Cost Effective Modifications for Vacuum Circuit Breakers
Control of electric power using vacuum switching is well proven in both switchgear and motor control applications. This technology is readily available in vacuum circuit breakersand vacuum contactors covering all applications in low and medium voltage levels. Joslyn Clark Controls manufactures vacuum contactors to cover all standard distribution voltage levels. This range includes low voltage options up to and inclusive of 1.5kV and medium voltage options up to and inclusive of 12kV. Our wide variety of products allows us to serve many demanding industries including mining, induction heating, deep well pumping, oil and gas, electrical utilities, and many more. Joslyn Clark’s modular contactor design also allows for multiple vacuum interrupters to be paralleled to service high current applications.
Advantages of Vacuum Contactors
Historically, systems were designed with circuit breakers because they were considered superior by consulting engineers over fused, air break contactors. Today’s vacuum and fuse technology advancements make vacuum contactors the desired switching device over circuit breakers. Cost increases, repetitive maintenance cycles, and relatively low mechanical lifespans lead users to convert circuit breakers to vacuum contactors.
Applications that require frequent switching duty will normally highlight all the downsides associated with using circuit breakers. Switching a circuit breaker three times a day, will mechanically exhaust the life of the breaker quickly. This is not desirable for equipment that is typically capitalized. In addition, extra downtime and unnecessary expense is spent in routine maintenance of the breakers.
As a solution, it is often a recommendation to retrofit the existing air breaker to a vacuum circuit breaker, but this is not ideal for your switching application! In this scenario, the vacuum circuit breaker will only provide a mechanical life of approximately 10,000 operations by “ANSI” standards. This modification will only lead to a small increase in contact life while the mechanics of the existing breaker continue to fail at a normal rate.
The best solution is to replace circuit breakers with a Joslyn Clark vacuum contactor accompanied by fuse circuit protection. Fuse circuits are available at most local electrical distributors. Installing this combination will remove the demand of the switching operations from the circuit breaker and put the demand on the more dependable fused vacuum contactor. The existing circuit breaker can be retained to provide short circuit protection on the line side of the current limiting fuses. Correct coordination between the existing circuit breaker, fuses, and vacuum contactor will ensure that the appropriate device operates at its appropriate current levels.
If you decide to completely replace a circuit breaker with a fused vacuum contactor, extra precautions should be taken to ensure suitable upstream short circuit protection and interlocked disconnect means are in place, allowing safe servicing of loads.
Benefits of Upgrading from Vacuum Circuit Breakers to Vacuum Contactors
- The equipment’s lifespan may increase by as much as two orders of magnitude, eliminating the problem of exhausted mechanical life.
- Existing circuit breakers that operate as a backup isolator to the contactor, only require annual on-load operation which eliminates routine downtime. This is an important factor to consider for continuous plant operation.
- Vacuum contactors require a simple overtravel check once every 500,000 operations. On a switching duty of 20 operations per day, a check would be required every 68 years, eliminating costly installation and maintenance routines.
- Joslyn Clark vacuum contactors have lower chopping current levels (typically 0.9A) and minimize the risk of motor winding failure, as opposed to circuit breakers. This is important considering the motor impulse level decreases with age.
- When the modifications are complete, the new and the existing installations perform as a virtually maintenance free system. This eliminates routine downtime, an important factor to consider for systems that require continuous operation.
- In most switchboard installations, transformer feeder or capacitor bank circuits are dispersed within motor starting circuits. Transformer feeders have more restricted operational duty, leaving plenty of mechanical life in the units controlling the circuits. The motor circuits in the switchboard can be easily modified, if necessary one at a time, without effecting the adjacent circuits at all.
- Circuit breaker modifications can be carried out individually and require minimum modifications to the control circuit wiring, inclusive of the close and trip circuits. Other trip circuits, such as ground fault protection and overload trip signals, can be wired into the contactor control circuits.
- Current limiting fuses can be obtained with trip indicating striker pins and a three-phase trip bar mechanically connected to an electrical contact. Which, in turn, is wired into the contactor hold or trip circuit. This arrangement provides protection against single phasing of the load in the event of a single fuse blowing on one phase.
- Various indicators can be installed in the new panel providing visual indication to the status of the contactor and the status of various tripping functions. Controls can be installed in the new panel although in general control switches are already in the existing circuit breaker panel, control of the motor can be maintained for the existing installation, in common with other feeder circuits such as transformer feeders or capacitor feeders which would probably not require modification.
- Joslyn Clark vacuum contactors can be applied to all existing circuit breakers with the appropriate current and voltage ratings. Joslyn Clark vacuum contactors can be ordered as an electrically held device operated by common AC or DC control voltages or as mechanically latched devices with appropriate AC or DC trip coils. We would recommend electrically held control circuits be used wherever possible to provide fail safe operation.
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