Power – Why Is It? So Dynamic?
Instead of focusing on a particular type of equipment, I thought it might be good to get back to basics and discuss electricity and the power options we have when we are putting together our facilities. It is important to review both capital expenses and operating expenses when selecting equipment. The cost of installing different power supplies varies by location and type.
One of the most frequent comments I hear is that every application should be with three-phase power. The reason I am consistently given is that it is cheaper. Let’s examine this closer.
We pay for the Kilowatts consumed from the municipal power grid. From the surface, it appears that if you had a choice to run 115 Volt equipment versus 230 Volt, the 230 Volt would be cheaper because it draws less amps, the same thought process is used when we talk about 230 Volt single-phase versus 230 Volt three-phase, etc. However, if you dig into it – the amount of Watts (or Killowatts) that we are using is pretty much the same.
In single-phase applications the simple equation is Amps multiplied by Volts equals Watts. There is a more complicated equation that has coefficients for power and there are also situational circumstances that can come into play but for the sake of demonstration, we will stick with the simple equation. A pump that pulls 10.5 full load Amps at 115 Volts would use 1,207.5 Watts. That same pump would be rated for 5.4 full load Amps at 230 Volts. The math is the same. 5.4 Amps multiplied by 230 Volts equals 1,242 watts. The motor pulls a similar number of watts regardless of if it is using 115 Volts or 230 Volts.
Let’s examine a three-phase power application; the equation for three-phase power becomes more complex because you can’t ignore the power coefficient. In the case of three-phase power, Watts equals Amps multiplied by Volts multiplied by 1.732 (power factor dictated by the specific municipal network). That said, a three-phase motor of a similar size to the one we used in the single-phase example would pull 3.6 Amps at 230 Volts which will use 1,434 Watts. Keep in mind that there will always be a bit of variability between a single-phase and three-phase motor comparison due to efficiencies and manufacturers. The point being that the number of Watts used by all three motors is very similar.
Why is all this important? It becomes really important when planning an expansion or new facility. The available power is often overlooked and under-examined.
Where it counts….
The following considerations are important when designing your expansion or new facility. One of the first questions that should be asked is whether there is three-phase power available on-site. If it is not already at the site then where is the closest supply? In many cases, the owner is required to pay for the installation of three-phase power up front which can also include the expense of bringing the power from the next closest location. I’ve seen associated installation costs upwards of $40K, so it definitely needs to be in the budget.
There is also a point where size matters and the equipment is only available in three phases. As a rule of thumb, any pumps of 3hp loads should ideally be run on three-phase power. There are larger horsepower pumps available in single phase, which is helpful for those locations where three phase is not possible or cost prohibitive. Most motors over 7.5 horsepower are only available in three phases. Keep in mind that even though the motor is available in single phase, the motors are most often custom made for OEM motor partners (pump manufacturers) which can cause a long lead time for replacements.
Assuming all things are equal, where is the savings when comparing 115V to 230V and 230V single-phase to 230V three-phase? The biggest savings is in the power line sizes. Appropriately sized electrical wiring can be costly. The lower the voltage, the lower the gauge wire that is required. Lower gauge wire means thicker wire and more materials.
Single-phase motors require capacitors to protect them and assist with starting rotation. Three-phase motors require motor starters and ideally phase protection. It is not uncommon to lose a “leg” when running three-phase power during high usage times. Without phase protection, this almost certainly means catastrophic failure of the equipment. Three-phase power is also more dangerous to work within the field. In all cases, a licensed electrician should be used when wiring any electrical appliance. And while we all know the rules, this one should not be broken when using three-phase power.
What happens when there is no three-phase power and you need the larger equipment? There are alternatives which require capital costs up front. The facility can invest in Buck-Boost Transformers and/or VFDs with single phase inlet power. These transformers and VFDs are able to take power and either increase the voltage or decrease depending on the application. Another option would be to use multiples of smaller pieces of equipment, which in turn also boosts redundancy for intensive RAS applications. And lastly, pay to upgrade to three-phase power if it is available.
The long and short of it is that it is best to do your homework when it comes to electrical requirements and what the best answer is for your application.