Common faults and solutions of SF6 circuit breakers

1. Switch refusal to close and refuse to open

When the opening and closing command is issued, the Circuit Breaker refuses to operate. The main reasons are:

• Poor conversion of auxiliary switches
• The lead wire of the electromagnet coil is disconnected or has poor contact
• The top rod of the primary valve is bent or stuck
• Low oil pressure, electric locking
• The closing valve maintains a large amount of leakage in the circuit
• The opening ball valve is not closed
• The one-way valve is not tightly closed, keeping the oil circuit blocked, and it opens again after closing
• The working cylinder is frayed and stuck
• The transmission system is stuck

2. Close the switch immediately after opening it

The immediate closing after opening is mainly due to the incomplete reset of the closing iron core or the first stage valve stem at the end of closing, which prevents the steel ball from fully resetting and prevents the closing oil circuit from being sealed. The main reason for this is that the collision rod of the closing moving iron core is bent manually, causing jamming due to loose collision heads. As long as the moving iron core is removed, calibrated, and reinstalled, it can be ensured that the iron core is not jammed in any position.

3. Immediately open the switch after closing it

The main reason for immediately opening after closing is that the opening moving iron core or the first stage opening valve stem is stuck in a certain position, causing the opening steel ball to not fully reset, or the closing holding valve check steel ball to not fully reset.

4. Frequent start-up and pressurization of the oil pump

Frequent starting and pressing of the oil pump can be divided into frequent starting and pressing at the open position; Frequent activation of pressure at the closing position; Frequent activation of pressure at the opening and closing positions. The main causes are external leakage and internal leakage. Generally speaking, it is because the joints and ports are not tightly sealed; The seal is not tightly sealed; Caused by inadequate sealing of opening and closing valves and oil discharge valves. The specific handling method is to dismantle and inspect, repair, grind and replace the joint or sealing ring.

5. Leakage of hydraulic operating mechanism can cause short-term frequent pump start-up or prolonged pressure replenishment time for the hydraulic mechanism. A large amount of oil leakage in the valve body can cause pressure loss faults. Hydraulic oil entering the nitrogen side of the pressure storage cylinder can cause abnormal pressure rise, which can affect the safe operation of Sf6 Circuit Breakers. Various malfunctions of hydraulic operating mechanisms, except for pressure detection devices and pressure components that are damaged or abnormal, resulting in abnormal oil pressure. The refusal to close or open caused by faults in the opening and closing solenoid coils and the first stage valve top rod, as well as signal assisted switches, is almost always due to leakage (including nitrogen gas leakage). The main oil leakage parts of hydraulic mechanisms include: three-way valves and drain valves, high and low pressure oil pipes, pressure gauges and pressure relay joints, as well as damaged seals on the working cylinder piston rod and accumulator piston rod, and sand holes in the low-pressure oil tank.

  (1) Leakage of pipe joints such as high and low pressure oil pipes, pressure gauges, and pressure relays

Pipe joint leakage accounts for a relatively high proportion of all hydraulic mechanism leaks, accounting for about 30% of leaks. Hydraulic oil pipes and pipe joints are sealed using "clamps". Improper machining accuracy, fastening strength, and burrs at the connection will cause oil leakage. When handling, tighten the joint slightly first. If there is still leakage, remove the oil pipe and align it again for assembly. The tightening torque should not be too large or too small during assembly to avoid damage to the sleeve and prevent oil leakage.

(2) Poor sealing and oil leakage

Hydraulic mechanisms generally have two sealing forms: rigid sealing and elastic sealing. Elastic seals include: "O" - shaped rubber seals that use their elastic deformation to create static and dynamic seals in a flat or circular shape. The V-shaped seal has directionality, and the V-shaped opening must face the high-pressure side.

Poor quality and improper installation of the sealing ring, burrs on the piston rod or impurities in the oil, and wear during movement can cause the sealing ring to fail. Insufficient compression, aging, and damage can all lead to leakage. When this situation is discovered, the seal should be replaced.

(3) Poor sealing of valve body and oil leakage

Three way valves, oil discharge valves, and other valve body joint surfaces are often sealed with rigid seals, usually the valve line seal of the valve body. For example, ball valves use steel balls to tightly fit with the valve surface to form a seal, while cone valves use their conical surfaces to tightly fit with the valve port to form a seal.

The oil leakage of the valve body joint surface is mainly caused by the following reasons: poor sealing fit accuracy, large errors in sealing surface roughness and flatness, poor machining accuracy, impurities in the joint surface during assembly or operation, causing damage to the sealing surface.

The processing methods include: cleaning the burrs on the relevant components; If the hydraulic oil is dirty or unqualified, replace or filter it; The poor sealing of the ball valve requires reassembly. It is important to note that the sealing surface of the valve port should not be too wide, and new steel balls must be used with high precision requirements. If the sealing of the conical surface is poor, it must be carefully ground for repair. If the seal is severely worn and cannot be repaired, replace it as a whole.

(4) Leakage of the shell

The leakage of the shell is usually caused by the expansion of defects in castings and welded parts due to the pressure impact of the hydraulic system. If there is any weld leakage in the fuel tank or nitrogen cylinder (accumulator), it needs to be repaired by welding.

(5) Supplement of SF6 gas

Before inflating SF6 circuit breakers, qualified SF6 gas should be used to blow the inflation pipeline for 5 seconds to eliminate the air in the pipeline. During the operation, attention should be paid to the cleanliness of the inflation interface. In high humidity conditions, an electric hair dryer can be used to dry the interface. It is best to adjust the inflation pressure to be basically consistent with the SF6 pressure inside the circuit breaker, and then connect it to the inflation pipeline interface. The inflation pressure difference should generally be less than 100kPa. Do not inflate directly with high pressure without using a pressure reducing valve. The gas pressure filled into the circuit breaker should be slightly higher than the specified pressure to supplement the amount of gas consumed for future gas humidity measurements.

(6) Detection of SF6 gas humidity

The humidity of SF6 gas has a significant impact on the arc extinguishing performance, insulation strength, and service life of electrical equipment. When the humidity exceeds the specified limit, it will decompose into toxic or corrosive compounds at high temperatures generated during arc extinguishing, corroding the metal components inside the arc extinguishing chamber and causing circuit breaker explosions. Therefore, after 24 hours of SF6 gas filling into the equipment, gas humidity measurement should be carried out. Before measurement, the SF6 gas pressure inside the body should be checked for micro rated pressure. The measurement should be carried out in dry and low humidity weather, and a dedicated pipeline with a length generally within 5 meters must be used. Before measurement, dry nitrogen or qualified new SF6 gas should be used to flush the measurement pipeline.

(7) Leak detection of SF6 gas

The leakage parts of SF6 circuit breaker body include: scratches on the pillar drive rod and sealing ring, poor sealing of the inflation valve, cracks at the root of the pillar porcelain sleeve, flange connection, sand holes on the top cover of the arc extinguishing chamber, cover plate of the triple box, gas pipeline joints, density relay interfaces, secondary pressure gauge joints, welds and sealing grooves that do not match the size of the sealing ring (gasket), etc. Before measurement, blow away the SF6 gas around the tested area, and then slowly move the leak detector probe 1-2mm away from the tested point. Under normal circumstances, the pointer on the leak detector should not move in a stable state. If the pointer on the leak detector is unstable and is considered to be residual gas, it can be blown away for 1 hour before continuing the measurement.