ESYS 57C Chapter 2 Electrical Drawings

inverter duty & vector duty motors

"Inverter duty" and "vector duty" describe a class of motors that are capable of operation from a variable-frequency drive. Low temperature rise in this class of motor is accomplished with better insulation systems, additional active material (iron and copper), and/or external fans for better cooling at low speed operation. Part of this particular design includes an independent cooling fan to cool down the motor so that it can operate within a wide speed range without any heating problem. page 33

numerical cross referencing

"Numerical cross-referencing" is used in conjunction with the rung numbering to locate auxiliary contacts controlled by coils in the control circuit. At times auxiliary contacts are not in close proximity on the ladder diagram to the coil controlling their operation. To locate these contacts, rung numbers are listed to the right of L2 in parentheses on the rung of the coil controlling their operation. page 20

wire identification method 1

"wire identification" is required to correctly connect the control circuit conductors to their components in the circuit. The method used for wire identification varies for each manufacturer. Figure 2-10 illustrates one method where each common point in the circuit is assigned a reference number: • Numbering starts with all wires that are connected to the L1 side of the power supply identified with the number 1. • Continuing at the top left of the diagram with rung 1, a new number is designated sequentially for each wire that crosses a component. • Wires that are electrically common are marked with the same numbers. • Once the first wire directly connected to L2 has been designated (in this case 5), all other wires directly connected to L2 will be marked with the same number. • The number of components in the first line of the ladder diagram determines the wire number for conductors directly connected to L2. page 21

block diagram

A block diagram represents the major functional parts of complex electrical/electronic systems by blocks rather than symbols. Individual components and wires are not shown. Instead, each block represents electrical circuits that perform specific functions in the system. The functions the circuits perform are written in each block. Arrows connecting the blocks indicate the general direction of current paths. page 25

compound DC motor

A compound DC motor (Figure 2-24) uses a combination of a shunt field (many turns of fine wire) in parallel with the armature, and series field (few turns of heavy wire) in series with the armature. page 27

conduit layout diagram

A conduit layout diagram indicates the start and the finish of the electrical conduits and shows the approximate path taken by any conduit in progressing from one point to another. Integrated with a drawing of this nature is the conduit and cable schedule, which tabulates each conduit as to number, size, function, and service and also includes the number and size of wires to be run in the conduit. page 23

load

A load is a circuit component that has resistance and consumes electric power supplied from L1 to L2. Control coils, solenoids, horns, and pilot lights are examples of loads. At least one load device must be included in each rung of the ladder diagram. Without a load device, the control devices would be switching an open circuit to a short circuit between L1 and L2. page 19

PLC

A programmable logic controller (PLC) is an industrial grade computer that is capable of being programmed to perform control functions. The programmable controller has eliminated much of the hardwiring associated with conventional relay control circuits. Other benefits include easy programming and installation, high control speed, network compatibility, troubleshooting and testing convenience, and high reliability. page 16

series DC motor

A series DC motor (Figure 2-23) uses a very low resistance series field winding, made up of very few turns of heavy wire, connected in series with the armature. page 27

shunt DC motor

A shunt DC motor (Figure 2-22) uses a comparatively high resistance shunt field winding, made up of many turns of fine wire, connected in parallel (shunt) with the armature. page 27

single line diagram

A single-line (also called a one-line) diagram uses symbols along with a single line to show all major components of an electric circuit. Some motor control equipment manufacturers use a single-line drawing, like the one shown in Figure 2-18, as a road map in the study of motor control installations. The installation is reduced to the simplest possible form, yet it still shows the essential requirements and equipment in the circuit. page 24

stator

A stationary loop of wires around the rotor in which electricity is produced. the stator, which contains the series field winding and the shunt field winding. page 27

wye and delta 3-phase motor connections

All three-phase motors are wired so that the phases are connected in either wye (Y) or delta (Δ) configuration.

contacts

Contacts from control devices such as switches, push buttons, and relays are considered to have no resistance in the closed state. Connection of contacts in parallel with a load also can result in a short circuit when the contact closes. The circuit current will take the path of least resistance through the closed contact, shorting out the energized load. page 19

dynamic braking for a DC motor

Dynamic braking for a DC motor is very effective, but the braking effect becomes weaker as the armature slows down. Dynamic braking (DC motor-generated energy is fed to a resistor grid) can be obtained with DC motors on applications requiring quick stops, thus eliminating the need for, or reducing the size of, a mechanical brake. page 27

interlocked

In Figure 2-12 the vertical broken lines on the forward and reverse push buttons indicate that their normally closed and normally open contacts are mechanically connected. Thus, pressing the button will open the one set of contacts and close the other. The broken line between the F and R coils indicates that the two are mechanically interlocked. Therefore, coils F and R cannot close contacts simultaneously because of the mechanical interlocking action of the device. page 21

capacitor start split phase motor

In a capacitor start , in which the capacitor phase is in the circuit only during starting. A capacitor in series with one of the stator windings to optimize the phase difference between the start and run windings for starting. The result is a higher starting torque than a split-phase motor can produce. page 29

DC motors

Industrial applications use DC motors because the speed- torque relationship can be easily varied. DC motors feature a speed, which can be controlled smoothly down to zero, immediately followed by acceleration in the opposite direction. In emergency situations, DC motors can supply over five times rated torque without stalling. page 26

IEEE

Institute of Electrical and Electronics Engineers establishes the standards for motor testing and test methodologies. page 26

dual voltage motor connections

It is common practice to manufacture three-phase motors that can be connected to operate at different voltage levels. The most common multiple-voltage rating for three-phase motors is 208/230/460 V. Always check the motor specifications or nameplate for the proper voltage rating and wiring diagram for method of connection to the voltage source. page 30

NEMA

National Electrical Manufacturers Association prepares the standards for motor performance and classifications. page 26

tap

Open terminals (marked by an open circle) and arrows represent connections made by the user.

multispeed motor connections

Some three-phase motors, referred to as multispeed motors, are designed to provide two separate speed ranges. The speed of an induction motor depends on the number of poles built into the motor and the frequency of the electrical power supply. Changing the number of poles provides specific speeds that correspond to the number of poles selected. The more poles per phase, the slower the operating rpm of the motor. RPM = 120 × Frequency / Number of poles Two-speed motors with single windings can be reconnected, using a controller, to obtain different speeds. The controller circuitry serves to change the connections of the stator windings. These motors are wound for one speed but when the winding is reconnected, the number of magnetic poles within the stator is doubled and the motor speed is reduced to one-half the original speed. This type of reconnection should not be confused with the reconnection of dual-voltage three-phase motors. In the case of multispeed motors, the reconnection results in a motor with a different number of magnetic poles. page 31

split phase motor

The "split-phase motor" is most widely used for medium starting applications ( Figure 2-26). The operation of the split-motor is summarized as follows: • The motor has a start and main, or run, winding which are both energized when the motor is started. The starting winding produces a phase difference to start the motor and is switched out by a centrifugal switch as running speed is approached. When the motor reaches about 75 percent of its rated full load speed, the starting winding is disconnected from the circuit. • Split-phase motor sizes range up to about ½ horsepower. Popular applications include fans, blowers, home appliances such as washers and dryers, and tools such as small saws or drill presses where the load is applied after the motor has obtained its operating speed. • The motor can be reversed by reversing the leads to the starting winding or main winding, but not to both. Generally the industry standard is to reverse the start winding leads. page 29

AC induction motor

The AC induction motor is the dominant motor technology in use today, representing more than 90 percent of installed motor capacity. Induction motors are available in single-phase (1ϕ) and three-phase (3ϕ) configurations, in sizes ranging from fractions of a horsepower to tens of thousands of horsepower. They may run at fixed speeds— most commonly 900, 1200, 1800, or 3600 rpm—or be equipped with an adjustable-speed drive. page 28

rungs

The horizontal lines (called rungs) are connected across L1 and L2 and contain the control circuitry. Ladder diagrams are designed to be read like a book, starting at the top left and reading from left to right and top to bottom. page 2

squirrel cage

The name given to the rotating part of an induction motor. Is named because of the aluminum or copper squirrel cage imbedded within the iron laminates of the rotor. There is no physical electrical connection to the squirrel cage. Current in the rotor is induced by the rotating magnetic field of the stator. page 28

Combo ladder & wiring diagram

Wiring diagrams are often used in conjunction with ladder diagrams to simplify understanding of the control process. An example of this is illustrated in Figure 2-17. The wiring diagram shows both the power and control circuits. A separate ladder diagram of the control circuit is included to give a clearer understanding of its operation. By following the ladder diagram it can be seen that the pilot light is wired so that it will be on whenever the starter is energized. The power circuit has been omitted for clarity, since it can be traced readily on the wiring diagram (heavy lines). page 24

wiring diagrams

Wiring diagrams are used to show the point-to-point wiring between components of an electric system and sometimes their physical relation to each other. They may include wire identification numbers assigned to conductors in the ladder diagram and/or color coding. Coils, contacts, motors, and the like are shown in the actual position that would be found on an installation. These diagrams are helpful in wiring up systems, because connections can be made exactly as they are shown on the diagram. A wiring diagram gives the necessary information for actually wiring up a device or group of devices or for physically tracing wires in troubleshooting. However, it is difficult to determine circuit operation from this type of drawing. page 23

wound rotor AC induction motor

Wound-rotor models, in which coils of wire turn the rotor windings, are also available. These are expensive but offer greater control of the motor's performance characteristics, so they are most often used for special torque and acceleration applications and for adjustable-speed applications. page 29

Variable Frequency Drive (VFD)

a device that changes AC frequency (and sometimes voltage) to vary the speed of AC motors. Variable-frequency drive controls the speed of an AC motor by varying the frequency supplied to the motor. The drive also regulates the output voltage in proportion to the output frequency to provide a relatively constant ratio (volts per hertz;V/Hz) of voltage to frequency, as required by the characteristics of the AC motor to produce adequate torque. The function of each block is summarized as follows: • 60-Hz three-phase power is supplied to the rectifier block. • The rectifier block is a circuit that converts or rectifies its three-phase AC voltage into a DC voltage. • The inverter block is a circuit that inverts, or converts, its DC input voltage back into an AC voltage. The inverter is made up of electronic switches, which switch the DC voltage on and off to produce a controllable AC power output at the desired frequency and voltage. page 25

dual voltage split phase motor

a dual-voltage split-phase motor (Figure 2-27), the running winding is split into two sections and can be connected to operate from a 120-Volt or 240-V source. The two run windings are connected in series when operated from a 240-V source, and in parallel for 120-V operation. The start winding is connected across the supply lines for low voltage and at one line to the midpoint of the run windings for high voltage. This ensures that all windings receive the 120 V they are designed to operate at. With any type of dual-voltage motor, the higher voltage is preferred when a choice between voltages is available. The motor uses the same amount of power and produces the same amount of horsepower when operating from a 120-V or 240-V supply. However, as the voltage is doubled from 120 V to 240 V, the current is cut in half. Operating the motor at this reduced current level allows you to use smaller circuit conductors and reduces line power losses. page 29

wire identification method 2

an alternative method of assigning wire numbers. With this method all wires directly connected to L1 are designated 1 while all those connected to L2 are designated 2. After all the wires with 1 and 2 are marked, the remaining numbers are assigned in a sequential order starting at the top left of the diagram. This method has as its advantage the fact that all wires directly connected to L2 are always designated as 2. Ladder diagrams may also contain a series of descriptions located to the right of L2, which are used to document the function of the circuit controlled by the output device. page 21

broken lines

indicate mechanical connections and are not part of an electrical circuit. page 21

rectifier block

is a circuit that converts or rectifies its three-phase AC voltage into a DC voltage.

inverter

is a circuit that inverts, or converts, its DC input voltage back into an AC voltage. The inverter is made up of electronic switches, which switch the DC voltage on and off to produce a controllable AC power output at the desired frequency and voltage.

motor control circuit

is a means of supplying power to and removing power from a motor. page 15

NEC

motors shall be installed in accordance with Article 430 of the National Electrical Code (NEC). page 26

permanent-split capacitor start split phase motor

permanent-split capacitor , in which the capacitor phases in the circuit for both starting and running. The permanent-split capacitor motor, illustrated in Figure 2-28, uses a capacitor permanently connected in series with one of the stator windings. This design is lower in cost than the capacitor-start motors that incorporate capacitor switching systems. Installations include compressors, pumps, machine tools, air conditioners, conveyors, blowers, fans, and other hard-to-start applications. page 29

phase reverse relay

phase reversal relays are used to protect motors, machines, and personnel from the hazards of open phase or reversed-phase conditions. page 32

regenerative braking

regenerative braking (DC motor-generated energy is fed back into the DC motor supply) can be obtained with DC motors on applications requiring quick stops, thus eliminating the need for, or reducing the size of, a mechanical brake. page 27

armature

the rotating portion of a motor. page 27

two-value capacitor start split phase motor

two-value capacitor , in which there are different values of capacitance for starting and running. page 29

rails

vertical lines used to connect power source and are identified as line 1 L1 and line 2 L2,