Harmonics Generated from the Source

The subject company manufactures meat products such as sausage, salami, and bologna. Most of their load consists of HVAC and refrigeration as they have about 6000 sq. ft. of cold room storage. They also have machinery such as grinders, slicers, and presses. The facility is served by a 120/240V through a utility-owned 500 kVA High-Leg Delta transformer that they share with another factory.

Interruptions occurred when a main 1200 amp circuit breaker was tripped frequently. The events occurred often and sometimes several times a day. Previous measurements had not shown the reason for the events as the highest measurement of current shown was 760 amps, which was not enough to cause the breaker to trip.

From the recordings, the following was noted:

• At times the peak current exceeded the 1200A breaker rating without tripping the breaker. An interruption that was tied to such a peak current was detected only once during the measurement period. Further investigation from the wave forms captured determined that the voltages were distorted during such times. This distortion caused nuisance tripping of other breakers and caused the capacitor banks to fry.
• A long-term measurement showed that the capacity of the breaker could be reached when a combination of tasks occurred at the same time.
•  Since most of the load at this site is linear, no harmonics are generated from within the facility. When we looked outside the factory, the cause of the distortion was traced to a faulty power transformer.

David Jones of EEVBlog.com Reviews the Gossen Metrawatt METRAHIT ENERGY

The METRAHIT ENERGY is a compact, single phase Power and Power Quality meter/logger that includes multimeter functions.  It is intended for measuring AC and DC voltage, as well as current in single-phase systems, with current being measured either directly or via a current transformer. 

With a resolution of 60,000 digits, the METRAHIT ENERGY has more than 35 different measuring functions including: active power, reactive power, apparent power, power factor and energy.  This powerful multimeter is extremely rugged and reliable with a housing made of impact resistant ABS. 


Click on the link below and see the METRAHIT ENERGY in action: 


AA Alkaline Battery Capacity Measurement

Check out the METRAHIT ENERGY teardown by David Jones.

METRAHIT ENERGY

METRAHIT ENERGY Features:

• Digital hand-held multimeter with TRMS measurement
• Power measurement (W, VAR, VA, PF): active, reactive and apparent power, power factor
•  Energy measurement (Wh, VARh, VAh): active, reactive and apparent energy, mean power value with adjustable observation period, and maximum value
• Power Quality Analysis: recording of over and under-voltage,sags/dips, swells, voltage peaks, and transients in 50 and 60Hz systems
•  Harmonic analysis: RMS values and distortion components up to the 15th harmonic at 16.7, 50, 60, and 400Hz
•  Special measuring functions: crest factor CF, conductivity nS, low resistance RSL, duty cycle %, cable length
•  Resolution of 60,000 digits, triple backlit display
• 1KHz / –3 dB low-pass filter available
• Direct current measurement from 10nA to 10A, 16A for less than 30 seconds, current measurement with current transformer clamp and sensors, transformation ratio is taken into account on the display
•  Large data memory for up to 300,000 measured values Instrument is completely remote controllable using PC software, without using the unit’s rotary switch



For more information about this and other safety and measurement

products, visit www.gossenmetrawattusa.com.

Dranetz Case Study: Broadcast Studio Loses Video in Prime Time

In late 2011, a major broadcast company had a power outage that dropped live and pre-recorded television programming for 1½ hours to approximately 1/3 of the United States during the prime time viewing period.  The company lost vital revenue while electrical and facility engineers tried to determine the source of the problem and correct it.

Problem

After several failed attempts to restore the broadcasts, it was discovered that several new pieces of equipment had been brought online shortly before the outage.  The customer was able to restore broadcasting service by turning on all equipment except these new additions.

Upon further investigation, it was discovered that several of the electrical circuits which carry the load of the broadcast equipment were close to the maximum load rating. Adding the new equipment to these circuits was enough of a load to exceed the maximum rating, which tripped the circuit breakers and took down the entire broadcast system.  A review of the remaining facility showed that many of the electrical circuits were beyond 90% of their capacity.

Solution

The broadcast company installed three Dranetz Encore Series Branch Circuit Energy Monitoring (BCEM) systems.  The system is located in their primary broadcast distribution center and has 54 Dranetz ES210 DataNode’s.  The Dranetz BCEM and ES210’s will actively monitor the real-time loading and energy consumption across all of their primary electrical distribution circuits.  The BCEM’s were incorporated into their existing Encore Series Software server for real-time monitoring, alarming, and historical reporting of the electrical usage and patterns. In addition, the customers Building Management System (BMS) is simultaneously reading the BCEM data for redundant, centralized monitoring and alarming by the 24x7 building operational staff.

The Dranetz BCEM System (below) provides the broadcast company easy, centralized monitoring of energy, demand, power factor and much more from a single monitoring location.

"Organized Lightning" and Electrical Safety

This article found in the May 2013 Electrical Contractor was written by our own Rich Bingham.

George Carlin summed up the hazards of working with electricity quite well when he said, “Electricity is really just organized lightning.” Few people, except for some extreme golfers and Benjamin Franklin, would normally take extraordinary risks with lightning. Yet, too many electricians are still injured and killed each year on the job.

While there are sources of such incidents unrelated to electricity, including falls, vehicular accidents and tools, the unique aspects of electricity and its potential devastating effects on the human body rightly get significant attention from the safety agencies, as more than half of the fatalities are caused by exposure or contact to this hazard. In addition to electrocution, a few of the hazards that need to be considered include potential damage from radiant and convective heat (an electric arc is hotter than the sun), infrared and ultraviolet light damage to the eyes, excessive decibel levels to the ears, and pressure wave and concussive forces to external and internal body parts.

Electrical accidents are not limited to electricians. Fortunately, the figure below shows a decline for all construction workers, which is similar to the trend for all industries, declining 31 percent over the same time period.

Of the 67 deaths in 2011 from electrical contact in the construction industry, 34 were classified as electricians, along with an injury rate in 2011 of 3.6 percent to the 723,000 electricians. There are all sorts of statistics about age (fatalities over age 55 are nearly triple those under 24), season (June to September accounts for more than half of the injuries in a year), and many other categories. What matters more is why the accidents occur and how we can force that number lower.

Obviously, contact with wires is the source of the current, whether overhead, in the walls, or within equipment or tools. Strangely, it is at the power line frequencies (50–60 hertz) that the human body is most vulnerable to the amount of current; it creates a “can’t-let-go” situation. For most males, that is only 9 milliamps (mA) of alternating current, whereas it is nearly six times that for direct current, and likewise for 10 kilohertz. That is why the trip point for most ground-fault circuit interrupter (GFCI) receptacles is 5 mA.

Removing the hazard by de-energizing­ the circuit being worked on and any that could possibly be contacted is the ideal scenario, but, in some rare situations, that isn’t going to happen. Both NFPA 70E, Standard for Electrical Safety in the Workplace, and OSHA 29 CFR 1910 provide detailed information on who, what, where and how to create an electrically safe working condition. Anyone who is exposed to the hazards should know them. The following suggestions do not supersede or replace of those requirements, but rather they give brief perspective on creating them.

The overall process is to plan, do, check and act. Every company, whether a sole proprietor or a 250-person electrical contracting firm, should establish appropriate policies and practices to address worker safety. Conduct periodic training on preventive and protective measures with regard to the hazards and safe practices for all workers, no matter how many years of experience. Supervisors and co-workers should continually check that such practices are being followed and determine what corrective actions are needed. All must act to ensure that the process is continually reviewed and improved. Most workers are probably familiar with what they need to do, but cutting corners to get jobs done faster, complacency in using the proper tools and personal protective equipment, neglecting proper lockout/tagout procedures, a lack of understanding of the potential hazards, and neglecting to monitor the situation while at work are all contributing factors to accidents.

Of these factors, we have made great strides in wearing the proper PPE and understanding the arc flash hazard, which may explain a part of the declining injuries and fatalities trends. National Electrical Code 2011 Article 110.24 states that nondwelling service equipment is required to be field-marked with the amount of available fault current when installed or modified. OSHA requires that, where there is a risk of injury to a worker’s skin from fire or explosion, an employer or contractor shall provide the worker with—and require the worker to use—outer fire-resistant clothing that meets an approved industry standard and is appropriate to the risk.

Following these two requirements will minimize the damaging effects on the human body when inadvertent contact with energized circuits unleashes the “organized lightning.”