1. Define and/or discuss the following:
a. Farmstead a farm or the part of a farm comprising its main buildings together with adjacent grounds.
b. Electric load a device which takes electrical energy is known as the electric load. In other words, the electrical load is a device that consumes electrical energy in the form of the current and transforms it into other forms like heat, light, work, etc. The electrical load may be resistive, inductive, capacitive or some combination between them. The term load is used in the number of ways.
a) To indicates a device or a collection of the equipment which use electrical energy.
b) For showing the power requires from a given supply circuit.
c) The electrical load indicates the current or power passing through the line or machine.
c. Total Connected load (TCL) is the mechanical and electrical load (in kW) that will be connected (or to consumed) for that particular area.
d. Total demand or actual load is the sum of the operational load (including any tactical load) and nonoperational demand loads. It is determined by applying the proper demand factor to each of the connected loads and a diversity factor to the sum.
e. Distribution and Electrical Load Center are used to include on-site electricity generators and or storage in a simulation. The electric load center dispatches both generators and storage according to operation schemes and tracks and reports the amount of electricity generated and purchased. When using on-site generators, the program provides various reports for the electricity used, generated on site, stored, exported etc. There are two separate operation schemes, one for generators and a second for storage, and they can be different
f. Feeder lines is a peripheral route or branch in a network, which connects smaller or more remote nodes with a route or branch carrying heavier traffic. The term is applicable to any system based on a hierarchical network. In telecommunications, a feeder line branches from a main line or trunk line.
g. Voltage Drop is the decrease of electrical potential along the path of a current flowing in an electrical circuit. Voltage drops in the internal resistance of the source, across conductors, across contacts, and across connectors are undesirable because some of the energy supplied is dissipated.
2. What are the types of Distribution Centers? Illustrate.
There are three basic types of distribution system designs: Radial, Loop, or Network.
The Radial distribution system is the cheapest to build, and is widely used in sparsely populated areas. A radial system has only one power source for a group of customers. A power failure, short-circuit, or a downed power line would interrupt power in the entire line which must be fixed before power can be restored.
A loop system, as the name implies, loops through the service area and returns to the original point. The loop is usually tied into an alternate power source. By placing switches in strategic locations, the utility can supply power to the customer from either direction.
Network systems are the most complicated and are interlocking loop systems. A given customer can be supplied from two, three, four, or more different power supplies. Obviously, the big advantage of such a system is added reliability. However, it is also the most expensive. For this reason it is usually used only in congested, high load density municipal or downtown areas.
Central Metering and Distribution
· the most common type of distribution system on a farmstead has a centrally located distribution center
· generally, the power supplier’s meter will be located at this central or main service entrance location
· a service drop or feeder will run from this central point to each building or service area
3. What are the steps in locating the electrical load center? Provide an example.
A panelboard (also sometimes referred to as a load center) is an enclosure which contains overcurrent devices such as fuses or circuit breakers.
In a commercial building it is typical for space to be dedicated for electrical panels and equipment. Often a commercial building will have a main electrical service room and smaller electrical rooms on other floors.
The National Electrical Code requires “clear space”, referred to as working space around the panelboard to ensure easy access to the overcurrent devices and to provide adequate space for maintenance and inspection. Working space will vary as a function of the voltage of the electrical equipment and the surrounding equipment and walls as shown in the graphic below.
Dedicated working space must be provided in front of and above the panelboard. The width of the working space in front of the equipment must be at least 30” or the width of the equipment, whichever is greater. The working space also extends vertically from the floor or grade to a height of at least 6-1/2’ or the height of the equipment, whichever is greater. These requirements are found in article 110.26 and table 110.26(A) (1) of the National Electrical Code.
Local codes may also dictate acceptable working space dimensions. For example, the City of Austin requires that the working space extend vertically from the floor to the structure, which is beyond the 6 -1/2’ requirement of the NEC
In residential installations it is not typical for a space to be dedicated for the installation of an electrical panel. Panelboards are thus often installed in garages or basements in single family homes. In apartments or condo’s, the panels are often installed in bedrooms or halls. Article 240.24 lists the places where overcurrent devices, and thus by extension, panelboards may not be located. The code specifies that panelboards may not be located near easily ignitable material (such as clothes closets), bathrooms, over steps, in plumbing walls, or in close proximity to sinks or plumbing fixtures. The code is also careful to specify panelboards shall be located in a readily accessible location, meaning the top of the highest circuit breaker can’t be above 6’ 7” AFF or from working platform. Local codes also have limitations on panelboard locations.
Panelboards may be installed indoors or outdoors. Panelboards must be installed using the appropriate NEMA rating for the environment in which they are used. Panelboards installed indoors typically have NEMA 1 rating while panel boards installed outdoors typically have a NEMA 3R rating.
4. What are the factors in determining the resistance in the feeder lines? Show an example.
a) The length and the cross sectional area of the conductors.
Ex. length – the longer the wire, the greater its resistance. Cross-sectional area – the greater the area, the less its resistance.
b) The material the conductors made from, which means conductivity property.
Ex. The type material the conductors made from affects materials. Wires made from silver, copper, gold and aluminum have low resistance.
c) The temperature that the feeder line will operate at, conductivity changes when the temperature changes.
Ex. Heating a metal conductor makes it more difficult for electricity to flow through it. These collisions cause resistance and generate heat. Heating the metal conductor causes atoms to vibrate more, which in turn makes it more difficult for the electrons to flow, increasing resistance.
d) The frequency that your feeder lines will operate at, this because of the skin effect. Skin effect will increase the resistance and it’s increased when frequency increased (In AC lines only).
Ex. Skin effect reduces the effective cross-section area used by the current, and thus, the effective resistance increases.
e) The stranding of the conductors will increase the length of the wire and this will increase the resistance.
Ex. A stranded wire will have higher resistance than a solid wire of the same diameter because the cross-section of the stranded wire is not all copper; there are unavoidable gaps between the strands (this is the circle packing problem for circles within a circle).
f) The proximity effect will increase the resistance, and this depends on how much the phases are close together (In AC lines only).
Ex. The proximity effect can significantly increase the AC resistance of adjacent conductors when compared to its resistance to a DC current. The effect increases with frequency. At higher frequencies, the AC resistance of a conductor can easily exceed ten times its DC resistance.
5. What is the effect of voltage drop in the electrical energy distribution in the farmstead?
Voltage drop across switchgear and feeder and branch circuit conductors can quickly reduce the output voltage of the power supply to an unacceptable limit. Although UL doesn't specifically require equipment manufacturers to specify an acceptable operating voltage range for a given piece of equipment, manufacturers typically recommend that the electrical circuit operate at no less than 90% of the equipment voltage rating. But why should you concern yourself with low-voltage situations? Because operating electrical equipment outside of its acceptable voltage rating can lead to premature equipment failure and hazardous situations.
Inductive loads like motors and ballasts can overheat, shortening equipment life and increasing energy consumption if they operate below their voltage rating. In addition, under voltage can cause sensitive electronic equipment like computers, PLCs, and copy machines to lock up or suddenly power down. This can result in lost data, increased production costs, and the increased probability of equipment failure due to excessive heat.