Fundamental Electricity Student Study Notescf.linnbenton.edu/eit/mec/greend/upload/Electrical... · Web viewword definition of ohm's law is: Current in a circuit is proportional to

Electrical Troubleshooting & Troubleshooting Motor ControlsStudent Study Notes

2011 - 2012

© Denis Green 1988, 1994, 1998, 2001, 2005, 2006, 2008, 2009, 2011. Students at Linn Benton Community College in Albany, Oregon are free to use this material for study purposes. Instructors at Linn Benton Community College in Albany, Oregon are free to use this material for instructional purposes for classes offered through Linn Benton Community College, excluding Internet and video courses. All other uses must be granted by Denis Green.

WARNING INSTRUCTOR OR LAB AIDE SUPERVISION IS ABSOLUTELY REQUIRED FOR ALL LAB ACTIVITES SINCE EVEN THE LOW VOLTAGES USED IN MOST OF THESE LABS CAN BE FATAL.

Electrical Safety

1. List at least 10 rules of electrical safety. Decide which two are the most important and why you think these two are so important. Make this list neat and clear since you and your instructor will be signing it.

2. How does low voltage kill?

3. What safety precautions will you take when you must work on live electrical circuits?

4. Why work one-handed near panel boxes?

5. What happens when a person becomes grounded?

6. What is the function of a ground circuit?

7. What happens when you become grounded?

8. What is the purpose of a ground fault circuit interrupter (CFCI)?

9. How does extremely low amperage kill a person?

10.What national code regulates electrical safety?

11.

Learning Activities:

1. Study Industrial Maintenance (IM), ELECTRICAL SAFETY p. 43 - 48.

1

Lockout/Tagout

1. What is the title and purpose of the law that governs lockout and tagout?

2. What must be posted near each complex machine?

3. List the steps for applying and removing a lockout.

4. What must happen at shift change?

5. How do lockout and tag out rules apply to outside workers coming into the facility?

6. State the rules regarding locks used for lockouts.

7. State the rules for tags used for tag outs.

8. List all the types of energy sources that must be locked out.

9. List the three groups of workers and describe their level of involvement with logout and tag out.

10. State the rules regarding inspections of lockout and tag out procedures.

11. How are group lockouts managed?


1. Industrial Maintenance (IM), LOCKOUTS AND TAGOUTS p. 48 - 49

2

Power Distribution

1. Briefly describe how electricity is distributed from the power generation plant to a

load in a commercial facility. (Fig. 4-12)

2. What is the function of a service entrance switchboard?

3. What is the function of a distribution switchboard?

4. What is the function of a circuit breaker panel?

5. How will you decide what type of electrical enclosure to use?

6. Describe the construction of a plug-in busway.

7. Where do feeder circuits run?

8. Where do branch circuits run?

9. What is the total voltage drop allowed for a circuit?

10.Sketch and label one cycle of a 1Ø sine wave. (Fig. 4-14)

11.What is RMS in relation to the sine wave?

12.Sketch and label one cycle of a 3Ø sine wave.(Fig. 4-15)

13.Sketch and describe the various types of DC voltage. (FIG4-16)

14.Sketch the voltage measurements between the wires of a 120 V circuit, a 208 V

1ø circuit, a 208 V 3ø circuit, and a 460 V 3ø circuit.

15.Sketch and describe a residential120/220 V 1Ø service

16.What is the purpose of a ground circuit? (Fig. 4-17)

LEARNING ACTIVITIES:

1. Sketch and describe the power distribution system of a space in a commercial facility.

2. IM POWER DISTRIBUTION p. 120 -1243. Pod cast and slide show

LAB: Test a 3 phase power supply

If a load like a 3ø motor is not working at all one of the tests you might choose is to verify that the correct voltage is available. This is called testing source voltage and it is a voltage rise. A 3ø power supply consists of three hot wires and a safety ground wire. Connecting the volt meter probes between any two of the three wires should produce a

3

reading of source voltage +/- 5% 208 voltage source: between line 1 and line 2 = 208, between line 1 and line 3 = 208, and between line 2 and line 3 = 208, between line 1 and ground = 120, between line 2 and ground = 120, between line 3 and ground = 120.

480 voltage source: between line 1 and line 2 = 480, between line 1 and line 3 = 480, and between line 2 and line 3 = 480, between line 1 and ground = 277, between line 2 and ground = 277, between line 3 and ground = 277.

The test might be conducted at a fused disconnect, at a receptacle plug-in, or at a 3ø circuit breaker.

LAB: Test a 1 phase power supply

Some motors high voltage single phase motors with two hot leads powering the motor. A high voltage 1ø power supply consists of two hot wires and a safety ground wire. Connecting the volt meter probes between any of the two wires should produce a reading of source voltage +/- 5% 208 voltage source: between line 1 and line 2 = 208, between line, between line 1 and ground = 120, between line 2 and ground = 120.

The test might be conducted at a fused disconnect, at a receptacle plug-in, or at a high voltage 1ø circuit breaker.

Electric Circuits

1. What is the purpose of any electrical circuit?2. What happens to the electrons in the wire when a voltage source is applied to

the wire?3. Are electrons consumed like firewood or gasoline?4. What are the characteristics of a good insulator, a good conductor, and a semiconductor? Give an example of each type of material.5. What must every electric circuit contain?6. Sketch and describe an open circuit.7. Sketch and describe a closed circuit.8. Sketch and describe a short circuit.9. Why is a short circuit dangerous?10. What is a dead short?11. Sketch and describe a voltage drop and a voltage rise. IM p. 125 Fig 4-19

4

LAB: Sketch and describe how to locate an open circuit and test contacts using a voltmeter.

The circuit will be de-energized if there is a series open, for example a light switch that turns off all the lights.

If the switch you are testing with your voltmeter and switch is closed you should read nearly .000 volts. This means that no voltage is being used “dropped” across the contacts. You do not want contacts using voltage or they will heat up and eventually fail. Depending on the sensitivity of the meter you might actually see a very small reading, for example 136 mV instead of .000V. When you read the meter display make sure you read not just the numbers but the units that the numbers represent. The trick is to watch the meter readout since it will change as the contact change position. When switch is open you should read source or ghost voltage, more on ghost voltage later. Individual lengths of wire can be tested using voltage with the same good and bad results.

If a switch is open and you use a jumper wire to bridge the switch the equipment should start. Use extreme caution since the circuit will energize. If the circuit energizes properly then the component that is jumpered is defective. Be sure that you do not jumper around a load since this will cause a short circuit. Make sure the jumper is removed after the circuit is repaired. Use jumper wires of an odd colored wire so that you will notice it if it is left on the circuit.

LAB: Sketch and describe how to test contacts using an ohmmeter.

Always remove the component being tested from the circuit to get an accurate measurement and to avoid damaging your meter, or worse. Contacts will read nearly .000 ohms when closed, OL when open. Contacts that do not operate in this fashion are not operating correctly. The trick is to watch the meter readout since it will change as the contact change position. If the closed contacts offer higher than expected resistance they are dirty or worn and must be replaced, or they are not closing completely and need adjustment.

IM p.128, Fig. 4-35 p. [138].

LAB: Sketch and describe how to locate multiple opens in series.

If there are several opens in series a high quality digital meter will register ghost voltage when the probes bridge one of the opens. Ghost voltage is usually a low voltage that has no logical explanation in terms of circuit operation. It results from the increased sensitivity of digital meters which are probably measuring the capacitive energy across the opens.

5

The voltmeter will register near source voltage when the probes bridge all of the opens.

IM Open Circuits p.139-140 Fig 4-36, Testing Contacts p. 144 Fig. 4-40.

Check-off Method

As you troubleshoot circuits you will work from a wiring diagram or schematic. Use the check off method to ensure that each wire is installed correctly and securely. Working from the schematic find and trace each wire. When the wire is checked and verified to be correctly placed, place a check mark on that wire on the schematic to indicate that it is installed correctly. Work in a logical order and make sure to check each and every wire. This method can be applied to almost any electronics circuit and even hydraulic and pneumatic circuits. Make sure the circuit is deenergized when using the check off method since you are likely to come into contact with potentially live components, or you could pull loose a live wire that might cause a dangerous short circuit.LEARNING ACTIVITES:

1. Use the Check-off Method on all lab activities.2. Pod cast and slide show

LAB: Describe how you will find an operational short or a wiring problem.

This is an application for the check-off method. The circuit will be malfunctioning but the fuse or circuit breaker might not blow. For example, two lights might light when only one should light. Study the system prints and locate the part of the circuit that must contain the fault then use the check-off method to locate the problem. Look for crossed wires connecting two branches of a circuit, incorrectly installed wiring, or incorrectly numbered wires or swapped wires, 6 for 9 for example.

Series Circuits

1. Sketch and describe a series circuit.

2. What happens if there is a break in a series circuit?

3. Describe the rule of current flow in a series circuit.

4. Sketch and describe what we mean by the term "in series with".

5. Describe the rule of voltage drops in a series circuit.

6. Describe the rule of total resistance in a series circuit.

6

7. Why are fuses and circuit breakers connected in series with the components

being protected?

8. What can occur when loads are mistakenly wired up in series with other loads,

for example two lights?

9. What problem could occur if a high resistance like a loose connection was wired

in series with a load?


1. Lab exercises: wire series circuits and prove the rules of series circuits using a high quality DMM (digital multimeter). INSTRUCTOR or lab aide supervision required.

2. IM Series Circuits p. 114

Parallel Circuits

1. Sketch and describe a parallel circuit.2. What happens in a parallel circuit if an open happens in one of the current

paths?3. Sketch and describe what we mean by the term "in parallel with".4. Describe the rule for total current in a parallel circuit.5. What happens to current flow if you add more loads to a parallel circuit?6. Describe the rule of total voltage drops across each branch load in a parallel

circuit.7. Describe the rule for total resistance in a parallel circuit.8. Describe the rule for current in any branch of a parallel circuit.9. What happens if you have a short circuit in a parallel circuit?


1. Study IM Parallel Circuits P. 105 [115].2. Wire up parallel circuits and prove the rules of parallel circuits using a high

quality DMM.

LAB: Sketch and describe how to locate a dead short circuit.

In a circuit with a dead short the circuit breaker or fuse will be open. If you reset the circuit breaker or replace the fuse it will blow open as soon as the circuit is re-

7

energized. This occurs because total resistance for the circuit is very near zero ohms. This allows extremely high amperage that trips the breaker or blows the fuse.

If you find a tripped circuit breaker or open fuse and you suspect a short circuit, look for signs of overheating, burn marks etc. This is the obvious location of the short. The overheating is caused by high amp flow. Look for frayed wires or wires touching each other or metal.

If you need to use a meter to find the general location of the short completely isolate the circuit from any electrical source. Connect the ohmmeter to the circuit to read total resistance. If there is a dead short it total resistance should read near .000 ohms. Make sure that all switches are closed manually or with jumper wires when taking this measurement so that you are reading total circuit resistance

With the meter connected to read total resistance, isolate one branch of the whole circuit. If the resistance does not change from near .000 when you isolate a branch that branch does not contain the short circuit. If the resistance does not change then that branch is good. Reconnect the branch then move on to test the next branch.

When the resistance reading jumps for near .000 to some resistance after you isolate a branch, that branch contains the short circuit. Inspect that branch for signs of overheating to locate the short circuit. That should be the exact location of the short.

IM Short Circuit p.140 Fig. 4-37 141

LAB: Sketch and describe how to locate a high resistance short to ground.

A high resistance short to ground might not blow the fuse but it will likely create localized heating at the sight of the short. It will act like an additional parallel load.

It is caused when a current carrying conductor touches grounded metal through a section of high resistance causing current to flow in the ground circuit. It is very dangerous because you could touch grounded metal and being an easier electric path to ground current could flow through your body.

Look for signs of heating, cracked wire, or a build-up of dirt or debris around a wire. If the circuit has a ground fault interrupter (GFI) the GFI should open, de-energizing that part of the circuit.

If you see nothing obvious, attach an ammeter to the grounded metal or the ground circuit. Note the amount of current flow in the ground circuit; a good ground circuit

8

should have nearly .000 Amp flow. Starting at the far end of the circuit disconnect one parallel branch at a time. If the current flow does not drop, reconnect the circuit and move on to the next circuit. When the amperage reading takes a sudden drop after a branch is removed the branch just removed contains the high resistance short to ground. Inspect that section for the exact location of the short.

Series/Parallel (Compound) Circuits

1. Sketch a series/parallel (compound) circuit.

2. What is the voltage available at a parallel section of the circuit?

3. What happens when a load is placed in series with a parallel circuit? What

problem does this cause? How would you troubleshoot this problem?


IM Series/Parallel Circuits p. 116Wire up series/parallel circuits and determine the effects of a load placed in series with parallel circuits.

Lab: Sketch and describe how you will find the cause of low voltage at a load

Develop DG

IM p. 142, p. 143 4-39

Digital Multimeters

1. Sketch how to measure a voltage rise and a voltage drop. (IM p. 125, Fig 4-19)

2. How is a voltmeter connected into a circuit?

3. Why is a voltmeter a high resistance instrument?

4. Sketch how to use a clamp-on ammeter. (IM p. 126, Fig. 4-20)

5. How does a clamp-on ammeter measure amperage?

6. Sketch how to take an in-line ammeter measurement.

7. What does an ohmmeter measure? How does one work?

8. Why do you never use an ohmmeter on a live circuit?

9

9. What are the values of the following symbols: K = kilo = , M = mega =

m = mille = ?

10.How can a meter load applied to an electronic circuit and cause a faulty reading

or damage the electronic circuit?

11.What are the uses of a bar graph on a DMM?

12.How are ghost voltages produced? What is a practical application of using ghost

voltages when troubleshooting circuits?


1. Study IM ELECTRICAL TEST EQUIPMENT p. 99 -106 & Prefixes & Conversion Table p. 372 & 374.

2. Locate the manual for the meter you are using and study the manual. All Fluke manuals are available on-line.

LAB: Sketch and describe how to test a heat element using an ohmmeter, voltmeter and ammeter.

Testing a heat element on volts is similar to testing a relay coil or an incandescent light bulb. The bulb actually contains a resistive element similar to a heating element. Place the probes off your volt meter across the connections to the heat element. Before the heat element is energized it should read near zero volts. If it reads source voltage or ghost voltage the element is likely bad. When the heating element is energized it should read slightly less than source voltage. Holding the probes on the element connections while the element is energized should result a change in the meter reading from near zero to nearly source voltage if the element is good.

If the element appears to be bad, usually with an open, it is also possible to test it element using an ammeter. Before the element is energized it should draw zero amps. When the element is energized, check the amp draw by using a clamp-on ammeter on each individual wire feeding the element. The element is good if the current is at the manufacturer’s specifications or compared to a known good circuit. If there is no current flow, check the element using an ohm meter since there is likely and open in the element.

To test the element on resistance, completely disconnect the wires leading to the element and ensure that power to the electrical equipment is de energized. Place the probes of the ohmmeter on the two connection points for the elements. A good element will read some resistance (compare to manufacturer specification or a known good element). A bad element will read OL (infinite resistance) since there is an open in the element.

10

IM Testing HEAT ELEMENT p.147 – 148 Fig. 4-44

Ohm's Law

1. Define the term “one amp”.

2. Define amperage.

3. Amps are represented by the two letters ____.

4. What is the electromotive force (voltage)?

5. Define resistance.

6. Ohm is represented by the Greek letter ______.

7. How do you determine wattage (power)? How would you use this formula? IM

Figure 4-4 p .

8. The

9. word definition of ohm's law is: Current in a circuit is proportional to voltage and

inversely proportional to resistance. Proportional means as one goes up or down

the other goes up or down (as E rises so does I if R remains constant). Inversely

proportional means as one goes up the other goes down, or as one goes down

the other goes up (as R goes down I goes up as long as E remains constant).

Amperage is controlled by resistance and voltage.

10.What happens to its resistance when an electrical device or conductor is

heated?

11.Why do we need a potential difference between electrical conductors to make

current flow?


1. Prove Ohm's law on simple circuits.2. Study IM Ohm’s Law p. 112, Fig 4-3.Battery Operation

1. How does a battery work? 2. Which terminal is larger, the negative or the positive?

11

3. Red is positive, black is negative.4. If you receive an acid burn wash the wound and get immediate first aid.5. Charge a battery at low rates to prolong battery life.6. How does a battery short out?7. What basic maintenance will a battery require?

Battery Voltage vdc State of Charge12.7-12.9 100%12.5-12.6 80%12.3-12.4 60%12.1-12.2 40%11.9-12.0 20%

Resistors

1. Why is resistance added to circuits?2. In what two values are resistors rated?3. What is a variable resistor?4.All carbon resistors marked with a rating or color coded:

The 1st band is

The 2nd band is

The 3rd band is

The 4th band is

5. 1000 ohms =

1 000 000 ohms =


1. Determine the values of various resistor color codes using a DMM.

Fuses

1. Sketch and describe the operation of a quick acting and a time delay fuse. Fuses may be quick blow or slow blow. Dual element fuses provide short circuit and overload protection.

12

2. What is the purpose of a fuse?3. How are electric motors protected?4. Sketch the ohmmeter test you will use to find a blown fuse.5. What ohmmeter reading will you get from a blown fuse?6. Sketch the voltmeter test to find a blown fuse.7. Why do you not put in a higher rated fuse if the lower rated fuse keeps blowing?8. What is the purpose of a fused disconnect?9. What is the purpose of a circuit breaker?10. How will you troubleshoot a circuit breaker? 11. What maintenance do circuit breakers or any seldom used switches require?


1. IM Over Current Protection Devices p. 136-138 Fig 4-34 & 4-35.

LAB: Test fuses and a circuit breaker using a voltmeter and an ohmmeter.

An individual fuse is tested using a volt meter using the same method as testing a switch or a set of contacts on a relay. The probes are placed across, one on each side of the fuse. If the fuse is receiving voltage a good fuse will register near zero volts, a bad fuse will register source voltage or ghost voltage.

I you think the fuse is bad (open), de energize the circuit and remove the fuse from its holder using a fuse puller only. Place the fuse on a non conductive surface like wood and place the probes of the ohmmeter on either side of the fuse. A good fuse will register a very small resistance; a bad fuse will register OL.

Fuses in a 3 phase fused disconnect are tested by placing one probe of the voltmeter on the line side (top) of one fuse, and the other on the load side (bottom) of the fuse next to it. The test proceeds as if you were testing a three phase power supply.

208 voltage source: between line side fuse 1 and load side fuse 2 = 208, between line side fuse 1 and load side fuse 3 = 208, and between line side fuse 2 and load side fuse 3 = 208.

480 voltage source: between line side fuse 1 and load side fuse 2 = 480, between line side fuse 1 and load side fuse 3 = 480, and between line side fuse 2 and load side fuse 3 = 480.

If you think one of the fuses is bad, remove it from the circuit and test it as described above.

13

A circuit breaker is tested by looking at the position of its operator (handle). An operator in the middle is tripped. Move it to the off position then into the on position. You should feel the resistance of the contacts moving into the open then closed position. If the operator will not stay in the on position there is likely a short circuit. If the contacts of the circuit breaker are bad they are tested using the same method as for testing a set of contacts.

Testing CB p. 136 Fig 4-35.

Ampacity

1. Define ampacity.2. What effect does wire diameter have on ampacity?3. What effect does the temperature of the wire have on ampacity?4. What effect does length of the wire have on ampacity?5. Describe the American wire gage AWG ratings.6. What is the common sense way to select the correct wire size?7. What % voltage drop is allowed for branch and feeder circuits? 8. What three key ratings will you consider when selecting an electrical wire?9. Why must you be concerned about the insulation quality of the wire? Where will

you look to determine the quality of the wire insulation?10. What is the NEC code ampacity for AWG 10, AWG 12, and AWG 14?


1. IM Wire Size p. 124.

Electromagnetism

1. Make a sketch illustrating the magnetic field produced around a single wire and around a coil.

2. Describe the operation of an electromagnet.3. Can lines of electric flux touch or cross?4. How do you insulate an object from magnetic flux lines?5. Unlike poles attract (north & south), like poles repel.6. Sketch and describe the basic operation of a solenoid.7. How do you troubleshoot a solenoid or any coil?8. Describe the basic operation of an alternator.


1. IM Solenoids p. 147.

14

LAB: Test a coil for a solenoid or a relay.

Testing a coil is similar to testing a heat element. Place the probes of your volt meter across the connections to the coil. Before the coil is energized it should read near zero volts. If it reads source voltage or ghost voltage the coil is likely bad. When the coil is energized it should read slightly less than source voltage. Holding the probes on the coil connections while the coil is being energized should result a change in the meter reading from near zero to nearly source voltage if the coil is good.

To test the coil on resistance, completely disconnect the wires leading to the coil and ensure that power to the electrical equipment is de energized. Place the probes of the ohmmeter on the two connection points for the coil. A good coil will read some resistance (compare to manufacturer specification or a known good coil). A bad coil will read OL (infinite resistance) since there is an open in the coil.

TESTING COILS Fig 4.41

Inductive Circuits

1. In a pure resistive circuit the voltage and current sine waves are in phase. Sketch an in-phase current and voltage sine wave.

2. Give two examples of pure resistive ac circuits.3. What device does any inductive circuit contain?4. Sketch and describe the process of electrical inductance in a coil and a single

wire.5.Define inductance and name its unit of measurement.6. What is inductive reactance?7. In a pure inductive circuit the voltage and current sine waves are out of phase by

90 electrical degrees. Sketch an out of phase-phase, inductive current and voltage sine wave.

8. What is impedance?9. Describe the electrical problem created by the CEMF produced by inductive

devices.10. How can poor power factor be corrected?11. What problems are caused by poor power factor?12. What might happen if a signal wire like a thermostat wire was run parallel to a

wire carrying a high current?

Transformers

Sketch and describe the basic operation of a transformer.

15

What is the difference between a step up transformer and a step down transformer?Transformers are almost 100% efficient so power in VxA = power out VxA. What controls amp flow in the primary?What is the purpose of a tapped transformer?All transformers hum. How can transformer hum be reduced?What happens if the installation of the transformer windings deteriorates?Describe basic transformer maintenance.How are transformers rated?How is a transformer derated?


1. IM Testing Source Voltage p. 134.

LAB: Testing a transformer

Develop

Capacitance

1. Define capacitive reactance.2. Describe the construction and operation of a capacitor in an

AC circuit.3. The unit of capacitance is a farad.

A micro farad uf =

A pico farad =

4. What happens when a capacitor shorts out?5. What can cause a capacitor to fail?6. In a pure capacitive circuit the voltage and current sine waves are out of phase.

Sketch an out of phase capacitive current and voltage sine wave. In a pure capacitive circuit, current leads voltage by 90 electrical degrees.

7. Total opposition to current flow in a capacitive circuit is called impudence and its unit of measurement is the ohm.

8. What will you do before working on any circuit containing a capacitor?How are run and start capacitors for motors identified?

LAB: Sketch and describe how to discharge and test a capacitor.

Develop

Relays

16

1. Sketch and describe the operation of a simple relay. Sketch how you can identify

the coil and the normally open and normally closed contacts using an ohmmeter.

2. What is a general purpose relay?

3. Describe the operation of a normally open and a normally closed contact.

4. How can you test a relay contact using a voltmeter or ohmmeter?

5. How can you test a relay coil using a voltmeter or ohmmeter?

6. Describe the construction and operation of a contactor and a magnetic motor

starter.

7. Where are knife blade switches still found?

8. Describe the construction and care of modern contacts.

9. Why should disconnects be operated occasionally.

10.Describe the maintenance for relay

11.Pole, break, and throw:

A pole is the number of separate circuits that can be opened or closed by a switch or relay. A single pole contact can carry current through only one circuit at a time. A double pole switch can carry two circuits at a time.

A break is the number of separate places on a contact that open or close an electrical circuit. A single break contact breaks and electrical circuit in one place. A double break (DB) contact breaks the electrical circuit in two places.

_A throw is the number of closed contact positions per pole. A single throw contact can control only one circuit. A double throw contact can control two circuits.

When ordering a relay ensure that it has the same pole, through, break, coil voltage, and contact voltage and amperage capacity as the relay being replaced.


1. IM Relays p. 136 [146]2. Wire and test various relays

17

LAB: Test a relay, coil and contacts.

LAB: Sketch and describe how you will test a coil using a voltmeter and an ohmmeter.

Resistance Remove the coil from the circuit and test it using the resistance function. A good coil will offer resistance (you probably will not know the exact resistance unless you check manufacturer's specifications or the resistance of a known good coil). A bad coil will read OL if open.Voltage When a good coil is energized it will give a voltage drop reading, close to voltage source. When a good coil is not energized it will read nearly .000 volts. If it reads voltage or ghost voltage the coil is bad.

IM Testing Coils p.145

TITLE: WYE Windings and DELTA Windings

1. Sketch and describe a wye winding, marking in the voltage readings you would expect to find for high and low voltages.

2. What is the other name for a wye winding?3. Why do we not need a neutral for three phase operation?4. Sketch and describe a delta winding marking in the voltage readings you would

expect to find for high and low voltages.


1. Study IM P. 154, Fig 4-51.

Three Phase Squirrel Cage Motors

1. Describe the operation and construction of a squirrel cage induction motor.2. What is the synchronous speed of a motor?3. Why is it best to hook up a motor to the highest voltage possible?4. Why does maximum amperage flow occur at motor start-up?5. What is single-phasing and what will it do to a motor?6. What causes a three phase motor to start? What specialized relays are used to start a three phase motor?7. Sketch and describe how to hookup and test a three phase refrigeration compressor.8. Sketch and describe how to hookup and test a three phase squirrel cage induction motor.

18

9. What can you learn from a motor data plate?10. How do you reverse the direction of a three phase motor?11. Describe the basic operation of a variable speed three phase motor drive.


1.2. IM Three-Phase Motors p.151, Variable Frequency Drives p. 155, Inverters p. 184 -185, Fig. 5-18.3. Connect a motor for high and low voltage.

LAB: Test single and dual voltage three phase motors.

Single voltage 3 phase motors will have 3 terminal connections, a good motor will have equal resistance between each of the three connections, and read OL to ground.

Three-phase IM p. 153 – 154 Fig. 4-51

Single Phase Motors

1. How is a single phase motor different from a three phase motor?2. Sketch and describe the construction and operation of a split phase motor.3. Sketch and describe the construction and operation of a capacitor start motor.4. Sketch and describe the construction and operation of a cap run and cap start

motor.5. How do you reverse the direction of a single phase motor?6. Sketch and describe how to hookup and test single phase refrigeration

compressors. 7. What is the purpose of a potential relay found on single phase compressors and

how does it work? 8. What is the purpose of a current relay single phase compressors and how does it work?9. What is the purpose of a positive temperature coefficient start device and how

does it work?


1. IM Single Phase Motors p. 144 [154].2. Test single phase motors for bad windings.

Electrical Motor Maintenance

19

1. List five basic items of electrical motor maintenance.

2. Describe the operation of a megometer.

3. What does a megometer measure in comparison to an ohmmeter when testing

motor windings?

4. Why must motor windings be discharged after being tested with a

megometer?

5. How can a megometer be used to test a refrigeration compressor?

6. What elements of power quality must be of concern in electrical

maintenance?

7. Within what % of rated voltage should you find the incoming power to the

motor?

8. Why must you try to find out why the motor fails in addition to replacing the

motor?

9. What factors will contribute to motor control failure?

10. What conditions can be monitored for any three phase electric motor?

11.How can you determine if the trouble is in the control circuit or in the power

circuit?

12. What are the first two tests for any motor starter that is not working?


1. IM PREVENTIVE MAINTENANCE p. 157.

POWER QUALITY

DEVELOP


1. IM POWER Quality p. 327 – 133..

LAB: Determine voltage and current unbalance.

20

IM p. 130 - 132

Motor Control: line and wiring diagrams

1. Line diagrams are also called ladder diagrams. Why?2. What is the purpose of a ladder diagram?3. How you read ladder diagrams? 4. Sketch a set of normally open (N.O.) contacts as shown in a line diagram.5. Sketch a set of normally open (N.O.) contacts as shown in a line diagram.6. Manual control requires someone to operate the circuit. Automatic controls a

device to operate the circuit.7. Ladder diagrams are drawn in the position before the signal that starts the

operation of the circuit has arrived at the circuit.8. Define a wire or common wire group as it applies to the check off method of wiring for line diagrams.9. List the steps in wiring controls using the check off method.10. List the four rules of line diagrams. Sketch a basic stop start line diagram and label

where each rule is applied to the diagram. Sketch a two-wire control.11. What do we mean by the signal, decision, and action sections of a rung on a line

diagram?12. Interpreting a line diagram simply means being able to completely understand the operation of a circuit. What energizes the circuit? What de-energizes the circuit? What does the circuit do? What happens to the circuit when the power goes off then comes back on?13. What do the numbers on the right side of the line diagram indicate?14. What is the purpose of a wiring diagram?15. Sketch and define AND, OR, NOT, NAND, and NOR logic.16. Describe the basic function and operation of a motor control center.


1. Study IM Diagrams and Drawings p. 116, Circuit Wiring p. 140.2. Class handout

Magnetic motor starter overload protection

1. What devices are used in magnetic motor starters to protect electric motors?2. What is locked rotor current?3. Why do motors have inrush current at start-up?4. How large can inrush current get?5. What type of fuses compensate for high inrush current?6. Describe the general operation of motor protection overloads.

21

7. What will you do before and after restarting tripped overloads?8. Why are trip indicators built into starters?9. Sketch and describe the basic operation of an overload current transformer.10. Describe the basic operation of an inherent motor protector.11. How will you select the type of enclosure needed for a specific location?12. What is the full load current rating (FLC, FLA)?13. What is the service factor of a motor? What does this mean?14. Describe the steps in connecting a motor and selecting the correct heaters. Sketch basic low and high voltage connections for a WYE connected motor.


1. IM Magnetic Motor Starter P. 153

Lab: Select the correct overload protection for a magnetic motor starter.

SOLENOID OPERATION

1. Describe the operation of a solenoid.2. What happens to current flow when a solenoid is first energized? Why does this

happen?3. What is the pick up voltage, the seal in voltage, and the drop out voltage for a

solenoid or any coil? 4. How will the solenoid be damaged if high voltage is applied to it?5. How will the solenoid be damaged if low voltage is applied to it?6. What produces excessive humming in a solenoid?7. What will happen to a solenoid when the armature is prevented from moving or

closing completely? Why?8. What care and maintenance will a solenoid require?9. Describe the process for troubleshooting a solenoid using a voltmeter and an

ohmmeter.


1. IM p. Solenoids p. 147

TIMERS

1. What is a timer?2. Describe the construction and operation of a motor driven timer also called a

synchronous timer.

22

4. What result will a one shot timer produce?5. What result will a recycling timer produce?6. What results will a multiple function, programmable timer produce?

ON DELAY TIMERS

1. Describe the general operation of an ON DELAY timer.2. Describe the operation of an ON DELAY, timed closed contact.3. Describe the operation of an ON DELAY, timed open contact.4. Give an example of where you might use an ON DELAY timer.

OFF DELAY TIMERS

1. Describe the operation of an OFF DELAY timer.2. Describe the operation of a normally closed timed closed contact.3. Describe the operation of a normally open timed open contact.4. Give an example of an OFF DELAY timer operation.


1. IM Timers P. 182

CONTROL DEVICES

1. Sketch and describe the operation of a mechanical limit switch. 2. Sketch and describe the operation of a pressure switch.3. Sketch and describe the operation of bimetal controls. 4. Sketch and describe the operation of a flow control switch.5. How does a simple float switch operate?6. How else can the liquid level be controlled?7. Sketch and describe how to troubleshoot a set of contacts with an ohmmeter,

voltmeter, and jumper wire. 8. Describe the operation of a bi-metal switch.9. Describe the operation of a thermocouple.10. Describe the operation of a thermistor.11. Describe the general operation of any transducer.

Various Motor Control Circuits

How do you reverse a one phase motor?

23

How do you reverse a three phase motor?Describe the basic construction of a reversing starter and explain why a reversing starter must be interlocked.Describe two types of interlocks.Frequent reversing is hard on a motor and will require a special motor, high service factor.Why must large motors be started with reduced voltage? (As voltage is reduced, current is reduced, and torque is reduced.)Describe primary resistance reduced voltage starting.Describe the general operation of “soft start” electronic motor drives.Describe the operation of a friction brake, plugging and electric braking.In what two ways can an ac motor's speed can be changed?How does a multi speed motor starter change the speed of a motor?How does a mechanical variable drive change motor speed?

MAKING LINE AND WIRING DIAGRAMS

1. How do you create wiring diagrams?

Draw all loads in their exact location. Draw in all control devices in their exact location. Trace all wires from each load to L1 and L2, including all input devices. All wires should have numbers and colors to match the actual wiring.

2. How do you create line diagrams from actual wiring?

Draw in each load. Using the check-off method trace each wire back from the load. Sketch in each input that operate each load. Move from the load back to L1. Make sure there is a complete pathway from the source to all control devices and

the loads.

3. You do you figure out how a circuit works?

Obtain the line diagram or schematics and manuals from the manufacturer. Use industry standard wiring and line diagrams.

Study the equipment operation when it is working normally. Make a written description of how the machine works. Study the wiring and line diagrams and written descriptions. Study the machine while doing maintenance.

4. How do you create line diagrams from word descriptions?

24

Write out a word description of machine operation. List and name all loads. List and name all inputs. Start line diagram by placing all loads on the right side. Sketch the inputs that will energize and de-energize each load. Line diagram interpretation should match the word description.

25

Documents

Fundamental Electricity Student Study Notescf.linnbenton.edu/eit/mec/greend/upload/Electrical... · Web viewword definition of ohm's law is: Current in a circuit is proportional to