SCADA

What is SCADA

SCADA (Supervisory Control And Data Acquisition) system refers to the combination of telemetry and data acquisition. It consists of collecting information, transferring it back to a central site, carrying out necessary analysis and control, and then displaying this data on a number of operator screens.The SCADA system is used to monitor and control a plant or equipment. Control may be automatic or can be initiated by operator commands.

What is telemetry

Telemetry is usually associated with SCADA systems. It is a technique used in transmitting and receiving information or data over a medium. The information can be measurements, such as voltage, speed or flow. These data are transmitted to another location through a medium such as cable, telephone or radio. Information may come from multiple locations. A way of addressing these different sites is incorporated in the system.

What is data acquisition

Data acquisition refers to the method used to access and control information or data from the equipment being controlled and monitored. The data accessed are then forwarded onto a telemetry system ready for transfer to the different sites. They can be analog and digital information gathered by sensors, such as flowmeter, ammeter, etc. It can also be data to control equipment such as actuators, relays, valves, motors, etc.

What are the differences between SCADA and DCS

Similar to the SCADA systems are the Distributed Control Systems (DCS). The DCS is usually used in factories and located within a more confined area. It uses a high-speed communications medium, such as local area network (LAN). A significant amount of closed loop control is present on the systemThe SCADA system covers larger.geographical areas. It may rely on a variety of communication links such as radio and telephone. Closed loop control is not a high priority in this system.

Components of SCADA System

Components of a SCADA System A SCADA system are composed of the following:

1.  Field Instrumentation
2.  Remote Stations 
3.  Communications Network
4.  Central Monitoring Station

Field Instrumentation refers to the sensors and actuators that are directly interfaced to the plant or equipment. They generate the analog and digital signals that will be monitored by the Remote Station. Signals are also conditioned to make sure they are compatible with the inputs/outputs of the RTU or PLC at the Remote Station. The Remote Station is installed at the remote plant or equipment being monitored and controlled by the central host computer. This can be a Remote Terminal Unit (RTU) or a Programmable Logic Controller (PLC). The Communications Network is the medium for transferring information from one location to another. This can be via telephone line, radio or cable.
The Central Monitoring Station (CMS) refers to the location of the master or host computer. Several workstation may be configured on the CMS, if necessary. It uses a Man Machine Interface (MMI) program to monitor various types data needed for the operation. The following is a sample configuration of a SCADA system for water distribution.

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Why did Jesus Speak In Parables

It has been said that a parable is an earthly story with a heavenly meaning. The Lord Jesus frequently used parables as a means of illustrating profound, divine truths. Stories such as these are easily remembered, the characters bold, and the symbolism rich in meaning. Parables were a common form of teaching in Judaism. Before a certain point in His ministry, Jesus had employed many graphic analogies using common things that would be familiar to everyone (salt, bread, sheep, etc.) and their meaning was fairly clear in the context of His teaching. Parables required more explanation, and at one point in His ministry, Jesus began to teach using parables exclusively.

The question is why Jesus would let most people wonder about the meaning of His parables. The first instance of this is in His telling the parable of the seed and the soils. Before He interpreted this parable, He drew His disciples away from the crowd. They said to Him, "Why do You speak to them in parables?" Jesus answered them, "To you it has been granted to know the mysteries of the kingdom of heaven, but to them it has not been granted. For whoever has, to him more shall be given, and he will have an abundance; but whoever does not have, even what he has shall be taken away from him. Therefore I speak to them in parables; because while seeing they do not see, and while hearing they do not hear, nor do they understand. In their case the prophecy of Isaiah is being fulfilled, which says,

‘Hearing you will hear and shall not understand, And seeing you will see and not perceive; For the hearts of this people have grown dull. Their ears are hard of hearing, And their eyes they have closed, Lest they should see with their eyes and hear with their ears, Lest they should understand with their hearts and turn, So that I should heal them.’ But blessed are your eyes, because they see; and your ears, because they hear. For truly I say to you that many prophets and righteous men desired to see what you see, and did not see it, and to hear what you hear, and did not hear it" (Matthew 13:10-17).

From this point on in Jesus’ ministry, when He spoke in parables, He explained them only to His disciples. But those who had continually rejected His message were left in their spiritual blindness to wonder as to His meaning. He made a clear distinction between those who had been given “ears to hear” and those who persisted in unbelief—ever hearing, but never actually perceiving and “always learning but never able to acknowledge the truth” (2 Timothy 3:7). The disciples had been given the gift of spiritual discernment by which things of the spirit were made clear to them. Because they accepted truth from Jesus, they were given more and more truth. The same is true today of believers who have been given the gift of the Holy Spirit who guides us into all truth (John 16:13). He has opened our eyes to the light of truth and our ears to the sweet words of eternal life.

Our Lord Jesus understood that truth is not sweet music to all ears. Simply put, there are those who have neither interest nor regard in the deep things of God. So why, then, did He speak in parables? To those with a genuine hunger for God, the parable is both an effective and memorable vehicle for the conveyance of divine truths. Our Lord’s parables contain great volumes of truth in very few words—and His parables, rich in imagery, are not easily forgotten. So, then, the parable is a blessing to those with willing ears. But to those with dull hearts and ears that are slow to hear, the parable is also an instrument of both judgment and mercy.

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Parallel Operation of Transformers

There are several reasons for operating transformers in parallel. Some of these reasons are: 

• When the load of a transformer on a transmission line system exceeds the designed capacity of the transformer, one method to solve this problem is to replace it by a transformer of a larger capacity. but the cost of such changes will be greater than if the original transformer is paralleled with another to carry a portion of the load.

• When the amount of power transformed is greater than can be transformed by using a single transformer, it is necessary to use two or more transformers in parallel.

• Spare transformer units are required to ensure continuity of service in case of damage and hence it is desirable to supply the load through two or more transformers and thereby reduce the size of spare parts. This procedure may reduce the total installed capacity.

Parallel Operation At no Load:

Transformers connected in parallel.

The Transformer primaries are connected in parallel across the line of distribution system and the secondaries are paralleled too. The figure above shows the parallel connection of transformers. Primary voltages across the two transformers are equal since both of them are from the same source. Ea and Eb are the induced voltages across the two transformers at no load. If the turns ratio are not equal, then Ea is not equal to Eb.

Transformer A will supply a reactive load to the secondary of Transformer B and the primary of Transformer B will feed this load back to the primary circuit. This will cause a reduction in voltage at the secondary of Transformer A and a rise in voltage on the secondary of transformer B. The Terminal voltage on the secondaries after paralleling is common to both transformers and is the voltage V2

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