Geothermal Systems Need Shaft Grounding

When people think of renewable power, wind and solar usually come to mind.  But there are other fully sustainable power generation methods.  One that's rapidly becoming more important is geothermal power. There are a few different geothermal generation schemes, but they all involve pumping hot water out from deep in the earth and using its heat energy to spin a turbine. (Geothermal energy can be used for district heating as well.)


 Krafla Geothermal Power Station in Iceland
Like wind and solar, geothermal energy has low-to-no CO 2 emissions.  But geothermal also has the big advantage that it's always on.  The sun goes down, and wind comes and goes, but the center of the earth is always hot.  That heat can be used to generate electricity at any time, day or night, breezy or calm.  As of 2015, geothermal power produced 12.8 gigawatts (GW) of electricity.  By 2020, that total is expected to reach 14.5-17.5 GW.

But geothermal generation also has problems.  Good sites can be difficult to find.  And the steamy and briny conditions at running plants are corrosive, both to pumps and the motors that drive them.  More about those motors:  Geothermal plants run 24/7, and demand for electricity (and heat) varies daily (and seasonally).  So the pump-driving motors need to be run at variable speed.  Faster when demand is high; slower when it's low.  Usually the motors' speed is controlled by variable frequency drives (VFDs).  But VFD operation causes problems of its own.


An AEGIS ring installed on a vertical pump motor in a geothermal power station

The pulses of power that VFDs put out create voltage on the shafts of the motors they control.  If shaft voltage builds up high enough, it will arc through the motor or pump bearings, causing electrical damage.  This damage builds up over time, and causes premature bearing failure.  When the motor or pump bearings fail, they must be replaced, an expensive operation.  The failure may also cause unplanned downtime and massive loss of revenue.

The solution is to provide a low resistance path from the shaft to ground.  This is exactly what AEGIS® Shaft Grounding Rings provide.  With an AEGIS ring installed, charge flows safely through the ring, instead of discharging through a bearing.  For motors up to 100 hp (75 kW), an AEGIS ring is all the electrical protection you need.  Larger motors need an AEGIS ring along with one insulated bearing.  (The insulated bearing protects against circulating currents, which are a problem in larger motors on VFDs.)

AEGIS rings are available factory-installed in several makes and hundreds of models of motor.  AEGIS comes installed inside everything from general purpose to explosion proof to vertical hollowshaft motors from makers like US Motors.

AEGIS Rings also come with a 2-year extended warranty against bearing fluting damage. No other form of protection against VFD-caused bearing damage offers a warranty like this.

2-Year Extended Warranty

To learn more about AEGIS shaft grounding and best practices for electrical bearing protection, sign up for a training. We offer monthly live training webinars, and - pandemic restrictions permitting - we can also visit your facility to review your exact application.

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