CN203774759U - Direct current inhibition apparatus of transformer neutral point - Google Patents

Abstract

The utility model discloses a transformer neutral point DC current suppressing device, which comprises: a DC blocking capacitor connected between the neutral point of the transformer and the ground; a quick-closing switch connected in parallel with the DC blocking capacitor; a rectifier bridge, The input end is connected to both ends of the DC blocking capacitor, and the AC voltage at the neutral point of the transformer is converted into a DC voltage and output to the trigger module; the output end of the trigger module is connected to the tripping coil of the quick-close switch, and the trigger module detects the output voltage of the rectifier bridge in real time voltage value, when an overvoltage is detected, the trigger is turned on, so that the trip coil is energized, and the normally open contact of the quick-close switch is quickly closed. At this time, the DC blocking capacitor is short-circuited by the quick-close switch, and the neutral point of the transformer passes through Close the switch to ground, and automatically exit the DC blocking capacitor. The utility model can prevent direct current from flowing into the AC transformer, not only protect the neutral point of the transformer, but also protect the capacitance of the device itself; it not only improves the reliability of the device, but also avoids further expansion of power grid accidents.

Description

Transformer Neutral Point DC Current Suppression Device

technical field

The utility model relates to the technical field of electric power system voltage automatic control, in particular to a transformer neutral point DC current suppressing device, which is used to protect capacitors and prevent transformer neutral point overvoltage. the

Background technique

At present, with the development of UHV DC transmission technology, more and more UHV DC transmission lines are put into operation, and the impact of UHV DC transmission on AC systems is becoming more and more obvious. One of the main effects is that when the DC transmission line operates with a single pole or a two-phase unbalanced operation, the ground will be used as a current return loop. At this time, a part of the DC current will flow into the AC system through the AC transformer with the neutral point grounded. After DC flows into the AC transformer, the transformer will generate a DC bias phenomenon, which will affect the safe and stable operation of the transformer. the

In recent years, power plants and substations near the grounding pole of DC transmission lines have been affected by DC bias to varying degrees. the

Utility model content

The purpose of this utility model is to provide a transformer neutral point DC current suppressing device, which can realize that when the device is completely de-energized and an overvoltage occurs at both ends of the capacitor, the device can still automatically withdraw from the capacitor to protect the capacitor and prevent the transformer from The effect of neutral point overvoltage reliably solves the problem of transformer DC bias. the

The utility model adopts the following technical scheme: a transformer neutral point direct current suppression device, including:

The DC blocking capacitor is connected between the neutral point of the transformer and the ground;

The quick-close switch, the quick-close switch is connected in parallel with the DC-blocking capacitor. When the quick-close switch is opened, the spring energy is stored for the quick-close switch, which is the rapid closing capacity of the quick-close switch. At this time, the neutral point of the transformer passes through the DC-blocking capacitor grounding;

The rectifier bridge, the input end is connected to both ends of the DC blocking capacitor, and the AC voltage at the neutral point of the transformer is converted into a DC voltage and output to the trigger module;

Trigger module, the output terminal is connected to the tripping coil of the quick-closing switch. The triggering module detects the voltage value output by the rectifier bridge in real time. The contacts are quickly closed, at this time the DC blocking capacitor is short-circuited by the quick-closing switch, the neutral point of the transformer is grounded through the quick-closing switch, and the neutral point of the transformer automatically withdraws from the DC blocking capacitor.

It also includes a protection gap, and the protection gap is connected in parallel with the DC blocking capacitor. the

The breakdown voltage of the protection gap is set at 2000V. the

The trigger module includes an overvoltage trigger unit and a thyristor, the signal input end of the overvoltage trigger unit is connected to the first output end of the rectifier bridge, the signal output end of the overvoltage trigger unit is connected to the gate of the thyristor, and the anode of the thyristor is connected to the rectifier The cathode of the first output end of the bridge is connected to the trip coil of the quick-close switch, and the other end of the trip coil is connected to the second output end of the rectifier bridge. the

The thyristors are two thyristors, and the two thyristors are connected in parallel. the

The utility model connects the quick-closing switch in parallel at both ends of the DC-blocking capacitor, and the quick-closing switch can trigger the conduction current to drive the quick-closing switch to close through the overvoltage of the trigger module when the device is completely de-energized, thereby serving as the neutral point of the transformer. Capacitive grounding and direct grounding can prevent DC from flowing into the AC transformer, which not only protects the neutral point of the transformer, but also protects the capacitance of the device itself; it not only improves the reliability of the device, but also avoids the further expansion of power grid accidents and avoids further Big loss. the

Description of drawings

Fig. 1 is the circuit schematic diagram of the utility model. the

Detailed ways

As shown in Figure 1, the utility model provides a transformer neutral point DC current suppression device, including: a DC blocking capacitor 1, a quick switch, a rectifier bridge 3, a trigger module and a protection gap 7,

The DC blocking capacitor 1 is connected between the neutral point N of the transformer and the ground;

The quick-close switch, the quick-close switch 2 is connected in parallel with the DC blocking capacitor 1. When the quick-close switch 2 is opened, the spring energy storage is performed on the quick-close switch, which is the rapid closing and accumulation capacity of the quick-close switch. At this time, the neutral point of the transformer is N Ground through DC blocking capacitor 1;

The rectifier bridge 3, the input end of which is connected to both ends of the DC blocking capacitor, converts the AC voltage at the neutral point N of the transformer into a DC voltage and outputs it to the trigger module;

The trigger module includes an overvoltage trigger unit 5 and a thyristor 4, the signal output terminal of the overvoltage trigger unit 5 is connected to the gate of the thyristor 4, the anode of the thyristor 4 is connected to the first output terminal of the rectifier bridge 3, and the cathode is connected to the quick-close switch. The tripping coil 6, the other end of the tripping coil is connected to the second output end of the rectifier bridge 3. The trigger module detects the voltage value output by the rectifier bridge in real time. When an overvoltage is detected, the trigger is turned on, and the tripping coil 6 is energized, and the normally open contact 2 of the quick-close switch is quickly closed. At this time, the DC blocking capacitor 1 is blocked. The quick-closing switch is short-circuited, and the neutral point N of the transformer is grounded through the quick-closing switch, and the DC blocking capacitor 1 is automatically withdrawn.

The thyristor 4 described herein is a dual thyristor parallel connection mode; the dual thyristors are simultaneously triggered and turned on by the overvoltage trigger unit. The flow capacity of the circuit can withstand higher fault currents. It saves cost than using only one thyristor with large flow capacity. the

The protection gap 7 is connected in parallel with the DC blocking capacitor 1. The breakdown voltage of the protection gap 7 is set at 2000V as a backup protection for the neutral point of the capacitor and the transformer. When the overvoltage trigger unit cannot be triggered, the protection gap can be Play the role of preventing the neutral point voltage of the transformer from being too high, and further protect the neutral point of the transformer. the

The quick-closing switch described in the utility model has a spring energy storage and a tripping coil mechanism inside to ensure that the switch can still be quickly closed by the fault current of the thyristor when the switch is completely de-energized, and the closing time is only about one cycle ( 20ms). The quick-close switch adopts the SH8C-2500 quick-close switch produced by Shanghai Lixin Electric. When the speed switch is opened, it is driven by the motor to store energy for the spring inside the switch. The function of the speed switch is very important. It plays the role of state transition between the neutral point capacitor grounding of the transformer and the direct grounding. When the quick-close switch is turned on, the neutral point of the transformer is grounded through the capacitor, which can effectively block the flow of DC current into the neutral point. When the voltage across the DC blocking capacitor 1 is greater than the trigger voltage threshold, the overvoltage trigger unit will trigger the thyristor 4 to conduct , the thyristor conducting current drives the tripping coil 6 of the quick-closing switch to quickly close the quick-closing switch 2, the capacitor is short-circuited by the quick-closing switch, and the neutral point of the transformer is directly grounded through the quick-closing switch. This process does not rely on external power supply, and relies entirely on the overvoltage of the thyristor to trigger the conduction current to drive the quick-close switch to close. The utility model can realize that when the device is completely de-energized, when an overvoltage occurs at both ends of the DC blocking capacitor 1, the device can still automatically withdraw from the capacitor to protect the DC blocking capacitor 1 and prevent overvoltage at the neutral point N of the transformer. The neutral point can still be reliably returned to direct ground. the

Claims (5)

1. a transformer neutral point DC current restraining device, is characterized in that: include:

Partiting dc capacitor, is connected between the neutral point and ground of transformer;

Speed combination switch, fast combination switch is in parallel with partiting dc capacitor, when described fast combination switch is opened, fast combination switch is carried out to spring energy-storage, is the quick-make savings ability of fast combination switch, and now transformer neutral point is by partiting dc capacitor ground connection;

Rectifier bridge, input is connected with the two ends of partiting dc capacitor, converts the alternating voltage of transformer neutral point to direct voltage output to trigger module;

Trigger module, output connects the tripping coil of fast combination switch, trigger module detects the magnitude of voltage of rectifier bridge output in real time, in the time overvoltage being detected, triggering and conducting, obtains tripping coil electric, the normally opened contact rapid closing of fast combination switch, now partiting dc capacitor is by fast combination switch short circuit, and transformer neutral point is by fast combination switch ground connection, and transformer neutral point exits partiting dc capacitor automatically.

2. transformer neutral point DC current restraining device according to claim 1, is characterized in that: also include protection gap, protection gap is in parallel with partiting dc capacitor.

3. transformer neutral point DC current restraining device according to claim 2, is characterized in that: the puncture voltage in described protection gap is adjusted at 2000V.

4. according to the transformer neutral point DC current restraining device described in claim 1 or 2 or 3, it is characterized in that: described trigger module includes overvoltage trigger element and thyristor, the signal input part of overvoltage trigger element connects the first output of rectifier bridge, the signal output part of overvoltage trigger element connects the gate pole of thyristor, the first output of the anodic bonding rectifier bridge of thyristor, negative electrode connects the tripping coil of fast combination switch, and the tripping coil other end connects the second output of rectifier bridge.

5. transformer neutral point DC current restraining device according to claim 4, is characterized in that: described thyristor is two thyristors, two thyristor parallel connections.