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ElectricalDiagrams

Control and drive

Functional Diagrams

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AGENDA

GENERAL

SINGLE WIRE DIAGRAMS

FUNCTIONAL DIAGRAMS

Introduction

AC functional diagrams

Control and drive functional diagrams

Practical criteria to design diagrams

WIRING DIAGRAMS

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Auxiliary elements of drive and control These devices are employed to connect and disconnect the coils in

the breaking devices, the more utilised are pushbuttons and control switches.

The pushbuttons are found in the local controls of the automatic circuit breakers, disconnectors, etc., while the control switches are usually installed in the switchboards in the control centres of substations or generating stations.

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Pushbuttons The pushbuttons are devices that, when pressed, momentarily

change the position of its contacts. There are two types of pushbuttons: start buttons and stop buttons.

The start button for switches driving has its contact normally opened and is closed while pressing. It representation is as follows:

The stop button is precisely inverse to the former and its representation is:

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Control switches It is a control breaker which purpose is to remotely connect or trip a

device.

From this point of view is similar to the pushbutton; however, due to its large number of contacts and the options to change their situation in different moments, the control switch offers more possibilities that the pushbutton or set of pushbuttons.

The control switches can have two or more positions and in each position the situation of their contacts is different

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Control switches Table 1 shows a control switch with eight contacts for pushing and

two for turn. According to the needs of every installation, the number of used

contacts will change; the represented control switch is used in the circuit breakers bays in substations.

The mark in each square [X] means the contact is closed for that position. Hence, in the open position, the contact 21-021 is closed, and the rest of the contacts are in open position.

At this position, pushing will lead the contacts 1-01, 3-03, 5-05 and 7-07 to close position; they will return to their original open position when the push is released.

CONTACT POSITION 1

01 2

02 3

03 4

04 5

05 6

06 7

07 8

08 20 020

21 021

RECORD

X X X X X OPEN

X X X X X CLOSE

FUNCTION PUSH TURN

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Travel stop The travel stops are contacts mechanically operated, when a

mobile device reaches a limit previously fixed.

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Pressure relays, thermostats, level switches In many systems, the trip or connection of a pump, compressor,

transformer, automatic circuit breaker, etc., depend of a pressure, temperature or level; this leads to the utilisation of pressure relays, thermostats, and contacts of level.

A pressure relay is a mechanical device with one or more contacts, which position changes when the pressure reaches given values (maximum or minimum). These contacts are generally included in the circuits of starting or stopping pumps and compressors, or they are employed to energize an alarm, as in the case of overpressure automatic valves of a power transformer

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Pressure relays, thermostats, level switches The thermostat is a device

similar to the pressure relay, with the difference that it is the temperature instead of the pressure what changes the position of the contacts

The thermometers installed in the power transformers are devices with optical indicator of temperature and contacts, with characteristics alike to the thermostats.

ALARM TRIP

THERMOSTAT

LID

POWER TRANSFORMER

TANK

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Pressure relays, thermostats, level switches The contacts of level, as indicated by its name, are contacts which

position changes with the level of a deposit or tank.

In the electric diagrams that represent the contacts of all this instruments, there shall be a label that indicates their adjustments of operation.

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Arc extinguishers

Terminals

Terminals

Fixed and mobile contacts: “poles”

Contacts frame

Magnetic circuit

Base frame

Encapsulated coil

Electromagnetic switch It can be defined as a

current breaker which operations of closing and opening are performed in a no-manual fashion, by means of any mechanism capable of establish, stand and break currents in normal operation conditions of a circuit, even in overloaded conditions.

In an electromagnetic switch, the mobile parts leave their steady state when an electromagnet that operates the closing mechanism is electrically activated.

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Electromagnetic switch Closing the contact 1-1C of the control

switch, the coil B42 is energised and the electromagnetic switch is closed; its poles close in the power circuit and the receiver begins to operate.

If an overload takes place in the power circuit that activates the thermal relay (49), the auxiliary contact installed with the control circuit (49) will open and the coil B42 will be disconnected, and the poles of the switch open the power circuit.

The circuit remains inoperative until the thermal relay is reset.

Under normal load conditions, opening the contact 1-1C of the control switch to the stop position, will open the electromagnetic switch.

RECEIVER

POWER CIRCUIT CONTROL CIRCUIT

50.- Magnetic protection52.- AC circuit breaker42.- Switch49.- Thermal relayCS.- Control switchFU.- Fuse

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Automatic circuit breakers An automatic circuit breaker is a mechanical device of connection

capable to establish and break currents under normal conditions of supply; as well as to establish, withstand during a given time and break currents under abnormal conditions, such as short-circuit currents.

The breaking and connection of lines, power transformers, capacitors, etc., is performed by means of circuit breakers. These breakers are not usually manually driven, but activated by means of pushbuttons or control switches from remote locations. With this purpose, there are electric circuits that activate the mechanism placed in the circuit breaker drive.

POLES

DRIVE

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Automatic circuit breakers Fig. shows the closing circuit in the

conditions of open circuit breakers and tightened springs.

If the springs are unloaded, the contacts IF (57-54, 53-58) are closed and the contacts IF (55-56) and (56-1) are opened.

The motor is then fed, which begins to tighten the springs; the circuit breaker cannot be closed since the contacts 55-56 and 56-1 are opened. When the springs are tightened, the contacts 57-54 and 53-58 open and disconnect the motor, thus closing the contacts 55-56 and 56-1 and leaving the closing circuit ready for energising.

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Automatic circuit breakers If under the conditions of Fig., the contact of the

pushbutton PC is closed, the coil Be will be energised, closing the circuit breaker and unloading the springs, which closes the contact If (57-54), thus beginning to tighten the springs.

By closing the circuit breaker, the contact 1CS (2-50) is closed, thus the tripping mechanism is ready for opening as soon as is fed by means of control switch or protection signalling.

By opening the circuit breaker, the contact 1CS (55-59) of the closing mechanism is closed, thus the system is reset to its initial state, waiting for the voltage to fed the closing system.

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Low Voltage Magneto-thermal Circuit Breakers Currently, to protect the control circuits, the magneto-thermal circuit

breakers are commonly used, instead of fuses, obsolete nowadays.

These breakers are manually driven, with automatic disconnection by overload or short-circuit, and they usually include auxiliary contacts to energise alarms. Their representation is:

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Relays The relay is an electromechanical device that, according to the variation

of a physical magnitude (electrical or not), operates another device (electrical or not).

The contacts of the relays inserted in the driving circuits activate the opening and closing of circuit breakers, switches, etc.

The operation of the contacts of a relay can take place in three means: Instantaneous Action: The relays of instantaneous action have not

delaying devices, thus operating in the same instant in which the controlled physical measure (current, voltage, etc.) surpasses the previously adjusted value.

Inverse Delay: They have not a fixed delay, but it varies with the value of the controlled physical measure and it is inversely proportional to the value of the controlled measure.

Fixed delay: The temporisation is always the same.

The relays can be divided in two groups, as following: Auxiliary Relays

Protection Relays

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Auxiliary Relays These are the relays that combined with switches, circuit breakers, etc.,

aid establishing control circuits more or less complex. They mainly comprise an electromagnet fed with alternate or direct current and a series of working or resting contacts.

The auxiliary relays are miniature switches of low power that have no power contacts (poles), since the small control devices consume low energy.

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Auxiliary Relays The auxiliary relays can be classified in:

Instantaneous: When the change of position of its contacts is instantaneous, either energising or disconnecting.

Delayed: When the change of position of its contacts has a controlled delay. These relays can be of two kinds: Delayed to energising: When the change of position of its contacts is

delayed for energising, and instantaneous to disconnecting.

Delayed to disconnecting: When the change of position of its contacts is delayed for disconnecting, and instantaneous to energising.

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Auxiliary Relays Tiltable relays. These are auxiliary relays with two coils, one for

operation and one for reposition. When the operation coil is energised, the position of its contacts changes;

however, the operation coil is immediately disconnected, but the contacts keep their position until the reposition coil is energised.

The tiltable relays have an operation similar to the automatic circuit breakers, since in both the first coil is used to close the contacts in the relay or the poles in the circuit breaker (closing coil), and the second coil is utilised to open the relay contacts or the circuit breaker poles (tripping coil).

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Protection Relays A protection relay is a device that operates over any element of its own

circuit or an auxiliary one, whenever there is a change of conditions in a power circuit, whether it is a current rise, voltage surge or rise, power inversion, accidental fault to ground, etc.

There are different kinds of protection relays; the more used are: Distance relay (21) operates when the admittance, impedance or resistance

of a circuit varies outside the inferior and superior fixed limits.

Synchronizing relay (25) impedes the connection of two circuits if the phase angle between them is superior to a given limit value.

Undervoltage relay (27) operates when the voltage reaches a given minimum value.

Field relay (40) operates when the field (excitation) is excessively low.

Thermal relay (49) operates when the temperature rises due to an overload.

Instantaneous overcurrent relay (50) operates instantaneously in the presence of overcurrents.

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Protection Relays There are different kinds of protection relays; the more used are:

AC time overcurrent relay (51) operates with a fixed delay in the presence of overcurrents.

Overvoltage relay (59) operates when the voltage rises over a given value.

Voltage balance relay (60) operates when there is a difference of voltage between two circuits.

Ground detector relay (64) operates when there is a failure to ground in the insulation.

Alarm relay (74) operates whenever it receives a signal and transmits it to an optical, acoustic or luminous display.

Frequency relay (81) operates when the frequency reaches a given value.

Lockout relay (86) operates electrically but requires manual reposition; it is generally used as an auxiliary

Differential protective relay (87) operates when there is a difference of currents between both sides of a machine due to an internal failure.

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Connection diagrams One of the applications of the tiltable relays, is as a lockout relay (86).

The rectangle in the bottom left part of the diagram encloses the two coils of the tiltable relay, called 86 according to its function. The coil b-a is energised by closing the contact CP (protections), the coil

changes the position of the contacts 86/CS, the 8-80 opens and the 7-71 closes.

If the circuit breaker is closed, the activation of the contact 86/CS (7-71) opens it.

CLOSING CIRCUIT

52 C

OPENING CIRCUIT

52 A

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Connection diagrams Under these conditions, if it is desired to close the circuit breaker, it is not

enough to energise the closing circuit 52C by closing the contact of the control switch CS/C, since the contact 8-80 is opened. To electrically close the circuit breaker, first it is necessary to energise the

coil d-c of the relay 86, by means of the reset pushbutton PR/86, hence changing the position of the contacts 86/CS, the 7-71 opens and the 8-80 closes.

CLOSING CIRCUIT

52 C

OPENING CIRCUIT

52 A