JPH1042469A - Power supply system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply system in which the adverse effect of voltage drop can be minimized at the time of starting a motor. SOLUTION: In a power supply system where the secondary bus 4 of a transformer 1 is connected with a base load and an induction motor 6 being turned on/off relatively frequently, a compensator 7, principally comprising an inverter, is provided in order to feed reactive power for improving the power factor to the bus 4. The power supply system further comprises a section 16 for determining the power factor from the voltage and current, and a section 17 for controlling the compensator 7 based on an output from the detecting section 16, such that the power factor on the bus 4 has a desired value. The compensator 7 is brought into operating state, at least when the induction motor 6 is started. Power factor is improved by feeding a reactive power having a phase lead to the bus 4 at the time of starting the induction motor 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention compensates for reactive power at the time of starting an induction motor, reduces the influence on a power system due to a voltage drop at the time of starting, and suppresses harmonics by supplying a compensation current. A power supply system including a compensator using an inverter.

[0002]

2. Description of the Related Art When starting a large-sized induction motor, a squirrel-cage induction motor, in particular, has a poor power factor, lowers the secondary bus voltage of the transformer, and causes a reduction in starting torque. It may adversely affect other devices. To prevent this, you can reduce the% impedance of the transformer,
For example, a reactor start or condorfa start is used to start the motor.

[0003]

However, even in consideration of the starting method of the transformer and the electric motor, there is a problem that the short-circuit current of the large electric motor increases.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a power supply system capable of minimizing adverse effects caused by a voltage drop at the time of starting a motor.

Another object of the present invention is to provide a power supply system capable of sufficiently suppressing harmonics of a bus current.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a power supply system in which a base load and an induction motor which is turned on and off relatively frequently are connected to a secondary bus of a transformer. A compensator mainly comprising an inverter, a power factor detecting unit for obtaining a power factor from a voltage and a current of the bus, and a power factor of the bus based on a detection output of the detecting unit. A power factor improvement control unit that controls the compensating device so as to obtain a power factor, wherein the compensating device is in an operating state at least when the induction motor is started.

Further, according to the present invention, in a power supply system in which a base load and an induction motor which is turned on and off relatively frequently are connected to a secondary bus of a transformer, reactive power for improving a power factor is supplied to the bus. A compensating device mainly including an inverter, a power factor detecting unit for obtaining a power factor from a voltage and a current of the bus, and a power factor of the bus based on a detection output of the detecting unit. A power factor improvement control unit for controlling the compensating device, and a harmonic suppression command unit for detecting a bus current and issuing a compensation current command for canceling a harmonic component thereof.

[0008]

FIG. 1 shows an embodiment of the present invention. In the figure, 1 is a transformer, 2 is a primary circuit breaker, 3 is a secondary circuit breaker, and 4 is a secondary bus of the transformer 1. The bus 4 is connected with an induction motor 5A or other load 5B as a base load, and an induction motor 6 that is turned on and off relatively frequently, and further provided with a compensator 7 that mainly uses an inverter to compensate for the reactive power. Connected. The compensator 7
The reactive power generated by the inverter is actively utilized to supply the reactive power of the leading or lagging phase to the bus 4 to improve the power factor or to generate a compensation current for canceling the harmonics of the bus current. For example, it is constituted by a voltage source inverter and a capacitor on the DC side. 8-10
Is a circuit breaker, 11 is a power fuse (PF), and 12 is a vacuum electromagnetic contactor (VCS). 13 is an instrumentation transformer (PT) provided on the secondary side of the transformer 1, 14 and 15 are current transformers (CT) for detecting the entire current of the bus 4, and 16 is a voltage from the PT13 and CT14. The power factor detecting unit 17 that receives the current signal and calculates the power factor of the bus 4 receives the detection output of the power factor detecting unit 16 and gives the compensating device 7 a desired power factor (set value). Power factor improvement control unit that sends control signals,
Reference numeral 18 denotes an active filter function unit that detects a harmonic component included in the current of the bus 4 from the detected current of the CT 15 and generates a command value of a compensation current for canceling the harmonic component. It is provided to the device 7 to generate a compensation current that cancels out harmonics.

Next, the operation will be described. First, a case without the active filter function will be described. In this case, the circuit breaker 10 is turned on before the induction motor 6 is started, and the compensator 7 is brought into the operating state. In the operating state of the compensator 7, the power factor is set to a desired value (for example, lead 0.8, 1..
0 or lag 0.8). Thereafter, when the breaker 9 is turned on to start the induction motor 6, the power factor of the bus 4 is significantly deteriorated with the start of the induction motor 6. This is detected by the power factor detection unit 16 and the power factor improvement control unit 1
7 issues a power factor improvement command to the compensating device 7. That is, the reactive power is supplied from the compensator 7 to the bus 4 so as to have a desired power factor set value. As a result, the power factor is immediately improved, sufficient starting torque is obtained, and adverse effects on other devices are greatly reduced.

If the closed state of the circuit breaker 10 is maintained even after the start of the induction motor 6 is completed, the entire power factor is controlled to a desired value even in a normal state. In this case, if the active filter function is provided, a harmonic of the bus current is detected by the active filter function unit 18, and a compensation current command value for canceling the harmonic is given to the compensator 7. As a result, the compensation device 7 generates a compensation current,
This is supplied to the bus 4. Thereby, harmonics of the bus current are suppressed.

[0011]

As described above, according to the present invention, a compensator mainly composed of an inverter is connected to a secondary bus of a transformer to which an induction motor for deteriorating a power factor is connected at the time of starting. Since the power factor is improved by supplying the reactive power of the phase, it is possible to start a large induction motor without increasing the short-circuit capacity, even though it is a simple starting circuit such as a direct start. The capacity can be reduced. In addition, it can contribute to the improvement of the power factor after starting the induction motor. Further, by additionally providing the active filter function, it is possible to accurately perform harmonic suppression, which is also effective for harmonic countermeasures.

[Brief description of the drawings]

FIG. 1 is a single-wire connection diagram showing an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Transformer 2 ... Primary circuit breaker 3 ... Secondary circuit breaker 4 ... Secondary bus 5A, 5B ... Base load 6 ... Induction motor 7 ... Compensation device mainly with an inverter 13 ... PT 14,15 ... CT 16: Power factor detection unit 17: Power factor improvement control unit 18: Active filter function unit

Claims (2)

[Claims] 1. A base load on a secondary bus of a transformer,
In a power supply system connected to an induction motor which is turned on and off relatively frequently, a compensator mainly composed of an inverter for supplying reactive power for power factor improvement to a bus, and a power factor based on a voltage and a current of the bus. And a power factor improvement control unit that controls the compensator so that the power factor of the bus becomes a desired power factor based on the detection output of the detection unit. A power supply system, wherein the compensator is in an operating state at the time of starting. 2. A base load on a secondary bus of the transformer,
In a power supply system connected to an induction motor which is turned on and off relatively frequently, a compensator mainly composed of an inverter for supplying reactive power for power factor improvement to a bus, and a power factor based on a voltage and a current of the bus. And a power factor improvement control unit that controls the compensator so that the power factor of the bus becomes a desired power factor based on a detection output of the detection unit, and a bus current is detected. A power supply system comprising: a harmonic suppression command unit that issues a compensation current command for canceling the harmonic component.