Globalisation and the advancements in transportation and logistics has enabled us to address the growing demand by setting up ad-hoc power plants using reciprocating engine driven gensets; this has also meant that gensets are being used in harsher environmental conditions. It has therefore become critical for us to understand the impact of these environmental conditions on the alternator and design suitable protection mechanisms.
Environmental conditions impacting performance of an alternator: Where the alternator is installed in the world (geography) and the application type (mining, marine, oil & gas) affect the type of environmental conditions the alternator is exposed to. Figure 1 shows the temperatures across different parts of the globe.
Contamination of the winding and the insulation by the dust can lead to deterioration of winding insulation system and can negatively impact insulation life. Combined with moderate to strong winds, dust/sand could erode the winding insulation leading to premature failure of windings or reduced thermal capacity of windings at the very least. Additionally, dust/ sand could block air-flow leading to elevated temperatures in the alternator windings.
II. Water / High Humidity
Water or high humidity in the air reduces the insulation resistance of the windings and diminishes the design life of the insulation system. Water / high humidity may also enter the connections used in electronic circuits damaging them. Salt water / water vapour is a conductor and could lead to accelerated breakdown of the insulation system.
III. Ambient Temperature
The temperature rise in the alternator is highly sensitive to the temperature of the air entering the machine. Higher ambient temperature means higher thermal stress leading to winding insulation degradation (and diminished alternator life) due to high temperature in the windings. It is therefore very important to ensure that either the ambient temperature is controlled or the right alternator/rating selected for the ambient temperature.
Air at higher altitudes has a lower electrical breakdown resistance to voltage and electrical machines therefore require enhanced insulation capabilities to prevent breakdown. Clearance distances will also need to be considered depending on the altitude. Additionally, a derate dependent on the altitude is required to negate the effects of reduced cooling caused by thinner air.
Presence of salt may cause corrosion of the electrical parts such as rectifier and windings. This can result to degradation of the insulation resistance and increase of the contact resistance. Salt also corrodes metallic components like bearings, shaft limiting the mechanical strength and capability. Figure 2 shows the picture of an exciter of a machine exposed to salt mist. The corrosive effects of salt are clearly visible.
VI. Other factors
Vibration/shock or Chemicals could also have a significant negative impact on the alternator performance and life and are dependent on the application type ' eg:- alternators used in mining, chemical industry standby.
How alternators are typically protected from environmental conditions'
1) IP and IC enclosures: - IP refers to ingress protection and IC refers to the cooling circuit arrangement used in the alternator according to IEC 60034-5 and IEC 60034- 6 respectively. Ingress Protection or IP is a critical part of the alternator design and is used to protect the alternator from dust/solid particles and water ingress. The Ingress Protection or IP capability of the alternator can be used to protect the alternator from severe environmental conditions like chemicals, salt, dust, humidity, etc,' Figure 3 shows an image of theIP44 configuration offered by Cummins Generator Technologies on some designs of its products.
2) Varnish / Impregnation / Coating on Winding and / or metallic components of the alternator: Alternatively, the manufacturer may recommend the application of an additional coat / varnish / impregnation to protect the windings and metallic components from environmental conditions like salt, humidity, dust and chemicals.
Cummins Generator Technologies has been involved in a variety of activities to understand these applications and develop key criteria that allow selection of the right alternators for these harsh applications. Our team of experienced engineers work with our customers to develop product solutions that target specific application condition requirements.