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Z Meters ZM100 Distribution
Analysis System plays an important role in Arc Flash studies. |
Z Meters, Impedance, and Arc Flash studies
Z Meters was formed in collaboration with Summit Technology, Inc., manufacturers of the PowerSight power analyzers www.powersight.com. A version of the PowerSight PS4500 was developed for the needs of Z Meters. The distinction with the ZM100 is that it brings a new measurement technology to the power monitoring and instrumentation market - the measurement of impedance of distribution systems, and while under actual operating conditions.
Z Meters inception started with the idea of measuring impedance to look at power quality problems in the impedance domain, as well as simultaneously measuring in the voltage, current and frequency domains. Impedance plays a significant role in power quality problems, such as sags, bad or loose connections, overloaded transformers, harmonic saturation, carbonized or corroded contacts etc. The ZM100 also performs the usual RMS volts, amps, watts, VA, VAR, Pf, THD measurements that are commonly recorded and logged in power studies. During the development of the ZM100 we became aware of the recent arc flash labeling requirements for NFPA 70E and, serendipitously, the impedance technology developed in the ZM100 matches the objectives of arc flash studies.
NFPA 70E states that arc flash studies must be done on all panels or equipment that service personnel work on. An arc flash study takes into account the wiring, loads, breakers, fuses, fault currents, and protective device coordination to calculate the amount of energy that would be released in an arc flash incident at each location in the distribution system. NFPA 70E ultimately requires a label at each location informing electrical workers of the degree of hazard in calories/cm2 and the level of personal protective equipment to wear (PPE). Given this recent code requirement there are tens of thousands, if not millions of panels and equipments in North America that are yet to have arc flash analyses done and their labels affixed. Every facility, commercial or industrial, is confronted with complying with this new requirement.
The arc flash calculation requires impedance data for the distribution system under study, specifically of the conductors and cables. In a new facility the electrical engineer can easily calculate arc flash energy using popular electrical design software while laying out the one-line circuit diagram when designing the system - such software is available from Easy Power, ETAP, EDSA, and SKM and others. However, calculating arc flash energy in older existing facilities can be a significant undertaking, especially if the one-line diagram is out-of-date or missing – a common situation. Thus, the one-line diagram often needs to be recreated or verified before the arc flash calculations can be completed.
The bulk of the effort in arc flash studies is in gathering all the information and data necessary for recreating one line diagrams and taking the inventories of distribution systems. This is where most of the costs are borne. Once you have all the data the arc flash hazard can be computed in just a few seconds by a PC. Consider, however, that it could take weeks of effort to get all the infrastructure data; i.e. tracing the wiring topology accurately, identifying panels, characterizing the types of loads, as well as identifying breakers and other protective devices. Determining the wiring layout is a major challenge when it is not easy to visually identify how cables and conduits are routed.
The existing methods to recreate wiring diagrams often rely on "guesstimates" obtained by walking the site to determine the circuit topology i.e. tracing how conductors and cables are routed, and what the conductor run lengths are. This method is fraught with inaccuracies and errors when conductor runs disappear behind walls, floors, or ceilings, and when branches and splices are hidden. Once a diagram has been established, impedances are estimated based on the lengths and conductor types using wire gauge tables. If the lengths are incorrect because of assumptions and guesswork, and have not been subject to verification, then the impedance data will be erroneous.
The upshot of such errors results in an incorrect calculation of arc flash energy and therefore misleading data on the on the final label. If the energy is overestimated workers may be required to wear PPE at a higher rating than is necessary. Above you can see a worker in a level 4 PPE suit, often referred to as the "Homer Simpson" suit. Workers can not tolerate being in such claustrophobic suits for long periods and must frequently disrobe and re-hydrate themselves. We have heard of some union rules that limit the worker to a maximum of 15 minutes out of each 90 minutes of work. This not only adversely affects worker productivity, but what is not readily acknowledged is that such cumbersome attire discourages workers from perfoming electrical work. Conversely, if the energy is underestimated, workers could be exposed to a dangerous situation without the appropriate warnings and required PPE.
Z Meters has developed a technology for recreating one-line diagrams where they don't exist, or for verifying one-line diagrams from older documentation that may well be inaccurate. In addition to confirming circuit topologies, the ZMI system measures conductor impedances and conductor lengths plus their X/R ratios. These are vital data that are necessary for calculating the arc flash hazard values. We submit that in order to perfom rigorous arc flash calculations, a verfied one-line diagram is the basis of a meticulous arc flash study, along with actual measurements of cabling and impedance data. To do this the system does not need to be shut down. While the wiring layout is being verified, the ZMI system authentically measures impedances during actual operating conditions.
Thus, the ZM100 Distribution and Analysis sytem is designed to reduce the time and the costs of performing arc flash studies in two important ways:
1) Re-creating or verifying the one-line diagram.
2) Providing authentic impedance and cable data for the final calculation.
We believe that as the awareness of the need to perform Arc Flash studies grows and the benefits of impedance measurements emerge there will be great interest in an instrument that can verify one-lines, measure cable lengths, and provide impedance measurements and X/R values. The ZM100 has a technical distinction therefore when compared to the other meters in the market place that do not have this capability.
Plus, there are other benefits that the ZM100 meter system will provide. The heart of our technology is in comparing the measurements of two synchronized meters. Besides impedance measurement, the two-meter techniques we are developing have other applications such as accurate efficiency measurement of any power device (transformers, UPS systems etc.) and the correlation of power quality at two locations to determine, for example, whether sags are occurring inside a facility or are due to utility behavior, based on the coincidence and severity of the sags.
Contact Information
Michael Daish
Vice President Sales & Marketing
Z Meters, Inc.
3350 Scott Blvd., Bldg. 55-2
Santa Clara, CA 95054
408.844.9495