Generator Motor Maintenance (GMM)

1. Motor Maintenance

When detecting damage to the motor, it is important for a technician to follow the procedure, so that it will save time on repairs, checks, and replacement of spare parts. Damage to the motor is usually easy to find out through simple component checks. For that, a technician must understand the functions of each component so that he can analyze and repair the damage to the motor.

Motor damage analysis should begin with listening or visual inspection. First, check the motor for obvious damage, such as a broken bell, motor housing, shrunken or frozen rotor shaft holes, or burned wire windings. All of these problems can be quickly fixed by isolating the damaged part. Noisy motor or frozen rotor shaft holes are usually the main signs of bearing damage. Check the motor for bearing damage by turning the rotor shaft, then try to move the rotor shaft up and down. A rotor shaft that does not turn, feels like it is dragging, or has problems moving may indicate bearing damage.

The basic techniques used in checking electric motor damage include:

1. Test lamp
2. Current measurement,
3. Growler, and
4. Megohmeter.

1). Test-Lamp Testing

Before the technician tries to run the motor, he should first test the motor to check for circuit damage such as grounded circuits, short circuits, and open circuits. In the previous explanation, the grounding result from the winding makes electrical contact with all metal parts in the motor. Poor grounding results will insulate the wire connection between the stator and the warning bell. A motor that has a grounded winding may be caused by a fuse reaction, overheating, or lack of power. Shock can be caused by a grounded motor. Therefore, maintenance must be carried out frequently when checking the grounded motor.

Figure 4.32: Checking the Motor for Grounding with a test lamp

Figure 4.33: Test-lamp (open circuit test)

To check the motor for ground, connect a lamp test lead to one of the motor leads. Then, connect another test lamp (test lamp technique) to the stator or motor frame. The lamp lights up indicating that the motor is grounded. Figure 4.33 illustrates this checking procedure. An open circuit causes the motor to stop moving because the current flow is stopped. The motor will not run with an open circuit. Usually, if one of the three phases is open, the motor will not move. To determine if there is an open circuit in the motor, connect the test lamp lead to the motor lead wire. If the lamp does not light, it means there is an open circuit in the motor. However, if the lamp lights up, the circuit is properly closed. Figure 4.34 illustrates this procedure. A short circuit in the motor is caused by damage to the motor because two wires in the motor are connected and cause a short circuit. If the reading in amperage exceeds the ampere listed on the motor nameplate, the motor may be shorted. Still consider other factors such as low-line voltage, faulty bearings, or the motor being overloaded, which can cause the motor to draw excessive current.

The motor smokes because high temperatures cause a short circuit in the phase. A motor with a short circuit can experience an increase in temperature, the motor heats up, fails to start, or runs slowly. A growling sound is often present in small motors. If power is applied to a single-phase motor and the motor is groaning at that time, turn the shaft by hand. If the motor starts to turn, then the problem is in the starting circuit. If the motor moves erratically, moves slowly, then starts again, the problem is in the drive circuit.

2). Megohmmeter Testing

In addition to these methods, the best way to check a motor is with a mehgometer (figure 4.28). To check a grounded motor, connect one end of the mehgometer to the motor frame and the other end to one of the motor terminals. A grounded motor will read zero or around zero on the mehgometer pointer. To check for an open circuit, connect the mehgometer to each part of the motor phase. A motor that is open circuit will show a high number on the mehgometer. An ohmmeter can also be used to check for grounded and open circuit motors.

Figure 4.34: Ground Testing with a Megohmmeter

Figure 4.35: Open circuit testing with a Megohmmeter

Another way to check the field windings for shorts is to disassemble the motor and apply a small voltage to the stator winding. Each coil is now acting as an electromagnet. Place the handle of a screwdriver in each coil and slowly pull it out, noting the magnetic pull it produces. Each coil should have the same amount of magnetic pull. The coil with the lowest magnetic pull is probably shorted. If you touch each coil and find that one is hotter than the others, then the hottest coil is probably shorted.

Before disassembling the motor, mark the two end bells and the frame as a reference for the others. Usually, these two marks indicate the front of the motor, and the other indicates the rear of the motor. Marking the motor will make it easier for the technician to reassemble the parts of the motor. The front shaft should also be marked. This can be done by making an X mark on the end of the shaft. The body should also be marked as a reference for the front of the motor. Many technicians scratch a mark on the rotor shaft with a knife or small file, indicating the actual position of the rotor. This mark is usually placed on the front of the shaft closer to the back of the bell.

To check the grounding on the motor, we usually need to disassemble the motor and note the windings to place the part of the circuit that is connected to the metals on the motor. After placing and correcting the problem, clean the windings if they are dirty or charred. Clean the windings with solvent. Re-insulate the windings by spraying an epoxy coat or other airrying that insulates the enamel. If the epoxy coat is visible, it means the motor is damp. Dry with a warm oven or fan.

The causes of open circuits include defective switches or imperfect centrifugal switches, capacitor defects, or wire damage in the motor circuit. When placing an open circuit in a motor that has a capacitor, first check the capacitor. There are several ways to check the condition of the capacitor. First, by replacing the capacitor with a new capacitor that has the same rating. If the open circuit does not work, it means that the capacitor used is wrong. Another way to test a capacitor is with a spark test. Connect the capacitor across the terminals that are supplied with 115 V mains voltage for one second.

Figure 4.36: Short-circuit test for stator

After transferring the 115 V voltage, use the tip of a screwdriver to connect the two terminals on the capacitor. A good capacitor will show a spark. The absence of a spark indicates a defective capacitor.

A test lamp can be used to check the capacitor grounding. Connect one of the test lamp leads to one of the capacitor terminals. Connect the other test lamp to the capacitor metal case. If the lamp lights up, the capacitor is grounded and cannot be used. Other methods used to check capacitors include using an ohmmeter, a capacitor tester, and a combination of an ammeter and voltmeter. Centrifugal switches sometimes cause single-phase motors to open. The switch should be checked first to see if the contacts can close or not. If the contacts are open, a washer may need to be added to the rotor shaft. Also check the condition of the centrifugal switch, because it is possible that the centrifugal switch is damaged and needs to be replaced.

The motor windings should also be checked for damage. One or more broken wires can cause an open circuit. If the windings are burnt, or damaged and in need of repair, the windings on the motor should be replaced.

The connection in the stator winding can be checked with an internal growler. Place the growler on the stator lamination and the back of the coil. At that time the growler and coil function as a transformer. The growler, which has a built-in feeler tip, will vibrate strongly when placed on the problematic coil (figure 4.30). When there is an indication of this, immediately replace the stator winding. Damage to the armature coil is usually indicated by discoloration and insulation damage.

Figure 4.37: Short Circuit Test for Anchor

The motor armature can be checked for damage using an internal growler. Place the armature in the growler with the metal strip placed on top of the armature. Rotate the armature. If the metal strip vibrates rapidly, it indicates that the armature is damaged. Figure 4.31 illustrates the principle of using an internal growler and hacksaw blade.

Checking the ground on the anchor (armature) can be done with a test lamp. Connect one end of the test lamp on the commutator with the other end of the Motor that is experiencing damage to the anchor (armature) is weak, vibrating, humming, not working, or emitting fusion. on the anchor shaft (armature). If the lamp lights up, it means the anchor (armature) is grounded.

3). Anchor Winding Testing

Test to check whether the anchor winding is functioning properly, there is no break or short circuit with the anchor core, check Figure 4-32. The anchor shaft is placed on a stand that can rotate freely.

Flow DC electricity through the commutator, bring a compass close to the anchor, observe the compass needle will rotate towards the anchor. This proves the presence of an electromagnetic field in the anchor, meaning the anchor coil is functioning properly. But if the compass needle is still and does not react, it means there is no electromagnetism because the coil is broken or short-circuited to the anchor core.

Figure 4.38: Short Circuit Test on Anchor

2. Generator Maintenance

Generator maintenance and repair is almost the same as electric motor maintenance. The main problems with generators are fuses burning, regulators not working, low or high voltage output, unstable voltage (fluctuating).

The first procedure is to perform a visual inspection of the connectors and terminals for rust, or contamination with liquids, dust, etc.

Figure 4.39: Procedure for Measuring Core Losses

1). Short circuit testing

Can be done by turning off the power supply, measure the resistance of the suspected terminals. If the resistance value is zero, then a short circuit occurs, conversely if the resistance value is very large, then this means the connection is open.

2). Regulator Testing

If the regulator does not work. Make adjustments. If it still does not work, replace it with a new one. The problem that generally occurs is when the load is attached to the generator and the output voltage is too low or fluctuates, it will cause damage to the regulator. Assuming that the measuring instrument used is good, accurate and there are no broken connections, then the generator may need to be disassembled and its components tested.

Figure 4.40: Dismantling of Exciter (Excitation Amplifier) ​​with Crane and Rope

3). Procedure for dismantling and inspecting the generator

1. Turn off the power source
2. Mark and identify all cables and parts that are dismantled to make them easier to reassemble later.
3. Use appropriate winches and lashings
4. Remove all fasteners and all related parts or components to avoid further damage, especially for large and heavy generators.
5. Check the stator for loose, frayed, or burnt windings
6. Measure the resistance between the leads, match it with the factory data. For example, a value of 20 ohms may still be good. If the resistance value is zero, then there is a short circuit in the winding, and if the value is infinite then the winding is open.
7. Perform a grounding test between the frame and the coil using a megohmmeter.

Damage also often occurs in the generator diode. Therefore, also check the resistance on the diode. If damaged (burned / shorted / open) replace it with a new one.

Rotor Disassembly

To dismantle the rotor of a large and heavy generator, use a combination of a crane and a special dismantler, as shown in Figure 4.35. Remove the rotor carefully, without touching the related parts to prevent damage to the rotor or its windings. In general, damage occurs in the diode. Diode testing can be done by the resistance test method, using an ohmmeter. The diode resistance should read large from one direction of measurement, and read small in the opposite direction of measurement.

Figure 4.41: Dismantling of Excitation Amplifier Using Crane and Special Dismantler

4). Bearing Maintenance

Periodically check the condition of the bearing. If damaged, replace it with a new one. Use the appropriate bearing removal disc. Replace the lubricant inside the bearing with new lubricant. Fill the new lubricant through the cap hole. The filling should not exceed this cap hole.

Figure 4.42: Removing Bearings with a Puller and Heater.

3. Preventive Maintenance

Maintenance against dirt or dust

The life of electrical machines is determined by how they are maintained. Poor maintenance is indicated by the presence of thick dust, rust, or traces of liquids or other chemicals, and so on.

Preventive maintenance, such as periodic inspection, component recording and servicing, bearing replacement, motor cleaning, oil changes and so on will reduce repair costs and time. All of these maintenance activities should be recorded in a maintenance logbook or backlog.

Dust, rust or other contamination can cause the generator's air holes to become blocked, and this can cause the commutator to conduct. Water splashes can cause the windings to short out or the armature to ground, causing the motor to break down.

For repulsive motors, periodic maintenance of brushes and commutators is required. Check the tension of the brushes, then adjust the brushes and their holders.

Axle inspection

The rotor shaft should be checked periodically. Check the straightness of the shaft with a dial indicator. Clean all contacts and switches with fine sandpaper or contact cleaner.

Nut and bolt inspection

Check all bolts and nuts, tighten them if any are loose, if any are broken or cracked, then replace them with new ones. Also check all winding insulation. Repair if any are damaged.

Summary

• Electrical machines consist of static machines (transformers) and dynamic machines (motors and generators). In the discussion of this book, what is meant by an electric machine is a generator or motor.
• The construction of motors and generators is basically the same, namely consisting of a Stator (the part that does not move or is still) and a Rotor (the part that moves).
• The working principle of the motor follows Flamming's left hand law, namely if the magnetic field generated by the north-south pole of the magnet is cut by a conductor wire carrying a direct current with four fingers, then a motion force will arise in the direction of the thumb. This force is called the Lorentz force, which is the same as F [Newton]. While the generator basically works according to Flamming's right hand law, namely if a piece of conductor carrying a direct current with four fingers cuts the magnetic field generated by the north-south pole, then it will cause a motion in the direction of the thumb.
• Basically there are two types of generators, namely DC generators and AC generators. Likewise with motors, there are DC motors and AC motors.
• There are two types of DC motors, namely: separately excited motors, and self-excited motors. Self-excited motors include: series motors, shunt motors and compound motors which are a combination of series motors and shunt motors. While the generator is basically the same, but the one that is often used is the separate generator type.
• Characteristics of Separately Excited Motor: its excitation current is independent of the voltage source that supplies it. The armature rotation will decrease if the torque moment increases.
• Shunt Motor Characteristics: The excitation circuit of a shunt motor is parallel to the armature. The rotation will decrease with the increase in torque. At no-load conditions, the characteristics of a shunt motor are similar to those of a separately excited motor.
• Characteristics of Series Motor: The excitation circuit of a series motor is connected in series to the armature. Among other types of DC motors, series motors require the largest initial torque. It should be noted that series motors should not be operated under no-load conditions.
• Characteristics of Compound Motor. In a compound motor, the main pole contains series and parallel circuits. In no-load conditions, a compound motor has properties like a shunt motor. In conditions of applied load, with the same torque, a slightly higher rotation will be obtained.
• Maintenance of electrical machines is generally aimed at extending the life of the machine. This can be done through preventive maintenance. For large-scale industries, maintenance has been considered as a company investment, so that maintenance problems need to be planned and a special system created. Things that can be done in preventive maintenance include: cleaning the machine from dirt, dust, rust, and so on; checking cable connections or wire conductor coils, carbon brushes and other connections; checking insulation resistance; checking bearings, shafts, checking nuts and bolts, and so on.
• The basic techniques used in checking electric motor damage include: 1). Test lamp 2). Current measurement, 3). Growler, and 4). Megohmeter.

Exercises

1. What are the things included in electrical machines?
2. Mention how the Flamming left hand method sounds? And also mention the Flamming right hand method?
3. Explain the working principle of a motor! Also explain the working principle of a generator!
4. Describe the basic construction of an electric motor that you know. Is there any difference between the basic construction of a motor and a generator? If so, mention it!
5. Explain the characteristics of the following electrical machines: shunt motors, series motors and compound motors!
6. What is the use of a test lamp on a motorcycle? Explain the procedure for testing a motorcycle with a test lamp.
7. What is the use of megohm testing? What is the procedure for testing a motor with megohms?
8. Explain the procedure for testing the armature winding on a motor?

Group task

Create study groups consisting of 3-5 people per group. Each group looks for a case of damage to an electrical machine (for example, a transformer, fan, hair dryer, washing machine, etc.). Find the manual for the damaged equipment. Under the teacher's supervision, conduct testing and measurements, so that you know the cause of the damage to the machine.

Understanding Synchronous Motors

The construction of a synchronous motor is the same as an asynchronous motor. Inside the stator there is a rotating current coil to generate a rotating magnetic field. The rotor with pole core pieces contains an excitation coil through a direct current drag ring. This rotor will become an electromagnet (radial pole). The number of poles is the same as the number of turns of the stator pole.

Figure 4.31: Powering the Rotor

The advantage of a synchronous motor is that when rotated it becomes a synchronous generator. To start rotating, a synchronous motor requires the help of an initial rotation.

Understanding Three Phase Induction Motors

Induction motors are asynchronous motors. Asynchronous motors are the most important motors. The rotating field stator will induce the rotor with a voltage value. Through this voltage the rotor can rotate. The type of asynchronous motor is distinguished by its rotor construction.

Asynchronous motors are induction motors. The rotor current is obtained from the induction of the stator windings.

1. Motor Construction with Short-Connected Rotor

An induction motor generally consists of a stator and a rotor. The stator consists of a stator housing and stator windings. The stator construction is multi-layered and forms a groove for the wire windings. The ends of the coils are connected to the terminals to facilitate connection to the voltage source. Each stator winding has several poles. The number of poles will determine the speed of the motor. The rotor consists of a grooved cage and a layer of windings that are attached together. The rotor is made of aluminum or copper.

Figure 4.30: Rotor Rotating Current Section of a Short-Circuited Motor

2. Working Principle

The working principle of an induction motor or the occurrence of rotation in a motor can be explained as follows:

If the stator coil is supplied with three-phase voltage, a rotating field will be created at a speed of

• Ns = number of rotations or motor speed (rpm)
• f = frequency of the resource (Hz)
• P = number of magnetic poles.

The rotating stator field will induce the conductors in the rotor, so that an induced voltage arises in the rotor.

The voltage that occurs on the rotor causes current to arise in the rotor conductor. Furthermore, the current in the magnetic field causes a force (F) on the rotor.

If the initial couple produced by the force (F) on the rotor is large enough to support the load couple, the rotor will rotate in the same direction as the stator rotating field.

In order for induction voltage to arise in the rotor, there must be a relative difference between the speed of the stator rotating field (Ns) and the speed of the rotor (Nr). The difference in speed between Nr and Ns is called Slip (S), and is expressed by the equation.

• S = Slip
• Ns = number of motor rotations or motor speed
• Nr = number of stator turns.

If Nr = Ns the voltage will not be induced and the current will not flow in the rotor armature coil, so that no coupling is produced. The coupling in the motor will occur if Nr is smaller than Ns.

Example 4-4. A 4-pole rotary motor rated at 50 Hz has a rotational speed of 1440 1/min. What is the slip?

Asynchronous motors require slip to induce current in the rotor.

Understanding Synchronous Generators (AC)

Synchronous generator is a machine that produces AC electrical energy. Like a motor, a generator also has a construction consisting of a stationary part (stator) and a moving part (rotor). Figure 4.23 is the rotor of a synchronous generator. The induced voltage produced by a synchronous generator depends on the excitation current and the number of rotations. The frequency of the AC voltage produced depends on the number of radial rotations of the poles. The voltage can be adjusted by adjusting the excitation current.

Figure 4.28: Rotor Types of Synchronous Generators, (a) 3-pole, (b) 1-pole (Fachkunde Elektrotechnik, 2006, p. 448)

The magnitude of the AC voltage produced by a synchronous generator is determined by the number of rotor rotations and by the magnitude of the excitation current. While the frequency of the AC voltage is determined by the number of radial rotations of the rotor.

Figure 4.29. 6 Pole Synchronous Generator

Shunt Synchronous Generator

A synchronous (AC) generator can be connected in parallel to another synchronous generator) or to the mains voltage if the instantaneous voltage (AC voltage) of both is the same as the voltage of the connected generator. With generators connected in parallel, the generators will have voltages with the same phase, the same frequency and the same effective value.

Understanding DC Motors

An electric motor is an electrical machine that converts electrical energy into mechanical energy. The construction of motors and generators is basically the same. DC motors develop large torque and allow for the regulation of the number of rotations without stages. The number of rotations of the motor can exceed its rotating field. Based on the source of magnetic current for the magnetic poles, electric motors are divided into two types, namely:

1. A separately excited DC motor, when the current for the magnetic pole windings comes from a direct current source located outside the motor.
2. A self-excited DC motor, if the current for the magnetic pole windings comes from the motor itself.

Meanwhile, based on the relationship between the magnetic amplifier windings and the anchor windings for motors with their own amplifiers, they can be grouped into:

1. Shunt Motor
2. Series Motor

1. DC Motor Working Principle

In general, the construction of DC motors and generators is the same, consisting of a stator and rotor. DC motors initially require a large torque (torque force) and do not require rotational speed control. The rotational speed of the motor will then be controlled by the magnetic field. In a DC motor with a separate amplifier, the excitation source is obtained from outside, for example from a battery. The occurrence of torque on the anchor is caused by the interaction of two magnetic field lines. The magnetic poles produce magnetic field lines from north to south passing through the anchor. The anchor coil that is supplied with DC electric current produces a magnet with a direction to the left as indicated by the arrow (Figure 4.22).

Figure 4.21: Excitation Field and Armature Field

Figure 4.22: Excitation Field and Armature Field

The interaction of the two magnets from the stator with the magnet produced by the anchor causes the anchor to get a counterclockwise rotational torque force. To obtain a stator magnetic field that can be adjusted, an electromagnet winding is made whose excitation current can be adjusted.

DC machines can function as DC generators or as DC motors. When as a DC generator its function is to convert mechanical energy into electrical energy. While as a DC motor it converts electrical energy into mechanical energy.

2. Starting and Speed ​​Control of DC Motors

DC motors have very small armature resistance. If this motor is suddenly connected to a large voltage, then the current flowing in the armature resistance (RA) will be very large, and this will cause a jolt. Therefore, in large DC motors, starting resistance (Rv) is needed which is used to inhibit the starting current. The value of Rv = R -- RA, where R = total resistance on the armature.

Figure 4.23. Armature Equivalent Circuit

Example 4-3. A DC motor has an armature resistance of 0.5 ?. The armature current IA is measured to be 10 A at an armature voltage of 220 V. If the multiple of the armature current is 1.5 IA, what is the starting resistance required?

3. Characteristics of DC Motors

a). Characteristics of Separately Excited Motors

In a separately excited motor, the excitation current is independent of the voltage source that supplies it. The armature rotation will decrease with increasing torque, as shown in Figure 4.25b.

b). Shunt Motor Characteristics

The excitation circuit of the shunt motor is parallel to the armature. The rotation will decrease with the increase of the torque. At no-load conditions, the characteristics of the shunt motor are similar to those of a separately excited motor.

Figure 4.24. Characteristics of Separately Excited Motor

Figure 4.25. Shunt Motor Characteristics

c). Characteristics of Series Motors

The series motor excitation circuit is installed in series with the anchor. Among other types of DC motors, series motors require the largest initial torque. It should be noted that series motors should not be operated under no-load conditions.

d). Characteristics of Component Motors

In compound motors, the main poles contain series and parallel circuits. Under no-load conditions, compound motors have properties like shunt motors. Under applied load conditions, with the same torque, a slightly higher rotation will be obtained.

Figure 4.26. Characteristics of Series Motors

Figure 4.27. Compound Motor Characteristics

Definition of Generator

A generator is a device that converts mechanical energy into electrical energy. Generators are used in a wide range of fields: airports, hospitals, transportation, computers, construction, industrial processes, and more. There are basically two types of generators, namely AC and DC generators. There are basically two types of generators, namely AC generators and DC generators. Because AC generators produce AC current, they are often referred to as alternators. DC generators produce DC current.

1. DC generator

DC generators are divided into several types based on the magnetic winding circuit or excitation amplifier to the anchor. DC generator types:

1. Separate amplifier generator
2. Shunt generator
3. Compound generator.

1. Construction of DC Generator

In general, generators are made using permanent magnets with 4-pole rotors, digital voltage regulators, overload protection, excitation starters, rectifiers, bearings and generator housings or chassis, and rotor parts. Figure 4.7 shows a cross-sectional image of the DC generator construction. DC generators consist of two parts, namely the stator, which is the stationary part of the DC machine, and the rotor, which is the rotating part of the DC machine. The stator consists of: motor frame, stator winding, carbon brushes, bearings, terminal box. The rotor consists of: commutator, rotor winding, rotor fan, rotor shaft.

The part that must be paid attention to for routine maintenance is the carbon brush which will shorten and must be replaced periodically. The commutator must be cleaned from dirt from the remaining carbon brush that sticks and carbon dust that fills the gaps in the commutator, use fine sandpaper to clean the stains from the carbon brush.

Figure 4.7: DC Generator Construction

2. Working principle of DC generator

The generation of induced voltage by a generator is achieved in two ways:

1. by using a drag ring;
2. by using a commutator.

Method 1) produces alternating induced voltage. While method 2) produces DC voltage. The process of generating these induced voltages can be seen in Figure 4.8 and Figure 4.9.

Figure 4.8: Generation of Induced Voltage

If the rotor is rotated under the influence of a magnetic field, then there will be an intersection of the magnetic field by the wire coils on the rotor. This will cause an induced voltage. The greatest induced voltage occurs when the rotor occupies a position such as Figure 4.8 (a) and (c). In this position, the maximum intersection of the magnetic field (by the conductor) occurs. While the anchor position in Figure 4.8. (b), will produce zero induced voltage. This is because there is no intersection of the magnetic field with the conductor on the anchor or rotor. This field area is called the neutral area.

Figure 4.9: Rotor voltage generated through drag rings and commutator

If the end of the rotor winding is connected to a slip ring in the form of two rings (this is called a drag ring), as shown in Figure 4.9.(1), then sinusoidal AC electricity is produced. If the end of the rotor winding is connected to a single-ring commutator in Figure 4.9.(2) with two halves, then DC electricity is produced with two positive waves.

The rotor of a DC generator will produce alternating induced voltage. A commutator functions as an AC voltage rectifier.

The magnitude of the voltage produced by a DC generator is proportional to the number of rotations and the magnitude of the excitation current (field booster current).

3. Separate Amplifier Generator

In a separate generator, the excitation winding (exciter) is not connected to the rotor. There are two types of separate excitation generators:

1. Electromagnetic amplifier (Figure 4.10.a);
2. Permanent magnet (Figure 4.10.b).

The electrical energy produced by the electromagnetic amplifier can be regulated by regulating the excitation voltage. Regulation can be done electronically or magnetically. This generator works with an external DC power supply that is inserted through the F1-F2 windings.

Figure 4.10: Separately Excited Generator

The permanent magnet amplifier produces a constant generator output voltage from the rotor terminals A1-A2. The voltage characteristic V is relatively constant and the voltage will decrease slightly when the load current I is increased to approach its nominal value.

Figure 4.11 shows the characteristics of a separate excited generator at full excitation (Ie 100%) and at half-full excitation (Ie 50%). Ie is the excitation current, I is the load current. The generator output voltage will drop slightly if the load current is greater. (2) Voltage loss due to armature reaction; (3). The voltage drop due to armature resistance and armature reaction, then results in a decrease in the supply of exciter current to the magnetic field so that the induced voltage becomes small.

Figure 4.11: Characteristics of a Separately Excited Generator

4. Shunt Generator

In a shunt generator, the excitation amplifier E1-E2 is connected in parallel with the rotor (A1-A2). The initial generator voltage is obtained from the residual magnetism contained in the stator magnetic field. The rotor rotates in a weak magnetic field, producing a voltage that will strengthen the stator magnetic field, until its nominal voltage is reached. The regulation of the excitation current passing through the shunt winding E1-E2 is regulated by the sliding resistance. The greater the shunt excitation current, the greater the shunt amplifier field produced, and the terminal voltage increases until it reaches its nominal voltage. The circuit diagram of a shunt generator can be seen in Figure 4.12.

Figure 4.12: Shunt Generator Circuit Diagram

Characteristics of Shunt Generator. Shunt generator has characteristics as shown in Figure 4.12. The output voltage will drop more than the output of a separate generator for the same increase in load current. As a voltage source, this characteristic is certainly not good. The generators above should have a constant output voltage.

Figure 4.13: Shunt generator characteristics

If the shunt generator does not receive excitation current, then there will be no residual magnetization, or if the excitation winding is misconnected or if the direction of rotation is reversed, or the rotor is short-circuited, then there will be no voltage or electrical energy produced by the generator.

5. Compound Generator

The weakness of the two types of generators above (output voltage will decrease if the load current increases), is corrected by using a compound generator. The compound generator has two excitation amplifiers on the same main pole core. One excitation amplifier is a shunt amplifier, and the other is a series amplifier. The circuit diagram of a compound generator is shown in Figure 4.14. The magnetic field regulator (D1-D2) is located in front of the shunt winding.

Figure 4.14: Compound Generator Circuit Diagram

Characteristics of Compound Generators

Figure 4.15 shows the characteristics of a compound generator. The generator output voltage appears constant with increasing load current, both at full excitation current and 50% excitation. This is due to the strengthening of the series winding, which tends to increase in voltage if the load current increases. So this is a compensation for the shunt generator, which tends to decrease in voltage if the load current increases.

Figure 4.15: Characteristics of Compound Generator

6. DC Generator Anchor

The anchor is a place where the coils on the rotor are shaped like a grooved cylinder. The coils are where the induction voltage is formed. In general, the anchor is made of a strong material that has ferromagnetic properties with quite large permeability.

Figure 4.16: DC Generator Anchor

Large permeability is needed so that the anchor coil is located in an area with large magnetic induction, so that the induced voltage generated is also large. The anchor coil consists of several coils installed in the anchor groove. Each coil consists of a wire coil or a rod coil.

7. Anchor Reaction

The magnetic flux generated by the main poles of a generator when no load is called the Main Field Flux (Figure 4.17). This flux cuts the armature coil so that an induced voltage arises. When the generator is loaded, an armature current arises in the armature conductor. This armature current causes a flux to arise in the armature conductor and is usually called the Armature Field Flux (Figure 4.18). The emergence of the armature field will weaken the main field located to the left of the north pole, and will strengthen the main field located to the right of the north pole. The effect of the interaction between the main field and the armature field is called the armature reaction. This armature reaction causes the main field not to be perpendicular to the neutral line n, but to shift by an angle ?. In other words, the neutral line will shift. The shifting of the neutral line will weaken the nominal voltage of the generator. To return the neutral line to its original position, an auxiliary magnetic field (interpole or auxiliary pole) is installed, as shown in Figure 4.20(a). The auxiliary magnetic coil is in the form of a magnetic pole whose physical size is smaller than the main pole. With the shifting of the neutral line, the brush placed on the surface of the commutator and located exactly on the neutral line n will also shift. If the brush is maintained in its original position (neutral line), sparks will occur, and this has the potential to cause fire or other hazards. Therefore, the brush must also be shifted according to the shifting of the neutral line. If the brush is not shifted, the commutation will be bad, because the brush is connected to a conductor containing voltage.

Figure 4.17: DC Generator Excitation Field

Figure 4.18: Armature Field of a DC Generator

Figure 4.19: Anchor Reaction

Figure 4.20(a): Generator with Auxiliary Poles

This anchor reaction can also be overcome by compensation attached to the main pole leg both on the north pole and south pole coils. Now in the DC generator circuit there are three magnetic coils, namely the main magnetic coil, the auxiliary magnetic coil (interpole) and the compensation magnetic coil. Figure 4.20 (a) and (b) show a generator with a commutator and its compensation coil.

Figure 4.20(b): Generator Main Pole, Auxiliary Pole, Compensation Winding

Understanding DC Machines

A DC machine consists of a stator section, consisting of a magnet set with steel rings and protruding wire windings with a main pole core, pole shoes made of electroplates and excitation wire windings such as, and auxiliary pole cores as shown in Figure 4.4. This construction is usually found in DC machines with a maximum power of 20 kW. This type of machine will work as long as there is magnetization. For machines with a power of up to 1 kW, it consists of a main pole commutator, made of steel or electroplates with wire windings. The pole shoes of the main poles have compensation windings.

The rotor section (often called the armature in DC machines) is made of a grooved steel shaft and wire wound in the grooves. Figure 4.4 shows a section of a DC machine, with the commutator at the end of the motor. The carbon brushes are part of the stator. These brushes are held by brush holders.

Figure 4.4: DC Machine Starter

A commutator consists of copper segments, each end of which is connected to the end of the rotor winding. The commutator is a part of an electrical machine that needs frequent maintenance and cleaning. This part is in contact with carbon brushes to introduce current from the grid to the rotor. Figure 4.6 shows the parts of a commutator and other related parts.

Figure 4.5: DC Machine Section

One of the disadvantages of DC machines is the mechanical contact between the commutator and the carbon brush that must be maintained and routinely maintained. But DC machines also have advantages, especially for obtaining stable and smooth speed control. DC motors are widely used in the paper industry, textiles, diesel electric trains and so on.

Figure 4.6: Commutator & Brush Holder

Major Faults of Motor Traction Disorders

1. Preparation & Attention when Working

1. Imperfect preparation
2. Mica is too high
3. Mica that is not clean on the sides
4. Lamel edges are not beveled after undercutting
5. Needs regular cleaning
6. The cooling air duct is not flowing smoothly.

2. Assembly and Adjustment

1. The location of the Carbon Brush is incorrect
2. Carbon Brush distance is not the same
3. Brush Holder is not straight
4. Carbon Brush tilt position is incorrect
5. The spring pressure on the Brush Holder is not correct
6. Interpole installation or adjustment is incorrect
7. Incorrect series coil installation or adjustment

3. Mechanical Failure of Motor Traction

1. Carbon Brush cannot move in Brush Holder
2. Carbon Brush is too loose in Brush Holder
3. Brush Holder is not attached securely or the attachment is loose
4. In the motor traction there is a broken coil
5. The coil or kern of the pole coil is loose
6. There was damage to the Motor Traction Bearing
7. Air gaps are not equal
8. The distance between the poles is not the same
9. No balance
10. The distance between the poles is not the same
11. Not balanced.

4. Electrical Failure in Traction Motor

1. The relationship is open or there is high resistance to
2. Imperfect connection at Shunt terminal
3. There is a short circuit in the magnetic field winding or in the armature
4. Ground occurs on the magnetic field coil or Armature
5. There is a polarity reversal in the magnetic field coil or Interpole

5. Motor Traction Characteristics

1. Zone for commutation is too narrow
2. Zone for commutation is too wide
3. Carbon Brush is too thin
4. Carbon Brush is too thick
5. Interpole magnets are too saturated
6. Interlamellar tension is too high
7. Comparison of Carbon Brush contacts with too large
8. Coil Armature branch connection is not enough

6. Loading or Operating Conditions

1. Overload
2. Load changes too fast
3. Reversal of non Interpole Coil work
4. Electricity flow is blocked
5. Dynamic braking
6. The current on the Carbon Brush is too low
7. Contaminated atmosphere
8. Contact poisons
9. There is oil or air containing oil vapor
10. There is coarse dust in the air
11. Humidity is too high
12. Humidity too low
13. Mixed with silicon.

7. External Influence

1. Weak Motor Traction Mount
2. Vibration from outside
3. There was a short circuit outside with a very large current.

8. Carbon Brush Error

1. Commutation factor too high
2. Commutation factor too low
3. Contact drop on Carbon Brush is too high
4. Contact drop on Carbon Brush is too low
5. Friction coefficient too high
6. There is a film layer formed on the Carbon Brush
7. There is a layer that covers the Carbon Brush
8. Carbon Brush erodes
9. Lack of carrying capacity

Summary

Electrical wiring in industry plays a role as a medium for distributing electrical resources to electrical equipment, such as electrical machines, controls, and other electrical devices.

In principle, the electrical wiring circuit in industry is divided into four parts, namely the power source, transmission line, control device and devices that use electrical power.

The power supply source usually consists of a distribution panel for 220 V/ 340 V, the total ampere capacity of which is generally 60 -- 200 A. Each circuit in the panel box is connected to the neutral ground line and the phase line.

Electricity is distributed through distribution lines. Distribution lines can be made above ground or buried in the ground.

In industry and at home, we often find control equipment, for example switches to turn lights, machines or other devices on or off, either manually or in a programmable manner, so that many human tasks can be replaced by control equipment.

Most devices in industry work using electrical power sources, both AC and DC, ranging from lighting systems, control systems, information systems, measuring and entertainment equipment, and so on.

In the CC-202 locomotive, the diesel engine as a power source converts heat energy into rotary mechanical energy, which rotates a 3-phase AC electric generator. The generator functions to convert rotary mechanical energy into electrical energy. The electric current that has been generated by the generator through service tools and control systems is channeled to the traction motor to be converted into rotary mechanical energy to rotate the locomotive's drive wheels on the rails.

Maintenance of all equipment in the industry is generally scheduled. Equipment maintenance and repair procedures must follow the specified procedures. These procedures are usually listed in each equipment maintenance manual. For the CC-202 locomotive, the maintenance and repair manual consists of 13 modules.

Motor Traction Maintenance

1. Motor Traction

Traction motor is one of the important components in diesel electric locomotive. Diesel locomotive produces mechanical power from a diesel engine with a power of 2,000 HP which is connected to a DC power plant called the main generator (Main Generator) with a power of 1.2 Mega Watt. Electric power from the Main Generator is distributed to the Traction Motor which is installed on the Locomotive wheel axle. Figure 8.24 Traction Motor is cooled by a Blower which is located separately outside the Traction Motor. The rotation of the Traction Motor cooling Blower is rotated by the Diesel Engine mechanic.

The direction of rotation of the motor can be changed by reversing the electrical voltage connected to the anchor circuit. The rotation of the traction motor is regulated by adjusting the amount of voltage connected to the anchor circuit.

The voltage reversal to reverse the rotation of the motor above is the same as when the Traction Motor is used for dynamic braking. This means that dynamic braking is done by reversing the voltage connected to the traction motor. During dynamic braking, the traction motor functions as a generator that is shorted with a grid resistor. The carbon brush holder is made resistant to impact, fatigue and Flash-Over. The connecting cable is clamped to increase the tensile strength that occurs.

2. Stator

Traction Motor Stator, Figure-8.25 is made of cast steel which functions as a motor housing as well as to place bearings at the ends of its shaft. On the Stator are placed magnetic poles produced by the stator magnet windings. Magnetic poles are always paired North-South, so the number of magnetic poles is four.

Magnetic poles are often also referred to as magnetic fields. There are two types of magnetic fields, namely the main pole of the magnetic field and the auxiliary pole of the magnetic field (Interpole magnetfield). The main pole of the magnetic field is larger in shape while the auxiliary pole of the magnetic field. its physical shape is slimmer. Both types of magnets are connected in series.

Figure 8.25. Traction Motor Stator

3. Rotor

Traction Motor Rotor, figure 8.26 consists of several windings, each end of which is connected to the Commutator by means of a strong solder connection. Rotor windings are often also called Anchors. Anchor windings are placed on the Rotor grooves, the number of which is an even number.

The number of Rotor grooves is the same as the number of Commutator lamellae, this is because each Rotor winding will occupy two grooves and each end of the winding is connected to the Commutator. The rotor is made from a stack of thin plates of ferro Magnet material, the purpose of which is to minimize hysteresis losses in the Anchor.

4. Commutator

The commutator on a simple single loop consists of only two lamellas, the conductors on the DC motor are wrapped in a cylindrical iron sheet and given grooves to place the wire coils which are then called Rotor coils. The commutator in Figure-8.27 consists of tens or even hundreds of lamellas, depending on the number of grooves in the Rotor. The commutator is installed on one side of the shaft end with the Rotor. The Commutator lamellas must be cleaned periodically from dirt produced by contact between the commutator and the carbon brush. Between the two lamellas is limited by an insulating material to separate the two different windings.

Figure 8.27: Commutator

5. Charcoal Brush and Brush Holder

Carbon Brush is made of compacted Ferro Carbon. The carbon brush is placed facing the commutator, so that the carbon brush is always connected to the commutator lamellas. The carbon brush is placed in a brush holder equipped with a spring.

Figure 8.28, the spring will press the brush to the commutator surface. The spring pressure must be measured, not too weak or too strong. Carbon brushes must be checked periodically. If they are too short or damaged, they must be replaced with new ones.

Figure 8.28. Charcoal Brush and Brush Holder

6. Stator and Rotor Wiring Relationship

From the Traction Motor wiring diagram, Figure-8.28 it can be explained that the Traction Motor D-29 has the following components:

1. The stator has four (4) main magnetic fields (Main Field) with terminal notation F -- FF and has four auxiliary magnets (Interpole) which are directly connected in series with the anchor winding.
2. Rotor, in the form of an Anchor winding which is given the notation A-AA. The connection from the Anchor winding to the outer terminal is via four (4) Carbon Brushes. The ends of the anchor winding are connected in series with the Auxiliary Magnet winding (Interpole).

Figure 8.29: Traction Motor Stator and Rotor Wiring

7. Motor Traction Rotation

When assembling the Traction Motor, the cable must be placed correctly according to the direction of rotation. If an error occurs at this stage, it can cause damage to the Traction Motor and Generator. The difference in Wiring Diagram, figure 21, the connection on the old and new motors is the connection of cable "A" and Brush Holder, and the connection between the Interpole and Brush Holder. The direction of rotation of the motor can be read by observing the Nose Suspension when the Traction Motor is given electric current.

Slip Safety System (Poka-Yoke)

The slip safety system is to keep the wheels on the locomotive have the same rotation. The main purpose is to avoid damage to the Traction Motor due to slippage on the locomotive wheels.

What is meant by slip here is that there are 2 (two) types, namely more rotation simultaneously together on all wheels. The popular term door-slag may be more appropriate for this incident and another type of slip is the unequal wheel rotation between a pair of wheels with other wheels.

The slip safety system is primarily used to detect unequal rotation of the locomotive wheels with a WST transducer, which is installed on two current flows on two traction motors. In a state where the current flow to the Traction Motor is the same, the transducer is in a balanced state and in this state the WST does not generate a detection signal. If there is an electric current flowing to the Traction Motor that is not the same size, then the WST is unbalanced, resulting in a signal being given to the WS Module.

Figure 8.19: WST-2 Transducer

1. Wheel Slip Module (WS Module)

The WS module is used to control the slippage of locomotive wheels when the detector, namely the slippage wheel transductor or bridge circuit, gives a slip signal. Three levels of slip controlled by the transductor can be detected, then only one level of slip can be detected by the bridge circuit. The WS module is equipped with a test switch to be used to test the operation of the slip safety system.

The sensitivity of the slip wheel transductor and the responsiveness of the WS Module reduce slip simultaneously by controlling slip before loss of adhesion occurs. Therefore, the WS Module maintains the locomotive power at an optimal value below the values ​​of the lowest traction and adhesion during repeated slip events. Therefore, with this control, the traction of the train load takes place smoothly, the driver does not need to lower the throttle handle.

Figure 8.20. Wheel Slip Module WS Module

2. First Level Slip Control

First level slip when there is a slight slip. Control by sharply reducing the signal that must be given to the Transistor base in the FP Module. This sharp decrease is made without discharging the capacitor in the RCe Module, or changing the position of the arm on the load regulator. This signal decrease results in a gradual reduction in excitation in the Main Generator magnetic field, ultimately reducing the output power in the Main Generator.

When slip occurs, the voltage flowing to the TI transformer increases equivalent to the slip speed of the wheel. This signal is then flattened to be used as a slip wheel control signal in the WS Module circuit consisting of several Transistors, Zeners, Resistors, capacitors and other electronic devices.

3. Second Level Slip Control

This second-level slip control occurs when the signal from the slip wheel transductor exceeds the specified limit value. When the second-level slip control occurs, the sander works to provide sand to the wheels which is done by the SA Module (sanding Module) and also the capacitor in the RCe Module quickly empties its storage current.

The magnitude of this signal causes the current flowing to the Transistor on the WS Module to be large as well. This causes the current flowing to one of the Resistors to increase and this will penetrate a Zener Diode if the voltage flowing to the Resistor is more than 10 Volts. With the penetration of the Zener Diode, it will work on a relay and then work on the driving system on the SA Module. If the slip wheel has been able to stop its slip, it will return to normal and the locomotive power will return slowly (smooth) and the driving will stop.

4. Third Level Slip Control

The output of the slip wheel detectors is used as a quantity in the detector circuit consisting of several diodes, capacitors, and a detector relay. The detector relay responds to the magnetization of a strong slip wheel signal, according to the magnitude of the increase in the slip wheel signal. The relay will operate if the signal increases above a predetermined value.

Relay WL will provide one feedback that causes the WS lamp to light up. Relay L will work if the slip wheel signal increases above a predetermined value. The work of relay RAA and RAB provides control when control occurs at the second level. Relay L will continue to work until the slip condition has stopped or after the power reduction has been able to reduce the slip wheel signal which can stop relay L from working.

By releasing the L relay, the WL, RAA, RAB relays will return to normal and as a result the locomotive power will also be normal.

5. How the WS Module Works in Dynamic Braking

The wheel slip transductor is not used to detect wheel slip even though the wheel slip bridge circuit is connected via a pair of frequently attached Traction Motor armatures.

The wheel that experiences slippage (slipping) is made in such a way that it produces a voltage difference through one of the bridge series.

To detect such conditions is done by a bridge circuit that works because of the operation of the WS relays, one of which is 3 WS relays. With the operation of the WS relay, there will be a gradual reduction in locomotive power by functioning the K resistance between the RCe Module and the load regulator. In addition, it also provides flow to the WL relay, RAA relay, and RAB relay. Each relay functions as a WL relay to provide flow to the WS lamp, the RAA relay regulates the rapid discharge of the capacitor on the control capacitor, and the RAB relay works on the transmitter Modula (SA Module).

The wheel slip transductor is not used to detect wheel slip even though the wheel slip bridge circuit is connected via a pair of frequently attached Traction Motor armatures.

The wheel that experiences slippage (slipping) is made in such a way that it produces a voltage difference through one of the bridge series.

To detect such conditions is done by a bridge circuit that works because of the operation of the WS relays, one of which is 3 WS relays. With the operation of the WS relay, there will be a gradual reduction in locomotive power by functioning the K resistance between the RCe Module and the load regulator. In addition, it also provides flow to the WL relay, RAA relay, and RAB relay. Each relay functions as a WL relay to provide flow to the WS lamp, the RAA relay regulates the rapid discharge of the capacitor on the control capacitor, and the RAB relay works on the transmitter Modula (SA Module).

If the slipping wheel event has been stopped by the slip safety system, the WS relay will return to normal. This will release the Resistor connection between the RC Module and the load regulator. The slip level control capacitor will be charged at a normal level. The deceleration due to the decrease in power will gradually return to its original power and the spinning will continue for a moment until the RAB relay returns to normal.

6. Slip Wheel Bridge Assembly

This circuit functions to detect wheel slippage during braking with dynamic brakes. This circuit consists of 2 Traction Motors, 2 2 kilo ohm Resistors and a WS relay. In a locomotive, there are 3 pairs of the same in each circuit. Under normal conditions, the circuit is balanced. If wheel slippage occurs during braking with dynamic brakes, the condition is unbalanced and this will be detected by the WSR relay. By working the WSR relay, it will reduce the excitation of the Traction Motor which at that time functions as a Generator. In addition, it also does the sanding.

7. Slip Wheel Bridge Assembly

The slippery wheel transductor consists of two iron cores, two alternating current coils and two single bias coils from the Traction Motor in the form of Traction Motor current flow cables. The two iron cores are isolated from each other and each has an alternating current coil. The bias coils from the Traction Motor current flow bias together with the two iron cores.

Figure 8.22. Transductor - Japan Railway Instruction Manual, 1978

The direction of the Traction Motor current flow is made in such a way that it can detect the difference in the magnitude of the electric current flowing to the Traction Motor. Under normal circumstances, the magnitude of the induction of two Traction Motors is more or less balanced. Because of the installation in the opposite direction, the induction of the two motors will cancel each other out and as a result the magnetic field will disappear. As a result, there is no bias that will affect the emergence of signals by the WST.

When the wheel slips, the current flowing to the Traction Motor is different, resulting in a magnetic field of different magnitude in the bias coil. This will create the effect of reactance on the electric current coil flowing to the Traction Motor. With this decrease in reactance, the current flowing in one of the Resistors will increase. Furthermore, this increase in current is a signal to the WS module which is proportional to the difference in current flowing to the Traction Motor.

In the event that the door-slag wheel slips, this does not cause a difference in electric current in the bias coil so that the transductor cannot detect this condition.

8. Dynamic Brake

What is meant by dynamic brake is braking by using an electrical load on the Generator that is generating electric current. With this load, the energy that is discharged through a resistance with a certain price will cause a resistance to tend to stop or reduce the rotation of the Generator. By adhering to the principles of generation in a Generator, the factors that must be considered are rotation, magnetic field and coil.

This rotation is obtained from the friction of the locomotive mass as kinetic energy that slides. The Traction Motor attached to the locomotive wheels will rotate due to the mechanical connection through the spiral gear and the gear on the axle. The Traction Motor in braking with dynamic brakes is changed to a Generator that generates voltage and electric current.

In order for the rotary traction to function as a Generator, there must be an electric field as the main requirement of the Generator principle. The electric field created by the electric current originating from the Main Generator will generate excitation. The amount of excitation during dynamic brake braking depends on the position of the amount of current flowing into the excitation system and this is determined by the amount of voltage generated by the Main Generator and the position of the dynamic brake handle.

In order for the rotary traction to perform its role as a Generator, there must be an electric field as the main requirement of the Generator principle. The electric field created by the electric current originating from the main Generator will create excitation. The amount of excitation during dynamic brake braking depends on the position of the amount of current flowing into the excitation system and this is determined by the amount of voltage generated by the main Generator and the position of the dynamic brake handle.

In order for braking to occur, the current generated by their traction which has changed its function as a generator is discharged through a GRID DYNAMIC BRAKE and discharged as heat energy.

When the heat energy is released, this will become a burden on the traction meter so that the traction meter tends to decrease in rotation, which will then inhibit the movement of the locomotive mass that is sliding.

Figure 8.23. Power System Wiring

The connection of the traction meter during braking with dynamic brake is to separate the field and armature in such a way that all fields are connected in series with each other. Field TM2 --- Field TM5 --- Field TM6 --- Field TM1 --- Field TM4 --- Field TM3. The field is then connected to the main generator to create excitation.

The armatures are arranged in 3 (three) series arrangements, each consisting of 2 (two) armatures. The current generated by the armature is then channeled to the GRID.

These grids have a certain value. By remembering Ohm's Law, namely E = I x R, then because the resistance value R is fixed, if the voltage increases the current I will be greater.

Since Watt Power is = I2 x R, then the power is also greater. The amount of kinetic energy converted into electrical energy is proportional to the amount of WATT. So the amount of braking power from 0 to maximum is as a result of the increasing current flowing to the GRID Dynamic Brake along with the increasing speed of the locomotive.

With the increase in electric current means Watt will also increase. Because the amount of WATT can be changed into PK, the braking power can be calculated. From the definition above, it can be written as follows:

The general formula is divided by 736, because there are various losses, then in the calculation it is divided by 746. One of the losses here, for example, is when the current is discharged to the GRID, the GRID cooling cannot reach normal temperature, there is still heat that cannot be cooled.

9. Excitation on Motor Traction

The excitation current flowing to the field during braking is controlled by the dynamic brake handle and the DR Module (dynamic braking regulator Module). The DR Module senses the current/voltage flowing to the GRID (one of them) which is proportional to the current flowing to the GRID.

The DR module works by limiting the excitation current to a value to avoid current that exceeds the armature and GRID, but achieves braking power within safe limits. In addition, the DR module is also equipped with a safety circuit in case of a disconnection on the dynamic brake grid.

When braking occurs, the DB grid will be hot and it is cooled by the grid cooling blower. This blower gets electric current by branching the electric voltage flowing to the grid. Therefore, if the voltage flowing to the grid is large, the blower rotation will be faster and the cooling will be greater.

The DP module consists of a meter field safety circuit (MFP) and a brake warning circuit (BWR). The MFP works to secure the meter field if there is a failure in excitation. If there is no safety device, there will be an increase in electric current above the permitted price.

BWR provides security by sensing from the DB grid and also securing the grid itself. If the current flowing to the grid increases above the permitted value, the BWR circuit works to reduce the electric current going to the main generator as a source of electricity flowing to the Traction Motor series field circuit. This also means reducing the electric current going to the grid. Thus the grid is protected from excess current that can damage the grid.

Dynamic Brake Protection Module (DP) provides protection to the Traction Motor field and to the GRID DB in case of failure in operation (DR). The DP module disconnects the excitation on the main Generator if the excitation on the traction motor and the current flowing to the grid increases above the permitted value.

This DP is installed in a safety circuit by pairing it parallel with the Traction Motor field during braking with dynamic brake. Therefore, it works by detecting changes in the excitation voltage in the Traction Motor field. The DP that acts as a grid safety consists of a detector circuit and a trigger circuit.

Detector circuit is placed on one of the Dynamic Brake grids. It will work on the trigger circuit if there is excessive current. Then the trigger circuit will work and will cut off the excitation on the main Generator. The module (DP) is made with Transistor, Capacitor, Diode resistor, Zener, and other semi-conductor devices.

10. Dynamic Brake Regulator Module (DR Module)

DR limits the maximum electric current of 355 to 380 amperes when braking with dynamic brake. This current limitation is by sensing the voltage in such a way that it is comparable to the current flowing in the GRID. In addition to one of the GRIDs and when working will reduce the excitation of the main Generator field when the current flowing in the grid increases above 355 to 380 amperes.

The DR module also regulates the current flowing to the grid at a value that is proportional to the position of the handle where it is at the time of braking. The way this regulation works is by comparing the signal that is proportional to the current flowing to the grid compared to the signal indicated by the position of the dynamic brake handle.

For the purpose of control when working on Dynamic brake, a tool is used that is useful for inserting contact connections and is useful for changing the Traction Motor function into a Generator. Like the reverser whose contacts are driven by the reverser motor. In the contact for this purpose, using an electric motor as its driver. The way this motor works is the same as that used in the reverser system.