TranSwitcher: How to Minimize Voltage Drop Problems in Transformers

According to NEC, a voltage drop of 3 percent (i.e. for a branch circuit conductor) plus a 5 percent feeder is enough to guarantee efficiency in any general circuit. However, when a sensitive electronic load is at play, the circuit must have a voltage drop of about 1.5% at full load and 2.5% voltage drop when it comes to the feeder as well as branch circuits. In these cases, you can apply certain practical approaches to minimize voltage drop related issues. They include:

  • Boosting the number and size of conductors
  • Cutting down on load current for the circuit
  •  Reducing conductor length
  •  Reducing conductor temperature

This article is going to delve into these top ways of minimizing voltage drop related problems.

Increasing the Number and Size of Conductors

It’s important to note that parallel and oversized conductors tend to have lower resistance per length when compared to Code-required min conductors. This reduces the voltage drop. Consequently, energy efficiency is increased. This also means that the losses are minimized.

Also, you can limit neutral-to-ground based voltage drop by installing a distinct, full-sized neutral based conductor. However, the installation should be done to each phase conductor when it comes to applications that are characterized by single-phase branch circuits.

On the other hand, avoid downsizing the grounded based conductor or neutral when dealing with three-phase feeder based circuits. If you anticipate a significant amount of non-linear loads in three-phase circuits, consider installing grounded and neutral conductors. However, ensure that the grounding is done with double the phase conductor capacity.

Decreasing Load Current

Decreasing the load current is another way of minimizing voltage drop problems. Here is how to do it; Limit the number of equipment that are connected to one circuit. It will play a key role in limiting load current on that explicit circuit. Also, consider cutting receptacle numbers on every branch to about three to six. It’s also important to consider installing each branch circuits to a sensitive electronic-based load or a load featuring high inrush current.

If you want to reduce voltage drops in residential building, consider installing outdoor receptacles that don’t surpass 50 linear feet from the receptacles. However, ensure that there is more than one outdoor-based receptacle on either side of your building. Each branch circuit should have at least a 12 AWG on every receptacle.

Decreasing Conductor Length

The conductor length also plays a key role when it comes to voltage drop problems. However, you can deal with these issues by decreasing the length of the conductors. Doing so reduces conductor resistance. Consequently, the voltage drop is reduced. Of course, circuit length is fixed in nature. However, you can still use some control during the design stage to alter the conductor length. This is possible if the panels and sub-panels are located close to the loads—particularly when it comes to sensitive electronic pieces of equipment.

Adjusting Conductor Temperature

Factors that influence the conductor temperature include:

  • The number and size of conductors
  • The load current
  •  Conductor length

Thus, the heavier the load, the hotter the circuit will run. It’s also important to note that conductor length influences the conductor resistance. Consequently, it can lead to a voltage drop. According to IEE, copper’s electrical resistance coefficient (α) is 0.00323/°C. This represents a resistance change of around 0.3 percent for a temp change of 1°C. The following equation is used to determine the effect of temp:

R2 = R1 [1 + α · (T2 – T1)]

Here, R1 represents the resistance in (Ω) at a temp T1. On the other hand, R2 is used to donate resistance at a temp point T2. Normally, engineers reference temperature T1 at 75°C. At high conductor based loading, the temperature drop can be a great concern. This is because, at this point, temperatures are high. So, the best thing to do is to reduce the conductor temperate using the above formula. Consider changing the parameters in the formula to reach the ideal conductor temperature. However, if you don’t have the know-how, consult an electromechanical (mechatronics) engineer.

Protecting Your Transformer from Surge Current Damages

Change in current can have an adverse effect on a power supply. That’s is why you need to look at the current variations of your transformer and look for solutions to counter it. Remember, current variations can lead to overheating. Consequently, the wires might meet and lead to damages. Here is how to protect your transformer from surge current related damages.

Use Fuses at H.V and L.V Terminals

Use fuses at the H.V and L.V terminals—they can do an excellent job when it comes to dealing with overloads caused by slow line surges as well as high current overloads.

Dealing with a Lightning Strike

A lightning strike can destroy your transformer. If a lightning strike occurs on either the primary or secondary side. Thus, your transformer can be damaged. The only solution to this is to use spark gaps across both sides of the transformer.

Thermal Overload Relay

You can use a thermal overload relay to protect a transformer from overloads relay. With this technique, you have a solution to that damaging overloads. It works by stimulating the temperature of the windings of your transformer. It’s also important to note that this stimulation is dependent on the transformer’s current capacity and the thermal constant.  Certain types of relays have the capability to factor in current harmonics effects resulting from non-linear loads like rectifiers, computers, as well as variable speed drives. Plus, thus relay evaluates the amount of time remaining before emitting a tripping order. It can also evaluate the time remaining before the transformer is reenergized. Additionally, thermostats that come with oil-filled transformers can perfectly control the oil temperature.

On the other hand, heat sensors—common in Dry-Type transformers—can be used to detect changes in the hottest parts of the transformer’s windings

The Bottom-Line

The above are common ways you can use to minimize the voltage drop related issues. From increasing the number and size of conductors to reducing conductor temperatures—these tips will help you deal with all voltage drop related problems once and for all. Use them and boost the performance of your transformer. Also, you can use TranSwitcher from Southern States to protect your transformer for improved performance.

Adam Hansen