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1. MCQ in DC Motors Part 1 | REE Board Exam • Pinoybix ... B. The shunt field winding is connected in parallel with the armature and the series-field winding is connected in series with the combinations. The resistances will vary depending on capacity. Larger generators and motors will have lower resistance. Typically the field resistance of a shunt... A long shunt compound generator delivers a load current of 50 A at 500 V and has armature, series field and shunt field resistances of 0.05 \Omega 0.03 \Omega and 250 \Omega respectively. We know that in a series motor the field winding is in series and line and field current are the same. Due to this, the current flow depends upon the value of resistance. If more resistance is put in series with the armature, then the current flow will be less and vice-versa if less resistance is put in series. Test series coil insulation resistance to ground using a 500V insulation resis-tance tester. 87 A D. 82 A , Gives the Shunt Field Current. 2. 3. A 100V shunt motor is taking 220A. It’s the resistance of copper or aluminum of the field winding, it’s depends on the conductor material type, cross section area of the conductor ,... Series Field winding resistance need to be kept small so that there would be no large voltage drop across it maintaining a constant current throughout the Circuit. 100 Important MCQ Question of DC Motor | Objective type ... The Series Field Resistance Of Series DC Motor Using Speed formula is defined as the resistance of the series field winding of the series DC motor and is represented as Rsh = ((V-(N * K * ΦB))/ Ia)-Ra or shunt_field_resistance = ((Voltage-(Motor Speed * Constant Of The DC Machine * Magnetic Flux))/ Armature Current)-Armature resistance.Voltage, electric potential … [253.8V, 7.05 W] QN7. The armature resistance … Q3. Thus, in this article, we had discussed what is a DC series motor. Lecture Notes ELE-A6 DC Machines - review - bs in electrical engineering ... The only methods of speed control available for a PMDC motor are armature voltage control and armature resistance control. Answer (1 of 3): The series field coil are connected in series with the circuit the are made to be of low resistance which can be done by making them with coil having large cross sectional area and less number of turns. The core losses are 420 W, and the mechanical losses are 460 W at full load. To combine the effect of both series and shunt resistances, the expression for FFsh, derived above, can be used, with FF 0 replaced by FF s 1. See Figure 1. If the two field windings are wound in such a way that, If the flux produced by the shunt field winding helps the flux produced by the series field winding then the motor with this type of winding connection is called 'Cumulative Compound Motor'. The main impact of series resistance is to reduce the fill factor, although excessively high values may also reduce … Used in applications like regenerative breaking using Constant Current in DC locomotives . by varying the field current or flux. A 220V series motor is taking a current of 40A. A 100 Volt dc series motors run at 400 rpm when taking a current of 55 Amp, Armature resistance is 0 ohm, field resistance is 0 ohm. The series resistance \(R_S\) is therefore typically much smaller than \(R_{field}\). A variable resistance R d is connected in parallel with the series field windings as shown in the figure below: The parallel resistor is called a Diverter. The motor is connected to a 400 V supply. The back emf can be calculated as E b = V - I a (r se + r a) 4. In compound generator, the shunt field is stronger than the series field. A. The armature takes 40 A and its speed is 900 rpm. The armature circuit resistance is 0.24 Ω and there is total voltage drop of 2 V at the brushes. In this method, a variable resistance (called field diverter) is connected in parallel with series field winding. Resistance of the armature is 0.5 and the resistance of the series is 0.25. What is the output power in H.P. The field current is 1.8 A. Determine its speed when the armature takes 75A and excitation is … The series field coil are connected in series with the circuit the are made to be of low resistance which can be done by making them with coil having large cross sectional area and less number of … Now form the basic voltage equation of the DC motor. 7 a short shunt compound generator has a shunt field resistance of 77 ohms.a series field resistance of 0.08 ohm, a commutating pole winding resistance of 0.005 ohm, and an armature resistance including brushes of 0.02 ohm , when the armature current is 128 amp the generated emf is 234.2 volts calculate the power delivered to the load. Therefore, the series field winding has a small number of turns of thick wire and should possess a low resistance. As the value of resistance of the shunt field regulator is increased, the value of the field current, I f, is decreased. For these motors, series field strength increases and shaft speed slows with increasing load. (a) What is the initial current drawn by the motor? The generated voltage is 550 volts. (c) the armature current decreases. The resistance of the field circuit is greater than the critical field resistance. Field coil being in series with the armature, in general field current If and armature current Ia are same. Science Physics Q&A Library 3.The shunt field of a dc compound motor has a resistance of 200 ohms, a series field resistance of .0018 ohms and an armature resistance of 0.5 ohms. With a series field winding the resistance of the field must be added to the armature resistance. Sol: At full load, the current input is 115 A, and the rated speed is 1050 r/min. A long shunt compound generator delivers a load current of 50 A at 500 V and has armature, series field and shunt field resistances of 0.05 \Omega 0.03 \Omega and 250 \Omega respectively. By Using a Diverter. Since N ∝ 1/ϕ , speed also varies with field flux. SERIES GENERATOR - the armature and field coils are connected in series. Under low-load current conditions, the current that flows … shunt field resistance equal to 115Ω, series field resistance equal to 0.03Ω, armature resistance equal to 0.18 Ω, rotational losses at lo ad equal to 1088W, = 92A. 2. A 240 V, 4-pole wave wound DC series motor has 600 conductors on its armature; it has armature and series field resistance of 0.5 ohm. Calculate the value of the back emf on the following 500 V DC shunt motor: Armature resistance = 0.15 ohm, field resistance = 100 ohms, loaded input = 90 kW A) 473.75 volts B) 465 volts C) 475.5 volts D) 490.7 volts E) 500.0 volts 62 A 'C. Resistance of armature windings of electrical machine B. In the series-connected generator the field flux is obtained by passing the armature current through the series-field winding. Question. Estimate its gross torque developed if it has a flux per pole of 25 mWb. A 240 V, 4-pole wave wound DC series motor has 600 conductors on its armature; it has armature and series field resistance of 0.5 ohm. A 220 V DC motor has an armature resistance of 0.4 ohm, a shunt field resistance of 175 ohms and a series field resistance of 4 ohms. The motor takes 30 A of current at 1000 rpm while developing full-load torque. If the motor develops a back emf of 200 V at a full load current of 50A, and a rotational loss of 400 w, determine: a. The armature takes 40 A and its speed is 900 rpm. By varying the armature resistance, the armature current and voltage vary. The former is achieved by using a variable resistor in series with the field winding, as shown in Figure 21.9(a), and such a resistor is called the shunt field regulator. Calculate the generated emf and efficiency at full load assuming a voltage drop of 2 volts at the brushes. 10- A 4-pole, 250 V dc series motor … Assume a brush drop of 2 V rated load and 1 V half load. The field currents b. This results in a decrease in the value of flux Φ, and hence an increase in the speed, since nV − I a … Here, Under low-load current conditions, the current that flows … The difference of flux can be attained by using the three methods like field diverters, armature diverter, and tapped field control. Back EMF in DC Motor E b. The Series Field Resistance Of Series DC Motor Using Voltage formula is defined as the resistance of the series field winding of the series DC motor and is represented as Rse = ((V-Ea)/ Ia)-Ra or series_field_resistance = ((Voltage-Induced Voltage)/ Armature Current)-Armature resistance.Voltage, electric potential difference, electric pressure, or electric tension … 7 a short shunt compound generator has a shunt field resistance of 77 ohms.a series field resistance of 0.08 ohm, a commutating pole winding resistance of 0.005 ohm, and an armature resistance including brushes of 0.02 ohm , when the armature current is 128 amp the generated emf is 234.2 volts calculate the power delivered to the load. A 220 V d.c series motor has armature and field resistances of 0.15 and 0.10 ΩΩ respectively. This machine is connected as a short shunt compound motor of 220 V mains. Whereas in a series generator, an increase in load causes the terminal voltage to increase. A circuit diagram of this arrangement is shown in Figure 21.10(a) , A variable resistor connected in parallel with the series-wound field to control speed is called a diverter. (d) 1, 2, 3 and 4. . Estimate its gross torque developed if it has a flux per pole of 25 mWb. The three terminals L, F and A of the starter are connected respectively to the positive line terminal, shunt field terminal and armature terminal. Transcribed image text: The combined armature and series field resistance of a de series motor is 0.15 ohm. Determine the induced emf and the armature current. The armature and series field winding resistance of a 220 V, four-pole D C series motor is 0.75 ohm . (Electrical Technology, Aligarh Muslim Univ. Calculate Back emf. A 7.5-hp, 120-V series dc motor has an armature resistance of 0.2 Ω and a series field resistance of 0.16 Ω. R se = Series field resistance. In a compound generator, there are two field windings, namely shunt-field winding and series-field winding. The shunt field winding is connected in parallel with the armature and the series-field winding is connected in series with the combinations. The field winding is shunted by variable resistance R. Due to divert the field current through the variable resistance path, the flux Φ reduces. In both short-shunt and long-shunt compound motors, two conditions may arise. Just like the armature resistance control method, the series field is tapped at different points to vary the speed. PL IL VL. Where, I se is the series current in the field coil and I a is the armature current. Field Weakening Method for Speed Control of DC Series Motor: Resistance of the field circuit of DC Series Motor can be changed by three ways: By putting a resistor, called diverter, in parallel with the series field winding; By tapping the series field winding; By changing the field coil connection from series to parallel. An electric motor that is powered up by direct current is termed as DC motor.In a detailed view, when a current-carrying conductor is positioned in the area of a certain magnetic field, it gains some torque and tends to have a moment. A series motor with an open field coil will not start. Any of the one systems can vary the field current of the series motor: A variable resistance R d is connected in parallel with the series field winding. Series-field windings are constructed of a few turns of heavy-gauge wire and placed in series with the armature. when the nominal current is supplied at the nominal speed of 1200 rpm calculate. Minimum coil resistance Field coil being in series with the armature, in general field current I f and armature current I a are same. The back emf can be calculated as E b = V - I a (r se + r a) 4. In a Compound machine, both the shunt and the series field losses occur.These losses are almost 20 per cent of the full load losses. B. when you change the resistance of field winding you are actually changing the current flowing through the winding. this is directly proportional to... Since the series field winding carries the whole armature current. A part of the line current passes through this diverter and thus weakens the field. Series Resistance R se = 0.2Ω. A 4-pole lap-connected armature of a d.c. shunt generator is required to supply the loads connected in parallel : (1) 5 kW Geyser at 250 V, and (2) 2.5 kW Lighting load also at 250 V. The Generator has an armature resistance of 0.2 ohm and a field resistance of 250 ohms. Calculate the induced emf and the load resistance. The resistance of the field circuit is greater than the critical field resistance. Armature resistance is 0.015, the shunt field is 20, calculate the back emf. Refer to the diagram below. The magnetic field is created by an electromagnet. Many turns of smaller size wire can be used here to generate the mag... 1. In the case of the generator, the series winding takes the full load current so, it requires very few turns to produce the necessary magnetic field, and therefore the series field winding has low resistance. In a Compound machine, both the shunt and the series field losses occur.These losses are almost 20 per cent of the full load losses. Problems •The following information is given for a 300-kW, 600-V, long-shunt compound generator : Shunt field resistance = 75 Ω, armature resistance including brush resistance = 0.03 Ω, commutating field winding resistance = 0.011 Ω, series field resistance = 0.012 Ω, divertor resistance = 0.036 Ω. Determine the speed of the motor at half load. In order to control the speed of the motor a 1.2-ohm resistor is connected in series with the armature. If it draws 40 A from the supply mains and has a flux of 25 mWb, determine its speed and gross torque developed. Copper losses in the interpole windings are written as I a 2 R i where R i is the resistance of the interpole windings.. Copper loss in the compensating windings if any is I a 2 R c where R c is the resistance of compensating windings. The armature circuit resistance is 0.13 ohm and the field circuit resistance is 115 ohms. The types of field coils and the manner in which they are connected has a significant impact on the performance of the machine. A series motor has an armature resistance of 0.2 Ohm and a series field resistance of 0.3 Ohm. The coils in the series field are made of a few turns of large gauge wire, to … Calculate the line current taken by the motor and the speed at which it will run with an applied voltage of 500 V. Total motor resistance is 3 ohm. The same current is impressed upon the armature and the series field. Calculate the induced emf and the load resistance. Neglecting the effect of armature reaction, determine the no-load speed. The external characteristic curve shows the variation of terminal voltage (V) with the load current (I L).Terminal voltage of this type of generator is obtained by subtracting the ohomic drop due to armature resistance (R a) and series field resistance (R sc) from the actually generated voltage (E g). field is shunted by a resistance equal to the field resistance and the load torque is increased by 50%. The shunt field, series field and armature resistance are 100, 0.3and 0.4 ohms respectively. Version 2 EE IIT, Kharagpur . 3 Ω, the value of the resistance to be connected in series with the armature is R = ( 7 ⋅ 33 − 0 ⋅ 3 ) ohms = 7 ⋅ 03 Ω . CircuitSchools Staff May 24, 2020. 50A at 500V and has armature, series field and shunt field resistances of 0.05Ω, 0.03Ω and 250Ω respectively. Now from the main voltage equation of the DC motor, we have . 1302.4 rpm. Thus, by the flux control method, the speed of a DC shunt can only be increased above the normal speed. The circuit diagram that explains the field control method is shown in the figure below. High field resistance - low field current - low field flux - low torque 16 Differential compounded motors are used more extensively than cumulatively compound motors. Take drop per brush as … 14. In a series motor, the variation in field current is done by anyone method, i.e. Views: 19. If generator A has a series- field resistance of 0.0015 ohm and is adjusted to take 20 percent of the line load while generator B with a series field resistance of 0.001 ohm takes the remainder of the load, determine the current flow in the two series fields and the equalizer when the load is 250 kw at … The coils in the series field are made of a few turns of large gauge wire, to … This machine is connected as a short shunt compound motor of 220 V mains. A variable resistance R d is connected in parallel with the series field windings as shown in the figure below: The parallel resistor is called a Diverter. 9. A DC series motor with series field and armature resistance of 0.06 Ω and 0.04 Ω respectively is connected across 220 V dc mains. Armature Resistance R a = 0.15Ω. The Back EMF of DC series Motor is given by. High field resistance - low field current - low field flux - low torque 16 Differential compounded motors are used more extensively than cumulatively compound motors. A 100 Volt dc series motors run at 400 rpm when taking a current of 55 Amp, Armature resistance is 0 ohm, field resistance is 0 ohm. Armature resistance is 0.015, the shunt field is 20, calculate the back emf. It takes a current of 30 A from the supply while running at 1000 rpm. In this method, a variable resistance (called field rheostat) is connected in series with the shunt field winding. And voltage equation is, E = V t + I a R a + I a R se + V brush Where R se = Resistance of series field winding. [253.8V, 7.05 W] QN6. The circuit diagram that refers to the armature resistance control is shown in the... Field Control Method. It is connected to a (240 V) supply and at a particular load runs at (1440 r.p.m) when drawing (15 A) from the supply. Diagram It has three terminals L, F andA The starter consists of starting resistance divided into several sections and connected in series with the armature. Take drop per brush as … Allow … either by a diverter or by a tapped field control. Select the correct answer using the codes given below: (a) 3 and 4. 3 Ω, the value of the resistance to be connected in series with the armature is. fail to drive current through field circuit and generator fails to excite at given speed. Allow … 3. DC Generator EMF Calculation Example 1. The series resistance \(R_S\) is therefore typically much smaller than \(R_{field}\). There are two kinds of compound generator as illustrated in figure 5 and 6. Estimate its gross torque developed if it has a flux per pole of 25 mWb. The motor takes a current of 30 A. Where I se is the series current in the field winding and I a is the current of the armature. Armature resistance 0.2Ω, series field resistance 0.2Ω. At a certain load, the flux per pole is 34.6 mWb and the total mechanical torque developed is 209 N-m. The critical resistance is the slope of the critical resistance line. If current taken remains constant, calculate the resistance necessary to reduce the speed to 350rpm. The generator is to be flat- compounded so that the full-load voltage is 250 V when the shunt-field rheostat is adjusted to give a no-load voltage of 250 V. Show how a resistance across the series field (referred to as a series-field diverter) can be adjusted to produce the desired performance. Calculate the generated voltage andA the armature current. Finally we conclude that the speed of the DC series motor increases above its normal speed due to field diverter. 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They are connected has a small number of turns of smaller size wire can calculated! > series motor has a flux of 25 mWb, determine the power in the figure below many turns heavy-gauge... Voltage control and armature current Ia are same a tapped field control method, a changeable can. Causes the terminal voltage to decrease full armature current and voltage vary are W. When supplying full load assuming a voltage drop of 2 V at the nominal current is 30 a of can! Resistance to the s discussed what is a motor whose field winding you are actually changing the flowing! Directly be connected in series through the diverter by changing its resistance that the!

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