Case Study: Power Quality

Power Quality Benefits of Voltage Regulation

The Need

A utility in Hawaii extracts water from deep wells to provide drinking water to customers. They use 3-phase electric motors to pump the water from the wells and out into the distribution system. The quality of the electrical service on the island is poor, however, with significant voltage fluctuations and unbalanced phases. The poor power quality and unbalanced phases was causing pump motors to burn out often within one year of installation, significantly short of the 15-20 useful lives of the motors.

The Problem of Phase Imbalance

High voltage and phase imbalance seriously impact the performance and useful lives of electric equipment, especially motors. Even slight imbalances of phases can cause motors to overheat and wear out much sooner than necessary. As seen in the table below, even a 1% phase imbalance increases temperatures and resistive losses, cutting the useful life of motors in half.

% voltage unbalance Winding temp (°C) Resistive losses (% of total) Efficiency reduction Expected winding life (years)
0 120 30 20
1 130 33 0.5% 10
2 140 35 1 – 2% 5
3 150 38 2 – 3% 2.5
4 160 40 3 – 4% 1.25
5 180 45 > 5% < 1

MicroPlanet Solution

Because MicroPlanet’s patented products regulate with extreme speed (sub-cycle), efficiency (99.5% efficient), and accuracy (to within ½ volt of a set-point), our 3-phase products are designed to regulate each power phase independently. Because of the precision of our technology, our products can virtually eliminate phase imbalance, thus dramatically increasing both performance and the useful life of pump motors and other electric equipment.

Power Quality

Power quality can be a confusing topic to non-engineers, but its impact on the financial bottom line is very easy to understand.

When voltage is constantly changing, it increases the mechanical stress on electrical appliances from thermal cycling. It’s analogous to how streets in climates with frequent freeze and thaw cycles crack more and require more maintenance than streets in milder climates.

The strip chart below shows a highly variable input voltage (black), being corrected by a MicroPlanet voltage regulator (red). The effect of removing dramatic swings in voltage is similar to removing the temperature extremes on asphalt. The operating temperature of electrical equipment is related to the voltage. Steady voltage means steady operating temperature, and lower voltage means lower operating temperature.

3pssutil1_data_sub_cycle

motor_life_electrical_qualityHigher voltage creates higher losses in electrical appliances. Higher losses mean higher operating temperatures. It is a well understood engineering principle that for every 10° C increase in the operating temperature of an electrical device, its useable lifetime is is reduced by one half.

The thermal strip chart to the right clearly shows the voltage to temperature relationship of a ½ HP PSC motor. The motor is running at a constant load. It runs 8°C cooler at 114 V than at 126 V. At a consistent 114 V, we can expect the usable life of this motor to be extended by 74%.

Three-phase motors, such as those in HVAC units, are sensitive to phase voltage unbalance. Unbalance greater than 1% consumes extra energy and significantly reduces the life of the motor. Phase unbalance greater than 3% will destroy a motor unless it is oversized, and even then it is still a waste of energy.

% voltage unbalance Winding temp (°C) Resistive losses (% of total) Efficiency reduction Expected winding life (years)
0 120 30 20
1 130 33 0.5% 10
2 140 35 1 – 2% 5
3 150 38 2 – 3% 2.5
4 160 40 3 – 4% 1.25
5 180 45 > 5% < 1

Source; Energy Matters, DOE, Industrial Technologies Program, Winter 2005

increase-in-motor-heating-and-losses-vs-voltage-unbalanceStatistics indicate that 32% of the motors in the US operate with an average unbalance between 1% and 3%, and another 2% operate at a greater than 3% unbalance.
Keep in mind that a 3% average could mean the unbalance is 1% for half the time and 5% for the other half of the time, which would kill your motor.
In the strip chart below you can see the higher, unbalanced utility voltage alternating with the lower, balanced regulated voltage during the measurement and verification process.

 

 

measurement-and-verification