Hints for maintaining type SP SF6 power circuit breakers

02/01/2004 - Volume I - Issue I

Thorough periodic inspection is important to satisfactory operation. Inspection and maintenance frequency depends on installation, site, weather, and atmospheric conditions, experience of operating personnel, and special operation requirements. Because of this, a well-planned and effective maintenance program depends largely on experience and practice. The following tips and upgrade solutions are useful during maintenance inspections, troubleshooting, and long-term maintenance planning:

 

----Mechanism hints------

 

Air valve leaks

 

Some customers have reported leaking air valves. In our investigation to determine the cause, we have concluded that temperature plays a large part in causing the leaks, especially in areas with high ambient temperatures. This has resulted in hardened "o-rings" which leak in some valves. A contributing factor is the heater which is located below the air valve.

 

The air valve heater is used for two functions: to prevent condensation inside the mechanism and to prevent ice from freezing up the valve during operation when the ambient temperature is approximately 45 degrees Fahrenheit and below.

 

Siemens has developed an alternate heater arrangement since we need to retain both of the above functions. This consists of another heater energized continuously to control condensation and controlling the heater below the valve with a thermostat to be on only when needed.

 

The mounting holes for the new heater and thermostat already exist and are shown along with the required wiring changes on an instruction drawing.

 

Upgrade kits have been developed which include a new valve, thermostat, and heater. New "o-ring" kits for the valves should also be ordered. Since all circuit breakers are not the same at time of manufacture due to specification variances, please include the circuit breaker serial number when requesting a repair kit.

 

Pneumatic mechanism slow reset on trip free latch

 

We have also received reports of circuit breakers with slow reset times on the trip free latch or the mechanism going trip free on a close open operation. The first thing to check is to make sure that the circuit breaker lever system is set correctly. This is accomplished by using horizontal linkage system setting gauge 7358D12H14 according to Figure 4 of the instruction book. We have found that the problems with the trip free latch may be caused by slight changes in the open position stop bolt setting.

 

Motor pulley - pneumatic mechanism

 

Any time routine maintenance is done on the motor compressor assembly, check the motor pulley set screw for tightness. If a set screw should be found loose or is removed for some reason, on re-installation clean with Loctite Primer T and apply a couple of drops of 242 (blue) Loctite before tightening the set screw to 120 in.-lb. torque. Check the pulley and motor shaft for unusual wear.

 

Mechanism linkage lubrication

 

For circuit breaker applications that require frequent operations, the following points should be checked and lubricated with Molykote (00337271095):

  1. The pins in the horizontal linkage, particularly those that connect the horizontal tie pipe to the drive levers of each phase.
  2. The nose of the hydraulic shock absorber plunger that makes contact with the bell crank lever.
  3. The rollers that move vertically in operating mechanism guide rails (on ends of A and B pins).

Stuck hand jacks - pneumatic mechanism 

 

There have been several reported cases of stuck hand jacks. Apply Molykote to threads of piston rod and jacks before screwing on jacks. If the jack is forced on it may result in a stuck jack. Attempts to loosen a stuck jack have resulted in breaking the joint at the crosshead, requiring extensive tear down of the mechanism to repair. To avoid this, screw the jack on by hand (without jack handle) until the thrust bearing is in contact with the spring housing. If this cannot be done use another jack--do not force it.

 

---Interrupter / bushing maintenance hints---

 

Loose moving contact nuts

 

Another reported incident on circuit breakers manufactured before January, 1988, is loosening of the nut on the interrupter that attaches the moving contact assembly to the interrupter tube. This occurrence is associated with circuit breakers that frequently operate in applications such as capacitor switching.

 

We recommend that circuit breakers in such applications be checked at the earliest convenient time. We also recommend that other circuit breakers of this vintage be checked at the time of major maintenance. The nuts should be cleaned with Loctite Primer and a couple drops of 242 (blue) Loctite applied to the thread of the nut before retightening to 25 f.-lbs. torque.

 

Interrupter lubrication

 

The Molykote lubrication in the interrupter may dry out in the warmer climates. Re-lubrication with Beacon325 (W962030) is recommended. Apply a light film of the Beacon325 as shown in Figure 9A of the instruction book. If resistance measurements are made at that time, the resistance (with 100amps flowing) measured between the base of the contact carriers where the bushing plug in should be less than 40 micro ohms.

 

Leaking bushings at top

 

When installing terminal pads on the top of bushing, make sure the threads in the terminal pad and on the bushing stud are free of burrs. The terminal pad should easily screw to the bushing stud. If this is not the case, it may be possible to overcome the 100 ft.-lbs. of torque used during bushing assembly which could result in a loose stud and a leaking bushing. The direction of screwing the terminal pad on is in the direction to loosen the bushing stud. Bushing studs should be lubricated with a conductive grease such as No-Ox.

THIS CHECKLIST DOES NOT REPRESENT AN EXHAUSTIVE SURVEY OF MAINTENANCE STEPS NECESSARY TO ENSURE SAFE OPERATION OF THE EQUIPMENT. PARTICULAR APPLICATIONS MAY REQUIRE FURTHER PROCEDURES. SHOULD FURTHER INFORMATION BE DESIRED OR SHOULD PARTICULAR PROBLEMS ARISE WHICH ARE NOT COVERED SUFFICIENTLY FOR YOUR PURPOSES, THE MATTER SHOULD BE REFERRED TO THE LOCAL SIEMENS SALES OFFICE. DANGEROUS VOLTAGES ARE PRESENT IN THE EQUIPMENT WHICH CAN CAUSE DEATH, SERIOUS INJURY, OR PROPERTY DAMAGE. ALWAYS DEENERGIZE AND GROUND EQUIPMENT BEFORE MAINTENANCE. MAINTENANCE SHOULD BE PERFORMED ONLY BY QUALIFIED PERSONNEL. THE USE OF UNAUTHORIZED PARTS OR SUPPLIES IN THE REPAIR OF EQUIPMENT OR TAMPERING BY UNQUALIFIED PERSONNEL WILL RESULT IN DANGEROUS CONDITIONS WHICH CAN CAUSE DEATH, SERIOUS INJURY, OR EQUIPMENT DAMAGE. FOLLOW ALL SAFETY INSTRUCTIONS CONTAINED HEREIN, ON THE EQUIPMENT, OR IN SIEMENS’ OTHER INSTUCTIONS.

 

Major inspection

 

Major internal inspections require the removal of gas from the circuit breaker to determine the condition of the interrupters, contacts, and other internal components. The following are some factors to be considered in determining the frequency of a major inspection procedure:

  • 20 times the accumulated interrupting rating (i.e. 20 full-rated faults, 40 half-rated faults, etc. or 600kA, whichever comes first)

  • 2,000 mechanical operations

  • Information received from 3-year and 6-year inspections

  • Accumulated experience of circuit breaker characteristics and duty

  • Pole unit contact touch during slow closing is .19 inch or less from the pole unit indicator closed position marks.

Recommended maintenance kits

  • Major inspection kit

  • Norgren pilot valve repair kit

  • Norgren control valve repair kit

Available uprate kits

  • Interrupter uprate kit – 31.5kA rank liner increases short circuit rating from 23kA to 31.5kA.

  • Interrupter uprate kit – 40kA additional capacitors increase short circuit rating from 31.5kA to 40kA.

  • Voltage uprate kit – 72kV additional voltage shields increase voltage rating from 15kV to 72kV.

  • Amperage kit – 2000Amps new bushings increase continuous current rating from 1200Amps to 2000Amps.

Available life extension kits

  • Tank heater kit – 120VAC avoids condensation in low-voltage control cabinet, thereby preventing corrosion.

  • Density switch application avoids alarms due to ambient temperature changes.

  • Tank heater / thermostat – 120VAC kit increases ambient temperature resistance from -30C to -40C for cold weather applications.

  • Arrestor support kit supports installation of lighting arrestors, thereby increasing protection.

  • Solenoid application kit - additional trip coils provide redundancy.

  • Temperature shield application kit avoids alarms due to different sunlight absorption rates on different surfaces of the circuit breaker.

  • Tie pipe assembly - upgrade increases reliability by installing new tie pipe.

  • Manifold assembly kit - new copper tubing (replaces stainless) prevents corrosion and leakage.

  • Liner assembly - after opening breaker and leaving it exposed for an extended time during maintenance, liner paper absorbs moisture out of ambient environment which can cause decreased dielectric strength and sagging of the liner.