If the lights are on, everything is fine with the electrical system. This is a common assumption, but issues sometimes can be lurking behind the scenes.
Figure 1. Performing the manufacturer’s recommended maintenance and testing of a circuit breaker will extend the equipment’s useful life.
Switchboards and switchgear are utilized to distribute electricity within a facility. Switchboards are more commonly used in commercial and light industrial applications, while switchgear is usually specified in heavy industrial applications, where the demands on the equipment require more robust construction. To maximize the useful life of the equipment and to mitigate the risk of an unscheduled power outage due to equipment performance, it’s critical to properly test and maintain the switchgear and switchboards that distribute electricity throughout the power distribution system (Figure 1).
Maintenance requirements
Electrical switchgear has two types of components, which can be referred to as passive and active. The passive components include such things as the steel framing channels, cover plates, barriers, and horizontal and vertical bus structures, as well as components that make up the mechanical structure of the equipment. The critical active components are the power circuit breakers or fused devices that comprise the overcurrent protective system.
The main function of the active components is to protect assets and personnel. Both the passive and active components require regular maintenance to ensure equipment integrity, as well as proper mechanical and electrical functionality, and to provide protection for the equipment’s useful life. Major electrical equipment manufacturers generally recommend annual maintenance for power circuit breakers to ensure proper operation and maintain equipment warranties. This maintenance consists of cleaning and lubrication of the primary and secondary disconnects, racking mechanisms, and cell interlocks. A thorough on-site maintenance workscope for low voltage power circuit breakers includes:
Figure 2. Even with proactive maintenance, circuit breakers can be upgraded, while the switchgear structure, conduits, cabling and footprint are left intact.
The use of new or refurbished parts or subassemblies may be required to return a circuit breaker to good operating condition.
A more intensive maintenance option for circuit breakers is in-shop reconditioning. The breaker is initially tested against ANSI standards and then completely disassembled, cleaned, and inspected. Damaged parts are refurbished or replaced, and pivot points are relubricated before the circuit breaker is reassembled. The reconditioned breaker, including the new assemblies, is retested against ANSI standards. This option should be performed when the on-site maintenance workscope can’t bring the breaker within tolerances defined in current industry standards. As part of this service, the trip unit can be retrofitted to a modern digital device.
Figure 3. One advantage of replacing with new switchgear is the ability to take advantage of current technology.
Even with annual maintenance, however, power circuit breakers may need additional upkeep or upgrades (Figure 2). Factors to consider include the operating environment, availability of spare parts, reliability, and the cost of ongoing maintenance. There may also be the need to increase the switchgear’s fault or continuous current rating, or the desire to upgrade technology. As a result, facility managers are often faced with the choice of maintaining aging or obsolete equipment or replacing it with a new switchgear lineup to take advantage of current technology (Figure 3).
Circuit breaker failures
Electrical equipment life can be defined as the duration until the equipment no longer performs its intended function, either mechanically or electrically. Although passive components require maintenance, it’s typically the nature of the active components, along with insulation life, that defines the expected life of the switchgear. When circuit breakers don’t operate properly, there are typically no advance indicators, unless electrical testing has been utilized to track performance. Industry groups, such as the IEEE Circuit Breaker Quality and Reliability working group, have analyzed the factors that affect the condition and performance of circuit breakers.
Depending on when a breaker was installed and how it has been utilized, a circuit breaker may be in a condition somewhere between satisfactory performance and non-functional, that usually occurs as equipment approaches the end of its expected design life. If maintenance has not been regularly performed, this zone may be entered prematurely, and a shortened useful life of the breaker may be the result. In these cases, options should be considered to replace, recondition, or modernize the breaker. There are other reasons a user may want to upgrade to a new technology circuit breaker, such as taking advantage of the rich feature set and capabilities found in many newer circuit breakers, including trip unit communication capability for energy monitoring; enhanced reliability; decreased maintenance requirements; on-board diagnostics; the potential to reduce arc-flash incident energy levels and ultimately life extension of the existing asset.
Replace or continue to repair?
When considering whether to maintain equipment or replace it, facility managers must take into account the initial capital cost, along with potential disruption to the facility’s processes and workflow during the course of changing out the equipment. Unless process loads can be rerouted temporarily during the demolition of old equipment and installation of the new switchgear, the cost of lost production can be substantial.
Figure 4. Aging or obsolete circuit breakers need to be replaced, but plan for the unexpected.
Another consideration that is often overlooked is conduit placement. Installing new switchgear, which is usually smaller than the older or obsolete equipment it is designed to replace, may require that existing conduit above and below the equipment be moved. Cabling may need to be replaced or spliced, as well. This is an expensive and time-consuming process, often costing more in labor and material than the cost of the new equipment (Figure 4).
Facility managers now have another option to consider for the repair-versus-replace dilemma. New design capabilities exist to modernize and extend the life of the active components, such as circuit breakers, while leaving the existing switchgear structure intact.
Modernize and upgrade LV and MV switchgear
Modern power circuit breakers are designed to offer very high fault current withstand capability without the use of limiter fuses. Retrofitting is a general term that is used to define any process which allows for modernization and life extension. Several different retrofit strategies exist for adapting modern circuit breakers into existing low-voltage and medium-voltage switchgear structures.
Direct replacement and retrofill solutions
ANSI: American National Standards Institute.
Direct replacement: Retrofit process where a new circuit breaker and adapter cradle fit into an existing switchgear cubicle.
Interrupting rating: The highest current at rated voltage available at the incoming terminals of the circuit breaker. When the circuit breaker can be used at more than one voltage, the interrupting rating will be shown on the circuit breaker for each voltage level. The interrupting rating of a circuit breaker must be equal to or greater than the available short-circuit current at the point at which the circuit breaker is applied to the system.
OEM: Original equipment manufacturer.
Overcurrent: Any current in excess of the rated continuous current of equipment or the ampacity of a conductor.
Primary disconnect contacts: An electrical plug-on connector in the main current path between the drawout components and the cradle mounted in the switchboard or switchgear.
Racking interlock: An interlock to prevent racking of a drawout circuit breaker when the enclosure door is open by not allowing the racking crank to be inserted into the circuit breaker.
Retrofill: Retrofit process where an existing switchgear cell and bus are modified to accept a new circuit breaker.
Secondary disconnect contacts: An electrical plug-on connector in the secondary (control) circuit between a drawout circuit breaker and its cradle in the switchboard or switchgear.
Trip unit: A programmable device which measures and times current flowing through the circuit breaker and initiates a trip signal when appropriate.
UL: Underwriters Laboratories Inc.
Direct replacement circuit breakers and circuit breaker retrofill solutions fall under the general category definition of retrofits. Though different processes, both are designed to have the same end result: improved power system reliability and lower life cycle costs.
Direct replacement: A new circuit breaker and adapter cradle fit into the existing cubicle.
A low-voltage or medium-voltage circuit breaker and adapter cradle are designed to fit directly into the existing OEM switchgear, with little to no modification to the switchgear cell. A direct replacement solution reduces downtime since there is minimal,, if any, outage on the equipment bus.
Retrofill: The existing switchgear cell and bus are modified to accept the new circuit breaker.
This process usually requires a longer bus outage, during which time the internal circuit breaker cell is modified to accept the new circuit breaker. A retrofill solution is often used in lieu of the direct replacement option for larger devices such as main breakers and tie breakers. In these cases, because of the size of the replacement device, there may not be adequate room in the existing circuit breaker cell to allow for the intermediate cradle that is used in the direct replacement option.
In both retrofill and direct replacement options for low voltage applications, new cubicle doors need to be provided to match the existing equipment and new circuit breaker face. For medium voltage applications, the door and protective relay can remain intact; however it should be considered to upgrade the relay while the circuit breaker is being upgraded. In this case, a new door can be provided with the relay pre-installed on it.
Hal Theobald is product manager at Schneider Electric. Contact him at (513) 755-4226 or [email protected].