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A schematic diagram (often called schematic) shows all the components in a circuitand how each component is electrically connected, but not necessarily in theirproper physical locations. It also shows how the circuit is designed to operate. Fig.5.1-5 is the "power circuit" of a "motor control circuit", identifying the componentsin the circuits as follows:

The dotted line at the circuit breaker indicates that the 3 breaking mechanism areganged and they move together.. The symbols represent the power source, components and the devices of the

circuits.. The function numbers and abbreviations represent type of switch, relay or device.. The lines represent the conductors connecting the devices.Schematics are usually designed to be read from left to right and from top to bottom.They typically use standard electrical diagram symbols and device functionnumbers. The position of the contacts and switches are shown as they would be inthe de-energized state.The electrician should determine the following conditions from the catalog or fromthe notes on the drawing:. The initial conditions at which the diagram is drawn.

. The normal conditions at which the systemwill operate.. The stop/trip conditions.EXAMPLE 5.1-1In the single line diagram for electrical network in Fig. 5.1-6:. Unit 1 feeds bus bar A . Unit 2 feeds bus bar B. Unit 3 feeds bus bar C . Unit 4 feeds bus bar D. Bus Tie 1 disconnected. Bus Tie 2 disconnected

. Bus coupler 1 connected. Bus coupler 2 connecteda) What is the load of transformers Tl andT2?

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1. Motor 2. Circuit breakers 3. Starter contactors (Magnetic starter)4. Fuses 5. Overload protection 6. Magnetic protection (short circuits)

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b) What is the load of transformers Tl and T2 if Bus Tie 1 is connected?c) If Bus Tie 1 is connected and the feeder F6 disconnected, what is the load ofT 1and T2?d) If Bus Tie 1 is connected and the unit 1 is tripped, what is the load of TI and T2?

BUS BAR 230 KV

F140MW

230169 KV80 MVAMAX,60 MWF450MW

t:.B

U160MWU260MW U360 MW U460MW

NOTES:U -UNITF -FEEDERT -TRANSFORMER rtJ SWITCH POSITION INDICATOR FOR CIRCUIT BREAKERCl> SWITCI-IPOSITION INDICATOR FOR IsqLATOR

Fig. 5.1-6 Single Line Diagram for electrical NetworkSOLUTIONa) The electrical network is divided into two sections (left and right) because bus tie1 & 2 are disconnected.

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Left Section UI +U2=60+60= 120MWFI + F2 + F3 = 40 +50 + 50 = 140 MWThe generated MW from UI and U2 is not enough (20 MW lost)to feedthe feeders F 1,F2 and F3 /TransformerTI willreceive20MWfrom230kV networkto balancethenetwork.

Right Section U3 + U4 = 60 + 60 = 120MWF4 + F5 + F6 = 50 + 50+ 10= 110 MWThe generated MW from U3 and U4 is more than required (10 MWmore) for feeders F1,F2 and F3.Transformer T2 will send 10 MW from 69 kV network to 230 kVnetwork to balance the network.

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b) If Bus Tie 1 is connected, all the network connected together (no sections) and thetransformers TI and T2 will divide their loads together.UI + U2 + U3 +U4 = 60 + 60 + 60 + 60 = 240 MWFI + F2 + F3 + F4 + F5 + F6 = 40 +50 + 50 + 50 + 50 + 10 = 250 MWThe generated MW from UI, U2, U3 and U4 is not enough (10 MW lost) to feedthe feeders FI, F2, F3, F4, F5 and F6.So, Transformers TI& T2 will divide their load and receive 5 MW for each from230 kV network to balance the network.

c) If Bus Tie 1 is connected and the feeder F6 disconnected:UI + U2 + U3 +U4 = 60 + 60 + 60+ 60 = 240 MWFI + F2 + F3 + F4 + F5 = 40 +50 + 50 + 50 + 50 = 240 MWEach Transformer (TI and T2) will load zero MW.

d) If Bus Tie 1 is connected and the unit 1 is tripped:U2 + U3 +U4 = 60 + 60 + 60 = 180MWFI + F2 + F3 + F4 + F5 + F6 = 40 +50 + 50 + 50 + 50 +10 = 250 MWThe generated MW from U2, U3 and U4 is not enough (70 MW lost) to feed thefeeders FI, F2, F3, F4, F5 and F6.So, Transformers TI& T2 will divide their load and receive 35 MWfor each from230 kV network to make balance in the network.

SUMMARY. Block diagrams represent all electrical network equipment as blocks to show

power flow.. Single line or one line diagrams are shown by single lines and graphic symbols.. Schematic diagrams are the basic reference for control circuits and electricians

use them to understand the operation of control circuits.. Schematic diagrams are made of standard symbols, function numbers,

abbreviations and lines.

GLOSSARYUPS: Uninterruptible Power Supply LV: Low Voltage

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REVIEW EXERCISEI. The block diagrams with symbols facilitate troubleshooting be measuring input

and output signals.a) True b) False

2. The diagram may be used in a very general and abbreviatedmanner to illustrate broad systemideas or in a very detailed manner to illustrateall of the componentsin a particular part of the system.3. diagrams for a LV distribution cabinet shows the details of:

a) V0ltmeter and Ammeter connectionsb) Protection (fuses)c) Instrument Transformers (CTs)

diagrams are very useful to troubleshoot power control circuits..5. In the single line diagram for electrical network in Fig. 5.1-7:a) What is the load of transformers TI and T3?b) What is your action if transformer TI tripped (solution two)?c) What is the load of transformers TI and T3 if Bus Tie 1 is connected?d) If Bus Tie 1 is connected and the feeder F2 disconnected, what is the load ofTI and T3?e) If Bus Tie 1 is connected and unit 1 is tripped, what is the load ofTI and T3?

8US8AA 69 KV

1"15r4W F35MW

A cD

8USCOUPLER1 BUSCOUPlER 2

TS}O(8.9KV,380VU11MW U210MW

RI1MW F71MW Fa F91MW 1MW

Fig. 5.1-7

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