Category: Basic Electricity

What are Transformers, and What is Their Role in Power Distribution

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What are Transformers, and What is Their Role in Power Distribution

Introduction

Transformers are the of any electric utility distribution system. As a meter technician it is imperative that you have a good understanding of what a transformer is, and what it does. Let’s dive into the world of transformers and their crucial role in power distribution:

  1. What Are Transformers?
    • Definition: Transformers are electrical devices that transfer electrical energy from one circuit to another through electromagnetic induction.
    • Components:
      • Core: A magnetic core (usually made of laminated iron or steel) that provides a path for magnetic flux.
      • Primary Winding: The input coil where alternating current (AC) flows.
      • Secondary Winding: The output coil where induced voltage appears.
      • Insulation: Layers of insulation to prevent short circuits between windings.
  2. Significance in Power Distribution:
    • Voltage Transformation: Transformers step up or step down voltage levels. High-voltage transmission lines use step-up transformers to increase voltage for efficient long-distance power transmission. At substations, step-down transformers reduce voltage for local distribution.
    • Efficient Energy Transfer: Transformers minimize energy losses during transmission. Higher voltage reduces current, which decreases resistive losses in power lines.
    • Grid Stability: Transformers help maintain grid stability by balancing load and voltage across different parts of the network.
    • Isolation: They provide electrical isolation between primary and secondary circuits, enhancing safety for maintenance and preventing ground faults.
  3. Types of Transformers:
    • Power Transformers: Used in substations for transmission and distribution.
    • Distribution Transformers: Can either be pole-mounted overhead, or padmounted. They serve local neighborhoods and buildings.
    • Instrument Transformers: Used for metering and protection (current transformers and voltage transformers).
  4. Transformer Efficiency and Maintenance:
    • Regular maintenance ensures optimal performance.
    • Oil-Filled Transformers: Oil quality checks, cooling system maintenance, and DGA.
    • Dry-Type Transformers: Insulation checks, cleaning, and visual inspections.
  5. Safety Considerations:

Remember, transformers are the unsung heroes of our electrical infrastructure, silently enabling power distribution across cities and industries. If you want learn more about how to calculate the full load ampacity of a transformer, just follow the link. If you have any further questions, feel free to ask! 

How to Calculate the Full Load Ampacity of a Transformer

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Knowing how to calculate the full load ampacity of a transformers is a very important calculation to have in your bag of tricks as a meter technician. Here I want to show you how to do the calculation as well as provide why you want to calculate the full load ampacity of a transformer. Finally, I will show you how you can use the calculation to troubleshoot a transformer-rated metering installation.

How to calculate the full load ampacity of a Transformer

There a couple of things that you need to know before you start to calculate the full load ampacity of the transformer in question. First, what are you even calculating? You need to know what your answer represents before you go punching numbers into your calculator. The full load ampacity describes how many amps the transformer is designed to handle. This is important because it helps determine what size transformer is needed to handle a particular load.

Many times we receive information about load in terms of amps. Well, most transformers are sized based on KVA, kilovolt-amperes. Since transformer are sized based on KVA we need to convert this number to amps in order to know what the transformer is capable of handling.

Next we need to know a couple of other things. One is the line to line voltage of the secondary output of the transformer. You also need to know if the transformer is a single phase transformer or a three phase transformer. Once you know all of this information you can start with the calculation. For simplicity we will start with 100 KVA single phase 240v transformer. To calculate the full load ampacity use the following formula:

KVA x 1000

Line to Line voltage

So, for a 100 KVA transformer we will multiply 100 x 1000 and then divide it by 240v.

100 x 1000

240v

That gives us 416.67 amps. So, for a 100 KVA 240v single phase transformer the full load ampacity is 416.67 amps.

Next let’s calculate the full load ampacity of a three phase transformer. There is one more step that you have to do in order to find the full load ampacity and that is to use the square root of 3 which rounds out to around 1.732. Let’s do the same thing for a 120/208v three phase transformer. Use the following formula:

KVA x 1000

Line to Line voltage x 1.732

For a 120/208v three phase 100 KVA tranformer we calculate the full load ampacity as follows:

100 x 1000

208 x 1.732

That gives us 277.58 amps. So, for a 100 KVA 120/208v three phase transformer the full load ampacity is 277.58 amps.







Why Calculate the full load Ampacity?

Now that you know how to calculate the full load amps of a transformer you probably are wondering why in the world you did that in the first place.

One reason specific to metering is that it tells you the number of amps a transformer is capable of producing so you can size your CT’s accordingly. In both examples above you can get away with using 200:5 CT’s with a rating factor of at least 3. This covers the entire operating range of each transformer.

Another reason to know the full load amps is that it ensures that you are not over or undersizing your transformer. An undersized transformer is one that is going to have a shorter life span because of the excess heat that is generated due to being overloaded. An oversized transformer is a transformer that is being under utilized. This adds up in the form of increased system losses because even though the tranformer has plenty of capacity the coils still have to be energized and this can be thought of as waste.

Troubleshooting

Knowing how to calculate the full load ampacity of a transformer can help you troubleshoot the entire installation. You as the meter tech will most likely be going out and testing transformer-rated metering installations. Many of these will be installed on tranformers that are serving only one customer. When you test the site you will find out how many amps are on the service. You can then take this information and compare it to the full load capacity of the transfomer.

Another thing that you will do is look at the demand on a transfomer by looking at all of the meters being served by a particular transformer. Looking at each meter individually will only let you know what each service is pulling on its own. If you add each of these service together you will be able to tell whether or not the transformer is sized properly.

Conclusion

Finding the full load ampacity of a transformer is a very useful calculation to have on hand. It can alert you to problems that may arise on your system as well as help you install the right size CT’s.







What is the difference between voltage and current?

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Voltage and current are two different measures that are found in electricity. They are both present in every electrical circuit from the flashlight all the way to refrigerators. But, the question is what is the difference? To illustrate the difference between voltage and current we will look at the age old comparison of electricity to water.

Current Flow

Current is a bit easier to illustrate. We can compare it to water in a garden hose. Imagine you have a simple water wheel. To make this water wheel turn you need to pour water over it. Let’s say we have two different sized water hoses. One is 3/4″ and the other is 1″. Now, let’s pour the water over the water wheel with the smaller hose and see what happens. The water wheel turns. Now, the larger hose. What happens? The water wheel turns faster.

This is a result of more water flowing in the larger water hose. More water = faster water wheel. Pretty simple. We need to make sure that when we think of current in the same way as water in a hose that we always think of the hose as full all the time. That way when you turn the hose on you instantly have water flow.

In the early days of electricity it was a commonly held belief that electricity was a fluid. This fluid was made up of tiny particles that would flow into different materials.

Voltage, the Driving Force

Again we are going to compare voltage to the water system. First remember that voltage is the driving or electromotive force that is a part of electrical circuits. How does this translate to water? Think of the voltage as the pressure in a water system.








With the two hoses from the example above how can we make the smaller hose move the water wheel faster? With more pressure of course. So, with more pressure the smaller hose can make the water wheel turn faster. How does this relate to voltage?

Example

Look at the distribution lines above your head next time you are out and about. The wires on these lines carry thousands of volts. However, they are not very big. Remember Ohm’s Law? Let’s say you have a 2,500 watt motor. This is a multi-voltage motor. Meaning that you can wire it a couple of different ways depending on the voltage available. You need to run new wires to this motor, but what size do you need? That depends on the voltage.

Wait, I know what you are saying. Wire is sized by the number of amps. You are correct. However, depending on the voltage we may be able to run a smaller wire therefore possibly saving money. If the voltage in this case is 120 then the amperage will be 2,500/120 = 20.8 amps requiring a 10 gauge wire. If the voltage is 240 then the amperage will be 2,500/240 = 10.4 amps requiring a smaller 12 gauge wire.

Conclusion

Voltage and current are two different quantities that go hand in hand. Voltage is the driving force while current is the flow of electrons in the circuit.