Comprehensive Inspection, Problem Determination & Thermographic Scanning

Upon retention, our engineering consultants will visit your facility, to conduct a walk-through. MEC engineers analyze and inspect your equipment, power grids and other power supply units.

Testing, Diagnostics & Analysis

Before a strategy to correct power disturbances can be decided upon, it is strongly recommended that accurate, unbiased information be gathered about what problems, if any, exist on your electrical system. Only then can an informed and effective course of action be taken.

When evaluating your power quality, we also take into consideration the specific energy requirements of your equipment so that our recommendations are tailor-made. We also identify areas where you can prevent future problems before they impact your electrical system.

MEC utilizes the latest, state-of-the-art monitoring and analytical systems available today. Devices from such well-known companies as Dranetz BMI, and Hewlett Packard and Tektronics can efficiently locate, analyze and accurately portray any kind of electrical anomalies. By studying the collected data from these sophisticated devices, MEC engineers can identify the nature, magnitude and probable sources of your power problems. In addition to measuring supply voltage conditions, we also measure for and identify problems of improper or insufficient grounding, harmonics, electromagnetic and radio frequency interference noise and transmittance surges.

Reports & Recommendations

After detecting a source of the problem, MEC engineers generate a comprehensive report detailing system improvements that can protect sensitive equipment from power quality disturbances.

Solution Implementation

MEC engineers will work with your facility engineers or electrical contractor(s) to cutom install a TVSS or any other recommended devices. Careful attention is paid to pinpointedly locate the device at the right place in order to maximize its effectiveness.

Short Circuit & Coordination Study

Short Circuit and Coordination Study is one of the most important steps you may ever take to protect your personnel and electrical distribution system. When an electrical fault or overload exceeds the interrupting rating of the protective device, the consequences can be devastating including injury, damaged electrical equipment, and costly downtime.

Midwest Electrical Consultants will perform a Short Circuit Study using a computer model (SKM Software) that determines the 'worst case' fault level at the electrical distribution equipment. The fault levels are compared to the existing device interrupting ratings to determine if the protective devices are rated in accordance with the manufacturer's published data and applicable standards. If required, new ratings will be determined.

A Coordination Study looks at the protective devices from a slightly different angle to determine how to set protective devices in order to minimize the area of an outage. Selectivity of the protective devices is determined so that a fault can be interrupted within the affected circuit, thereby, minimizing the power disruption. Protection requirements are also analyzed.

The IEEE Electrical Power Distribution for Industrial Plants (Red Book) describes the purpose of Electrical Coordination Studies as follows:

The primary purpose of a coordination study is to determine satisfactory ratings and settings for the electric system protection devices. The protection devices should be chosen so that pickup currents and operating times are short but sufficient to override system transient overloads such as inrush current experienced when energizing transformers or starting motors. Further, the devices should be coordinated so that the circuit interrupter closest to the fault opens before other devices.

Determining the ratings and settings for protective devices requires familiarity with NEC requirements for the protection of cables, motors, and transformers, and with ANSI/IEEE C57.12.00-1980 for transformer magnetizing inrush current and transformer thermal and magnetic stress damage limits.

How do you know if a circuit breaker will work when it is called upon to interrupt an electrical fault or short-circuit? If you haven’t had a short-circuit/protection coordination study done on your electrical system recently, the answer is: you don’t know for sure.

Even the best designed and maintained power systems occasionally suffer short-circuits that draw unusually high currents. If these currents exceed the capability of the protective devices in the power system, a short-circuit event will cause the devices to explode like a bomb.

The First Step

A short-circuit study is an analysis of an electrical system that determines the magnitude of the currents that flow during an electrical fault. Comparing these calculated values against the equipment ratings is the first step to answering the question above and ensuring that the power system is safely protected. Once the expected short-circuit currents are known, a protection coordination study is performed to determine the optimum characteristics, ratings, and settings of the power system protective devices.

How is a Short-Circuit Study Done?

A short-circuit study is comprised of the following steps:

• Data collection — Information on all the components is obtained during a field visit and then tabulated. Additional data is obtained from the electric utility, manufacturers, or calculated from field data.
• One-line diagram — A power system diagram that shows how all components are electrically connected is created, or, if one already exists, updated. Additional data needed for the study, such as cable impedances, can be obtained with information from this diagram.
• Computer analysis — Using one of the many computer software programs available, the system data is input and the short-circuit currents at various points in the system are calculated.
• Tabulate results — The output of the computer program is typically put into a table for comparison with the ratings of equipment in the system. If the calculated short-circuit current at a given point exceeds the short-circuit rating of the equipment installed at that point, then that location is flagged as being inadequately protected.
• Final report — A detailed report that describes the scope of the study, all assumptions, the origin of the data, the methods used for calculating the currents, the tabulated results, and recommendations for corrective action is published at the conclusion of the study.

Protection-Coordination

An electrical power system is designed so that if a short-circuit occurs, a protective device (such as a fuse or circuit breaker) will operate to “open the circuit” and prevent the continued flow of electrical energy to the faulted area. To minimize interruption of electrical service to other areas of the power system, the system is also designed so that the protective device closest to the short-circuit operates first to “clear the fault.”

For example, if a short-circuit occurs on a downstream branch circuit cable as shown in Figure 1 (below), the branch circuit breaker feeding that cable (Circuit Breaker A) should open first to isolate the fault, rather than the Main Breaker in the panel which would interrupt service to all branch circuits.

If Circuit Breaker A failed to operate after a given time, then the Main Breaker would operate to open or “trip” the circuit, thus providing back-up protection. This time-sequence of operation is called “coordination of protective devices.” A protection-coordination study is done to determine the trip settings of each protective device in the power system so that maximum protection with minimum interruption is provided for all faults that may happen in the system.

How is a Protection-Coordination Study Done?

A protection-coordination study is comprised of the following steps:

• Short-circuit study — A described above, an analysis of available fault currents in the power system is performed.
• Data collection — In addition to the data collected for the short-circuit study, additional information on the present settings and ratings of all protective devices is needed.
• Manufacturer’s data — Each protective device has unique response characteristics, documented on manufacturer’s “time-current curves” that are needed for the study.
• Computer analysis — While protection-coordination studies can be done by hand, it is much easier to use computer software available in the market. Many of the programs have a library of time-current curves for most devices found in power systems. Those not in the library can be input and stored for future use.

The computer program then allows the engineer to determine the optimum settings that will provide the best protection for the system. In some cases, coordination between two devices is not possible. Engineering judgment is then used to determine the most appropriate settings that will minimize equipment damage.

• Tabulate results — The settings and ratings of each protective device (circuit breakers, fuses, motor controllers, etc.) as determined by the analysis is put in a table for comparison with present field settings and ratings.

Final report — A detailed report that describes the scope of the study, all assumptions, the origin of the data (including the time-current curves), the tabulated results, and recommendations for corrective action is published at the conclusion of the study.

Review a Sample Engineering Ground Testing Report