each other, so the electric current that flows through center line at each constantly all is zero.Just when the threephase load balance,, there is not electric current to flow through on it even connect the neutral line yet.When threephase load was uneven, then each phase load did not wait dividing potential drop.When the phase failure:

$I_B=I_C=\frac{U_{\mathrm{BC}}}{R_B=R_C}=\frac{380}{2R}$

${U^{\′}}_B=I_B{R}_B=\frac{380}{2R}R=190V$

${U^{\′}}_C=I_C{R}_C=\frac{380}{2R}R=190V$

Voltage on other two-phase heating element will change.In this moment asterism and the circuit between the N voltage be about 110V.In the heater course of work, during the heater circuit phase failure, voltage is 110V between heater asterism and the N, and relay K A (coil voltage is 110V) gets electric closure, cuts off heating power supply contactor KM, and makes alarm.

The advantage that the present invention has is simple in structure, easy to maintenance, cost is low is mainly used in industrial heater circuit field.

Description of drawings

Fig. 1 complete schematic

Fig. 2 circuit simplified schematic diagram

Simple and easy schematic diagram of Fig. 3 and winding diagram

Fig. 4 vectogram

Embodiment star connection three-phase electric heating circuit open-phase protection device of the present invention is by QF: circuit breaker, KM: contactor, KA: relay, SB: button, HL: indicator light, HA: buzzer is formed; the terminal electric heater 1 of three windings of three phase mains, electric heater 2, electric heater 3 are linked together; become a common point O; draw three end lines from top U, V, W, this connection is called " star connection " and claims " Y connection " again.The line voltage of star connection is phase voltage Times, and line current equals phase current.Under the condition of load symmetry, because the position between each phase current differs 120 ° mutually each other, so the electric current sum that flows through center line at each constantly is zero.Just when the threephase load balance,, there is not electric current to flow through on it even connect the neutral line yet.When threephase load was uneven, then each phase load did not wait dividing potential drop.When the phase failure, other two phase voltage will exceed the rated voltage of heating element.In this moment asterism and the circuit between the N voltage be 110V.

Claims (2)

1. star connection three-phase electric heating circuit open-phase protection device of the present invention is by QF: circuit breaker, KM: contactor, KA: relay, SB: button, HL: indicator light, HA: buzzer is formed.It is characterized in that: the terminal electric heater 1 of three windings of three phase mains, electric heater 2, electric heater 3 are linked together, become a common point O, draw three end lines from top U, V, W, this connection is called " star connection " and claims " Y connection " again.

2. star connection three-phase electric heating circuit open-phase protection device according to claim 1 is characterized in that: the voltage on other two-phase heating element will change.In this moment asterism and the circuit between the N voltage be about 110V.In the heater course of work, during the heater circuit phase failure, voltage is 110V between heater asterism and the N, and relay K A (coil voltage is 110V) gets electric closure, cuts off heating power supply contactor KM, and makes alarm.

Images