Manual Introduction to Alternating Current and Transformers

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Interfacing with an Arduino 4. Voltage Sensing. Basic: How to build an arduino energy monitor 1.

Calibration Procedure 2. Emontx error sources 3. CT and AC power adaptor installation and calibration theory 4. How good is your multimeter 5. Pulse Counting. Timeseries storage history in emoncms Fixed interval timeseries Fixed interval with averaging Variable interval timeseries Write load investigation URL Embed.

Introduction to Alternating Current and Transformers

Emoncms Internals. Using the Arduino IDE. Other Software. Energy 3. Snowdonia Energy Study 4. Snowdonia Energy Study: Data 5. Building on the ZeroCarbonBritain energy model 6. Community scale scenarios 7. Renewable Heat 8. Zero Carbon Energy Model. Variable Supply 2. Variable supply and flat demand 3.

What is Alternating Current (AC)?

Variable supply, traditional electricity demand and oversupply 4. Mixed supply and flat demand 6. Electric Vehicles 7. Household electric only model 8.

Building Energy Modelling. Fabric heat loss 3. Ventilation heat loss 4. The voltage can also be stepped down again so it is safe for domestic supply. Three-phase electrical generation and transmission is common and is an efficient use of conductors as the current-rating of each conductor can be fully utilized in transporting power from generation through transmission and distribution to final use. Three-phase electricity is supplied only in industrial premises and many industrial electric motors are designed for it.

Three voltage waveforms are generated that are degrees out of phase with each other. At the load end of the circuit the return legs of the three phase circuits can be coupled together at a 'neutral point', where the three currents sum to zero if supplied to a balanced load.

This means that all the current can be carried using only three cables, rather than the six that would otherwise be needed. Three phase power is a type of polyphase system.

Induced EMF

In most situations only a single phase is needed to supply street lights or residential consumers. When distributing three-phase electric power, a fourth or neutral cable is run in the street distribution to provide one complete circuit to each house. Different houses in the street are placed on different phases of the supply so that the load is balanced , or spread evenly, across the three phases when consumers are connected.

Thus the supply cable to each house can consist of a live and neutral conductor with possibly an earthed armoured sheath. In North America, the most common technique is to use a transformer to convert one distribution phase to a center-tapped 'split-phase' V winding; the connection to the consumer is typically two volt power lines out of phase with each other, and a grounded 'neutral' wire, which also acts as the physical support wire. Although this method has certain advantages, there are obvious potential dangers associated with it.

The use of "split phase" power, two volt power lines out of phase with each other, as described above, allows high-powered appliances to be run on V, thus decreasing the amount of current required per phase, while allowing the rest of the residence to be wired for the safer V. For example, a clothes dryer may need W of power, which translates to a circuit rating of 30 A at V. If the dryer can instead be run on V, the service required is only 15 A. Granted, you would then need two 15 A circuit breakers, one for each side of the circuit, and you would need to provide two 'hot' lines, one neutral, and a ground in the distribution wiring, but that is offset by the lower cost of the wires for the lower current.

Houses are generally wired so that the two phases are loaded about equally; connecting the high-power appliances such as clothes dryers, kitchen ranges, and built-in space heaters across both phases helps to ensure that the loads will remain balanced across the two phases. For safety, a third wire is often connected between the individual electrical appliances in the house and the main electric switchboard or fusebox.

The third wire is known in Britain and most other English-speaking countries as the earth wire , whereas in North America it is the ground wire. At the main switchboard the earth wire is connected to the neutral wire and also connected to an earth stake or other convenient earthing point to Americans, the grounding point such as a water pipe. In the event of a fault, the earth wire can carry enough current to blow a fuse and isolate the faulty circuit.

The earth connection also means that the surrounding building is at the same voltage as the neutral point. The most common form of electrical shock occurs when a person accidentally forms a circuit between a live conductor and ground. As many parts of the neutral system are connected to the earth, balancing currents, known as earth currents , may flow between the distribution transformer and the consumer and other parts of the system, which are also earthed, this acts to keep the neutral voltage at a safe level.

This system of earthing the neutral points to balance the current flows for safety reasons is known as a multiple earth neutral system. Unfortunately in some cases this 'protection' can have a cascading effect, because the switching-off of one circuit can lead to an overload of adjacent circuits that may switch off later. The amount of time taken to restore generation and reestablish that balance depends on the type of generation thermal, hydroelectric. The design of the power generators has three sets of coils placed degrees apart rotating in a magnetic field. Standard frequencies of rotation are either 50 Hertz cycles per second in Europe or 60 Hertz in North America.

The voltage across any pair of these three conductors, or between a single conductor and ground in a grounded system is what is known as "single phase" electric power. Single phase power is what is commonly available to residential and light-commercial consumers in most distribution power grids.

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In North America, the single phase that is supplied is developed across a transformer coil at the utility pole for aerial drop or transformer pad for underground distribution. This single coil is center tapped and the tap is grounded. The voltage from either side of the coil to the center tap ground is volts whereas the voltage between the two conductors on either end of the coil develops the full voltage of volts. An inverter is a circuit for converting direct current to alternating current. An inverter can have one or two switched-mode power supplies SMPS. This is then fed through a transformer to smooth the square wave into a sine wave and to produce the required output voltage.

More efficient inverters use various methods to produce an approximate sine wave at the transformer input rather than relying on the transformer to smooth it. Capacitors can be used to smooth the flow of current into and out of the transformer. It is also possible to produce a more sinusoidal wave by having split-rail direct current inputs at two voltages, positive and negative inputs with a central ground. By connecting the transformer input terminals in a timed sequence between the positive rail and ground, the positive rail and the negative rail, the ground rail and the negative rail, then both to the ground rail, a 'stepped sinusoid' is generated at the transformer input and the current drain on the direct current supply is less variable.

This output is converted to DC at the same voltage, and then inverted again to a quasi sine wave output about V RMS. A disadvantage of the modified sine wave inverters is that the output voltage depends on the battery voltage. It is quite difficult to obtain a good sine wave from an inverter. Most home systems use conventional lead acid batteries for storage.

They are cheap, and are deep cycle batteries, i. You cannot use automobile batteries in inverters, as they are only used to provide a large starting current, and are not meant to be discharged completely. The lead acid batteries have the disadvantage that they have to be replenished with distilled water every few months, and if it dries out, it cannot be repaired. However, they can provide the large surge currents which are required by many loads such as induction motors which may be connected to the system.

Wikipedia has related information at DC to DC converter. A switched-mode power supply , or SMPS or switching regulator, is an electronic power supply circuit that attempts to produce a smoothed, constant-voltage, output from a varying input voltage. Switched-mode power supplies may be designed to convert from alternating current or direct current, or both.

Alternating Current (AC) Introduction

They generally output direct current, although an inverter is technically a switched-mode power supply. As the switch is opened and closed, the secondary produces a voltage like that in [link]. This is not really a practical alternative, and AC is in common use wherever it is necessary to increase or decrease voltages. Calculating Characteristics of a Step-Down Transformer A battery charger meant for a series connection of ten nickel-cadmium batteries total emf of It uses a step-down transformer with a loop primary and a V input.

You would expect the secondary to have a small number of loops.


Solving for and entering known values gives. The current input can be obtained by solving for and entering known values. The number of loops in the secondary is small, as expected for a step-down transformer. We also see that a small input current produces a larger output current in a step-down transformer. When transformers are used to operate large magnets, they sometimes have a small number of very heavy loops in the secondary. This allows the secondary to have low internal resistance and produce large currents.

In this case the primary and secondary power is W. Verify this for yourself as a consistency check. So the AC output of the secondary coil needs to be converted into DC. This is done using something called a rectifier, which uses devices called diodes that allow only a one-way flow of current. Transformers have many applications in electrical safety systems, which are discussed in Electrical Safety: Systems and Devices. Generate electricity with a bar magnet! Discover the physics behind the phenomena by exploring magnets and how you can use them to make a bulb light.

Section Summary Transformers use induction to transform voltages from one value to another.