New equipment requires testing, and most maintenance shutdowns involve testing electrical distribution equipment. How do you test the equipment? Do you use the manufacturer or their organization's testing standards? Or, do you use another organization's standards?
Are your electrical tests substandard? Suppose you need to write a purchase specification for some important electrical equipment. At first, this task seems mundane and mind numbing. Then you realize purchasing and testing electrical equipment requires sound and correct specifications. But confusion surrounds the use of certain standards and specifications, especially when various organizations include information that seems the same.
Repetition runs rampant within the apparently excessive amount of engineering standards and specifications in our industry. Yes, most of them differ. But, there are so many! In the electrical industry alone, all of the following organizations develop standards and specifications:
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Institute of Electrical and Electronics Engineers (IEEE),
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American Society for Testing and Materials (ASTM),
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American National Standards Institute (ANSI),
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Canadian Standards Association (CSA),
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Insulated Cable Engineers Association (ICEA),
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National Fire Protection Association (NFPA),
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National Electrical Manufacturer's Association (NEMA),
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Occupational Safety and Health Administration (OSHA), and
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Underwriters Laboratory (UL).
Various committees and task forces make up these organizations, with each responsible for researching and recommending standards for approval and publication.
Other lesser-known standards organizations are also in our electrical industry. An especially active one is the interNational Electrical Testing Association, or NETA Like the other standards organizations, NETA has various task forces or committees. Unlike others, however, NETA specifications cover only the field-testing of electrical distribution equipment. They do not include test procedures or methodology. Due to the subjective nature of testing evaluations, NETA's approach centers on the principle that the person performing the test and procedure itself are equally important.
Field-testing separates into two distinct areas: acceptance testing and maintenance testing. Acceptance testing describes those tests done on recently installed or received equipment. Basically, you do acceptance testing to verify the functionality of your equipment. Maintenance testing, on the other hand, describes those tests done at routine intervals. Here, you're verifying the status of equipment.
NETA recognizes the difference between these two testing methods, publishing and updating two specifications:
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NETA Standard ATS: Acceptance Testing Specifications for Electrical Power Distribution Equipment and Systems.
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NETA Standard MTS: Maintenance Testing Specifications for Electrical Power Distribution Equipment and Systems.
Updates to these publications take place on a four-year cycle with the NETA ATS latest revision in 1995 and NETA MTS in 1997. Both break down into the same 10 sections:
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Section 1-General Scope
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Section 2-Applicable References
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Section 3-Qualifications of Testing Firm
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Section 4-Division of Responsibility
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Section 5-General
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Section 6-Power System Studies
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Section 7-Inspection and Test Procedures
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Section 8-System Function Tests
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Section 9-Thermographic Surveys
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Section 10-Tables
This arrangement differs from manufacturing standards in two ways. First, because various organizations produce manufacturing standards, no two standards are the same. Second, manufacturing standards separate inspection and test procedures in different standards by equipment type. NETA includes all the testing recommendations for electrical distribution equipment in one specification.
Manufacturer's standards address testing at the factory. NETA specifications address testing in the field. NETA is now obtaining ANSI recognition of their standards.
NETA specifications reference related manufacturing or industry standards whenever possible. What happens if no manufacturing standard exists? Or, what if an existing manufacturing standard doesn't function well as a field-testing standard? In both instances, NETA's Standards Review Council will arrive at testing methods or values after deliberation of comments from the industry and review of its members' data.
Let's compare how NETA and manufacturer standards cover molded-case circuit breakers (MCCBs), power circuit breakers (PCBs), and dry and liquid-filled transformers.
MCCB standards. NEMA publishes Standards Publication AB 4-1996, Guidelines for Inspection and Preventive Maintenance of Molded Case Circuit Breakers Used in Commercial and Industrial Applications. It's arranged as follows: Section 1-General; Section 2-Guidelines; Section 3-Inspection Procedures; Section 4-Preventive Maintenance; Section 5-Test Procedures; and Section 6-Accessory Device Test Procedures.
AB 4-1996 mentions these tests:
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Mechanical operation tests,
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Insulation resistance test,
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Individual pole resistance test (millivolt drop),
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Inverse-time overcurrent trip test,
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Rated hold-in test, and
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Instantaneous overcurrent trip test.
The NETA specification includes these tests except the rated hold-in test. It also lists two additional tests: short-time pickup and delay test and ground-fault pickup and time delay test.
Performing the NETA or NEMA tests, you must use, at minimum, a megohmmeter, current injection test set, digital multimeter, and a variable voltage supply.
NEMA AB-4 gives detailed and systematic instructions for doing each test. The NETA specifications include a list of the tests, assuming a qualified and certified person performs the tests. They do not include methodology or "how-to" information.
NEMA AB-4 mentions certain sections set guidelines for inspection, preventive maintenance, and testing. But, it lets you decide what sections to use for a good program. The NETA specifications list a multitude of tests for maintenance or acceptance testing. As with NEMA AB-4, you can decide whether to perform certain tests.
PCB standards. After an exhaustive two-day search through stacks of various standards and indexes, this author found only one applicable PCB standard: ANSI C37.50-1989, Low-Voltage AC Power Circuit Breakers Used in Enclosures-Test Procedures. It's arranged as follows: Section 1-General; Section 2-General Test Conditions and Requirements; Section 3-Design Test Requirements; Section 4-Accessory Devices; Section 5-Treatment of Failures within Test Sequences; Section 6-Production Tests; and Section 7-Production Monitoring and Product Test Requirements.
This ANSI standard relates only to manufacturing of the PCB. Each manufacturer supplies instructions for performing its recommended tests. These tests may differ from one manufacturer to another, making it difficult to standardize on any testing procedure. You can use the NETA standards to help develop a standardized testing routine for PCBs. The ANSI standard does give good detail on the following tests:
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Trip-device calibration,
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AC dielectric withstand-voltage,
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Continuous current,
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Overload switching,
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Endurance,
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Short-circuit current, and
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Short-time current.
NETA recommends using its standards with any applicable manufacturer standard. Of course, you still should use qualified personnel who are trained and certified in the equipment and test methodology. PCB test equipment is much the same type as MCCB test equipment.
Transformers. After another lengthy search, this author located a draft standard for testing liquid-filled transformers: IEEE 62-1995, Guide for Diagnostic Field Testing of Electric Power Apparatus-Part 1: Oil-Filled Power Transformers, Regulators, and Reactors. It's arranged as follows:
Section 1-Overview; Section 2-References; Section 3-Definitions; Section 4-Diagnostic Chart; Section 5-Safety; and Section 6-Test and Test Techniques.
The standard does not explicitly define what tests you should use for acceptance or maintenance. Instead, it includes "how-to" information (somewhat more than the NETA standards). The NETA standards allows you to determine what tests should constitute maintenance or acceptance.
For dry-type transformers, we have IEEE C57.94-1982, reaffirmed 1987, IEEE Recommended Practice for Installation, Application, Operation and Maintenance of Dry-Type General Purpose Distribution and Power Transformer. It's arranged as follows: Section 1-Scope; Section 2-References; Section 3-Definitions; Section 4-Application; Section 5-Installation; Section 6-Testing; Section 7-Operation; and Section 8-Maintenance.
This standard gives recommended tests and procedures for pre-service (acceptance) and periodic (maintenance) testing, giving test values for each test. The NETA standards list more tests in their specification.
To locate a manufacturing standard's recommended testing procedure, you must search through many standards. Once located, though, the manufacturing standard usually goes into still more detail. Even though the creation of NETA stemmed from a need for adequate field-testing standards, NETA and manufacturers work together toward a common goal: providing electrical reliability to the consumer for the least cost and maximum safety.
