JPS6169330A - Ground fault detection device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to a ground fault detection device used in an inverter device, and more particularly to a ground fault detection device having a noise filter function.

[Prior art and its problems] Conventionally, as a method to protect inverter elements from earth leakage ground fault current caused by insulation deterioration of induction motors, the inverter equipment side generally does not have to install a separate earth leakage breaker on the AC input side. Tori 4 = iu rokoto is often used. 1. However, installing an earth leakage breaker for each inverter device has the drawback of being expensive.

In addition, one large earth leakage breaker is installed in the AC input side's main input section C9, and the inverter device and other arbitrary equipment such as an electric water heater or electric wash machine can be wired in the subsequent stage. This is often done, but in this case, in order to avoid unnecessary operation of the earth leakage breaker, the earth leakage detection value is increased and the earth leakage breaker is disconnected after detecting the ground fault, which takes a long time. It was necessary to use a so-called low-sensitivity, slow-operation type inverter, which made it difficult to completely protect the inverter elements from all kinds of ground faults.

In addition, noise regulations have recently become stricter, and it may become mandatory to install noise filters in inverter equipment, so adding an earth leakage detection function to a noise filter is extremely difficult when considered as a product17. It can be of great benefit.

[Object of the Invention] The present invention has been provided in order to eliminate the above-mentioned problems, and provides a ground fault circuit in which a circuit is added within the noise filter to protect the inverter from fault current caused by ground faults in load equipment. The purpose is to provide a detection device.

[Structure of the Invention] This ground fault detection device includes a plurality of coils wound around the same iron core so as to have coil polarities in the same direction, and a zero-phase current detection coil wound on the iron core. and a capacitor connected between at least one line on the inlet side or the output side of the plurality of coils, and the output of the zero-phase detection coil is used to prevent the operation of the switching element of the inverter device. An embodiment of the present invention is shown in FIG. 1.

A smoothing capacitor 2 is connected to the output side of the three-phase bridge 1, and transistors T1-1'. This inverter bridge 3 is connected to an inverter bridge 3 consisting of
A load, for example an induction motor 4, is connected to the output terminal of the motor. Diodes D7 to DI2 are connected in parallel between the collector and emitter of each transistor T1 to T8, respectively. The control circuit 5 is a circuit for driving the transistors T, -T.

Reference numeral 6 denotes a ground fault detection device, in which a three-winding common mode coil 7 and a detection coil 8 are wound on the same iron core so that the coil polarities are in the same direction. The output of the coil 8 is connected to the control input terminal of the control circuit 5 -1-. A capacitor 9 is connected between each phase of the output side of the common mode coil 7.

The operation of the circuit configured as follows will be explained below.

The AC voltage is rectified by the three-phase bridge 1 and the smoothing capacitor 2, and this DC voltage is arbitrarily applied to the output terminals R, S, and T by a predetermined switching operation of each transistor T1 to TIl by the control circuit 5. A variable AC voltage with a frequency of is output. Diodes D7 to D12 are
Transistor T
1 to T6 protection.

A ground fault detection device 6 is inserted into the power supply side of the inverter device that operates as described above.

The common mode coil 7 is wound on the same iron core so that the coil polarities are in the same direction, so when a three-phase balanced load current flows through the common mode coil 7, the composite in the iron core Since the magnetic flux is zero, the detection output of the detection coil 8 wound on this iron core is zero.

Next, when an upward ground fault current flows due to the leakage of the induction motor 4,
The current flowing through the common mode coil 7 becomes an unbalanced load current, and a magnetic flux corresponding to this ground fault current, that is, a zero-sequence current whose return path is the earth, is generated in the iron core, and the detection coil 8 converts this magnetic flux to zero. Detected as phase voltage. This detection voltage is applied to the control input terminal of the control circuit 5, and when this detection voltage reaches a value equal to or higher than the set value, the control circuit 5
The drive signal to ~T6 is stopped, and the transistors T1~T
6 is off. In this way, failure of the transistors T1 to T6 is prevented from occurring due to excessive current caused by a ground fault.

Further, the common mode coil 7 and the capacitor 9 constitute a noise filter circuit, and the transistors T1 to T
This prevents noise consisting of harmonics generated by the switching operation of No. 6 from leaking to the power supply side.

FIG. 2 shows a second embodiment of the invention.

Note that the same parts as in FIG. 1 are given the same reference numerals.

A feature of the ground fault detection device 6 is that it is inserted into a DC circuit between the three-phase converter 1 and the smoothing capacitor 2.

Therefore, the common mode coil 7 of the ground fault detection device 6 has two windings, and the capacitor 9 is connected between the lines on the input side and the output side of the common mode coil 7, respectively. Detection coil 8
The function is similar to that of the first embodiment.

In this embodiment, ground fault detection is possible using the two-winding common mode coil 7. Note that the effect as a noise filter is the same as in the first embodiment.

FIG. 3 shows a third embodiment of the present invention, and the same parts as in FIG. 1 are given the same symbols.

A feature of the ground fault detection device 6 is that it is provided on the output side of the inverter device, and the configuration of the ground fault detection device 6 is exactly the same as that of the first embodiment.

The features of this embodiment will be explained below.

Transistor T1 used in inverter bridge 3~
To is generally attached to a cooling fin via a thin insulating sheet or the like, and this cooling fin is usually grounded.

Therefore, the transistor T I-T a is equivalently grounded via the stray capacitance C.

On the other hand, the transistors T1 to T8 do not repeat high-speed switching operations, and the sudden change in voltage during switching of the transistors T1 to T6, that is, the dV/dt is large.

? The current flowing to ground through the stray capacitance C increases in proportion to this dV/di.

Therefore, if the ground fault detection device 6 is installed at a location closer to the power supply than the inverter bridge 3, this ground fault detection device 6
Since the circuit always detects the current flowing through the stray capacitance C of the transistors 4' and .about.T6, it becomes difficult to identify a ground fault current at a small level.

On the other hand, in this embodiment (J), since the ground fault current is detected on the output side of the inverter bridge 3, this ground fault detection device 6 does not detect the current flowing through the above-mentioned stray capacitance C. Therefore, it is possible to detect a ground fault current, and it is possible to more reliably protect the transistors T1 to To.

In addition, the function of this ground fault detection device 6 as a noise filter is to prevent noise leakage to the load side of the inverter device, so it prevents noise from the wiring, which can be a problem when the wiring to the load equipment is long. Effective for radiation.

Furthermore, this ground fault detection device 6 can also serve as a smoothing glue that is normally provided on the output side of an inverter device.

[Effects of the Invention] As described in detail below, the ground fault detection device of the present invention has a simple circuit configuration, so it is small and safe, and since it is used by being incorporated into an inverter device, it has no problem with earth leakage. Unlike the case where the breaker is installed separately from the inverter device, there is no need for space and work for installation, and there is no inconvenience in maintenance.

Additionally, since this ground fault detection device is intended to protect the elements of the inverter, unlike conventional general-purpose earth leakage circuit breakers, the sensitivity current and time limit of the earth leakage detection device can be set to optimal values. , it is possible to reliably protect the inverter device from ground faults.

In addition, this ground fault detection device also has a function as a noise filter, and can prevent harmonics from flowing out.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the invention, FIG. 2 is a circuit diagram showing a second embodiment of the invention, and FIG. 3 is a circuit diagram showing a third embodiment of the invention. 1. Three-phase bridge, 2. Smoothing capacitor,
3... Inverter bridge, 5... Control circuit, 6
・Ground fault detection device, 7.Common mode coil, 8.
Detection coil, 9. Capacitor.

Claims (1)

[Claims] (1) A plurality of coils wound on the same iron core with coil polarity in the same direction, a zero-phase current detection coil wound on this iron core, and an input side or and a capacitor connected between at least one line on the output side, and the output of this zero-phase detection coil is connected to a cutoff means for blocking operation of a switching element of an inverter device. Ground fault detection device.