Cummins Generator Technologies products have an expectation from their customers that they are both reliable and durable: they expect it to deliver a lifetime of performance without any failure. However, it is rare for the customers to specify its time of life. So what is it that gives us a common understanding of expected product life? The Codes and Standards.
Codes and Standards fall into two categories:
■ Codes - which ensure products are safe and fit for purpose. Usually these are written into law and must be complied with.
■ Standards - where compliance is voluntary – but in order to sell product, ability to show compliancy with the standards becomes a market-based expectation. The standards are where the durability and life expectations are set.
When it comes to STAMFORD and AvK alternators, there are three principle standards that they refer to:
■ IEC 60034: Rotating electrical machines
■ NEMA MG-1: Motors and alternators
■ UL-1446: Systems of insulating materials
These standards define the methods and limitations of operation of electrical machines in order to deliver a certain lifetime, if operated in ideal conditions. There is a strong linkage between these standards and the standards they refer to. The diagram below shows the high-level relationships, but there are additional standards involved that define how the life of an insulation system and hence the life of a machine is defined.
The standards state that one of the principle ageing factors is – which translates as the relationship between the temperature that the insulation system sees, and how long it will last. This relationship is expressed as the thermal endurance graph, and requires the Temperature Index (TI) and halving Interval (HIC) of an insulation system to be defined.
The main standards relate to a number of other standards, of which IEC 60085: Electrical insulation — thermal evaluation and designation is the main reference to define how an insulation system is to be tested.
The aim of the IEC 60085 is to define the thermal life and limits of an electrical insulation system, which requires thermal ageing tests. The standards lay out how insulation systems can be tested to find the thermal life, or how the life can be determined from experience. The work to determine these values for a new insulation system is both extensive and time-consuming, which is why we rarely change our insulation systems.
Having defined how the insulation systems are to be tested, IEC 60085 also defines the thermal operating limits electrical machine, which is known as the temperature classes, class B, F and H. By operating the electrical machine within these, the standards define what life should be expected if the electrical machine is operated within the stated temperature class:
Thermal effects on the insulation system are one of the major factors influencing the life of electrical machines
This is repeated in IEEE – 1, so the standards are consistent in the declaration of their declaration of thermal class.
The standards also define the voltage and frequency limits that machines can be subjected to and still be expected to perform correctly because when a machine is operated at or beyond these limits, the machine will see temperature rises beyond that allowed by the thermal class which will reduce the overall life of the insulation system. IEC 60034 defines these voltage and frequency limits.
By declaring that our machines comply with IEC 60034, NEMA MG-1 and UL-1446 we are saying that the insulation systems of our alternators comply with the requirements of these standards, and will deliver a life as defined by the standards when operated in ideal conditions.
In reality, there are other factors that will affect the overall life of our machines, but the standards agree that thermal effects on the insulation system are the major factors influencing the life of electrical machines.
For more information please contact the Applications team