Application of Arc Protection Device in Hydropower Stations

The arc protection device is mainly used for the quick protection of the medium voltage busbar protection configuration of the hydropower station. This article will introduce the Necessity of an Arc Flash Device, the Benefits of using a dedicated busbar arc protection device, and the Application of an Arc protection device in a Hydropower Station.

The Necessity of Arc Flash Device

In the power system, busbars with a voltage level of 35kV and below are generally not equipped with busbar protection due to the lack of stability. However, due to the large number of outgoing lines on the medium and low voltage busbars, frequent operations, and the distance between the three-phase conductor lines and the ground is relatively close, it is easy to be harmed by small animals, and the quality of equipment manufacturing is worse than that of high-voltage equipment. Poor conditions, changes in system operating conditions, human and operational errors, and other reasons, the failure probability of medium and low-voltage buses is much higher than that of high-voltage and high-pressure buses.

But for a long time, people have not paid enough attention to the protection of medium and low-voltage buses, and no advanced and reasonable solutions have been found. expansion, resulting in huge economic losses. The reason is mostly because there is no medium and low voltage busbar protection, and the failure to quickly remove the fault is caused. Therefore, in order to ensure the operation of transformers and busbar switchgear, according to the requirements of rapid relay protection, it is urgent to configure special medium and low-voltage busbar protection.

Benefits of using a dedicated busbar arc protection device

Since the light and electricity measured by the arc protection device are two parameters with completely different physical properties, the operation principle of the double criterion of the light signal and the fault current signal determines that its misoperation rate is higher than that of other main protections in the system (Including generators, transformers, lines) the probability of misoperation is small, which can not only ensure the high-voltage open cabinet operation, but also not affect the normal production of the power station.

The use of a special busbar arc protection device has the following advantages:

1 Protect nearby workers from personal injury caused by arc light.

2 Protect medium and low voltage equipment from serious damage and prevent fires.

3 Protect the main transformer or plant transformer from damage due to severe impact.

4 Prevent the DC system from affecting the station and avoid huge economic losses.

5 Minimize the user’s power outage time (the user’s power outage recovery time is reduced from the original 2-3 weeks to within a few hours).

6 Extend the service life of existing switchgear.

How is The arc protection device configured in the hydropower station?

1 Arc protection device configuration

The arc protection device is generally composed of the main unit, the expansion unit, and the arc light sensor. Since the arc light sensor is used to detect the arc light, and the circuit breaker trip signal is output through the high-speed solid-state outlet, the reaction speed of the system to the arc light is from the detection of the arc light to the shortest time for sending out the trip signal is no more than 7 milliseconds.

The protection action mechanism of the arc protection device: After the sensor detects the bus arc fault, it transmits the arc light signal to the expansion unit, and then the expansion unit transmits the signal to the main unit through the bus. After the main unit receives the signal, it will send a trip signal to the circuit breaker to trip the incoming line circuit breaker, so as to prevent the development of arc light.

When the sensor detects an arc fault in the cable room, the extension unit can directly trip the circuit breaker of the cabinet without affecting the incoming line.

2 Electrical principle scheme of arc fault device

1) Under normal circumstances, the self-inspection of the device and the self-inspection of the arc sensor, if an arc fault is found, the arc fault information can be given, and at the same time, if the arc protection device is faulty, the trip outlet will be blocked to avoid misoperation; this signal can be sent by an alarm node Output to the small alarm bus or signal acquisition device.

2) The bus generates an arc light for some reason, and the arc sensor in the corresponding bus room detects the arc light and uploads the signal to the expansion unit.

3) If the bus is operated in sections, each main unit compares the current signals collected by itself while receiving the arc signal. If both the arc light and the current meet the criteria, then the arc light occurs on the busbar of this section, a trip signal is issued, and the incoming line circuit breaker of this section trips, thereby extinguishing the arc and giving a trip signal at the same time.

4) If an arc fault occurs in the cable room, the corresponding expansion unit will act and jump the corresponding circuit breaker of this cabinet.

5) If it is a single-entry operation with busbars I and II, the main unit of each busbar will immediately forward the arc signal to another main unit synchronously when receiving the arc signal. Then the main unit of the working incoming line receives the arc signal (signal from this section or forwarded by another main unit), and the current meets the conditions, then sends a trip signal to trip the section circuit breaker, thereby extinguishing the arc, and at the same time gives jump signal, and ensure the normal operation of other buses.

6) Failure protection: If the bus tie circuit breaker fails, the failure protection will be activated to trip the low-voltage side incoming line; if the low-voltage side incoming line fails, the failure protection will be activated to trip the high-voltage side circuit breaker.

7) If the main unit of each busbar is out of operation, the arc protection of this section will be out.

With people’s further research and understanding of arc faults, many hydropower stations have begun to apply arc protection device. For example, the 10kV high-voltage switchgear of the Hydropower Station is equipped with an arc protection device.

We suggest adding an arc protection device to the busbar below 35kV in the hydropower station as the main busbar protection, so as to make up for the current technical defect of only busbar backup protection. Reduce or avoid personal injury caused by arc faults inside the switchgear and improve productivity.