JP2659639B2 - Power supply for protective relay - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for a protection relay for applying a DC voltage to a control circuit such as a microcomputer in the protection relay.

[0002]

2. Description of the Related Art Conventionally, protective relays include a type in which a DC power supply required for operating a control circuit such as a built-in microcomputer is supplied from an external power supply, and a type in which a power supply is built in. There is. In the power supply unit built in the protection relay, after the line voltage of the circuit is reduced by a transformer,
Rectified by diode bridge and smoothing capacitor
The DC voltage was taken out after smoothing, and this DC voltage was supplied to the control circuit as a power supply voltage for operation. An example of this is shown in FIG. FIG. 2 is a circuit diagram of a conventional power supply device for a protective relay. In FIG. 2, 6 is a varistor for surge absorption,
7 to 12 are resistors, 13 to 17 are capacitors, 18, 19
Is a transistor, 20 is a diode, 21 is a battery, 22
Is a three-terminal regulator, 23 is a diode bridge, 2
4 is an input terminal connected to the electric circuit, and 25 is an output terminal connected to the control circuit. A is a rectifying unit that rectifies the line voltage of the electric circuit, B is a smoothing unit that smoothes the output of the rectifying unit A, C is a trickle charge of the battery 21 at all times, and the battery 21
This is an output unit that performs backup by using.

In this conventional power supply for a protective relay, in the rectifier A, after the line voltage of the electric circuit is reduced by the resistors 7 and 8 and the capacitors 13 and 14, the diode bridge 2 is turned on.
In step S3, full-wave rectification is performed, and the rectified voltage is output to the smoothing unit B.
In the smoothing unit B, the voltage from the rectifying unit A is smoothed by the capacitor 15, and the voltage almost smoothed by the capacitor 15 is smoothed by the three-terminal regulator 22 with higher accuracy.
Control circuit (not shown) from output terminal 25 through output section C
To supply a DC voltage as a power supply voltage for operation.

[0004]

In the case where a power supply is provided outside the above-mentioned conventional protective relay, stable power supply can be received, but a space for installing the power supply outside the protective relay is required. Become. Also, that power is supplied from an electric circuit independent of the protective relay,
When the control power is turned off, there is a problem that the protection relay itself does not operate.

[0005] In the case of the power supply device for a protective relay incorporated in the protective relay shown in FIG. 2, when the current flowing through the electric circuit is within the rated value, the voltage obtained from the rectifier A is also stable. However, when a short circuit or the like occurs in the electric circuit and an overcurrent flows through the electric circuit, the line voltage of the electric circuit drops significantly, the DC voltage appearing at the output terminal 25 drops, and the control circuit cannot be operated. was there.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a power supply device for a protective relay, which is built in the protective relay and can output a stable DC voltage even when a short circuit occurs in an electric circuit.

[0007]

A power supply device for a protective relay according to the present invention includes a first rectifier, a smoother, a second rectifier, and a voltage converter. The first rectifier receives the line voltage of the electric circuit as input, and the smoother receives the output of the first rectifier as input. The second rectifier receives the short-circuit current flowing through the electric circuit as an input, and the voltage converter receives the output of the second rectifier as a constant voltage.
The converted output is connected to a smoothing section via a backflow prevention element.

[0008]

According to the structure of the present invention , a power supply within a rated value
During normal times when the current is flowing, the first rectifying section supplies electricity to the smoothing section.
Power is supplied and a stable DC voltage is output from the smoothing section.
You. When a short circuit occurs, the line voltage drops and the first
Although the power supplied from the rectifier to the smoother decreases,
The short-circuit current exceeding the rated value flows.
Take out and rectify by the rectification part of 2, and it is constant voltage by the voltage conversion part.
And supply it to the smoothing section via the backflow prevention element.
Therefore, even when a short circuit occurs in the circuit,
DC voltage can be output. As described above, there is no large change in the input power to the smoothing unit before and after the occurrence of the short circuit, and a stable DC voltage can be output from the smoothing unit. Further, since the voltage conversion unit is coupled to the smoothing unit via the backflow prevention element, it is possible to prevent the power from flowing out of the first rectification unit or the smoothing unit to the voltage conversion unit in normal times.
It does not affect normal operation.

[0009]

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of a power supply device for a protection relay incorporated in a protection relay according to an embodiment of the present invention. In FIG.
1a, 1b are current transformers for taking out currents of the electric circuit for two phases, 2
Reference numerals a and 2b denote rectifying diode bridges, which constitute a second rectifying unit D. 3 is a Zener diode, 4 is a resistor, and these constitute a voltage conversion unit E. Reference numeral 5 denotes a diode which is a backflow prevention element. Components corresponding to those in FIG. 2 are denoted by the same reference numerals, and description thereof is omitted.

This protection relay power supply device differs from the conventional example shown in FIG. 2 in that a second rectifier D, a voltage converter E and a diode 5 are provided. First rectifying section A, smoothing section B
And the output section C Ri similar der the conventional example, the rated value to the path
During the normal time when the current of
Electric power is supplied to the sliding portion B, and the output terminal 25
Outputs a DC voltage. The second rectifying unit D extracts current from the two-phase electric circuit by the current transformers 1a and 1b, and rectifies the current by the diode bridges 2a and 2b. Voltage converter E
Is made constant by the Zener diode 3, and the output is supplied to the capacitor 15 of the smoothing unit B via the diode 5. Note that the second rectifier D has a short circuit in the electric circuit.
Short-circuit current Te flows, drops the line voltage of the electric path, when the electric power supplied from the first rectifying portion A to the smooth portion B is reduced, da
The potential on the anode side of the ion 5 is higher than the potential on the cathode side.
As a result, power can be supplied to the smoothing unit B via the voltage conversion unit E. In normal times, the diode 5
The potential on the node side is lower than the potential on the cathode side,
Of power from the rectifier A or the smoother B to the voltage converter E
Outflow can be prevented and normal operation is not affected.

In this embodiment, when a short circuit occurs, the short circuit
Current flows and the line voltage of the circuit drops. At this time, the power supplied to the capacitor 15 of the smoothing unit B is reduced by the supply from the first rectification unit A, but this reduction is compensated by the start of the supply from the second rectification unit D. You. Therefore, before and after the occurrence of the short circuit, there is no large change in the voltage between the terminals of the capacitor 15, and a stable DC voltage can be output from the output terminal 25.

[0012]

Effects of the Invention protective relay for power supply of the present invention, electrostatic
During normal times when a current within the rated value is flowing through the road,
Power is supplied from the smoothing section to the smooth section.
A current voltage is output. When a short circuit occurs, the line voltage
Drops and the power supplied from the first rectifier to the smoother decreases.
However, since the short circuit current exceeding the rated value flows in the electric circuit,
The short-circuit current is taken out by the second rectifier and rectified.
The voltage converter converts the voltage to a constant voltage, and the smoothing unit
Supply even when a short circuit occurs.
A stable DC voltage can be output from the sliding part. This
As described above, there is no large change in the input power to the smoothing unit before and after the occurrence of the short circuit, and a stable DC voltage can be output from the smoothing unit. Further, since the voltage conversion unit is coupled to the smoothing unit via the backflow prevention element, it is possible to prevent the power from flowing out of the first rectification unit or the smoothing unit to the voltage conversion unit in normal times, and to operate in normal times. Has no effect.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power supply device for a protective relay according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional power supply device for a protective relay.

[Explanation of symbols]

 5 Diode (backflow prevention element) A first rectifier B smoother D second rectifier E voltage converter

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-154015 (JP, A) JP-A-3-3612 (JP, A) JP-A-61-81119 (JP, A) JP-A-1- 252114 (JP, A) Japanese Utility Model 2-60439 (JP, U) JP 62-45767 (JP, B1)

Claims (1)

(57) [Claims] 1. A first rectifying unit that receives a line voltage of an electric circuit as an input, a smoothing unit that receives an output of the first rectifying unit as an input,
A second rectifying unit that receives a short-circuit current flowing through the electric circuit as an input, and an output that receives an output of the second rectifying unit and is converted into a constant voltage to the smoothing unit via a backflow prevention element. A power supply device for a protection relay, comprising a combined voltage converter.