By C.J. Joshlin
From the July 2013 issue of Today’s Facility Manager
With rapidly growing energy demand and expanding requirements in modern electrical distribution systems, there is an increasing call for approaches in coordination, configurability, monitoring, and maintenance that will help facility managers (fms) better control and maintain their electrical distribution systems properly. With complete monitoring activity in place, combined with proactive response initiative, there can be savings of up to 30% on costs of energy consumption and greater assurance that fms are meeting critical codes and standards.
Reduce Consumption, Optimize Costs
Intelligent use of an electrical distribution monitoring system helps to reduce the cost of energy at a facility by cutting energy consumption. Typically in the past, metering has only been cost-effective at the incoming distribution board. This is in part due to installation complexity and space limitations.
By integrating the metering functionality into molded case circuit breakers, the meter can be accommodated in approximately the same amount of space as a standard molded case circuit breaker, and allows fms to have an increased amount of data to leverage for their energy management programs. As a result, fms can monitor their entire system in order to raise awareness of energy consumption, identify cost savings, and ensure system reliability.
New generation molded case circuit breakers help fms combine the capability of electronic trip units, advanced metering, and open protocol communications in a single, modular unit. This allows for:
- the creation of a power monitoring point, which can be used to provide power quality data, energy management data, system capacity information, input to a facility supervisory control and data acquisition (SCADA) system, and preventive maintenance;
- enhanced selective coordination between the protective devices of the system with single-ampere adjustment capabilities in the trip unit;
- capacity for zone-selective interlocking, for reducing arc flash hazard at high energy locations and for coordination of similarly sized protective devices, without reducing system capacity; and
- reduction in the cost of installation by combining in a single package the functionality of a protective device with a meter capable of power quality readings and alarm functionality. This creates savings by reducing cost of equipment, installed equipment size, and installation time.
Power Quality, System Reliability
As dependence on electronic devices increases, electrical systems are becoming more sensitive to disturbances. Placing meters throughout a system can help track many parameters to ensure system reliability, providing a methodology for predicting system reliability and creating a predictive maintenance schedule.
Having the capability to collect power data through molded case circuit breakers can trigger required maintenance in a proactive and timely manner, instead of relying on only routine maintenance. In addition, alarm functions can help identify overloaded equipment before the operation of the protective device. Customizable alarms, which are built into some advanced metering trip units, allow each circuit breaker to be configured to trigger an alarm locally at the equipment or to the SCADA system in a way that is meaningful to that location in the system. This allows quick detection and analysis of potential events before a problem arises, minimizing downtime and maximizing the capacity of the system.
Tracking harmonic information is also an option that can help fms determine if it is acceptable to install a specific type of unit at a designated location or to determine if corrective measures need to first take place.
Proper system coordination is one of the most important aspects of protection in complex electrical distribution systems. For fms, selective coordination helps protect the facility and equipment if there is a fault, while still isolating the loss of power in the case of a trip to the smallest area of the system possible while maintaining power to the unaffected area of the system. Fms can achieve this level of protection by replacing standard thermal magnetic circuit breakers (which make it difficult to achieve optimum selectivity) with circuit breakers equipped with electric trip units (a phase fault at any point along that branch of the system will trip the appropriate protective device ensuring unaffected areas remain in service).
Options for coordination are also a critical consideration and can offer a wide range of potential settings for long-time, short-time, instantaneous, and ground-fault values. In addition, some trip units also have an optional zone-selective interlocking function, where smaller circuit breakers are equipped with an output that allows them to send a restraining signal to an upstream protective device when a fault is detected. When the upstream device receives the signal, it initiates a change in the trip characteristics of that device. This keeps stress on the equipment at a minimum, while still maintaining selective coordination and optimally protecting the electrical distribution system.
Benefits Of Modern Electrical Distribution Systems
Combining the many functions of electronic trip units, including advanced power quality metering, zone-selective interlocking, and alarming options, allows fms to save space, installation time, maintenance, and even procurement efforts. Increased metering capabilities provide an effective way to monitor each power distribution point of the system, making it possible to know where capacity exists in the system as new loads are added. This can potentially eliminate the need to purchase new distribution equipment, which can have a significant impact on potential future expansion costs.
Molded case circuit breakers with trip units can give fms the power to protect, monitor, and analyze their electrical distribution systems at every main and branch circuit, and take control of energy use. These units provide the ability to coordinate system protection, monitor energy consumption, and effectively execute preventive maintenance programs resulting in a cost effective solution.
Joshlin is a staff power system engineer at Schneider Electric. She works out of St Louis, providing a range of consulting engineering services, including system inspections, power quality analysis, short circuit, coordination and arc flash studies, and harmonic studies. She is a professionally licensed engineer in Kansas, Missouri, Nebraska, Iowa, and Tennessee.